10 in F10 newtonian
leondf
semi light polluted area. performance on planets etc.
CHASLX200
>From: "leondf" leo...@ix.netcom.com
>Date: 4/11/00 4:35 PM Pacific Daylight Time
>Message-id: <8d0coq$auf$1...@slb6.atl.mindspring.net>
>
>Anybody out there have a 10 in F10 Newtonian. Interested in performance in
>semi light polluted area. performance on planets etc.
I had a 10" f/10 Newt, years ago!
It was excellent on the planets!
But you will need a latter, and a very well built mount...
Chas P.
Tymewayst
configuration. Fresnel diagrams show that the light scatter introduced by such
obstruction is really highly accurately approxamately totally indistinguishable
from an unobstructed aperture. If you use a window to mount the secondary or a
curved vane and produce the mirror competently you will have a 10" apo!
Scott Rychnovsky
tyme...@aol.com (Tymewayst) wrote:
But would it really work any better than a high quality 10" F6 with an 18%
or smaller obstruction?
A 100" tube length is a but much for many of us to handle. What type of
mount would be needed to support a 10" F10 Newtonian?
Scott
--
Scott Rychnovsky
srychno...@uci.edu
Sue and Alan
for both lunar and planetary and deep sky viewing. The views of Mars,
Saturn, and Jupiter are breathtaking when the seeing is good. Of course I
can not get as wide a field as my wife can in her 10" f/6 - but you can not
get a very wide field out of any 10" scope anyway.
It is an awfully big telescope, and it is not worth doing unless you are
willing to make a mount to go with it. In reality, you are probably better
off making the best 10" f/6 or 7 that you can and putting up with the
somewhat larger secondary. I certainly would have gone shorter if I had
simply started off with the idea of a 10" Newtonian, rather than hearing of
an excellent 10" f/9.5 mirror that was available at a very good price.
If you have a top quality 10" f/7 and 10" f/10 I suspect the differences
would be rather subtle and have no reason to believe that there would be
much difference between the f/10 and the f/7 under moderately light polluted
skies. The f/10 might preserve contrast a very little bit better, but I
suspect the difference would be very minor as long the obstruction is twenty
percent or less.
Clear skies, Alan
leondf wrote in message <8d0coq$auf$1...@slb6.atl.mindspring.net>...
Larry Brown
I built a 10-inch f/6 Newtonian with a 1.25" flat. This yields a secondary
obstruction of 12 1/2%. A typical secondary mirror in commercial telescopes
presents a 20-25% obstruction, resulting in a noticable degradation of image
definition and contrast. The use of a small diameter upper tube end and a
low-profile focuser moves the focal point closer to the tube and allows the
installation of a smaller than usual secondary mirror. For me the result was
an instrument with a spectacular increase in contrast, crispness, color,
resolution, and overall image quality. Don't be afraid to use an even smaller
mirror (1") which results in a small but inconsequential light loss from
vignetting. The extra gain in contrast and resolution for planetary work is
well worth it. Of course, the scope is useless for photographic work but it
sounds like you are shooting for a visual planetary scope. Mine is almost as
good as a refractor.
Clear skies. --L. Brown
David M. Lent
tyme...@aol.com (Tymewayst) wrote:
> Oh my god you could have only about a 10% obstruction by diameter with
this
> configuration. Fresnel diagrams show that the light scatter
introduced by such
> obstruction is really highly accurately approxamately totally
indistinguishable
> from an unobstructed aperture. If you use a window to mount the
secondary or a
> curved vane and produce the mirror competently you will have a 10"
apo!
>
True. My friend has an 8" f/11 with a curved spider and I've seen the
Encke Division with it on two seperate occasions (even though people
keep telling me it can't be seen with less than a 10" scope).
--
David M. Lent,
http://www.astrosights.com
The Amateur Astronomy Web Directory, Forums and Classifieds.
Sent via Deja.com http://www.deja.com/
Before you buy.
Jim Harris
the details of how you constructed this scope and the
materials you used. Sounds very interesting.
Jim Harris
http://scifan.com
Hip
I built the same... and have been in the design stages of installing a
clock drive. I'm a bit curious about your statement that the 'scope
is "useless" for photography. I've no experience in this area, but
have been considering ordering an camera adapter just to fool around
with. I'm not asking for a course in astro-photography! Just like to
know what the limitations/expectations are in such a telescope.
