APO MAX Advertisement -- 5.2" vs 7.1" APO's
Thomas Back
To all that it may concern:
On page 122 of the December issue of Sky and Telescope, there
is an ad that reads an unsolicited comment from B. Murphy, at the
1996 AstroFest Telescope Convention. It goes as follows --
"Contrast and resolution equalled or exceeded a nearby 7" Apo.
Quality of machining on drawtube/focuser best of any commercial
unit I've seen."
Well, the nearby 7" Apo (actually a 7.1 inch f/9 Astro-Physics
EDT) was mine. The 5.2" apo is an HT Precision Optics f/12 "APO MAX."
Lets state some facts. Resolution is a measure of the resolving
power of a telescope and is determined by aperture. As long as each
system has a wavefront ~1/4 wave or better, then it is aperture that
will determine the ultimate resolution. I tested both telescopes and
can assure you that they both are better than 1/4 wave spherically.
In fact, my 7.1" lens was tested by green and yellow light interfero-
meter to better than 1/25 wave peak-to-valley at 555nm on the wavefront.
No 5.2 inch telescope on earth could equal or better the 7.1" lens in
resolution, as the laws of physics prevent this. Late into that night we
tested my scope on Gamma-2 Andromeda at 540x, and the pair was clearly
split into two cleanly merged stars, something that a 5.2" aperture
cannot do. BTW, this binary is now spaced at around .45 arc seconds,
so if you want to see this binary truly split, think about a 10" scope
with good optics and a night of excellent seeing.
Now we go on to the subject of contrast. This is not as clear-cut
as resolution, but there are ways of measuring it. One way is to measure
the Strehl ratio, which is defined as the illumination at the center
of the airy disk for an aberrated system expressed as a fraction of the
corresponding illumination for a perfect system. A Strehl ratio of .80
corresponds to a system that has a total wavefront aberration of 1/4
wave. At this quality, assuming an unobstructed system, 68% of the
light goes into the Airy disk and 32% goes into the contrast destroying
diffraction rings. My 7.1", as earlier stated, has a measured wavefront
of 1/25 wave P-V. This corresponds to a Strehl ratio of .9975! Or to be
blunt about it, perfect, and only limited by seeing. Now, other factors
must be considered, such as color correction, astigmatism, scatter and
spherochromatism. However, at f/9, using a very advanced triplet oil-
spaced design with the FPL glasses, Astro-Physics' new Opticam SX
microgrind system, supersmooth polishing techniques and interferometer
figured and tested lenses, the levels of these other aberrations are
vanishingly small. Thus, once again, aperture dominates the level of
contrast that will be seen though these two telescopes, with the 7.1"
at a much higher level, and this assumes that the 5.2" has a Strehl ratio
as high as my 7.1". As anyone who saw Saturn though my 7.1" during good
seeing at powers as high as 405x, the level of contrast and resolution
were much higher than the 5.2" APO MAX.
This is in no way downgrading the 5.2" APO MAX, as it is a fine
telescope. However, lets be careful with outrageous claims of optical
performance. I believe that optical quality is most important (otherwise,
I would not have purchased an Astro-Physics refractor!), but once an
optical system hits a Strehl ratio of .98 or a wavefront of ~1/10 wave
P-V, (assuming low higher order and chromatic aberrations), then aperture
and seeing will be the deciding factors in planetary performance.
Sincerely,
Thomas M. Back
Mark Cronan
am...@cleveland.Freenet.Edu (Thomas Back) wrote:
> This is in no way downgrading the 5.2" APO MAX, as it is a fine
>telescope. However, lets be careful with outrageous claims of optical
>performance. I believe that optical quality is most important (otherwise,
>I would not have purchased an Astro-Physics refractor!), but once an
>optical system hits a Strehl ratio of .98 or a wavefront of ~1/10 wave
>P-V, (assuming low higher order and chromatic aberrations), then aperture
>and seeing will be the deciding factors in planetary performance.
>Sincerely,
>Thomas M. Back
Bitter, are we?
I think all the original author meant was "wow, this is a really nice
scope." Your taking him a bit literally, arn't you?
faculty
Yes, well, I have this older 80mm Brandon that I am sure that will
outperform your "perfect" 7.1" Mr. Back! After all, I was told that one
can see detail on Ganymede with it! ;-)
Thomas Back wrote:
My 7.1", as earlier stated, has a measured wavefront
> of 1/25 wave P-V. This corresponds to a Strehl ratio of .9975! Or to be
> blunt about it, perfect, and only limited by seeing.
> Sincerely,
>
> Thomas M. Back
Chuck Lane
Hi Stew,
How does the price of the 5.2" APO MAX compare to the 5.1" AP?
I haven't seen any pricing on the new APOs.
Thanks
Chuck Lane
Stew Squires
In article <327A37...@mindspring.com> Chuck Lane wrote:
>How does the price of the 5.2" APO MAX compare to the 5.1" AP?
>I haven't seen any pricing on the new APOs.
>
AP has just opened a new run of 5.1's. They are still priced at $2,995.
Note that these are for an F/6. The APO MAX is an F/12 instrument and is
currently priced at $2,795. The AP comes with a 2.7" focuser and the APO MAX
comes with a 4" focuser. Projected delivery time is June 97 for the AP
5.1", HP Optics is just in the process of shipping some of the first scopes
in it's first run. Don't know about any additional runs at this time.
Note that I'm not affiliated with HP Optics, just liked what I read and what
I've heard about their scope.
-
Stew Squires
...islands lie behind the Sun that I shall raise ere day is done.
Bilbo's Last Song - J.R.R. Tolkein
Stewart Squires
Hi All,
My 5.2" APO MAX is scheduled to arrive on Monday. We are expected to go into
a weather pattern of increasing clouds on Sunday. While I have no
expectation that this 5.2" Super APO will come close to an Astro-Physics 7"
in times of excellent seeing (and certainly not the exquisitely AP-tweaked 7"
that Thomas has), there is the old line about smaller aperture performing
better in difficult seeing, due to the smaller column of air that the 5.2"
would be looking through. As the quote that generated this thread was
describing Jupiter, it may have been early in the evening and possibly low in
sky, when seeing would have been questionable. Whatever the case, for good
optics, we are back to largest aperture wins and seeing is the overall
decider of image quality, as Thomas has indicated.
As for the 5.2" APO MAX, I do expect superb optical performance for its
aperture, and I have already received reports to this effect from others that
have used it. From work done by John Ongutok and others on the OTF threads,
I believe it will compare well against the 7" Questar on planetary detail. I
will certainly let you all know.
-
Stew Squires
... islands lie behind the sun that I shall raise ere day is done.
Bilbo's Last Song, J.R.R. Tolkien
Thomas Back
>am...@cleveland.Freenet.Edu (Thomas Back) wrote:
>>Sincerely,
>>Thomas M. Back
>Bitter, are we?
Why do you consider my post as bitter? I'm just pointing out
the optical reasons why two optically excellent Apo's refractors of
different apertures will perform differently, with the larger aperture
performing better, under conditions of good seeing. Is that so hard
to understand?
Thomas M. Back
B Yen
> In article <327A37...@mindspring.com> Chuck Lane wrote:
> >How does the price of the 5.2" APO MAX compare to the 5.1" AP?
> >I haven't seen any pricing on the new APOs.
> >
>
> AP has just opened a new run of 5.1's. They are still priced at $2,995.
> Note that these are for an F/6. The APO MAX is an F/12 instrument and is
> currently priced at $2,795. The AP comes with a 2.7" focuser and the APO MAX
> comes with a 4" focuser. Projected delivery time is June 97 for the AP
> 5.1", HP Optics is just in the process of shipping some of the first scopes
> in it's first run. Don't know about any additional runs at this time.
>
> Note that I'm not affiliated with HP Optics, just liked what I read and what
> I've heard about their scope.
Can someone give some background/info on HP Optics (do they have a
homepage?).. I remember seeing an advertisement by AP, for an optician a
few yrs back. Was HP started by a former AP employee?
Stewart Squires
In article <byen-01119...@pas-ca13-01.ix.netcom.com> B Yen wrote:
>Can someone give some background/info on HP Optics (do they have a
>homepage?).. I remember seeing an advertisement by AP, for an optician a
>few yrs back. Was HP started by a former AP employee?
The company is owned by Fred Mrozek. He was formally associated with
Astro-Physics, but I believe it was many years ago. Their address and
numbers are:
HT Precison Optics (didn't get the name right in a previous post)
44 Main Street
German Valley, Illinois 61039-0097
815-362-2608
815-362-2234 (Fax)
Thomas Back
Well, I appreciate the post, but I do have to correct you a bit.
I never said my telescope is perfect (no optic is) but there is
a limit to what seeing and the eye can perceive. At a certain
quality level, you are just not going to see any more detail on
a planet, unless the seeing gets better or you have more aperture
with the same quality optics. Also, it was not the 80mm Brandon
that was quoted as being able to see detail on Ganymede, it was
the 94mm f/7 Brandon.
Thomas M. Back
R. Michael Harvey
>
>
> Also, it was not the 80mm Brandon
>that was quoted as being able to see detail on Ganymede, it was
>the 94mm f/7 Brandon.
>
>
>Thomas M. Back
>
>
>
Hello, Thomas!
It's good to see your postings again... seems forever
since the 'old days' on PRODIGY!
To those who do not already know...Thomas is one of our
foremost experts on optics... a fact I was not aware of when I challenged
his expertise' a couple of times years ago. My initial embarassment at
being corrected soon turned to profound respect for his skills and
knowledge.
To any of you who may confuse his matter-of-fact style
with arrogance or conceit...think again. Often this form of communication
is rife with misunderstandings of intent. Instead of being quick to take
offense when none is intended, take ADVANTAGE of his rich knowledge as a
resource of this forum.
P.S. Reports of 'detail' on Ganymede with small scopes
is not unknown. Dan Gordon, of Spectra Astrosystems, demonstrated this
with a 4" Takahashi at the Winter Star Party several years ago. In sub-arc
second seeing there was definitely a 'mottled' appearance to the
satellite's surface, although I'd classify it as more of a contrast/albedo
effect than real 'detail'. A number of experienced observers confirmed
this observation.
Mike Harvey
Thomas Back
Mike Harvey wrote --
Hello Mike,
Good to hear from you again, and yes, who could forget the
good old days at Prodigy! I must say we had a pretty wild time of
it back then. Thanks for the nice comments, and for helping me
express what the meaning of my post truly was.
As for seeing detail on Ganymede through a small telescope,
let me pass on some information, that may be of some interest.
In the Journal of the Royal Astronomical Society of Canada,
Issue No. 286, September 1939, E. M. Antoniadi (The greatest
of all planetary observers) wrote the article "On the Markings
of the Satellites of Jupiter in Transit". I'll quote one
paragraph -- "On 1849, February 11, the eagle-eyed Dawes, using
only a 6 1/3 inch refractor, discovered two roughly oval dusky
spots on this moon (Ganymede) in transit, which were situated
chiefly in its northern hemisphere, and which appeared separated
by a faint half-tone, stretching from south-west to north-east.
This is indeed a wonderful achievement....
I (E.M. Antoniadi) was enabled to confirm in 1926 and 1927,
at Meudon (with the 32.7 inch f/20 refractor!) the existence
of all these spots.
I think this puts to rest the misguided idea that it is
impossible for a small telescope (~6 inches) to see detail
on one of the moons of Jupiter. How small, I can't say, but
with today's improved Apochromatic refractors, with perfect
seeing and good eyesight, someone could possibly better Dawes
observation.
Sincerely,
Thomas M. Back
John Ongtooguk
R. Michael Harvey (#Mik...@popd.ix.netcom.com) wrote:
: To any of you who may confuse his matter-of-fact style
: with arrogance or conceit...think again. Often this form of communication
: is rife with misunderstandings of intent. Instead of being quick to take
: offense when none is intended, take ADVANTAGE of his rich knowledge as a
: resource of this forum.
I'll second that.
John Ongtooguk (jo...@vcd.hp.com)
Todd Gross
> To those who do not already know...Thomas is one of our
>foremost experts on optics... a fact I was not aware of when I challenged
>his expertise' a couple of times years ago. My initial embarassment at
>being corrected soon turned to profound respect for his skills and
>knowledge.
> To any of you who may confuse his matter-of-fact style
>with arrogance or conceit...think again. Often this form of communication
>is rife with misunderstandings of intent. Instead of being quick to take
>offense when none is intended, take ADVANTAGE of his rich knowledge as a
>resource of this forum.
Hi Mike and Thomas!
I agree with you are Mr. Back, very knowledgeable, as is yourself.
I actually have tapped both of you for good, knowledgeable information in the
past week, and I have identified a disagreement between the two of you.
Thomas feels that a 7" APO such as an A/P will show more detail on Jupiter,
etc, on low contrast features than a larger DOB with an exc. mirror (such as
Galaxy) if one looks real close. He claims the initial view will be more
impressive in the reflector, but it really won't compare in the end to the 7"
Mike, you feel that there is "no contest", that the 7" is incredible, and
indeed you are buying the new Televue 140.. but that the large aperture scope
will do better on Jupiter, and planets.
Thomas felt that perhaps Florida (where you are) was an exception with sub-1/2
arc second seeing, but still I feel there is a difference of opinion on this
matter, and I would like to get more opinions from you and very knowledgeable
planetary observers which route one would take for the best planetary view.
Thanks in advance!
Thanks! - Todd
_________________________________
BOSTON TV METEOROLOGIST TODD GROSS
Weather/Astronomy Home Page: http://www.weatherman.com
Administrator, Meade Advanced Product User Group: ma...@shore.net
Administrator, New England Weather Observer Mail List: wxob...@shore.net
IRC Channel Operator: #Weather (Undernet)
Originator of the NE.WEATHER newsgroup
_________________________________
Email: to...@weatherman.com Work Phone# (617)725-0777
Thomas Back
Hi Sue and Alan,
It's been a long time, hope everything is going well.
AstroFest '97 will be held on September 5, 6 and 7th.
Hope to see you there. I've heard the same about CompuServe,
and a lot of people are jumping to AOL now because of the
new pricing. I'll repost the first post in the thread for
your information.
diffraction rings. My 7.1", as earlier stated, has a measured wavefront
of 1/25 wave P-V. This corresponds to a Strehl ratio of .9975! Or to be
blunt about it, perfect, and only limited by seeing. Now, other factors
must be considered, such as color correction, astigmatism, scatter and
spherochromatism. However, at f/9, using a very advanced triplet oil-
spaced design with the FPL glasses, Astro-Physics' new Opticam SX
microgrind system, supersmooth polishing techniques and interferometer
figured and tested lenses, the levels of these other aberrations are
vanishingly small. Thus, once again, aperture dominates the level of
contrast that will be seen though these two telescopes, with the 7.1"
at a much higher level, and this assumes that the 5.2" has a Strehl ratio
as high as my 7.1". As anyone who saw Saturn though my 7.1" during good
seeing at powers as high as 405x, the level of contrast and resolution
were much higher than the 5.2" APO MAX.
Stewart Squires
I just received my 5.2" APO MAX. While I will go into more detail in future
postings (like after I return from Houston, near the end of the week) I
wanted to pass on my extreme pleasure at the outward appearance of this
telescope. Everything from the case to the machine work and finish looks
very nice indeed. As an f/12, it is very long. The 4" focuser is a
tremendous piece of work, and it appears that an extension tube for the
focuser and the 2" and 1.25" adapters are all here. I have to get my rings
(custom Parallax) drilled and an adaptor plate from Losmandy for the G-11.
It won't see first light till Saturday. Almost a moonless sky. Could this
be an end to the new scope = fresh clouds syndrome? Probably not, but one
can always hope.
Greg Granville
I'd like to see some planetary images taken with a 5"-7" APO that equal
those taken by Don Parker with his newtonian. Can anyone guide me to a web
site that has an example of such images?
Maybe someone should tell Parker than he's crippling himself with that
16" reflector :-)
~~~
Greg Granville Applied Research Lab - PSU
gr...@laser.arl.psu.edu gr...@penn.com
http://users.penn.com/~greg
Thomas Back
Hi Stew,
There maybe a misunderstanding of what I said to Todd about
the planetary performance of a 7" APO, compared to a 14.5" Dob.
Todd wrote --
>Hi Mike and Thomas!
>I agree with you are Mr. Back, very knowledgeable, as is yourself.
>I actually have tapped both of you for good, knowledgeable information in the
>past week, and I have identified a disagreement between the two of you.
>Thomas feels that a 7" APO such as an A/P will show more detail on Jupiter,
>etc, on low contrast features than a larger DOB with an exc. mirror (such as
>Galaxy) if one looks real close. He claims the initial view will be more
>impressive in the reflector, but it really won't compare in the end to the 7"
>Mike, you feel that there is "no contest", that the 7" is incredible, and
>indeed you are buying the new Televue 140.. but that the large aperture scope
>will do better on Jupiter, and planets.
>Thomas felt that perhaps Florida (where you are) was an exception with
>sub-1/2 arc second seeing, but still I feel there is a difference of opinion on
>this matter, and I would like to get more opinions from you and very
>knowledgeable planetary observers which route one would take for the best
>planetary view.
>Thanks in advance!
>Thanks! - Todd
Here in Ohio and Boston (plus a good part of the US) seeing limits
planetary definition to apertures of around 6" to 10", and a good
many nights to under 5". In locations like South Florida, Mount Wilson,
Hawaii, etc.. seeing can better 1/2 arc second, and for long periods of
time. Under these conditions, a large aperture Newtonian with excellent
optics and a small obstruction will be the ideal plantary scope (unless
you can purchase a 14" APO!). Just look at Don Parker's results.
However, being in this hobby for 30 years, and studying the planets
in crapy seeing with 100's of different telescopes of every optical
type and aperture, a very finely figured semi-large Apochromatic refractor
shows me the highest, most stable definition of any telescope. I do
not consider the typical fast newtonian a planetary instrument (and if the
truth would be known, most of these mirrors are in the 1 wave to 1/2 wave
P-V wavefront quality). Mike Harvey went the extra distance to have his
Galaxy mirror figured to a higher wavefront, and with the small obstruction
and the superb seeing in Florida, will without question, give him better
views of the planets than a 7" APO. But you must consider your seeing,
and how far you're willing to optimize your newtonian, if you want to
better the planetary performance of a Apochromatic refractor.
Sincerely,
Thomas M. Back
Jay Reynolds Freeman
> It won't see first light till Saturday. Almost a moonless sky. Could this
> be an end to the new scope = fresh clouds syndrome? Probably not, but one
> can always hope.
New telescopes do not always give rise to clouds. Volcanic eruptions
are an acceptable alternative. Enjoy your APO Max.
--
Jay Reynolds Freeman -- fre...@netcom.com -- I speak only for myself.
Stewart Squires
In article <toddg.964...@weatherman.com> Todd Gross wrote:
>Thomas feels that a 7" APO such as an A/P will show more detail on
> Jupiter,
>etc, on low contrast features than a larger DOB with an exc. mirror (such
> as
>Galaxy) if one looks real close. He claims the initial view will be more
>impressive in the reflector, but it really won't compare in the end to the
> 7"
What is the size of the central obstruction in the Dob. We should be well
away from the 30-33% we see in our Maks and SCTs. Perhaps John Ongtooguk
could prepare an OTF comparison between a 7" refractor and an 10, 12, or
maybe an 18" reflector with 20-25% obstruction. Also, how would this type of
analysis hold on low contrast features?
And I am reminded of a Celestron brochure showing the difference in lunar
detail between a 3.5" telescope and their 14" SCT. This was really amazing.
Gary Seronik
Thomas Back <am...@cleveland.Freenet.Edu> wrote in article
<55l8h6$c...@alexander.INS.CWRU.Edu>...
>Mike Harvey went the extra distance to have his
> Galaxy mirror figured to a higher wavefront, and with the small
obstruction
> and the superb seeing in Florida, will without question, give him better
> views of the planets than a 7" APO. But you must consider your seeing,
> and how far you're willing to optimize your newtonian, if you want to
> better the planetary performance of a Apochromatic refractor.
>
>
> Sincerely,
>
>
> Thomas M. Back
>
Hi Thomas:
Although I doubt that your intention was to leave readers with the opinion
that the APOs are magic, it is worth repeating that a well made and
properly baffled Newtonian of the same aperture will perform similarly to
the 7". I suspect that a long focus (f/7 or greater) 8" would give the 7"
a serious run for its money and perhaps even provide superior views if the
mirror is properly figured and SMOOTH. The point being that if you're
serious about planetary viewing and your seeing will not permit the use of
larger apertures, then the solution is a smaller scope - refractor OR
reflector. Having said that, you do have to pay the price for the level of
performance planetary viewing demands. This means that you're probably
going to wind up with an APO since superior quality Newtonians do not seem
to survive in the telescope market place. The only way to get a small high
quality Newtonian is to build it yourself. If a company lavished as much
attention and expense upon a Newtonian as Roland does his refractors, then
they'd probably cost about the same but perform the same. It's a shame
that there is not AP of Newtonians. The only thing that probably comes
close is Cerevolo's Mak-Newts, but having never seen one I can't comment
from direct experience. Alas, there are no magic telescopes - well made
scopes will always out perform those that are not, regardless of design.
In other words, the difference between a $5,000 scope and a $500 scope is
greater than the difference between refractors and Newtonians.
Gary in Vancouver
(Thomas, sorry for using your posting as an excuse to editorialize.)
spooner
Thomas Back wrote:
>
> In the Journal of the Royal Astronomical Society of Canada,
> Issue No. 286, September 1939, E. M. Antoniadi (The greatest
> of all planetary observers) wrote the article "On the Markings
> of the Satellites of Jupiter in Transit". I'll quote one
> paragraph -- "On 1849, February 11, the eagle-eyed Dawes, using
> only a 6 1/3 inch refractor, discovered two roughly oval dusky
> spots on this moon (Ganymede) in transit, which were situated
> chiefly in its northern hemisphere, and which appeared separated
> by a faint half-tone, stretching from south-west to north-east.
> This is indeed a wonderful achievement....
>
> I (E.M. Antoniadi) was enabled to confirm in 1926 and 1927,
> at Meudon (with the 32.7 inch f/20 refractor!) the existence
> of all these spots.
>
> I think this puts to rest the misguided idea that it is
> impossible for a small telescope (~6 inches) to see detail
> on one of the moons of Jupiter. How small, I can't say, but
> with today's improved Apochromatic refractors, with perfect
> seeing and good eyesight, someone could possibly better Dawes
> observation.
>
> Sincerely,
>
> Thomas M. Back
Hi,
I believe I read where Dawes used this scope to independently discover
the Crepe ring. His vision and optics were undoubtedly superb. Given the
drastic difference between my left and right eye, it would be hard to
think that more extreme differences could not help but exist between
individuals. As far as scopes, I have no preference other than better
quality over worse (same size). The APOs generally do very well but I
have not used many in truely excellent seeing. I did get a chance with a
virtually perfect 120ED in superb seeing but to the way my eyes work
(and I feel this is critical) I prefered the 6.5" Newtonian. But with
years of exposure to sun and age rearing its unkind presence, I really
need the extra light. Neither of these telescopes came from a dept.
store. There are excellent reflectors out there but they rarely show at
the same time as good seeing. Perhaps they are home because only the big
Newts get noticed at star parties. I would not purchase any telescope on
the hope that Ganymede would reveal detail. But I look with the ones I
have even with their faults. I'm not sure I discern contrast well enough
to ever succeed. I have little problem with Cassini's division or the
six members in the Trapezium (sp) as long as the magnification is
adequate (in a 6"). For most people the seeing is the limiting factor
most of the time. Seeing good enough to not limit a 6 to 8" scope is
somewhat rare in my experience although being willing to try and try
again increases the odds. Good scopes will definitely improve images
most of the time, but superb seeing is needed to let them work as
intended. I'm not willing to turn down any chance to look thru a nice
APO because I don't own one. Some day I hope I do have one if only to
get a chance to try it on that perfect night. But I've been building and
using telescopes for 30 years and I still find things that astound and
delight my eyes. After a few sights this past 2 or 3 years, I believe I
shall not doubt the abilities or accomplishments of others, but perhaps
try to exceed the limits I locked myself in with. One limit I must
retain until I can disprove it. That is that a perfect scope will not
outperform a larger perfect scope in perfect seeing (keeping obstruction
in its proper perspective). The trick may be in quantifying all these
conditions.
Don't really know what my point is except that I hope we don't limit
others by some of the things we consider on newsgroups such as this. I
NEVER looked for the Veil nebula for over 25 years because all I'd read
indicated futility. I SAW it with an unfiltered 6" reflector about 4
years ago and had an amazing OIII view thru a 4" AP this past summer.
All those years ...
Regards,
Mike
Todd Gross
Thomas, the below is what I suspected, and a very clear explanation, thanks
for the clarification!
As discussed, I am on the verge of buying such a scope, but also considering
that refractor!
Thanks
> Here in Ohio and Boston (plus a good part of the US) seeing limits
>planetary definition to apertures of around 6" to 10", and a good
>many nights to under 5". In locations like South Florida, Mount Wilson,
>Hawaii, etc.. seeing can better 1/2 arc second, and for long periods of
>time. Under these conditions, a large aperture Newtonian with excellent
>optics and a small obstruction will be the ideal plantary scope (unless
>you can purchase a 14" APO!). Just look at Don Parker's results.
> However, being in this hobby for 30 years, and studying the planets
>in crapy seeing with 100's of different telescopes of every optical
>type and aperture, a very finely figured semi-large Apochromatic refractor
>shows me the highest, most stable definition of any telescope. I do
>not consider the typical fast newtonian a planetary instrument (and if the
>truth would be known, most of these mirrors are in the 1 wave to 1/2 wave
>P-V wavefront quality). Mike Harvey went the extra distance to have his
>Galaxy mirror figured to a higher wavefront, and with the small obstruction
>and the superb seeing in Florida, will without question, give him better
>views of the planets than a 7" APO. But you must consider your seeing,
>and how far you're willing to optimize your newtonian, if you want to
>better the planetary performance of a Apochromatic refractor.
>Sincerely,
>Thomas M. Back
Thanks! - Todd
Thomas Back
>I'd like to see some planetary images taken with a 5"-7" APO that equal
>those taken by Don Parker with his newtonian. Can anyone guide me to a web
>site that has an example of such images?
>Maybe someone should tell Parker than he's crippling himself with that
>16" reflector :-)
>~~~
>Greg Granville
Greg,
What's your point? I said that Don Parker's images are better than
any smaller scope. I would suggest that you read my posts a little more
carefully!
Thomas M. Back
John Ongtooguk
Jay Reynolds Freeman (fre...@netcom.com) wrote:
: Amazing how expectations limit what you see. I was introduced to the
: Veil in the late 1970s by members of the San Jose Astronomical Association
: (San Jose, California), who regarded it as a moderately easy object in
: medium aperture. So I did not think twice about looking for it in
: apertures as small as a 7x50 binocular. And I found it.
True. Under a less than perfect but decent sky I've also found the
Veil in unfiltered 7x50 binoculars, and also with my 50mm refractor.
John Ongtooguk (jo...@vcd.hp.com)
Thomas Back
Hi Gary,
>Hi Thomas:
>Although I doubt that your intention was to leave readers with the opinion
>that the APOs are magic, it is worth repeating that a well made and
>properly baffled Newtonian of the same aperture will perform similarly to
>the 7". I suspect that a long focus (f/7 or greater) 8" would give the 7"
>a serious run for its money and perhaps even provide superior views if the
>mirror is properly figured and SMOOTH.
No, I'm sorry, I can't agree with this. At the Manhoning Valley
star party, I had my 7 setup next to the finest 10" f/9 newtonian
I've seen in my life. The seeing was excellent and the mirror was
very smooth. On Saturn, the belt and zone contrasts were much higher,
as well as the Cassini division and the crepe ring, as see through my
Astro-Physics 7.1". I don't call it magic, it's the transfer of
contrast though the whole system that made the difference.
Thomas M. Back
Thomas Back
>Hi Gary,
>>Hi Thomas:
>Thomas M. Back
I can see I opened myself up to another misunderstanding
(and Heaven knows a few people in this thread had this problem!).
I'm not saying a 10 Newtonian cannot better a 7.1" APO. What I
am saying is that under real world conditions, a superbly figured
7" APO outperformed (in contrast) a 10" newtonian. This is because
of many factors such as: Poorer wavefront than the APO; tube currents;
obstruction and spider diffraction; scatter from two mirror surfaces
(coating and the 16x factor of roughness of reflective surfaces vs
refractive surfaces); collimation and the greater sensitivity of the
larger aperture to seeing, plus the obstruction added seeing component.
There may be a 10" newtonian that has better contrast than my AP 7.1",
but I have not seen it.
Sincerely,
Thomas M. Back
Tim Gillespie
Thomas:
Interesting thread... However, first you point out that you had your
scope set up next to the "finest 10" f9 newtonian" you had ever seen,
and then you go on to say that the difference in contrast may be due to
(among other things) poorer wavefront in the newt. Isn't this a bit
contradictory? A well corrected newt should have no detectable wavefront
error. Furthermore, although the spider and secondary do induce some
broadening of the diffraction pattern (thereby reducing contrast), the
pattern envelope itself is narrowed due to the 30% larger diameter
(smaller pattern, hence greater contrast) of the aperture. Indeed, the
greater light grasp (almost twice as much) would also serve to
compensate for the obstructions effects. Finally, glass also scatters
light, albeit not as much as reflection off of a mirror surface. I am
curious, where did you get the 16x scattering figure for reflection
versus refraction? I am sure mirrors scatter more light than refractors,
but I didn't think it was that much more. A well polished mirror can be
every bit as smooth as a refractor element's surface, and if it is
overcoated, I cannot imagine it scattering 16 times more light. Hmmm.
Anyway, my point is that it is indeed possible for a 10" newtonian to
match and even outperform the 7.1 APO. Don't get me wrong, the AP is a
fine instrument. In overall craftsmanship, I am sure it is the jewel of
all of the star parties that you attend. I am truly envious.
However, no Ferrari owner, after shelling out huge bucks, wants to admit
that a Dodge Viper can out-perform his car for less that 1/4 of the
price. He takes solace, though, in knowing that his Ferrari is a truly
beautiful hand-crafted work of art.
For my money, though, I'll take the Viper...
--
___ _____
Tim .'/,-Y" "~-.
Gillespie l.Y ^.
/\ _\_
i ___/" "\
| /" "\ o !
l ] o !__./
\ _ _ \.___./ "~\
X \/ \ ___./
( \ ___. _..--~~" ~`-.
` Z,-- / \
\__. ( / ______)
\ l /-----~~" /
Y \ /
| "x______.^
| \
j Y
Jay Reynolds Freeman
> Don't really know what my point is except that I hope we don't limit
> others by some of the things we consider on newsgroups such as this. I
> NEVER looked for the Veil nebula for over 25 years because all I'd read
> indicated futility. I SAW it with an unfiltered 6" reflector about 4
> years ago and had an amazing OIII view thru a 4" AP this past summer.
Amazing how expectations limit what you see. I was introduced to the
Veil in the late 1970s by members of the San Jose Astronomical Association
(San Jose, California), who regarded it as a moderately easy object in
medium aperture. So I did not think twice about looking for it in
apertures as small as a 7x50 binocular. And I found it.