Oh... and the f/10 10" sounds fun though! I'd personally love to build
one.
-- hip
'82 FXRS
10" f/6 Forked Newt
"Be vewy, vewy, quiet! I'm hunting porchlights
In article <38F542AC...@fuse.net>,
!"
Larry Brown
Hip wrote:
> Larry:
>
> I built the same... and have been in the design stages of installing a
> clock drive. I'm a bit curious about your statement that the 'scope
> is "useless" for photography. I've no experience in this area, but
> have been considering ordering an camera adapter just to fool around
> with. I'm not asking for a course in astro-photography! Just like to
> know what the limitations/expectations are in such a telescope.
You'll need to use a barlow to extend the FOV out a couple of inches
so you can use a camera. But it will vignette pretty badly so if you want
to do photography you really need to use a larger secondary. I'll post a
photo of the scope on my web site shortly and give the URL. I just
subscribed to an ISP with an ADSL connection, so I have a new email
address. You have to delete the words "DeleteThis" from the address, which
were put in to spam proof it. I'll give my URL for the web site as soon as
I scan in and upload the photos.
This type of scope has been described as early as 1966 by Henry E.
Paul in his classic book "telescopes for skygazing", and more recently in
the ATM journal. Basically, it has been optimized for planetary viewing at
the expense of wide fields of view and photography. I used a curved spider
which smears the diffraction spikes so you don't get them on bright stars.
The extra light from the spikes forms a veil that affects threshold
definition and reduces the observer's ability to detect delicate contrast
and color differences on bright objects.
Some people maintain that curved spiders make no difference, and they
probably don't if they have a large secondary obstruction (larger than
15%). On a very small secondary obstruction the difference is definitely
noticable.
Clear skies. --Larry Brown
Del Johnson
assembly would have been just too long.
Del Johnson
In article <8d2vu...@news2.newsguy.com>,
Del Johnson
secondary with 2" eyepieces will be most significant. It is highly
unlikely that anyone would perceive any improvement by reducing the
obstruction below 15% (by diameters).
Are you quite certain that the improved view was not due to the quality
of your mirror?
Del Johnson
Larry Brown
> I beg to differ. The light loss due to using a grossly undersized 1"
> secondary with 2" eyepieces will be most significant. It is highly
> unlikely that anyone would perceive any improvement by reducing the
> obstruction below 15% (by diameters).
I may have misunderstood something. No, you cannot use 2" eyepieces with a
small secondary. But with standard eyepieces the improvement in contrast
is impressive. I have used several different sized mirrors. As the
secondary size was reduced, the improvement in contrast was amazing. If
you read ATM journals, many builders report the same thing. When you drop
below a 15% obstruction, the improvement is dramatic.
P. Edward Murray
Some months ago I had asked everyone to do so in hopes that anyone who
wasn't aware could go outside and see the Northern Lights....I'm sure
some people were able to!
Ed Murray
President
BMAA
Sue and Alan
A properly made truss certainly holds up just fine. Mine is a 6 pole truss
and I have no problems. A long tube may be a chimney, but that might well
make it cool down a bit faster.
Clear skies, Alan
Tom H. wrote in message ...
>Thats a long chimney, I might add. Would a truss this long hold up?
>
>Tom H.
>
>Del Johnson <deljo...@my-deja.com> wrote in message
>news:8d5lku$kmd$1...@nnrp1.deja.com...
>> I was offered a free 10" f/10 mirror and had to decline. The tube
>> assembly would have been just too long.
>>
>> In article <8d2vu...@news2.newsguy.com>,
>> "Sue and Alan" <Sue_and_A...@email.msn.com> wrote:
>> > I have a 10" f/9.5 on a very solid Dob style mount. It works
>> extremely well [SNIP]
Tom H.
Tom H.
Del Johnson <deljo...@my-deja.com> wrote in message
news:8d5lku$kmd$1...@nnrp1.deja.com...
> I was offered a free 10" f/10 mirror and had to decline. The tube
> assembly would have been just too long.
>
> Del Johnson
>
>
>
>
> In article <8d2vu...@news2.newsguy.com>,
> "Sue and Alan" <Sue_and_A...@email.msn.com> wrote:
> > I have a 10" f/9.5 on a very solid Dob style mount. It works
> extremely well
darr...@my-deja.com
virtually indestinguishable from an unobstructed system, except for the
diffracion spikes of course.
Darren Drake
In article <38F6750E...@fuse.net>,
ZodiacMan
Del Johnson <deljo...@my-deja.com> wrote:
> I beg to differ. The light loss due to using a grossly undersized 1"
> secondary with 2" eyepieces will be most significant. It is highly
> unlikely that anyone would perceive any improvement by reducing the
> obstruction below 15% (by diameters).
>
quality
> of your mirror?
>
> Del Johnson
>
I believe these 10 percenters or 15 percenters start by "throwing away"
their 2 inch eyepieces. I believe that they don't even bother putting
in a 2 inch focuser -- it would be a waste of money and additional
weight.
I imagine that some additional improvement might could be had with a
half inch m.a. secondary mirror if they made one, but then they might
have to throw away their 1.25 inch eyepieces as well. <grin>
It's quite a concept to throw away deep sky (and photography) with a
10+ inch aperture scope, but some are willing to do that to try to
squeeze the last bit out of a reflector for planetary only usage.
--
ZodiacMan
Excelsior Optics
I have experimented with the E-258 with both 2" and 1.25" secondaries, and
while the difference is visible, it doesn't exactly reach out and poke one in
the eye. I have chosen to use the 1.2" because the 'scope is intended to be
used mainly for planetary observing - both visual, and CCD imaging. Given that
the 2" secondary would offer no advantage to a telescope intended for those
uses, I opted for the slightly better image offered by the smaller diagonal.
Best,
Maurizio
Del Johnson
then draw conclusions about the effect of the secondary. This can only
be done by changing the obstruction on the same telescope during the
same night and noting the differences. When this is done in such a
controlled manner, it has been found there are diminishing returns with
reduced obstruction below 20%. There is no "dramatic" improvement in
contrast below 20%. It is very subtle. I have made such comparisons
with my own Zambuto-equipped reflector as I have two secondary mirrors.
What usually happens is that someone compares a very fine (and
expensive) telescope with little or no obstruction to another telescope
of lesser quality, and then erroneously attributes the difference to
the obstruction.
Del Johnson
In article <38F6750E...@fuse.net>,
Larry Brown <tangoDe...@fuse.net> wrote:
>
>
>
> I may have misunderstood something. No, you cannot use 2" eyepieces
with a
> small secondary. But with standard eyepieces the improvement in
contrast
> is impressive. I have used several different sized mirrors. As the
> secondary size was reduced, the improvement in contrast was amazing.
If
> you read ATM journals, many builders report the same thing. When you
drop
> below a 15% obstruction, the improvement is dramatic.
>
>
Del Johnson
then selects the appropriate secondary mirror size for a given viewing
situation.
Del Johnson
n article <20000414104602...@ng-ch1.aol.com>,
Excelsior Optics
Any option (within reason and my mechanical abilities) is available, as is
indicated on the "Biz" page, but it would seem to be illogical to take a format
that is intended to deliver the best planetary images, and configure it with a
less-than ideal secondary.
Best,
Maurizio
Tim Parker
Del Johnson wrote:
> I beg to differ. The light loss due to using a grossly undersized 1"
> secondary with 2" eyepieces will be most significant.
Why would you use a 2" eyepiece on planets with such an instrument? You
certainly wouldn't need to.
> It is highly
> unlikely that anyone would perceive any improvement by reducing the
> obstruction below 15% (by diameters).
I agree.
-Tim.
Del Johnson
can change them at will. I do this with my reflector. The extra cost
is relatively small and I am now optimal for both planetary and deep
sky viewing (they are both important to me). It takes me about 10
minutes to swap secondaries and recollimate the telescope.
Del Johnson
In article <20000414121535...@ng-ch1.aol.com>,
Del Johnson
when the secondary mirror is too small. I would not want a telescope
that was only good for planets.
Del Johnson
In article <38F7430B...@jpl.nasa.gov>,
Tim Parker <timothy....@jpl.nasa.gov> wrote:
> Del:
>
>
> Why would you use a 2" eyepiece on planets with such an instrument?