--
R. Michael Harvey
squi...@gnn.com (Stewart Squires) wrote:
>
>In article <toddg.964...@weatherman.com> Todd Gross wrote:
>>Thomas feels that a 7" APO such as an A/P will show more detail on
>> Jupiter,
>>etc, on low contrast features than a larger DOB with an exc. mirror (such
>> as
>>Galaxy) if one looks real close. He claims the initial view will be more
>>impressive in the reflector, but it really won't compare in the end to the
>> 7"
>
>What is the size of the central obstruction in the Dob. We should be well
>away from the 30-33% we see in our Maks and SCTs. Perhaps John Ongtooguk
>could prepare an OTF comparison between a 7" refractor and an 10, 12, or
>maybe an 18" reflector with 20-25% obstruction.
>
Stewart....
I use two different diagonals in my 18". A 4" for deepsky
observing at low power with a binocular viewer, and a 2.6" for high-power
planetary purposes. The latter produces a secondary obstruction of only
14%.
Todd.......
I replaced my big refractors (including a custom 6" f/15
APO Triplet from AstroPhysics) with the short-focus (f/4.5) Newtonian. I
have never regretted the decision. As I have stated previously, the custom
-figured mirror in the 18" performs wonderfully and produces planetary
images that are superior to ANY refractor I've ever used, including an 8"
Alvan Clark and a 10" Zeiss.
If Thomas has suggested that a 7" refractor (even if
perfect) will deliver superior images to an 18" reflector then that
posting has escaped me. I would agree, however, that this performance
advantage is quite likely when comparing that 7" to a 'garden-variety'
18". Before I comment further I'd like to read what Thomas has to say.
As I pointed out, it's awfully easy to misunderstand when you don't have
all the info in front of you. Thomas???
Mike Harvey
Gary Seronik
Thomas Back <am...@cleveland.Freenet.Edu> wrote in article
<55o3ds$3...@alexander.INS.CWRU.Edu>...
>
> Hi Gary,
>
> >Hi Thomas:
>
> >Although I doubt that your intention was to leave readers with the
opinion
> >that the APOs are magic, it is worth repeating that a well made and
> >properly baffled Newtonian of the same aperture will perform similarly
to
> >the 7". I suspect that a long focus (f/7 or greater) 8" would give the
7"
> >a serious run for its money and perhaps even provide superior views if
the
> >mirror is properly figured and SMOOTH.
>
>
> No, I'm sorry, I can't agree with this. At the Manhoning Valley
> star party, I had my 7 setup next to the finest 10" f/9 newtonian
> I've seen in my life. The seeing was excellent and the mirror was
> very smooth. On Saturn, the belt and zone contrasts were much higher,
> as well as the Cassini division and the crepe ring, as see through my
> Astro-Physics 7.1". I don't call it magic, it's the transfer of
> contrast though the whole system that made the difference.
>
>
> Thomas M. Back
>
Thomas:
I wasn't there so I can't comment upon what other variables were at play
(eg. baffling, eyepieces, seeing conditions, etc.) but regardless, you'r
certainly on the money when you talk about contrast being the key. Is it
your view then that the Newtonian design precludes contrast of the order
found in a APO, or are you saying simply that one seldom (ever?) sees such
contrast in a reflector. If it's the former, have I got a telescope for
you to look through...
Gary in Vancouver.
Gary Seronik
John Ongtooguk <jo...@vcd.hp.com> wrote in article
<55nvrg$e...@news.vcd.hp.com>...
> Jay Reynolds Freeman (fre...@netcom.com) wrote:
>
> : Amazing how expectations limit what you see. I was introduced to the
> : Veil in the late 1970s by members of the San Jose Astronomical
Association
> : (San Jose, California), who regarded it as a moderately easy object in
> : medium aperture. So I did not think twice about looking for it in
> : apertures as small as a 7x50 binocular. And I found it.
>
> True. Under a less than perfect but decent sky I've also found the
> Veil in unfiltered 7x50 binoculars, and also with my 50mm refractor.
>
> John Ongtooguk (jo...@vcd.hp.com)
>
How true. I remember finding NGC604 (a small HII region in M33) with my
4.25" one night. When I told another observer, who had a 12.5", he
exclaimed "that's impossible!" He had a look and sure enough he could see
it too. Good thing I didn't ask him about it before I went looking!
Gary in Vancouver.
Gary Seronik
Thomas Back <am...@cleveland.Freenet.Edu> wrote in article
<55oe0d$b...@alexander.INS.CWRU.Edu>...
>
>
> >Hi Gary,
>
> >>Hi Thomas:
>
> >>Although I doubt that your intention was to leave readers with the
opinion
> >>that the APOs are magic, it is worth repeating that a well made and
> >>properly baffled Newtonian of the same aperture will perform similarly
to
> >>the 7". I suspect that a long focus (f/7 or greater) 8" would give the
7"
> >>a serious run for its money and perhaps even provide superior views if
the
> >>mirror is properly figured and SMOOTH.
>
>
> > No, I'm sorry, I can't agree with this. At the Manhoning Valley
> >star party, I had my 7 setup next to the finest 10" f/9 newtonian
> >I've seen in my life. The seeing was excellent and the mirror was
> >very smooth. On Saturn, the belt and zone contrasts were much higher,
> >as well as the Cassini division and the crepe ring, as see through my
> >Astro-Physics 7.1". I don't call it magic, it's the transfer of
> >contrast though the whole system that made the difference.
>
>
> >Thomas M. Back
>
>
>
> I can see I opened myself up to another misunderstanding
> (and Heaven knows a few people in this thread had this problem!).
> I'm not saying a 10 Newtonian cannot better a 7.1" APO. What I
> am saying is that under real world conditions, a superbly figured
> 7" APO outperformed (in contrast) a 10" newtonian. This is because
> of many factors such as: Poorer wavefront than the APO; tube currents;
> obstruction and spider diffraction; scatter from two mirror surfaces
> (coating and the 16x factor of roughness of reflective surfaces vs
> refractive surfaces); collimation and the greater sensitivity of the
> larger aperture to seeing, plus the obstruction added seeing component.
> There may be a 10" newtonian that has better contrast than my AP 7.1",
> but I have not seen it.
>
>
> Sincerely,
>
>
> Thomas M. Back
>
Oops - didn't see this post until I dashed off my reply. Wish we could get
together Thomas, I have a 6" f/9 that you should look through. You might
change your opinion...
Gary in Vancouver.
David W. Knisely
Re: refractive vs reflective surfaces. I am curious, where exactly did
you get the figure for a "16x factor in roughness of reflective surface
vs refractive surfaces"?
--
David W. Knisely, KA0CZC email: dk8...@navix.net
1616 North 14th St., Beatrice, Nebr. 68310
Prairie Astronomy Club, Inc. http://www.infoanalytic.com/pac/
BABYLON 5: Our last best hope for QUALITY science fiction.
Todd Gross
>Anyway, my point is that it is indeed possible for a 10" newtonian to
>match and even outperform the 7.1 APO. Don't get me wrong, the AP is a
>fine instrument. In overall craftsmanship, I am sure it is the jewel of
>all of the star parties that you attend. I am truly envious.
>However, no Ferrari owner, after shelling out huge bucks, wants to admit
>that a Dodge Viper can out-perform his car for less that 1/4 of the
>price. He takes solace, though, in knowing that his Ferrari is a truly
>beautiful hand-crafted work of art.
>For my money, though, I'll take the Viper...
Tim, I appreciate your points quite a bit, but the money aspect is
irrelevant to the way this thread has transpired. I , and others, are trying
to determine , in the "real world" whether or not it is possible to outperform
the best 7" refractors with the best larger aperture reflectors.. given superb
seeing conditions. Thomas seems to feel that it is possible in the very best
seeing, with the very best instruments, such as Mike Harvey's situation...but
that he hasn't seen it himself.
Todd Gross
>>
>Oops - didn't see this post until I dashed off my reply. Wish we could get
>together Thomas, I have a 6" f/9 that you should look through. You might
>change your opinion...
>Gary in Vancouver
What scope do you have?
Michael Edelman
: >Anyway, my point is that it is indeed possible for a 10" newtonian to
: >match and even outperform the 7.1 APO. Don't get me wrong, the AP is a
: >fine instrument. In overall craftsmanship, I am sure it is the jewel of
: >all of the star parties that you attend. I am truly envious.
While a 10" newtonian can provide excellent images with a well-figured
mirror, it is still going to have much more coma than a well-figured
7" refractor- at least in the common focal lengths.
--mike
J. D. McDonald
David W. Knisely wrote:
>
> Re: refractive vs reflective surfaces. I am curious, where exactly did
> you get the figure for a "16x factor in roughness of reflective surface
> vs refractive surfaces"?
I'll let Mr. Back directly answer the question. He's posted his reply,
in the deep dark past, and I can't see any scientific reason it could be
wrong, so I guess we must assume it right.
Nevertheless, I do know that it is easy to get mirror surfaces that
scatter
less than one part in 100000 of light into all angles. The amount of
that
that goes into your eyepiece is negligible, unless your are trying
to look at prominences on the sun. And I know that
my SCT has surfaces whose scattering component is totally dominated
by dust.
As I well know from my lab experience (just yesterday I got a factor
or three increase in light transmission off of four successive deep UV
reflectors by simply washing them!) dust really is a big problem.
Those who say "don't clean your optics" must only be looking at
faint fuzzies.
Doug McDonald
Greg Granville
In article <55nrso$6...@alexander.INS.CWRU.Edu> am...@cleveland.Freenet.Edu (Thomas Back) writes:
> What's your point? I said that Don Parker's images are better than
>any smaller scope. I would suggest that you read my posts a little more
>carefully!
Tom,
Uh, I wasn't replying to your post, although it might have sounded like it. I
hadn't even read your message yet when I posted than.
I'm not sure, but it sounds like maybe we agree that larger aperture and good
optics are more important than the specfic design of the instrument.
Greg Granville
>However, no Ferrari owner, after shelling out huge bucks, wants to admit
>that a Dodge Viper can out-perform his car for less that 1/4 of the
>price. He takes solace, though, in knowing that his Ferrari is a truly
>beautiful hand-crafted work of art.
>For my money, though, I'll take the Viper...
Great analogy Tim...
Personally, I tend to think of Astro-Physics as being a type of jewelery.
Finely made, exquisite details which are beautiful to gaze upon, but they
really don't contribute to the optical performance of the instrument.
Now, nobody misunderstand, they DO have an excellent optical system.
Although very expensive, they are at least available to those you would pay
the price. The problem with aquiring a reflector that could compete with them
is that it's almost impossible to BUY one - you have to make it yourself.
But - many people *do* make them for themselves. And their's no doubt that
there are some of these that are very nearly equivalent to the best of
anything you can buy - APO refractors not excluded.
Greg Granville
In article <55q1t8$g...@cwis-20.wayne.edu> m...@bob.pass.wayne.edu (Michael Edelman) writes:
>While a 10" newtonian can provide excellent images with a well-figured
>mirror, it is still going to have much more coma than a well-figured
>7" refractor- at least in the common focal lengths.
>--mike
This is getting a bit complicated. How do we do a fair comparison? Of course
a 6" F4.5 reflector will have more coma than a 6" F9 refractor. But wouldn't
it be more fair to compare two instruments of the same focal ratio? They
will, afterall, be roughly the same length.
Here's an area where certain Cassegrain designs can better either
a refractor or a newtonian. (A Ritchey-Chertien for example)
J. D. McDonald
Greg Granville wrote:
>
> In article <327FD5...@mail.tds.net> Tim Gillespie <tgil...@mail.tds.net> writes:
>
> >However, no Ferrari owner, after shelling out huge bucks, wants to admit
> >that a Dodge Viper can out-perform his car for less that 1/4 of the
> >price.
Believe me, it can't outperform a top-line Ferrari or Porsche.
> He takes solace, though, in knowing that his Ferrari is a truly
> >beautiful hand-crafted work of art.
Ferraris are no more hand crafted than Dodges. Really! They are crafted
by the best computer-controlled machine tools money can buy. They used
to
be hand crafted, true ... and that was why they were unreliable. So
they went to the automated stuff to get reliability.
I think that the scope producers need the same idea: get the computer
controlled polishers that ... gasp ... Hughes does. But please,
unlike Hughes, **test the final product on a real star**!
Doug McDonald
Rich Neuschaefer
Greg Granville wrote:
-snip
->
-> Personally, I tend to think of Astro-Physics as being a type of
jewelery.
-> Finely made, exquisite details which are beautiful to gaze upon, but
they
-> really don't contribute to the optical performance of the instrument.
-> Now, nobody misunderstand, they DO have an excellent optical system.
->
Hi Greg,
I'm glad there is a company like Astro-Physics that takes pride in fine
craftsmanship both in the machanical and optical parts of their tele-
scopes. I think they are reasonably price for what you are getting.
Rich
(my opinion only)
-> ~~~
-> Greg Granville Applied Research Lab - PSU
Rich Neuschaefer
Rich Neuschaefer wrote:
-> Hi Greg,
->
-> I'm glad there is a company like Astro-Physics that takes pride in
fine
-> craftsmanship both in the machanical and optical parts of their tele-
^
Oops, I'm glad AP builds better scopes than I spell. (mechanical)
Rich
-> scopes. I think they are reasonably price for what you are getting.
->
-> Rich
-> (my opinion only)
Rich Neuschaefer
Getting back to the original point of this thread... it is hard to
rely on reports by people walking around at a star party.
Rich
(my opinion only)
David W. Knisely
Re: Cassegrain designs "bettering" refractors or Newtonians. Sorry, but
most Cassegrain designs need large secondary mirrors which block and
scatter light. A refractor (properly made, of course) will usually
outperform a Cassegrain to a certain degree for this and other reasons.
A 6" Ritchey-Chretien system will have no coma, but a 6" f/10 Newtonian
has very little as well (plus a much smaller secondary). A 6" APO is
better still. The R/C design also has field curvature unless a field
flattener is used. Each design has its advantages, but the Cassegrain,
like so many other systems, is a compromise. A good Apochromat will
generally outperform most other telescopes to some degree, but the
difference may not be all that great to some people. The cost of APO's
is the biggest reason why they are not the most popular instrument. I
like to get a lot of bang for my buck, thus, I will probably always like
the Newtonian the best. Clear Skies to you.
Jay Reynolds Freeman
How interesting and surprising, that the amateur telescope market
never seems to have had a successful niche for extremely high-quality
long-focus Newtonians. You'd think someone would be selling well-made
6- and 8-inch f/10s, with well-figured optics produced using every
trick in the book to make their surfaces smooth, with small diagonals
mounted on spiders with very narrow struts, and with "shorty" focusers
to get the focal plane close to the diagonal. They wouldn't have the
potential for very wide-field views -- one would probably want a fully
illuminated field only a few mm across. Yet I suspect we would all
agree, that their performance at medium to high magnification would be
much closer to a high-end refractor than to most contemporary
Newtonians and SCTs of the same aperture, and at only a fraction of
the price.
Would anyone care to speculate on why no one has tried producing
such units? Does anybody remember any that I have forgotten. (In
the 1960s, most 6- and 8-inch commercial Newtonians were f/8, and
the f numbers got shorter as apertures increased. I seem to remember
that Cave would make a large, long-focus Newtonian if you ordered it
that way; I wonder what percentage of their customers did.)
Clive Gibbons
In article <327FD5...@mail.tds.net>,
Tim Gillespie <tgil...@mail.tds.net> wrote:
(much snipped...)
>greater light grasp (almost twice as much) would also serve to
>compensate for the obstructions effects. Finally, glass also scatters
>light, albeit not as much as reflection off of a mirror surface. I am
>curious, where did you get the 16x scattering figure for reflection
>versus refraction? I am sure mirrors scatter more light than refractors,
>but I didn't think it was that much more. A well polished mirror can be
>every bit as smooth as a refractor element's surface, and if it is
>overcoated, I cannot imagine it scattering 16 times more light. Hmmm.
Tim,
Not that Thomas needs any help defending his claims, but I think
Texereau's book (How to Make a Telescope (?)), goes into some detail on
the surface roughness of reflector optics. If memory serves (and it often
doesn't <g>), the number Thomas quotes sounds about right.
In any event, mirrors *do* scatter a heckuva lot more light than lenses,
given equivalent surface polish.