You
> certainly wouldn't need to.
>
> > It is highly
> > unlikely that anyone would perceive any improvement by reducing the
> > obstruction below 15% (by diameters).
>
> I agree.
>
> -Tim.
>
>
Tim Parker
Del Johnson wrote:
> I meant why not sell both secondary mirrors to the user so that they
> can change them at will. I do this with my reflector. The extra cost
> is relatively small and I am now optimal for both planetary and deep
> sky viewing (they are both important to me). It takes me about 10
> minutes to swap secondaries and recollimate the telescope.
?!
Huh? Almost verbatum, that's what he said!
Some people won't take "yes" for an answer!
-planetarily,
-Tim.
>
>
> Del Johnson
>
> In article <20000414121535...@ng-ch1.aol.com>,
> mauri...@aol.com (Excelsior Optics) wrote:
> > >Why not offer the larger secondary as a changeout option?
> >
> > Any option (within reason and my mechanical abilities) is
> available, as is
> > indicated on the "Biz" page, but it would seem to be illogical to
> take a format
> > that is intended to deliver the best planetary images, and configure
> it with a
> > less-than ideal secondary.
> >
> > Best,
> >
> > Maurizio
> >
> >
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
--
***************************************************************
Dr. Tim Parker
JPL Mail Stop 183-501
4800 Oak Grove Drive
Pasadena, CA 91109-8099
***************************************************************
All opinions herein stated are mine, not those of Caltech, JPL,
or NASA. Trust me.
Jeff
actual experience.
Jeff
A.L.P.O.
On Thu, 13 Apr 2000 20:32:10 -0500, Larry Brown
<tangoDe...@fuse.net> wrote:
>
>
>> I beg to differ. The light loss due to using a grossly undersized 1"
>> secondary with 2" eyepieces will be most significant. It is highly
>> unlikely that anyone would perceive any improvement by reducing the
>> obstruction below 15% (by diameters).
>
Jeff
ears :) How's the f/23 Cass coming along? I have further
refinements for you from the old days when I made my first 12.5-inch
f/30. Don and I worked out a 22-inch f/50 for Chick once and the
optics are still around somewhere. The surface was so rough we gave
up on it and went for 16-inch F/50's using a 1.5-inch secondary.
While using the UH24 Cass, the 24-inch f/75 that Tombaugh designed, I
found that t he near zip obstruction in that machine produced very
high contrast images, much much more so that the Air Forces Cass next
door with their 20% obstruction. Oh well, who cares about actual
experience, huh?
Jeff
Jeff
Jeff
On Thu, 13 Apr 2000 22:41:52 -0400, "Sue and Alan"
<Sue_and_A...@email.msn.com> wrote:
>Tom,
>
>A properly made truss certainly holds up just fine. Mine is a 6 pole truss
>and I have no problems. A long tube may be a chimney, but that might well
>make it cool down a bit faster.
>
>Clear skies, Alan
>
>Tom H. wrote in message ...
>>Thats a long chimney, I might add. Would a truss this long hold up?
>>
>>Tom H.
>>
>>Del Johnson <deljo...@my-deja.com> wrote in message
>>news:8d5lku$kmd$1...@nnrp1.deja.com...
>>> I was offered a free 10" f/10 mirror and had to decline. The tube
>>> assembly would have been just too long.
>>>
>>> In article <8d2vu...@news2.newsguy.com>,
>>> "Sue and Alan" <Sue_and_A...@email.msn.com> wrote:
>>> > I have a 10" f/9.5 on a very solid Dob style mount. It works
>>> extremely well [SNIP]
>
>
Del Johnson
You should read Dickinson's "The Backyard Astronomer's Guide".
Dickinson described a carefully controlled experiment where he
suspended various obstructions in front of a refractor. His findings
were that he could not tell the difference between no obstruction and
about a 15% obstruction. He also stated that going from about 15% to
about 20% (I don't recall the exact figures) resulted in only the most
minute difference that was difficult for him to see. There is no
dramatic change in image quality between 15% obstruction and no
obstruction.