Cheers,
--
Clive Gibbons "I wasn't expecting the
Technician, Spanish Inquisition..."
McMaster University.
squi...@gnn.com
In article <3280D6...@tandem.com> Rich Neuschaefer wrote:
>Getting back to the original point of this thread... it is hard
to
>rely on reports by people walking around at a star party.
And I'm sure Fred Mrozek will appreciate all the times that 5.2"
APOMAX has shown up in our lists as a result of this thread.
Without looking at anything astronomical yet, I'm still very
impressed by this 5.2" telescope. Besides comparing it to
everything else I own, I will seek out other refractors to set it
up next to and start taking polls from those that pass by.
Stew Squires
Matt or Belinda Tarlach
Hi there!
I have a 1995 catalog from an outfit called Iowa Scientific Optical that
features a 6" f12 "planetary newtonian." They claim 1/16 wave optics
(which should be achievable, since a 6" f12 is darned close to
spherical). It uses a low-profile focuser, and mounts a 3/4" quartz
secondary (claimed 1/20 wave) in a curved-vane spider for no diffraction
spikes. The tube is "insulated aluminum." The tube assembly was
priced under $500 two years ago; with their own equatorial mount it
was a little over $1000.
_Astronomy_ magazine's telescope buying guide also shows a 6" f9 from
Parallax Instruments, with a 1" secondary. Their list price is quite
a bit higher.
Does anyone have experience with or knowledge of these instruments or
companies?
- Matt Tarlach, San Francisco
R. Michael Harvey
fre...@netcom.com (Jay Reynolds Freeman) wrote:
> How interesting and surprising, that the amateur telescope market
>never seems to have had a successful niche for extremely high-quality
>long-focus Newtonians.
>such units?
Jay......Joe Nastasi tried to do just that with his Parallax line of
Newtonians. They were extremely well crafted both mechanically and
optically and featured thin curved spyders, the smallest diagonals
possible, low-profile focusers etc. I used one of the 10" f/9's and found
it to be a teriffic planetary scope (although a verrrry large package...
finding a mount to match the scope was a problem!). Unfortunately there
does not appear to be a real market for such scopes. Joe only sold a few
and the company finally folded. I saw an ad in Starry Messenger a year or
so ago...Joe was selling his 'personal' 10". I seem to remember that it
was advertised at a ridiculously low price. Sad.
Mike Harvey
Dave Nash
fre...@netcom.com (Jay Reynolds Freeman) writes:
> How interesting and surprising, that the amateur telescope market
>never seems to have had a successful niche for extremely high-quality
>long-focus Newtonians. You'd think someone would be selling well-made
>6- and 8-inch f/10s, with well-figured optics produced using every
>trick in the book to make their surfaces smooth, with small diagonals
>mounted on spiders with very narrow struts, and with "shorty" focusers
>to get the focal plane close to the diagonal. They wouldn't have the
>potential for very wide-field views -- one would probably want a fully
>illuminated field only a few mm across. Yet I suspect we would all
>agree, that their performance at medium to high magnification would be
>much closer to a high-end refractor than to most contemporary
>Newtonians and SCTs of the same aperture, and at only a fraction of
>the price.
> Would anyone care to speculate on why no one has tried producing
>such units? Does anybody remember any that I have forgotten. (In
>the 1960s, most 6- and 8-inch commercial Newtonians were f/8, and
>the f numbers got shorter as apertures increased. I seem to remember
>that Cave would make a large, long-focus Newtonian if you ordered it
>that way; I wonder what percentage of their customers did.)
An intersting question, and one I'd be interested in hearing more on,
as I think that medium to long-focus reflectors are highly underrated
instruments.
I'd chalk it up to:
1) Aperture. Once Dobs got popular in the late 70s and early 80s a
lot of folks wanted the larger aperture, which tends to drive the
focal ratio down for various reasonably well-understood reasons
(sheer bulk reduction being the most apparent)
2) Need for transportability. Fifty years ago light pollution in all
but the biggest cities was much less of a problem than it is today.
People now often want telescopes they can put in the car and take to
a remote site (this probably accounts for at least part of the popularity
of SCTs as well). An f/4.5 telescope up to about 10" will fit easily in
most cars, but an f/8 will get difficult above an aperture of 6" or so
(for Newtonians at least; catadioptrics are another story of course).
As for historical long-focus reflectors: In the 50s the Fecker company
made a basic 4" f/8 or f/9 on an equatorial mount with a clock drive
(cost then: $200, and certainly a lot of that went into the mount and
drive) -- the University of Illinois Astronomical Society has one in
its scope collection. The UIAS also has a 12.5" f/6 of club design
and manufacture (commerical optics and components like focusers and
cells, homebuilt everything else) and a 10" f/6, both Dobs. The
latter is surprisingly easy for one person to transport, though some
care is needed with doorways.
There does seem to be a resurgence in longer focal lengths, at least
for Dobs up to 12" or so. In 1990, for instance, medium to large
reflectors much over f/5 were scarce unless you built your own. For
example you had the Coulter Dobs (all f/4.5) and the Meade DS-10 and
DS-16 equatorial Newtonians (also f/4.5). The Meade 10" and 12.5"
Dobs use similar OTAs and are still ~f/4.5 but Orion's 10" is f/5.6
and the Starmaster and Starsplitter truss tubed 10" Dobs are f/6. I
don't know of anyone who makes anything longer than f/6 in this size
range, but given the increasing popularity of truss-tube Dobsonians,
which partially relieve concern 2) above, I wouldn't be surprised if
some smallish company like Starmaster makes an 8" f/8 or even f/10
truss model sometime. Judging from this group, there'd be at least
some demand.
It's worth noting that with the appearance of good, well-corrected
wide-field eyepiece designs, a longer-focus scope can be more versatile
than it would have been, say 20 years ago. A 10" f/8 with a Nagler
would have a similar field of view to a 10" f/4.5 with an Orthoscopic
or similar design of the same focal length. The main problem here is
that a box full of such eyepieces is extremely expensive compared to
their older counterparts.
>--
> Jay Reynolds Freeman -- fre...@netcom.com -- I speak only for myself.
--
Dave Nash, School of Chemical Sciences, University of Illinois
E-mail: na...@aries.scs.uiuc.edu; WWW: http://www.scs.uiuc.edu/~nash/
--"It's 106 miles to the centerline, we've got a 10" scope, half a box
of eyepieces, it's getting dark, and we're wearing mylar glasses...HIT IT!"
Jay Reynolds Freeman
I wrote:
> > How interesting and surprising, that the amateur telescope market
> > never seems to have had a successful niche for extremely high-quality
> > long-focus Newtonians.
> > Would anyone care to speculate on why no one has tried producing
> > such units?
> Jay......Joe Nastasi tried to do just that with his Parallax line of
> Newtonians. They were extremely well crafted both mechanically and
> optically and featured thin curved spyders, the smallest diagonals
> possible, low-profile focusers etc. I used one of the 10" f/9's and found
> it to be a teriffic planetary scope (although a verrrry large package...
> finding a mount to match the scope was a problem!). Unfortunately there
> does not appear to be a real market for such scopes. Joe only sold a few
> and the company finally folded. I saw an ad in Starry Messenger a year or
> so ago...Joe was selling his 'personal' 10". I seem to remember that it
> was advertised at a ridiculously low price. Sad.
>
> Mike Harvey
Wow, I missed those entirely! I gather from your comments that they
were OTAs only. I would have thought that an optional Dobson mount
would have been feasible, and would have improved sales. I built a
12.5-inch f/6.3 for the San Jose club (my mounting, somebody else's
optics), that was usable at 500x -- I followed Mars through one
opposition with it quite nicely. That is an existence proof that one
can build Dobsons that can be used at substantial magnifications. A
10-inch f/8 would have the same tube length and less weight, an 8-inch
f/9 or f/10, or a 6-inch of that f-number, would have been feasible
and simple to mount.
Tim Gillespie
Jay Reynolds Freeman wrote:
[edited]
> Would anyone care to speculate on why no one has tried producing
> the 1960s, most 6- and 8-inch commercial Newtonians were f/8, and
> the f numbers got shorter as apertures increased. I seem to remember
> that Cave would make a large, long-focus Newtonian if you ordered it
> that way; I wonder what percentage of their customers did.)
>
Jay:
Being one who never passes up an opportunity to speculate... Although
some manufacturers have produced long-focus newts, they have npot been
entirely successful. The simple reason, IMO, is that the eyepeice is at
the wrong. Long newts are simply a pain to use, whereas long focus
refractors lend themselves nicely to comfortable observing positions.
--
___ _____
Tim .'/,-Y" "~-.
Gillespie l.Y ^.
/\ _\_
i ___/" "\
| /" "\ o !
l ] o !__./
\ _ _ \.___./ "~\
X \/ \ ___./
( \ ___. _..--~~" ~`-.
` Z,-- / \
\__. ( / ______)
\ l /-----~~" /
Y \ /
| "x______.^
| \
j Y
Carl Wilson
Greg Granville <gr...@laser.arl.psu.edu> wrote in article
<greg.100...@laser.arl.psu.edu>...
> In article <327FD5...@mail.tds.net> Tim Gillespie
<tgil...@mail.tds.net> writes:
>
> >However, no Ferrari owner, after shelling out huge bucks, wants to admit
> >that a Dodge Viper can out-perform his car for less that 1/4 of the
> >price. He takes solace, though, in knowing that his Ferrari is a truly
> >beautiful hand-crafted work of art.
>
> >For my money, though, I'll take the Viper...
>
> Great analogy Tim...
>
> Personally, I tend to think of Astro-Physics as being a type of jewelery.
> Finely made, exquisite details which are beautiful to gaze upon, but they
> really don't contribute to the optical performance of the instrument.
> Now, nobody misunderstand, they DO have an excellent optical system.
>
> Although very expensive, they are at least available to those you would
pay
> the price. The problem with aquiring a reflector that could compete with
them
> is that it's almost impossible to BUY one - you have to make it yourself.
> But - many people *do* make them for themselves. And their's no doubt
that
> there are some of these that are very nearly equivalent to the best of
> anything you can buy - APO refractors not excluded.
I've noticed that no one has mentioned the Meade APOs in this discussion.
How do they stack up compared with AP and other makers of refractors?
spooner
Jay Reynolds Freeman wrote:
>
> I wrote:
>
> > > How interesting and surprising, that the amateur telescope market
> > > never seems to have had a successful niche for extremely high-quality
> > > long-focus Newtonians.
> > > such units?
>
> > Newtonians. They were extremely well crafted both mechanically and
> > optically and featured thin curved spyders, the smallest diagonals
> > possible, low-profile focusers etc. I used one of the 10" f/9's and found
> > it to be a teriffic planetary scope (although a verrrry large package...
> > finding a mount to match the scope was a problem!). Unfortunately there
> > does not appear to be a real market for such scopes. Joe only sold a few
> > and the company finally folded. I saw an ad in Starry Messenger a year or
> > so ago...Joe was selling his 'personal' 10". I seem to remember that it
> > was advertised at a ridiculously low price. Sad.
> >
> > Mike Harvey
>
> Wow, I missed those entirely! I gather from your comments that they
> were OTAs only. I would have thought that an optional Dobson mount
> would have been feasible, and would have improved sales. I built a
> 12.5-inch f/6.3 for the San Jose club (my mounting, somebody else's
> optics), that was usable at 500x -- I followed Mars through one
> opposition with it quite nicely. That is an existence proof that one
> can build Dobsons that can be used at substantial magnifications. A
> 10-inch f/8 would have the same tube length and less weight, an 8-inch
> f/9 or f/10, or a 6-inch of that f-number, would have been feasible
> and simple to mount.
>
> --
>
> Jay Reynolds Freeman -- fre...@netcom.com -- I speak only for myself.
Hi Jay,
Sold the OTA of the 6.5 f/9.5 I had at the All Az Star Party for a
little over $300. I miss it already. It gave the best view of Saturn
I've seen to date. Most people wanted to look thru the 9" refractor I
had there and the views were pretty good in it, but I had to ask them if
they'd like a look thru a GOOD scope to look in a little Newt! The views
were actually pretty comparable, but in moments of superior seeing, the
reflector had a bit better contrast I felt. The scopes were at 308x in
the 6.5" and 270x in the 9". The 6.5 wasn't perfect with a bit of
roughness from using unmilled CeO to polish with and a very, very narrow
TDE that didn't bother. With a clear aperture of 6.3" it may have been
cramped a bit by the 7" aluminum tube but the images seemed okay to me
(probably biased to no end). :-)
I don't think steak will be the main diet of anyone building small long
focus reflectors for a living. But they're fun to build for a hobby!
Mike Spooner
P.S. We did have tremendous seeing at times at that star party at least
in my 30 years viewing.
Gary Seronik
Todd Gross <to...@weatherman.com> wrote in article
<toddg.965...@weatherman.com>...
>
> >>
> >Oops - didn't see this post until I dashed off my reply. Wish we could
get
> >together Thomas, I have a 6" f/9 that you should look through. You
might
> >change your opinion...
>
> >Gary in Vancouver
>
> What scope do you have?
>
>
>
It's home made - mirror and all. Did I mention it was a Newtonian?
Gary in Vancouver
Rich Neuschaefer
Hi Stew,
Rather than relying on "passers by" why not find some other APO owners
and do your own real side-by-side tests?
Rich
(my opinion only)
D. Brent Wilson
fre...@netcom.com (Jay Reynolds Freeman) wrote:
> How interesting and surprising, that the amateur telescope market
>never seems to have had a successful niche for extremely high-quality
>long-focus Newtonians. You'd think someone would be selling well-made
>6- and 8-inch f/10s, with well-figured optics produced using every
>trick in the book to make their surfaces smooth, with small diagonals
>mounted on spiders with very narrow struts, and with "shorty" focusers
>to get the focal plane close to the diagonal. They wouldn't have the
>potential for very wide-field views -- one would probably want a fully
>illuminated field only a few mm across. Yet I suspect we would all
>agree, that their performance at medium to high magnification would be
>much closer to a high-end refractor than to most contemporary
>Newtonians and SCTs of the same aperture, and at only a fraction of
>the price.
>
> Would anyone care to speculate on why no one has tried producing
>such units? Does anybody remember any that I have forgotten. (In
>the 1960s, most 6- and 8-inch commercial Newtonians were f/8, and
>the f numbers got shorter as apertures increased. I seem to remember
>that Cave would make a large, long-focus Newtonian if you ordered it
>that way; I wonder what percentage of their customers did.)
>
>--
>
> Jay Reynolds Freeman -- fre...@netcom.com -- I speak only for myself.
Our club (Milwaukee Astronomical Society) has two such Newtonians.
These monsters are both 12.5 inch scopes with f ratios of f/7.5 and
f8.5. Both are housed in seperate domes due to their great size. The
mounts are HUGE with 2 foot round setting circles. Both have great
mirrors and are excellent for planetary and deep-sky viewing.
Both scopes are old though, I don't know who produced them. But this
is just an example of such a design you mentioned. Both are used
daily by our clubs for all types of observing.
D. Brent Wilson
Senior Software Engineer
Penta Technologies, Inc. Views expressed are mine, and do
(414) 780-2432 not necessarily represent those
d...@PentaTechInc.com of Penta Technologies, Inc.
Wayne T. Hally
In article <freemanE...@netcom.com> fre...@netcom.com (Jay Reynolds Freeman) writes:
>From: fre...@netcom.com (Jay Reynolds Freeman)
>Subject: Re: APO MAX Advertisement -- 5.2" vs 7.1" APO's
>Date: Mon, 4 Nov 1996 17:01:45 GMT
>> It won't see first light till Saturday. Almost a moonless sky. Could this
>> be an end to the new scope = fresh clouds syndrome? Probably not, but one
>> can always hope.
> New telescopes do not always give rise to clouds. Volcanic eruptions
>are an acceptable alternative. Enjoy your APO Max.
Oh yeah???
I've had clouds 90% of all moonless nights since August when I got my new 8"
dob.
You'll never convince me!
(We don't have too many volcanos in NJ)
Wayne Tv
squi...@gnn.com
In article <328234...@tandem.com> Rich Neuschaefer wrote:
>Rather than relying on "passers by" why not find some other APO owners
>and do your own real side-by-side tests?
I thought I was being funny, but obviously not very.
Stew
Richard DeLuca
Does anybody remember any that I have forgotten. (In
> the 1960s, most 6- and 8-inch commercial Newtonians were f/8, and
> the f numbers got shorter as apertures increased. I seem to remember
> that Cave would make a large, long-focus Newtonian if you ordered it
> that way; I wonder what percentage of their customers did.)
>
> --
> Jay Reynolds Freeman -- fre...@netcom.com -- I speak only for myself.
Jay,
Let me tell you that back in the mid 70's I used an 'Optical Craftsman'
newtonian that was either f/9 or f/10. It had wonderfully contrasty
planetary images. If memory serves, it was the equal of my 6" AP apo.
Rich
Jim Van Nuland
>From: fre...@netcom.com (Jay Reynolds Freeman)
Regarding high-quality Newtonians....
> Would anyone care to speculate on why no one has tried producing
>such units? Does anybody remember any that I have forgotten.
When talking to beginners, I often recommend Newtonians vs.
Schmidt-Cass scopes. Then they go out and buy a S-C, often citing the
easily adaptable to photography. IMnsHO, they are fooling themselves,
as it is anything but cheap to buy the off-axis guider, camera, hypering
tank, etc. etc. etc. that will make the S-C "easily adaptable". I've
often wondered how many of these people will ever take a picture.
The short tube of the S-C and of the fast Newtonians is surely part of
the transportability issue. I will take issue with the need to go as
slow as f/8 to obtain very good images; my 8 inch f/6 performs very well
on planets, with Orthoscopic oculars. The wizzy high-end glass is needed
at f/4, but by f/6 things are much easier.
If I were to think about the "dream scope" for planetary observation, I
would probably think about 10 inches at f/6, small diagonal, low-profile
etc. And I would pay very close attention to having a very smooooooth
surface (just ordinary smooth is not enough); and an excellent figure,
f/10 at the eyepiece, to fully utilize those nights when the air seems to
have gotten out of the way.
Now if only I could dream up better eyeballs than my own....
___
X SLMR 2.1a X Jim Van Nuland, San Jose (CA) Astro.Assoc.; IOTA member
--
|Fidonet: Jim Van Nuland 1:143/11
|Internet: Jim.Van...@sjpc.us.com
|
| Standard disclaimer: The views of this user are strictly his own.
Ebert Steele
A few years ago I purchased a Criterion 6" f8 on Newtonian on an
equatorial mount in a garage sale for $10. The tube was in bad shape and
I dismanteled it and kept the parts. Mirror needs resilvering. Does this
classify as a "long-focus?" Is it worth rebuilding?
Thanks,
--
___________________________________________________
Ebert Steele
K5CAD
La Marque, Texas
Jim Van Nuland
> How interesting and surprising, that the amateur telescope market
>never seems to have had a successful niche for extremely high-quality
>long-focus Newtonians. You'd think someone would be selling well-made
>6- and 8-inch f/10s, with well-figured optics produced using every
>trick in the book to make their surfaces smooth, with small diagonals
>mounted on spiders with very narrow struts, and with "shorty" focusers
>to get the focal plane close to the diagonal. [...]
In the early '70s when I bought my own 8 inch f/6, there were a number
of companies making good Newtonians: Cave, Criterion, Optical Craftsmen.
Cave's were a bit longer, f/7, I think. They were general-purpose
scopes, so the diagonal was larger than your suggested one; and the tall
focusser was the only kind anyone had thought of. Mounts were all
equatorial, as nobody had realized that an alt/az mounting was practical.
Compared to today's scopes (that is, allowing for inflation) they were
expensive instruments.
You might ask "What happened to the market for such scopes?" We here in
the States have gotten too price conscious, unwilling to pay for quality.
Europeans have often commented about that, here and (especially) on
FidoNet's Astronomy echo. The result has been that most (surviving)
makers have concentrated on the low-end -- where the sales are. There
are a few U.S. makers of high-quality scopes, the Obsession, for one.
But these are large scopes! This, too, is part of the answer to your
question: buyers are looking for large scopes.
Recently, Peter Ceravolo has offered very high-quality instruments of
moderate aperture. I understand that they are superb, expensive (but
only as compared to the low end), and rare.
___
X SLMR 2.1a X
R.A.
Thomas Back wrote:
In article <327FD5...@mail.tds.net> Tim Gillespie
tgil...@mail.tds.net>
writes:
However, no Ferrari owner, after shelling out huge bucks, wants to admit
that a Dodge Viper can out-perform his car for less that 1/4 of the
price. He takes solace, though, in knowing that his Ferrari is a truly
beautiful hand-crafted work of art.
For my money, though, I'll take the Viper...
Great analogy Tim...
Personally, I tend to think of Astro-Physics as being a type of jewelery.
Finely made, exquisite details which are beautiful to gaze upon, but they
really don't contribute to the optical performance of the instrument.
Now, nobody misunderstand, they DO have an excellent optical system.
Although very expensive, they are at least available to those you would
pay
the price. The problem with aquiring a reflector that could compete with
them
is that it's almost impossible to BUY one - you have to make it yourself.
But - many people *do* make them for themselves. And their's no doubt
that
there are some of these that are very nearly equivalent to the best of
anything you can buy - APO refractors not excluded.
Greg Granville
Great analogy? I'd hate to be in the room of a Ferrari F-40 owner
after Tim made that comment. Tim, do you really think a Viper
will out-perform a Ferrari F-40? And that's not even their top-
of-the-line road car.
Astro-Physics being a type of jewelry? OK, that does it.
This will be my last post on this subject. There are people in
this world who can afford high quality instruments (of any kind)
and others who cannot or will not. The cannot's will always say
that their cheaper "instrument" is just as good as the more
expensive one. If it makes them feel better, that's fine. But until
you own one (and not just take a quick look at a star party), you
will NEVER know the quality of the images that are seen through
such instruments.
With my 7.1" Astro-Physics f/9 EDT, in the less than perfect
seeing and light polluted skies of Northern Ohio, I have seen
the following --
9 craterlets in Plato.
Olympus Mons on Mars with a 13 arc second disk.
6 stars in the Trapezium is a joke it is so easy.
The Alpine Valley cleft (and not just a section of it).>
Titan as a disk at 540X.
The moons of Jupiter showing easily the different diameters
and, hopefully in the future, under the best conditions, detail on
Ganymede. Jupiter itself is just covered with super fine
details, including detail in the red spot, the blue equatorial
festoons, numerous small and large white ovals and granulated
polar regions.
Saturn appears sharp and contrasty up to powers of 540X, and
Cassini's and the Crepe ring are now obvious in even average> seeing. On
the night of September 30, I saw the equatorial white
spot on Saturn, thus beating Tom Dobbins (see Sky and Telescope)
and E-mailed my sighting to Eric Jamison that night (which he can
confirm). This brings me to another point, that the real test of
an optic is how well it handles high magnification. While most good
scopes start to soften at powers around 250x on the planets (and
> I'm not talking about brightness) the Astro-Physics refractors
> can be pushed much higher. With my scope at 324X, I feel that
> it is just idling.
>
> Uranus and Neptune are beautiful and with well defined disks
> and colors. I have seen Triton on a transparent night.
>
> There is an aspect to the darkness of the starfields and
> pinpoint star images that no instrument can equal. What this
> does for open clusters, comets and large nebula must be seen
> to be appreciated. The aesthetics of these views are sublime.
> I, for one, cannot live without a scope unless it shows this
> type of quality from now on.
>
> Some people will understand what I'm saying, others will not.
> But I can assure you that my Astro-Physics telescope is much
> more than "Jewelry." It's a life long quest for my ideal
> telescope, and I will enjoy this telescope into my old age.
>
> On another subject -- 16x greater scatter of a single
> reflective surface vs. a refractive surface, I have gone
> over this subject too much already. If you don't believe
> this, read the following and also talk to James G. Baker
> (probably the greatest optical scientist of our time), or
> Jose Sasian PHD in Optics from the University of Arizona
> Optical Sciences, and M. Francon from France, who wrote
> on this subject in great detail.
>
> The effect of surface roughness can be estimated by
> considering the Strehl ratio. Strehl ratio = 1 -
> (RMS/lambda) 2 where lambda is the wavelength of light
> and RMS is the root mean square surface roughness.
> The Strehl ratio gives the ratio of the Airy disk peak
> to the peak of the unaberrated Airy disk. For a given
> surface roughness, a refractive surface introduces about half
> wavefront roughness as a mirror. This comes about because upon
> refraction or reflection the wavefront is deformed by the factor
> (n' - n) where n and n' are the indexes of refraction of the media
> before and after refraction or reflection. For light refraction
> the factor is 1/2, for reflection in air it is 2.
>
> Since surface roughness enters as the SQUARE in the Strehl
> ratio formula, light is scatter by a refractive surface, and
> a reflective surface in air in the proportions of 1 and 16.
>
> Well, let me try and make it easier to understand. The ratio of
> error in optical path between mirror and lens surface for the same
> mathematical departure from figure is 2/(n - 1) or about 4. The error
> in optical path affects the contrast rendition in the diffraction
> pattern as the square. The two factors combined lead to a 16 to 1 ratio.
> That is as simple as I can explain it.
>
> Sincerely,
>
> Thomas M. Back
Gosh Tom, Ive seen all that with a Meade 395 90mm refractor under
perfect seeing conditions. But then again, I'm a very experienced
observer and can see much more than most people because I am an
experienced observer.
In a 7inch AP F9, I have seen the Star Ship Enterprise...but I didnt
just peek thru the eyepiece, I observed it with my experienced eyes...
Carl Sagen was out with me that night and he has so much theory stored in
his head that he actually saw the actual fireball of the big bang, and
thats with out even looking thru the telescope!!! Wow, imagine what we
all have to look forward to with even more experience. Soon we can all
sell our telescopes because the optics will limit our vision!
Ralph
My personal feeling on jewlery is that is is strictly for impressing
people and nothing more!
Jim Van Nuland
>From: fre...@netcom.com (Jay Reynolds Freeman)
>Subject: Long-focus Newtonians (was: APO MAX Advertisement ...)
> How interesting and surprising, that the amateur telescope market
>never seems to have had a successful niche for extremely high-quality
>long-focus Newtonians. You'd think someone would be selling well-made
>6- and 8-inch f/10s, with well-figured optics produced using every
>trick in the book to make their surfaces smooth, with small diagonals
>mounted on spiders with very narrow struts, and with "shorty" focusers
>to get the focal plane close to the diagonal. [...]
Not so long ago, the early '70s when I bought my own 8 inch f/6, there
were a number of companies making Newtonians: Cave, Criterion, Optical
Craftsmen. They were general-purpose scopes, so the diagonal was larger
than your suggested one; and the tall focusser was the only kind anyone
had thought of. Mounts were all equatorial, and nobody had realized that
an alt/az mounting was practical. Compared to today's scopes (that is,
allowing for inflation) they were expensive instruments.
You might ask "What happened to the market for such scopes?" We here in
the States are too price conscious, unwilling to pay for quality.
Europeans have often commented about that, both here and on FidoNet's
Astronomy echo. The result has been that most (surviving) makers have
concentrated on the low-end where the sales are. There are a few U.S.
makers of high-quality scopes, the Obsession, for one. But these are
large scopes! This, too, is part of the answer to your question: buyers
are looking for large scopes.
Recently, Peter Ceravolo has offered very high-quality instruments. I
understand that they are superb, and rare.
* SLMR 2.1a * The sky is not the limit, only the beginning!
R. Michael Harvey
Jay...
Yes, I do believe that Joe only sold the OTA's (although he
could probably put together a complete package if necessary). I remember
than the long-focus 10" I used was really too much for the mount (a
modified Cave).
Re; your comment regarding high power and Newts: I use my 18"
Obsession primarily for planetary observing and regulary use as much
magnification as seeing permits. During Mars oppositions, for example, I
normally run 500X - 700X if conditions allow it...the scope is NEVER the
limiting factor.
Mike Harvey
Jay Reynolds Freeman
> A few years ago I purchased a Criterion 6" f8 on Newtonian on an
> equatorial mount in a garage sale for $10. The tube was in bad shape and
> I dismanteled it and kept the parts. Mirror needs resilvering. Does this
> classify as a "long-focus?" Is it worth rebuilding?
Depends on mirror quality. With careful attention to layout, a six-inch
f/8 could make do with a diagonal less than an inch in diameter, and would
be capable of very nice images.
Todd Gross
> Astro-Physics being a type of jewelry? OK, that does it.
>This will be my last post on this subject. There are people in
>this world who can afford high quality instruments (of any kind)
>and others who cannot or will not. The cannot's will always say
>that their cheaper "instrument" is just as good as the more
>expensive one. If it makes them feel better, that's fine. But until
>you own one (and not just take a quick look at a star party), you
>will NEVER know the quality of the images that are seen through
>such instruments.
Thomas.. Eric mentioned to me that they are going to discontinue this scope,
thus he has ordered one.
1. How much does it cost?
2. Why are they discontinuing it?
Thanks! - Todd
_________________________________
BOSTON TV METEOROLOGIST TODD GROSS
Weather/Astronomy Home Page: http://www.weatherman.com
Administrator, Meade Advanced Product User Group: ma...@shore.net
Administrator, New England Weather Observer Mail List: wxob...@shore.net
IRC Channel Operator: #Weather (Undernet)
Originator of the NE.WEATHER newsgroup
_________________________________
Email: to...@weatherman.com Work Phone# (617)725-0777
Todd Gross
> Todd.......
> I replaced my big refractors (including a custom 6" f/15
>APO Triplet from AstroPhysics) with the short-focus (f/4.5) Newtonian. I
>have never regretted the decision. As I have stated previously, the custom
>-figured mirror in the 18" performs wonderfully and produces planetary
>images that are superior to ANY refractor I've ever used, including an 8"
>Alvan Clark and a 10" Zeiss.
> If Thomas has suggested that a 7" refractor (even if
>perfect) will deliver superior images to an 18" reflector then that
>posting has escaped me. I would agree, however, that this performance
>advantage is quite likely when comparing that 7" to a 'garden-variety'
>18". Before I comment further I'd like to read what Thomas has to say.
>As I pointed out, it's awfully easy to misunderstand when you don't have
>all the info in front of you. Thomas???
You missed a good exchange! He clarified it by saying you refigured the
mirror, reduced the obstruction, and live in Florida, where the air is
stable. In most circumstances, he feels the refractor will do better, in his
experience, even with the best reflectors... due to a variety of factors. It
was a good post, perhaps Thomas can email it to you.
Do you notice a substantial difference when swapping secondaries????
> Mike Harvey
J. D. McDonald
Thomas Back wrote: (I think!)
>
> > Astro-Physics being a type of jewelry? OK, that does it.
> >This will be my last post on this subject. There are people in
> >this world who can afford high quality instruments (of any kind)
> >and others who cannot or will not. The cannot's will always say
> >that their cheaper "instrument" is just as good as the more
> >expensive one. If it makes them feel better, that's fine. But until
> >you own one (and not just take a quick look at a star party), you
> >will NEVER know the quality of the images that are seen through
> >such instruments.
This is the standard snob appeal argument. I discount it for telescopes,
it's just snob appeal.
But I understand it. I collect rocks. These are up to **far** more
expensive than telescopes, and have the additional factor of
rarity: AP can make as many APO scopes as Ohara will get them glass,
and Ohara can make as much glass as they feel like. But God makes
great rocks at His own, geological, pace.
And in rocks you CAN find ones at $500 that are really, truly, just
as good as "similar" ones at $3000 or $5000. It's just that the
$500 ones are labelled "Pachipacqui" and the $3000 one "Herodsfoot",
or "Mashamba West" versus "Bisbee".