Del Johnson
In article <38f845a6...@news.gte.net>,
Del Johnson
exclusive configuration, rather than having a complimentary set of
secondary mirrors. A telescope is not compromised with regard to
planetary viewing if the user can enable either configuration at will.
Del Johnson
In article <38F7AE89...@jpl.nasa.gov>,
Tim Parker <timothy....@jpl.nasa.gov> wrote:
>
>
>
> ?!
> Huh? Almost verbatum, that's what he said!
>
> Some people won't take "yes" for an answer!
>
> -planetarily,
> -Tim.
>
Larry Brown
Del Johnson wrote:
> I meant why not sell both secondary mirrors to the user so that they
> can change them at will. I do this with my reflector. The extra cost
> is relatively small and I am now optimal for both planetary and deep
> sky viewing (they are both important to me). It takes me about 10
> minutes to swap secondaries and recollimate the telescope.
>
> Del Johnson
This is an excellant option. I should have mentioned that I have other
scopes that I use for deep sky and for photography, so this is a
dedicated planetary instrument. I have posted photos of it on:
http://home.earthlink.net/~archlute/Newtonian.jpg
I have added setting cirlces and a motor drive since I took this photo,
but I don't have an updated photo. I would like to thank everyone who
posted a comment about small secondary mirrors. Many of the comments were
a welcome addition to my original post, and quite illuminating (no pun
intended).
Clear skies. --Larry Brown
Zane
>The Hubble Space Telescope seems to work just fine with its obstruction.
>
>You should read Dickinson's "The Backyard Astronomer's Guide".
>Dickinson described a carefully controlled experiment where he
>suspended various obstructions in front of a refractor. His findings
>were that he could not tell the difference between no obstruction and
>about a 15% obstruction. He also stated that going from about 15% to
>about 20% (I don't recall the exact figures) resulted in only the most
>minute difference that was difficult for him to see. There is no
>dramatic change in image quality between 15% obstruction and no
>obstruction.
(snip)
There's just over 7% drop in contrast for things corresponding to about
twice the Rayleigh limit in angle for a 15% obstruction versus none. Edges
are widened a little more.
The amount of light "smeared" by obstructions tends to be proportional to
the total area of the obstructions. (For example, a 20% mirror moves about
four times as much light around as a 10% mirror). Once you get down to
this level, the spider or stalk area can make a difference in comparing
things, so that mirror diameter comparisons on scopes with thick vanes will
not show as much improvement below 20% central obstructions as scopes with
smaller vane obstructions.
I don't know whether I can see less than a 7% change (e.g. 15% versus 10%
with a spider) with minutes between tries or not---certainly not dramatic,
as you say.
Zane
Larry Brown
I should mention that I am a precision machinist and model maker (using
a variety of cadcam systems) and that I built everything except the mirror
and the two roller-skate wheels. I have since added setting cirlces and a
motor drive. I usually create a virtual model in Surfcam or Solidworks,
then download the file to a machine that cuts the parts. That way,
everything fits together with + or - .001". I guess I'm lucky that my
company doesn't mind that I build a few things for myself on my own time. I
haven't figured out how to gring a mirror on NC equipment yet, only because
I can't cut glass.
Regarding small secondaries--see Henry E. Paul's classic work
"telescopes for skygazing", pp 115-116. He includes photos taken of
diffraction patterns of a star with five different sized diagonals. Also,
refer to "The size of secondary obstructions in reflecting telescopes
relating to contrast and resolution" by Dick Wessling, "The Ultimate
Newtonian" by Gregory Reeve, Telescope Making No. 23, and also the article
on Schiefspieglers in Telescope Making No. 4. All of these builders have
experienced an improvement in image contrast by downsizing the secondary and
provide an explanation of this phenomenon. I have lost track of how many
telescopes I have built over the years, but my current efforts are aimed at
optimizing a scope for a particular use, and building as lightweight as
possible. I have just finished an 80mm refractor out of ABS plastic that
weighs less than most finder scopes.
Larry Brown
Larry Brown
Larry Brown
--Larry Brown
Jeff
the bottom :)
Sometimes it's the ISP that messes up. I have had my ISP splatter
stuff all over the place in multiple postings.
A good machinist can make a changable secondary system to go right in
with much adjustment. Seems like I've seen some on the market for the
Cassegran/Newtonian duplex operation where you have to change
secondaries from one system to the other.