I would think long and hard about buying a $7000 AP scope, but would
buy a $25000 Chancarnillo Proustite the size of my (size 14) toe in an
instant.
Different snob appeals for different people.
Doug McDonald
Richard DeLuca
SNIP_
>
> >Personally, I tend to think of Astro-Physics as being a type of jewelery.
> >Finely made, exquisite details which are beautiful to gaze upon, but they
> >really don't contribute to the optical performance of the instrument.
> >Now, nobody misunderstand, they DO have an excellent optical system.
>
> >Although very expensive, they are at least available to those you would pay
> >the price. The problem with aquiring a reflector that could compete with them
> >is that it's almost impossible to BUY one - you have to make it yourself.
> >But - many people *do* make them for themselves. And their's no doubt that
> >there are some of these that are very nearly equivalent to the best of
> >anything you can buy - APO refractors not excluded.
>
>
> >Greg Granville
>
>
SNIP
>
> Astro-Physics being a type of jewelry? OK, that does it.
> This will be my last post on this subject. There are people in
> this world who can afford high quality instruments (of any kind)
> and others who cannot or will not. The cannot's will always say
> that their cheaper "instrument" is just as good as the more
> expensive one. If it makes them feel better, that's fine. But until
> you own one (and not just take a quick look at a star party), you
> will NEVER know the quality of the images that are seen through
> such instruments.
SNIP_
> Saturn appears sharp and contrasty up to powers of 540X, and
> Cassini's and the Crepe ring are now obvious in even average
> seeing.
Geez Tom,
WHERE WERE YOU when Mr. Granville was flaming me about easily resolving
the Cassini Division in ho-hum seeing. I've owned lots of scopes over 30
years of planetary observing and will surely own a couple more before my
eyes veil over. But the one I will never part with is my 6" AP apo....:-)
Clear Skies,
Rich
John Ongtooguk
Jay Reynolds Freeman (fre...@netcom.com) wrote:
: How interesting and surprising, that the amateur telescope market
: never seems to have had a successful niche for extremely high-quality
: long-focus Newtonians. You'd think someone would be selling well-made
But who consistently makes high quality Newtonians of any
configuration, much less a long focus model, say with the
same level of delivered quality as TeleVue, Astro-Physics,
Takahashi, etc. ? There's a Mak/Newt available that seems
like it's a safe bet but garden variety Newtonians seem
to struggle to meet a 1/4 wave tolerance. Per comments on
the 6in f8s of different wavefront errors that were tested
in S&T awhile back the 1/4 wave scope was judged to be
much better than almost all that the reviewers had seen,
and the 1/2 wave scope seemed typical.
As I've mentioned before one can improve the odds of getting
a decent scope by stopping down a larger mirror, or getting
real radical and building a scope optimized for off-axis use.
John Ongtooguk (jo...@vcd.hp.com)
Unknown
From: william...@nashville.com
Newsgroups: sci.astro.amateur
Subject: Re: APO MAX Advertisement -- 5.2" vs 7.1" APO's
References: <1352...@nashville.com>
X-Newsreader: Forte Free Agent 1.0.82
Lines: 13
gr...@laser.arl.psu.edu wrote:
>Personally, I tend to think of Astro-Physics as being a type of jewelery.
>Finely made, exquisite details which are beautiful to gaze upon, but they
>really don't contribute to the optical performance of the instrument.
>Now, nobody misunderstand, they DO have an excellent optical system.
Astro-physics telescopes are about as doodad-free as they can be. The
same can't be said for Questar.
Gary Seronik
J. D. McDonald <mcdo...@aries.scs.uiuc.edu> wrote in article
<328345...@aries.scs.uiuc.edu>...
> Thomas Back wrote: (I think!)
>
> >
> > > Astro-Physics being a type of jewelry? OK, that does it.
> > >This will be my last post on this subject. There are people in
> > >this world who can afford high quality instruments (of any kind)
> > >and others who cannot or will not. The cannot's will always say
> > >that their cheaper "instrument" is just as good as the more
> > >expensive one. If it makes them feel better, that's fine. But until
> > >you own one (and not just take a quick look at a star party), you
> > >will NEVER know the quality of the images that are seen through
> > >such instruments.
>
>
> This is the standard snob appeal argument. I discount it for telescopes,
> it's just snob appeal.
>
> But I understand it. I collect rocks. These are up to **far** more
> expensive than telescopes, and have the additional factor of
> rarity: AP can make as many APO scopes as Ohara will get them glass,
> and Ohara can make as much glass as they feel like. But God makes
> great rocks at His own, geological, pace.
>
> And in rocks you CAN find ones at $500 that are really, truly, just
> as good as "similar" ones at $3000 or $5000. It's just that the
> $500 ones are labelled "Pachipacqui" and the $3000 one "Herodsfoot",
> or "Mashamba West" versus "Bisbee".
>
> I would think long and hard about buying a $7000 AP scope, but would
> buy a $25000 Chancarnillo Proustite the size of my (size 14) toe in an
> instant.
>
> Different snob appeals for different people.
>
> Doug McDonald
Oooh Doug! Now you've done it...
I usually agree with your posts, but this time I'm not even sure I
understand you. Your analogy doesn't seem to fit very well, but since I
don't know anything about how the value of rocks is determined I'll have to
pass on commenting and just discuss telescopes.
I don't think one can dismiss Thomas' choice as being one of simple snob
appeal. Firstly, none of us knows Thomas' sense of taste well enough to
know if he would respond to mere snob appeal. I see no evidence for this
myself. Secondly, Thomas' stated reasons for owning such an instrument
have nothing at all to do with the price of the instrument. If I
understand his postings correctly, he just thinks it delivers the best
views for his viewing pleasure and circumstances. That fact that he can
afford to buy the instrument he thinks is best is irrelevant and should not
be held against him. Owning an expensive and cherished item does not in
itself constitute being swayed by "snob appeal" - it does not logically
follow.
While I would not choose the telescope Thomas has, or you for that matter,
I understand the journey he has been on - the quest for the perfect match
of optics, taste, and circumstances. This same quest has lead me in a
different direction as it has you too. My telescopes are home-made
Dobsonians mainly - hardly a snob's telescope. However, if I really
thought that a 7" AP was the answer to my observing dreams I would save my
pennies (for a long time to be sure) and eventually buy one. On that day
would I have been transformed into a snob? In addition to my Dobsonians I
also own a Questar. Does that mean that when I use my Dobby I'm OK, but on
the nights I use my Questar I become a snob?
Regards,
--
Gary in Vancouver
user2...@aol.com
Telescope snobs and even rock snobs are nothing compared to violin snobs.
The low end starts at about $20,000 for a serious contemporary instrument.
Third-rate 18th century Italians start around $35,000. Stradivaris start
around $200,000 and the sky is the limit. Good bows can run $10,000 or
more. A Tourte bow (early 19th century French) can run more than $50,000.
(Of course, these things do tend to appreciate in value once you've taken
the plunge.) Apochromatic refractors seem quite reasonably priced in
comparison.
Bill
Jay Reynolds Freeman
> But who consistently makes high quality Newtonians of any
> configuration, much less a long focus model, say with the
> same level of delivered quality as TeleVue, Astro-Physics,
> Takahashi, etc.?
I think that's a modern phenomenon; a few decades ago some of the
Newtonians produced were pretty good. Funny you should mention the
Japanese. I know Vixen makes some Newtonians, I wonder if anyone has
star-test results on one of theirs.
R. Michael Harvey
to...@weatherman.com (Todd Gross) wrote:
>
>
>
>Do you notice a substantial difference when swapping secondaries????
>
>
>
>
>
>
difference is not dramatic but quite apparent nonetheless. When you see first-hand how contrast is reduced, even at 22%, it gives yo=
u an idea of just how much is missing with those big SCT secondaries!
Mike Harvey
>
>
>
>
J. D. McDonald
Gary Seronik wrote:
>
> J. D. McDonald <mcdo...@aries.scs.uiuc.edu> wrote in article
> <328345...@aries.scs.uiuc.edu>...
> > Thomas Back wrote: (I think!)
> >
> > >
> > > > Astro-Physics being a type of jewelry? OK, that does it.
> >
> >
> > This is the standard snob appeal argument. I discount it for telescopes,
> > it's just snob appeal.
> >
> > But I understand it. I collect rocks. These are up to **far** more
> > expensive than telescopes, and have the additional factor of
> > rarity: AP can make as many APO scopes as Ohara will get them glass,
> > and Ohara can make as much glass as they feel like. But God makes
> > great rocks at His own, geological, pace.
> >
> > And in rocks you CAN find ones at $500 that are really, truly, just
> > as good as "similar" ones at $3000 or $5000. It's just that the
> > $500 ones are labelled "Pachipacqui" and the $3000 one "Herodsfoot",
> > or "Mashamba West" versus "Bisbee".
> >
> > I would think long and hard about buying a $7000 AP scope, but would
> > buy a $25000 Chancarnillo Proustite the size of my (size 14) toe in an
> > instant.
> >
> > Different snob appeals for different people.
> >
> > Doug McDonald
>
> Oooh Doug! Now you've done it...
>
> I usually agree with your posts, but this time I'm not even sure I
> understand you.
I am a snob, a serious rock snob. I can't stand faults in rocks.
They drive me crazy. The tiniest little defect makes me cringe.
If I as much as nick one of my perfect rocks, I get physically
ill. And here is the big one, that relates perfectly to
Mr, Back: I'd rather have a perfect 3" rock than a similar,
more expensive, buy slightly nicked, or slightly cloudy, 5" one.
I'd even prefer it if the 5" one were to cost less!!! **And even if the
5" one
contains a 3" section that's as perfect as the 3" one**. And
yes, that scenario actually happens (of course you could try to trim
the 5" one, and some people do ..... but it can cause the thing
to break in the wrong place, and saw cuts are a very serious no-no.)
>
> While I would not choose the telescope Thomas has, or you for that matter,
> I understand the journey he has been on - the quest for the perfect match
> of optics, taste, and circumstances.
That was my point.
But I'm not a telescope snob.
Doug McDonald
Ervin Thompson
I feel fortunate. Owning a lowly 5 inch C5, I am not inclined to get
into pissing contests over who has the most powerfull scope. Oh, I
suppose I could go down the street and challange the kid with his toy
binoculars, but why make the little brat feel bad?
Besides, I already tried that and his dad keeps beating me up.
Rich Neuschaefer
R.A. wrote:
-snip
-> In a 7inch AP F9, I have seen the Star Ship Enterprise...but I didnt
-> just peek thru the eyepiece, I observed it with my experienced eyes...
-> Carl Sagen was out with me that night and he has so much theory stored
in
-> his head that he actually saw the actual fireball of the big bang, and
-> thats with out even looking thru the telescope!!! Wow, imagine what we
-> all have to look forward to with even more experience. Soon we can all
-> sell our telescopes because the optics will limit our vision!
->
-> Ralph
->
-> My personal feeling on jewlery is that is is strictly for impressing
-> people and nothing more!
Gee Ralph,
Do you need to add a little sugar on those grapes? ;-)
Rich
(my opinion only)
Ervin Thompson
I have just begun reading Eyes on the Universe by Isaac Asimov, and am
a bit confused by a passage concerning one of Galileo's telescopes. If
I may quote from page 20:
"Back in Padua, Galileo carefully ground new and larger lenses and
built still better telescopes, including, eventually, one that was 4.4
centimeters (1.75 inches) in diameter, 1.2 meters (4 feet) long, and
capable of magnifying objects to thirty-three times their diameter. The
ability of a telescope to see detail has a theoretical upper limit
which depends on the diameter of the telescope lens. Thus, Galileo's
telescope could not have performed better than a modern binocular with
a lens 44 millimeters in diameter. At best it would then fall short of
modern 7 X 50 (magnification 70, lens diameter 50 millimeters)
binoculars."
What does the author mean by saying 7 X 50 is 'maginfication 70'?
Unless I am more ignorant than I first assumed, I would speculate this
was a mistake on the authors part?
Thanks for your feedback.
Skip
Jonathan Silverlight
Robert Provin
In article <odyssey-0811...@pm232.spectra.net>,
ody...@spectra.net (Richard DeLuca) wrote:
> Geez Tom,
>
> WHERE WERE YOU when Mr. Granville was flaming me about easily resolving
> the Cassini Division in ho-hum seeing. I've owned lots of scopes over 30
> years of planetary observing and will surely own a couple more before my
> eyes veil over. But the one I will never part with is my 6" AP apo....:-)
>
> Clear Skies,
> Rich
I second this one! I have been looking through telescopes for over 32
years now and have owned everything from a 60mm Tasco to an 18 inch
Dobsonian (with an excellent Galaxy mirror). And if I had to pick the
*one* scope that gave me the most pleasure by far...you guessed it...my 6
inch Astro-Physics EDF refractor. Like some one else in this thread
mentioned, you simply have to own one of these instruments to appreciate
what a truly superb telescope is all about!!!
Best wishes and clear skies,
Robert
--
Robert Provin
Department of Geography
California State University
Northridge, CA 91330-8249
phone: (818) 677 5647
http://voltaire.csun.edu/
Tim Gillespie
Thomas Back wrote:
>
> Great analogy? I'd hate to be in the room of a Ferrari F-40 owner
> after Tim made that comment. Tim, do you really think a Viper
> will out-perform a Ferrari F-40? And that's not even their top-
> of-the-line road car.
Well, I'm not getting into a pissing match about car specs. I do,
however, invite you compare the performance specs for a viper to a 328,
355, 512BB, even a Testarossa. F40..., probably not. But that F40 is
more like 7 or 8 times as expensive.
How about another analogy. I doubt you'll dispute this one. I can
unequivocally state that my Seiko watch performs every bit as well as a
Rolex that costs more than 20 times more. Is that better?
> Astro-Physics being a type of jewelry? OK, that does it.
> This will be my last post on this subject. There are people in
> this world who can afford high quality instruments (of any kind)
> and others who cannot or will not. The cannot's will always say
> that their cheaper "instrument" is just as good as the more
> expensive one. If it makes them feel better, that's fine. But until
> you own one (and not just take a quick look at a star party), you
> will NEVER know the quality of the images that are seen through
> such instruments.
What an unbelievably pompous and conceited statement! Lets see, just
because I do not own an extremely expensive instrument you conclude that
I cannot afford to own one! Increadible. By the same reasoning, then,
since I cannot afford an AP I certainly cannot afford a car (costing
many times more) or a house (costing another order of magnitude more).
Well, I do own a car (not a Ferrari, but a nice one none the less), I do
own a house (not a mansion, but certainly adequate for my family) and I
do own a couple of telescopes.
I'll thank you not to assess my financial status by how I spend (waste?)
my money. Some people (either "cans" or "cannots") choose to purchase
*value*, not status. Sometimes the two are one in the same, sometimes
thay are not.
It seems to me that it is YOU who is trying to massage his ego and
justify the investment by claiming that YOUR scope will outperform
larger scopes. I don't think that even the "cannots" (jeez, I still
can't believe you said that) will argue that *in its class* your scope
is probably the finest made.
[edited]
> There is an aspect to the darkness of the starfields and
> pinpoint star images that no instrument can equal. What this
^^^^^^^^^^^^^^^^^^^^^^^
> does for open clusters, comets and large nebula must be seen
> to be appreciated. The aesthetics of these views are sublime.
> I, for one, cannot live without a scope unless it shows this
> type of quality from now on.
I think it is this type of snobbery that people find distasteful. Are
you sure that no scope is the equal of your scope? I can attest to the
fact that you have never looked through MY scope, so I will stop short
of calling you a liar, and state that you simply don't have all of the
facts.
> Some people will understand what I'm saying, others will not.
> But I can assure you that my Astro-Physics telescope is much
> more than "Jewelry." It's a life long quest for my ideal
> telescope, and I will enjoy this telescope into my old age.
If, by understanding, you mean that they believe that your scope is one
"that no instrument can equal" then you won't get my understanding
(though I doubt you want it).
Well, thanks for dumbing it down. My training is in theoretical nuclear
physics and nuclear engineering, so I appreciate you couching it such
that a bumbling engineer like me can understand it.
I did not doubt your figure, I simply wanted to know where it came from.
I know I'm stupid, but I thought that modern coatings decreased
scattering in mirrors. I guess its too complicated for me.
--
___ _____
Tim .'/,-Y" "~-.
Gillespie l.Y ^.
/\ _\_
i ___/" "\
| /" "\ o !
l ] o !__./
\ _ _ \.___./ "~\
X \/ \ ___./
( \ ___. _..--~~" ~`-.
` Z,-- / \
\__. ( / ______)
\ l /-----~~" /
Y \ /
| "x______.^
| \
j Y
Todd Gross
>>
>>
>>
>> Todd.......Yes, there IS a noticeable difference...even though the larger
>diagonal STILL only represents a 22% obstruction. The =
>difference is not dramatic but quite apparent nonetheless. When you see
>first-hand how contrast is reduced, even at 22%, it gives yo=
>u an idea of just how much is missing with those big SCT secondaries!
>
> Mike Harvey
>>
Dave Kriege at Obsession was unaware of this fact in a recent discussion,
citing Suiter's book , he indicated a larger obstruction wouldn't really make
a difference, thanks for clarifying this!
I have had trouble reaching you by email (as usual, I lost your address), but
I did want to share the cert. sheet for the Pegasus mirror I have put a
deposit on, and get your opinion.
Stew Squires
Fred Mrozek, owner of HT Precision Optics, and the maker of the 5.2" APOMAX that this
thread is all about has been following it from the South Pole, where he presently is
working on some sort of telescope upgrade to the Yerkes observatory station there.
He has asked me to post this reply as he has email access only, no newsgroup access
to post.
>> In article <3280D6...@tandem.com> Rich Neuschaefer wrote:
>> >Getting back to the original point of this thread... it is hard
>> to
>> >rely on reports by people walking around at a star party.
Fred writes:
At last after much trouble with network connections I have been able to access a
news server back in the states and log on to s.a.a.
I note that much discussion has appeared under the above thread. Since I would
greatly appreciate the opportunity to reply to any questions anyone might have about
my telescopes, my advertisements, or anything else, please consider sending me
questions or comments via email that I may then reply to publicly here in this group.
At this time, let me guess that the main subject of the discussion was the comment
made by B. Murphy about my telescope that we used in our advertisement.
B. Murphy and a few others were going back and forth between telescopes for a
considerable time that evening at AstroFest. At the end of observing that evening B.
M. came over and said that after much scrutiny, he believed that my 5.2" was
comparable to the other 7" apos he was observing through. I asked for details and he
gave them. We compared opinions on performance and then I asked him if he would be
willing to write down his comments and if he would approve of my use of said comments
for ads or brochures. He agreed and we spoke again Sunday morning. The comment in
the ad is the one he wrote down for me.
Before using this comment in the ad though, I found his telephone number and
called him up to discuss the comments again, and to again review the observations we
both made and shared at AstroFest. In order to give him an "easy out", I actually
stated on both occasions, (at AstroFest and on the phone a few weeks later) that I
would not personally have gone quite as far in stating the relative performance
of my telescope. I told him that I would have agreed that in the early hours of
saturday evening, when Jupiter was low in the SE, the transparency was poor, and the
seeing was perhaps a "6/10", that the image of Jupiter in my APO MAX was as nearly
equivalent to the image in the 7" as I could judge. These Jupiter observations were
made through my 5.2" that had been soaking in the sunlight all day, and through
Tom's 7" that had just been set up minutes earlier was certainly still adjusting to
the slowly chilling evening air.
Once again, In my best possible objectivity, I would claim that my 5.2" equalled
the 7" under those circumstances.
When the evening went on and Saturn appeared, Tom was able to crank up to
magnifications with his 7" at which the 5.2" with half the light collecting power
could not follow, and under those conditions his scope did indeed out perform my
telescope in both the resolution of difficult detail (the little arc of cassinis
division at the ansa) and the ease with which the fainter moons were shown.
These observations were exactly what I told B.M. on two occasions essentially
giving him opportunity to reconsider his comments. He replied that after the rather
extensive comparisons he had done that evening, that he stood by his comments. Since
he spent much more time in the comparison process than I, and since I agreed fully
with his comments based on the Jupiter observations, I decided to use his comments.
Regarding the Saturn observations, it is important to note that a 7.1" scope has
about twice the light gathering power and 1.4 times the resolution. (Saturn, as the
inverse square law implies, has a much lower surface brightness than Jupiter.) Light
collecting power is therefore of the essence. The image I saw of Saturn through the
7" AP APO that evening was consistent with that difference - no more - and maybe even
a bit less. That is, I feel that a 7.1" version of the telescope I showed at
AstroFest would certainly have equalled the 7.1 AP, and I would venture to guess
that, seeing permitting, the improved color and spherochromatism of a longer f/ratio
refractor such as my APO MAX would give even better performance than an f/9 EDT
of equal aperture.
After the above mentioned comparisons of Jupiter were made in our two scopes, I
performed a star test on Vage through Tom's 7". (Vega). Though the general
symmetry of the disk passing through either side of focus indicated excellent
correction, there is a very easily noticeable region of turbulence concentrated in
the center of the intra and extra focal diffraction patterns. When such turbulence
uniformly affects the entire extra-focal pattern, seeing conditions far above the
telescope (and thus uniform across the aperture) are too blame. When they are
concentrated in the middle of your aperture (and the telescope is pointed nearly
straight up as was the case during this test) tube currents behind the lens or
immediately in front of the lens are to blame.
The currents I saw through Tom's scope during this star test on Vega confirm that
your lens was certainly not performing up to its thermally equalized limits at the
time about 30 minutes earlier when folks were comparing Jupiter images.
Two things are certain therefore. Tom's lens was not spherically corrected to
1/25th wave P-V at the time B. Murphy was observing Jupiter. And, even if the lens
elements had ZERO thermal expansion coef's. and the figure was 1/25th w. at all
temperatures, the air in front of the lens would be generating seeing by convections
until the lens cooled fully to ambient temperature.
Given these two effects, I would not be at all surprised if an impeccably
corrected 5.2" Apo showed "equal or better" images of Jupiter than a larger lens with
3 times greater mass of glass that has not yet reached ambient air temperatures. At
some point, a triplet can become so thick that it may always lag behind the falling
nightime temperatures. In this case, it would not matter a great deal if the lens was
1/100th wave at 68 deg F if it distorted to 1/4 wave for most of the evening as the
temperatures fell. And I repeat, no matter what the lens is made of, it must transfer
it heat into the air around it and this generates "seeing" that degrades planetary
images.
I know this reasoning is not lost on Tom Back since he has often in past
conversations lamented the long cool-down times for larger triplets.
Comment on optical quality and Strehl ratios: Dr. Richard Buchroeder has been
exploring possible lens designs for larger, faster lenses than my 5.2" APO MAX. We
hope to manufacture larger lenses if it is possible to acquire the glass - something
that is very, very iffy right now. It is a fact that the spherical aberration of
oil-contacted, ED triplets of moderate and fast f/ratios IS NOT uniform over the
visual spectrum. Thus, Tom's lens, while quite well spherically corrected over the
peaks wavelengths, is definitely less well corrected toward the blue and red ends of
the spectrum.
The lens designs we have reviewed for representative 7"f/8 -f/10 designs using any
of the ED glasses or CAF2 are really quite crummy off the visual peak wavelengths. In
fact, while the designer can bring perhaps a pair of wavelengths, say 586nm and 656nm
into diffraction limited obedience, all other wavelengths including the easily
visible 486nm line are quickly degraded to very low Strehl ratios. I was very
impressed that this considerable spherochromatism is not readily apparent in Tom's
7" f/9. I would have appreciated the opportunity to have conducted the star test
later in the evening after his lens had cooled down. And it would then have been
very informative to do that test through some interference filters which would reveal
the spherochromatism in the blue and in the red by masking the more powerful glare
of the peak wavelengths. In such a test, the superior spherochromatism correction
of the 5.2" APO MAX would stand out. Both chromatic and spherical aberations are
well under control in the APOMAX far beyond the point (probably around 650-700nm)
where Tom's 7"f/9 EDT ceases to diffraction limited.
This issue of the importance of spherochromatism is exactly analogous to the old
debate between really excellent doublet achromats and the upstart triplets. The
doublet lacks contrast due to out of focus light as a function of wavelength. The
new, fast triplet Apo's compromise the contrast that is potentially available in any
3-glass triplet by the inability to control the spherical aberration of the colors
that are otherwise shown to be "in focus" in paraxial color curve plots. So what the
old achromats did with color, the new fast triplets are also doing to some degree
with spherical.
Thus, if a 5.2" APO MAX were running a consistent 1/10th wave over the entire
range from 430nm to 1.5 microns, and another lens was similarly well corrected over a
much shorter range and fell to 1/2 wave in the blue and was simultaneously adversely
affected by its own thermal mass causing convection and seeing infront of the
objective - this also could explain a comment such as "equal or better".
The issue I am sure we are both interested in answering over the next couple years
is: how crummy can we permit the spherochromatic correction of the off-peak
wavelengths to become (in faster and faster f/ratios) before it impedes planetary
image contrast?
Tom's scope is certainly excellent. How much better might it be if it were an
f/12 instead of an f/9, or if its design afforded more extended spherical ab.
correction like the APO MAX design. I think Tom has an excellent theoretical idea of
the answer since he sent me some f/12 designs in which he pointed out the
superiority.
As Video and CCD imaging and through the eyepiece projection systems become more
popular amongst owners of Apochromats, I think that designs like APO MAX that correct
a broader region of wavelengths may be increasingly popular and valued. If not, and
if it proves possible for H T Prec. Optics to acquire Ohara glass in large sizes, we
too will manufacture short, fast 6" or 7" refractors. But for now, in my opinion, the
jury is out.
It may turn out that a performance vs. length compromise, such as APO MAX, offers
amateurs something that the short fast ones lack.
Finally, a last comment. During the weeks before AstroFest, a coating company
made some honest mistakes on the first sets of elements I sent out. The coating
mistakes and an error in shipping prevented the arrival of any usable elements to me
for assembly until about noon the friday of the fest. I had no control over which
front element and which rear element I could assemble since I had only one of each
that was properly coated. The lense I showed therefore is not even a good sample of
my work. Furthermore, Tom Back has related a rather interesting and lengthy tale of
the number of iterations he has gone through with AstroPhysics in order to acquire
the gem that he now enjoys. The story involved different lens designs, refiguring
operations, modifications to lens cells etc. etc. The story, if I remember
correctly, took years to pan out for Tom. What does the more common, "first
iteration" telescope look like? Is it, as Markus Ludes puts in his literature,
about 1/3rd of a wave P-V?
In another letter, at another time, we shall compare the relative merits of
different types of optical production machinery and polishing methods including
"supersmooth" (which has been in the literature for 20 years or so concerning
Etalons). Suffice it to say that the methods and personnel were out and about during
the last ten years or so during which, according to Tom Back, Astro-Physics average
wavefront quality was (Blank) (statistic deleted). I know I can do better than this
now. I know I will learn even more as I go along. Making lenses has been my dream
for over 15 years. My current standards are such that Brian Murphy and others who saw
the scope were inspired to make the comments at issue. Others, who had previously
owned AP refractors, placed orders. I know I still have a lot to learn, but I think
I have made a darn good start.
The big obstacle I see is getting consistent, excellent optical glass. Whether I
can continue to make cutting edge refractors depends almost entirely on Ohara
corporation. If they will supply glass in quatities I can afford to purchase -
I will continue. If I am required to order quantities at previously unprecedented
levels - my effort will likely go down the tubes.
I hope this helps answer some of the questions that may have been
asked in earlier posts that I have not been able to access. I may be
reached by email for a couple more weeks at this email address:
Sincerely,
Fred Mrozek
Stew Squires
...islands lie behind the Sun that I shall raise ere day is done.
Bilbo's Last Song - J.R.R. Tolkein
Akkana Peck
Reflections (no, make that refractions) a few days after a star
party at which a 7" Astro-Physics was present:
Large Astro-Physics refractors may be jewelry, but if so, they're damn
fine jewelry. I for one am very glad that there are owners of these
scopes willing to drag them out to dark sites and let the rest of
us look now and then so we can see what we're missing.
I doubt I'll buy one myself any time soon, because my real love is
galaxies. But every time I look through a 7" AP at Jupiter, Saturn,
or the moon, I lose myself in the view and practically have to be
dragged away to let other people look. I'm grateful for these chances,
and for the patience of the Astro-Physics owners who don't swat me
off the observing chair while I'm sitting entranced at the bino-view.
We now return you to your regularly scheduled name-calling.
...Akkana http://www.best.com/~akkana/astro.html
Scott M. Hinnrichs
Fred, thanks for the long discussion, it was quite interesting. It seems
that what transpired was your scope, at thermal equilibrium, was compared
against a scope that still needed another hour of cool down time, and your
scope provided better images. Not a surprise is it? In fact, just about
any other scope at thermal equilibrium would have also provided better
images, don't you think?
Thought I would also mention that all AP's meet or exceed 1/50th wave when
shipped (at least that is what the sign says on the wall at AP). Also the
EDT is an older design (different glass), and you should be comparing your
scope to the EDF models now shipping.
I have not talked to anyone that has received an other than perfect AP
upon initial delivery, though I am sure they must exist, anyone??
BTW, next time you get "unbelieveable" praise from someone about your
scope, don't publish it, we won't believe it ;)
Good luck, Scott
Stewart Squires
This whole thing has been very informative to me. Especially the parts about
how well these things are made and what you need to enjoy the views that the
heavens present. It seems, however, that in each case it is going to be a
personal decision about level of quality and affordability that will guide us
to that perfect scope or scopes for each of us.
Fred used to work at AP and certainly knows their quality. The quote in the
ad is just someone's opinion (who is this guy anyway?) and should be taken at
face value, albeit it is obvious that conditions were not the same for each
scope under evaluation.
I will star test this 5.2" refractor and I will compare it to other
refractors out there as a matter of personal interest, and to provide
feedback to the group. I hope it does well.
In article <smh-121196...@smh-ppc.netserv.com> Scott M. Hinnrichs
wrote:
>It seems
>that what transpired was your scope, at thermal equilibrium, was compared
>against a scope that still needed another hour of cool down time, and your
>scope provided better images. Not a surprise is it? In fact, just about
>any other scope at thermal equilibrium would have also provided better
>images, don't you think?
Now then, I have always thought of refractors as long narrow tubes out on
tripods. Cooldown never a problem. Fred points out that the 7.1" of Tom's
was some time away from thermal equilibrium. The above reply indicates that
it might have been over an hour away from settling down. Those of you with
the 5", 6", and 7" AP's, what kinds of cooldown periods do you normally
require for decent response?
>Thought I would also mention that all AP's meet or exceed 1/50th wave when
>shipped (at least that is what the sign says on the wall at AP). Also the
>EDT is an older design (different glass), and you should be comparing your
>scope to the EDF models now shipping.
This means nothing. As always it's important to specify what you mean by any
wavelenght measure. If it's per surface and you have six surfaces and you're
P-V then aren't you back to 1/8 wave system response? Just asking, because
it's not clear from your post. BTW Thomas Back mentioned that all AP
refractors are now meeting 1/10th wave P-V system response due to recent
improvements in manufacturing.
Questars, BTW, also are figured to 1/50th wave per surface. Only three
surfaces there so better performance? In the two I've got, my testing
reveals the 3.5 is that good, the 7" is only 1/8th wave P-V. Darn! Am I
still enjoying the views? You bet!
-
Stew Squires
... islands lie behind the sun that I shall raise ere day is done.
Bilbo's Last Song, J.R.R. Tolkien
Todd Gross
>Fred, thanks for the long discussion, it was quite interesting. It seems
>that what transpired was your scope, at thermal equilibrium, was compared
>against a scope that still needed another hour of cool down time, and your
>scope provided better images. Not a surprise is it? In fact, just about
>any other scope at thermal equilibrium would have also provided better
>images, don't you think?
>Thought I would also mention that all AP's meet or exceed 1/50th wave when
>shipped (at least that is what the sign says on the wall at AP).
WHAT! RMS, not peak to valley, I believe they won't even provide the specific
data, but indicate scopes will be 1/8th wave or better.. p-v Can you clarify
s'il vous plait.
>I have not talked to anyone that has received an other than perfect AP
>upon initial delivery, though I am sure they must exist, anyone??
heard of only 1, I believe, and it never made it to market. Company 7
indicated that in all the years they have tested, and sold them, they only ran
into one questionable scope.
my 4" gave a perfect star test on arrival..but operates well AFTER it cools
down totally (which doesn't take long.. I had a reflector that took hours)
Thomas Back
>Subject: Re: APO MAX Advertisement -- 5.2" vs 7.1" APO's
>From: s...@netserv.com (Scott M. Hinnrichs)
>Date: Tue, 12 Nov 1996 04:00:36 -0800
>Message-ID: <smh-121196...@smh-ppc.netserv.com>
>Fred, thanks for the long discussion, it was quite interesting. It seems
>that what transpired was your scope, at thermal equilibrium, was compared
>against a scope that still needed another hour of cool down time, and your
>scope provided better images. Not a surprise is it? In fact, just about
>any other scope at thermal equilibrium would have also provided better
>images, don't you think?
>Thought I would also mention that all AP's meet or exceed 1/50th wave when
>shipped (at least that is what the sign says on the wall at AP). Also the
>EDT is an older design (different glass), and you should be comparing your
>scope to the EDF models now shipping.
>I have not talked to anyone that has received an other than perfect AP
>upon initial delivery, though I am sure they must exist, anyone??
>BTW, next time you get "unbelieveable" praise from someone about your
>scope, don't publish it, we won't believe it ;)
>Good luck, Scott
Hi Scott,
Thank you for pointing out the obvious, and condensing what
Fred Mrozek's rambling's really meant.
Sincerely,
Thomas M. Back
Thomas Back
>Subject: Re: APO MAX Advertisement -- 5.2" vs 7.1" APO's
>From: squi...@gnn.com (Stew Squires)
>Date: Mon, 11 Nov 1996 20:11:52
>Message-ID: <568mgm$6...@news-c1.gnn.com>
>Fred Mrozek, owner of HT Precision Optics, and the maker of the
>5.2" APOMAX that this thread is all about has been following it
>from the South Pole, where he presently is working on some sort
>of telescope upgrade to the Yerkes observatory station there.
>He has asked me to post this reply as he has email access only,
>no newsgroup access to post.
>>> In article <3280D6...@tandem.com> Rich Neuschaefer wrote:
>>> >Getting back to the original point of this thread... it is
>>>hard to rely on reports by people walking around at a star party.
>Fred writes:
> At last after much trouble with network connections I have
>been able to access a news server back in the states and log on
>to s.a.a.
> I note that much discussion has appeared under the above
>thread. Since I would greatly appreciate the opportunity to
>reply to any questions anyone might have about my telescopes,
>my advertisements, or anything else, please consider sending me
>questions or comments via email that I may then reply to
>publicly here in this group.
And about 100 more lines of rambling text....
Fred,
This posting by you brings much disappointment to me.
That you would print an ad that uses my telescope (as an
inferior scope) as a way to peddle your scopes was bad
enough, but to break our trust by stating personal and
confidential information that I have given you upsets me
the most. DO NOT expect any further help, designs or
information from me!
I thought I would be considerate to you by not posting
the problems that I saw through your scope. Now I see
what fair game is. Your 5.2" APO MAX showed many problems
at AstroFest. It had considerable astigmatism (over 1/4
wave), horrid scatter (a problem that you admitted to
me), 1/8 wave of undercorrected spherical and noticeable
de-focused blue on Vega at high power.
Finally, you and Buchroeder's obsession with sphero-
chromatism beyond the c and f wavelengths really doesn't
hold water. The real problem with lenses is how well
they are nulled in the green-yellow visual peak wavelengths.
80% of the detail perceived by the eye is in these wavelengths.
If this wasn't the case, the great planetary observers of the
past using the large achromatic refractors wouldn't have
done the great work that they did. A lens with a design that
has zero spherochromatism but isn't figured beyond 1/8 wave
is a lost cause no matter how good the glass or design is.
Once a lens is figured beyond 1/16 wave P-V on the wave-
front, has spot diameters below the airy disk from c to f
(6563A to 4861A) and has an OPD below 1/4 wave or better
at these wavelengths, and doesn't blow out at the g wavelengths --
regardless of the f/ratio -- than you will have a superb planetary
telescope. Low spherochromatism beyond 7000A just doesn't
matter when it comes to what the eye perceives. If Dick would
like to refute this, I would be more than happy to hear his
explanation. Remember, the real problem with todays telescopes
is how well they are figured, and if this isn't done right,
everything else becomes meaningless in the quest of a superb
planetary telescope.
Sincerely,
Thomas M. Back
jose...@aol.com
I have to argue with the description of AP scopes as "jewelry". I can't
think of a single thing on mine that doesn't directly contribute to the
operation of the scope, whether in holding the optics or baffling the
light. True, the parts have nice finishes, but I don't think that makes
them jewelry.
Wait...it does have those StarFire EDT stickers.
Joe Bergeron
Matt or Belinda Tarlach
Scott M. Hinnrichs wrote:
>
> Fred, thanks for the long discussion, it was quite interesting. It seems
> that what transpired was your scope, at thermal equilibrium, was compared
> against a scope that still needed another hour of cool down time, and your
> scope provided better images. Not a surprise is it? In fact, just about
> any other scope at thermal equilibrium would have also provided better
> images, don't you think?
>
> Thought I would also mention that all AP's meet or exceed 1/50th wave when
> shipped (at least that is what the sign says on the wall at AP). Also the
> EDT is an older design (different glass), and you should be comparing your
> scope to the EDF models now shipping.
>
> I have not talked to anyone that has received an other than perfect AP
> upon initial delivery, though I am sure they must exist, anyone??
>
> BTW, next time you get "unbelieveable" praise from someone about your
> scope, don't publish it, we won't believe it ;)
>
> Good luck, Scott
When I read the ad in S&T I suspected that something like this was at
work- either the scopes weren't cooled off or the seeing was bad enough
that the image in the 5.2" was steadier than in the 7.1"
Some posters seem to feel that the use of this comparison is unfair, and
I agree that it would be better to spell out the conditions of the test
more clearly. But hey, it's a tiny ad and we should expect APO-MAX as
the "new kid on the block" to be very aggressive in their advertising.
And I actually see some value in this "flawed" comparison.
I use my scope (an 8" reflector, by the way, I'm only posting to this
thread to get my $.02 in) most often in the city, where I need to set up
quickly after work and get down to the business of observing right away
before the fog rolls in. Under these conditions a scope that can cool
down faster and perform fairly well before reaching thermal equilibrium
has a definite advantage. Of course, the 7" would be welcome to tag
along for those occaisional trips to the mountaintop! :-)
The ads for Meade's Apo refractors mention an advantage in cool down
time over the triplets. Does anyone out there have experience to
corroborate? I'm also curious as to why there is so little mention of
the Meade Apos in the newsgroup, given the big price difference. I saw
in the Adorama ad that you can get a 4" apo OTA for only a little more
than a Pronto. Yet everything seems to be A-P vs. Televue vs. Takahashi
and now APO-MAX. Are the Meade refractors really that bad as to not
deserve consideration? I am pretty new to this newsgroup- maybe this
has all been covered before. But I'm sure there are other newbies out
there who would also appreciate some quick comments.
Thanks! - Matt Tarlach
Stew Squires
In article <56abjk$5...@alexander.INS.CWRU.Edu> Thomas Back wrote:
> This posting by you brings much disappointment to me.
>That you would print an ad that uses my telescope (as an
>inferior scope) as a way to peddle your scopes was bad
>enough, but to break our trust by stating personal and
>confidential information that I have given you upsets me
>the most. DO NOT expect any further help, designs or
>information from me!
>
Clip
>
Fred Mrozek replys:
Tom,
Pardon me Tom. If I shared any information that was confidential
I am sorry. The only times I remember you asking for confidentiality
were in discussions of the glass types that you hypothesized AP
was using.
The lens you saw was hastily assembled from elements
belonging to two different lens sets. I thought that evening, that
I was not correctly collimated, but yes, there was astigmatism
present in that lens that night. Sorry, but when you the coater
mis-coats your sets, divides them up, and then ships them to the
wrong state the night before the convention... you assemble
what you can.
Scattering:
The front element of my triplet is a glass known as ZKN-7.
It has been purchased directly from Schott at substantial expense.
Turns out this glass has a nasty little "feature" - it scatters.
The scattering is subtle enough that I attributed it to other
causes when in my test apparatus. I am replacing all such elements
with new ones made by another manufacturer. In the pursuit of
the solution for this problem, I have uncovered another potential
source for low-level scattering in the triplet system, and when
I return from pole I shall correct that source as well.
You know that I know about the problem. And just in case
you will hold another violation of your confidentiality against
me, I guess we cannot further discuss the what you know about
this glass, this problem, and why I am not the only person
who has probably faced and solved this problem.
Undercorrected Spherical:
Your appraisal of 1/8th wave of spherical was accompanied
by the comment that this is exactly what you expected from a lens
that was as warm as mine was that early in the evening. But,
even if the 1/8th (P-V here not RMS) was intrinsic to the lens,
I am not ashamed of that. That is a damn fine figure compared
to: OOPS guess I can't talk about that...
Your observation of defocused blue is completely out
of left field. You did not mention it, I did not see it, and
it will perhaps be interesting to actually measure the color
curves of our two instrument sometime.
On Spherochromatism:
To quote you:
" Once a lens is figured beyond 1/16 wave P-V on the wave-
front, has spot diameters below the airy disk from c to f
(6563A to 4861A) and has an OPD below 1/4 wave or better
at these wavelengths..."
So 1/4 wave is now acceptable at 486nm, and at 656nm ?
It would be no better if the lens were 1/4 wave from say,
4300A to 7000A (or 15000A)? Since when has the quality of
an achromat been the standard, or are we discovering as I mentioned
in my previous ramble that fast triplets are doing with spherical
(1/4 wave at c and f), just what the old achromats did with color?
As for the suspension of any further assistance of any kind,
I am sorry to hear how offended you are. I truly thought the confidentiality
request pertained to the optical designs and glass combos. Since
everthing else seems to be common knowledge I do not feel very
apologetic about what I have written. Read the product comparisons
at the back of an AP catalogue and then come around again and
harrass me for quoting an honest observer with 20 years of
experience...
I really feel that I ought to be offended. It seems that
anything that company A does is OK with you, and if anyone questions
it or tries to strike a different compromise, they must be misguided
or foolish.
I have been at a pressure altitude of 10,700 feet for about
4 days. I am not nearly acclimated, and even when I am, I am
not the best writer. I am also typing with no ability to edit
as I go along. I have done my best to answer all the criticisms.
Rambling sincerely,
Fred Mrozek
Stewart Squires
In article <smh-121196...@smh-ppc.netserv.com> Scott M. Hinnrichs
wrote:
>Fred, thanks for the long discussion, it was quite interesting. It seems
>that what transpired was your scope, at thermal equilibrium, was compared
>against a scope that still needed another hour of cool down time, and your
>scope provided better images. Not a surprise is it? In fact, just about
>any other scope at thermal equilibrium would have also provided better
>images, don't you think?
>
>Thought I would also mention that all AP's meet or exceed 1/50th wave when
>shipped (at least that is what the sign says on the wall at AP). Also the
>EDT is an older design (different glass), and you should be comparing your
>scope to the EDF models now shipping.
Fred Mrozek from the South Pole sends:
Scott,
No Scott, I do not agree. The 5.2" APO MAX, with non-stock,
dark metallic blue paint job was basking in the sun all day. Had
I not been keen on getting the scope seen by people, I should have
hidden it away in the shade. (I think Tom kept his in his van, but
I am unsure.
In any case my 5.2" was exposed to an equal or greater
temperature differential during the early evening when Jupiter
was being examined.
I agree fully that I should be comparing my telescope
to the current, best AstroPhysics scopes. Now look very carefully
at your S&T back issues. WHO prints spots diagrams of their scopes
over MANY wavelengths in their ads ? WHO invites comparison
of STREHL ratio vs. Wavelength over the range of 400nm to 1.6
microns? Guess who Scott?
Please, please send me the material I need for that comparison
as soon as possible. Until then, full page print outs of Strehl
ratio vs. wavelength and Spot Diagram plots across the above mentioned
range shall, as always, accompany my literature. I offer the
info you need to make the comparison - it is in your S&T back issues.
If the other guy has removed even the limited amount of such data
from his literature, what does that tell you?
Be careful to specify RMS when you throw around the 1/50th wave
statistic. Indeed I agree that something like 1/8th wave P-V ought
to be the maximum permissible wavefront error on a refractor at
shipment. Tom Back, testing my scope immediately after sunset when
the lens cell was still noticeable warm, thought the correction
was already that good. (And remember the note about the circumstances
of the assembly of that lens... I had no control of the which
element pairs were returned properly coated about 8 hours before
we looked at Jupiter!)
From what Tom has told me in the past about the average
quality of AP scopes over the last ten years, and given his
appraisal of my scope that evening at AstroFest, I think I
have done quite well and that my lenses shall have figures
on par with AP. Combine an equal figure with a design that
has superior spherochromatism correction, and I think I will
be hearing more favourable comparisons in the future.
Here is an illustrative thought experiment. You can make
an Apochromat with three color crossings in a 7" size at, say f/5.
You can also get one wavelength to be PERFECTLY spherically corrected.
So this lens goes on an interferometer and is designed, figured and
tested at that one wavelength - and it comes out at say, 1/20 wave
P-V, or 1/80th wave RMS.
This same telescope would be a knock-out planetary telescope
only in a very narrow region of the spectrum. Other wavelenghts
would suffer severe spherical aberration.
Why do I suggest this thought experiment? Because I believe
that the best f/ratio for marketing apochromatic refractors and the
best f/ratio for observing planets and imaging with CCD's are not
the same. But time will tell.
Finally, you accuse me of publishing "unbelievable praise".
I have said about all I can say. I have been as truthful as possible
regarding the performance of Tom Backs telescope, later in the
evening, on Saturn. But the conditions under which B. Murphy
and I fully agree (equally good images on Jupiter) are not
unusual conditions. The temperature gradients a telescope
will experience during the other three seasons at Northern latitudes
will put an even greater thermal burden on a large lens. Thus, the
statement reveals an advantage of a very well-made, smaller
refractor in conditions that are fairly typical.
For those who can afford a price in the range of $5K to $6K
for a custom, 7" refractor, and are quite willing to wait for it
to cool down (or who use sites with small Diurnal temp. changes),
I am more than willing to make that telescope.
Better yet, how about an 8"f/6.5 Petzval ED with two
ED element groups ? Such a lens would cost alot, but would solve
virtually all the problems associated with a fast triplet. If anypone
is interested in such a telescope, please contact me.
Sincerely,
Fred
jose...@aol.com
Matt, the Meade refractors don't deserve to be called apochromats (neither
did the earliest APs, IMO). They show quite noticeable false color on
bright objects. Nor are they made to the same standards of accuracy as the
other scopes being discussed here. I've seldom if ever heard an evaluation
that rated them as comparable to AP.
Joe Bergeron
Fred Burger
Hello Thomas!
Wow, that really sounds like a nice instrument, but I still think
that I have you beat. Thanks for starting such a fun thread!
Best Wishes and Clear Skies,
Julie :-)
Fred Burger f...@sos.net