Jeff
observing with a variety of telescope for a very long time it may be
that you still have some experience to catch up on. I don't mean
glancing into someone's telescope at a star party, I mean observing
and study of objects. I have observed Mars for hours at a time and
believe me I can surely tell the difference between 20% and 15%
obstruction. Mars is a difficult object to study and every bit of
contrast increase helps one study the little glaring disk and its
wisps and blobs.
Jeff Beish
A.L.P.O.
On Sat, 15 Apr 2000 16:10:15 GMT, Del Johnson <deljo...@my-deja.com>
wrote:
>The Hubble Space Telescope seems to work just fine with its obstruction.
>
>You should read Dickinson's "The Backyard Astronomer's Guide".
>Dickinson described a carefully controlled experiment where he
>suspended various obstructions in front of a refractor. His findings
>were that he could not tell the difference between no obstruction and
>about a 15% obstruction. He also stated that going from about 15% to
>about 20% (I don't recall the exact figures) resulted in only the most
>minute difference that was difficult for him to see. There is no
>dramatic change in image quality between 15% obstruction and no
>obstruction.
>
>Del Johnson
>
>
>
>In article <38f845a6...@news.gte.net>,
> cecr...@NOWORMS.gte.net wrote:
>> You are correct Larry. Experienced observers and ATM know this from
>> actual experience.
>>
>> Jeff
>> A.L.P.O.
>>
>> On Thu, 13 Apr 2000 20:32:10 -0500, Larry Brown
>> <tangoDe...@fuse.net> wrote:
>>
>> >
>> >
>> >> I beg to differ. The light loss due to using a grossly undersized
>1"
>> >> secondary with 2" eyepieces will be most significant. It is highly
>> >> unlikely that anyone would perceive any improvement by reducing the
>> >> obstruction below 15% (by diameters).
>> >
>> >I may have misunderstood something. No, you cannot use 2" eyepieces
>with a
>> >small secondary. But with standard eyepieces the improvement in
>contrast
>> >is impressive. I have used several different sized mirrors. As the
>> >secondary size was reduced, the improvement in contrast was amazing.
>If
>> >you read ATM journals, many builders report the same thing. When you
>drop
>> >below a 15% obstruction, the improvement is dramatic.
>> >
>>
>>
>
>
Jeff
brightness of, say some galaxy, if you were to increase aperture from
8 to 10 inches. However, experienced observers will tell you they can
see the difference. It really comes down to what you call "dramatic."
for me I can detect subtle differences in contrast and brightness
between my 12.5 and 16 inch telescopes. In fact the 16 renders
planets much brighter. However, there is not a dynamic difference in
aperture or square area between the two scopes.
These things also depend on one's eyesight and acuity. When comparing
my ability to see dm objects and detect subtle surface features on
Mars of Jupiter with that of Steve O'Meara we have found we both can
see nearly the same stuff. However, Steve can see more than me using
larger apertures. This may be just the age thing. The last time he
observed with my 16-inch he came away in awe at the high contrast and
crisp images. That says a lot about fine tuning telescopes.
Jeff
On Sat, 15 Apr 2000 16:40:24 GMT, zane...@sansnetcom.com (Zane)
wrote:
>Del Johnson <deljo...@my-deja.com> wrote:
>
>>The Hubble Space Telescope seems to work just fine with its obstruction.
>>
>>You should read Dickinson's "The Backyard Astronomer's Guide".
>>Dickinson described a carefully controlled experiment where he
>>suspended various obstructions in front of a refractor. His findings
>>were that he could not tell the difference between no obstruction and
>>about a 15% obstruction. He also stated that going from about 15% to
>>about 20% (I don't recall the exact figures) resulted in only the most
>>minute difference that was difficult for him to see. There is no
>>dramatic change in image quality between 15% obstruction and no
>>obstruction.
>
Zane
>I suppose you could also say there isn't a dramatic increase in
>brightness of, say some galaxy, if you were to increase aperture from
>8 to 10 inches. However, experienced observers will tell you they can
>see the difference. It really comes down to what you call "dramatic."
I agree. I'm not saying that no one can see the difference; I just
thought it would be helpful to put some numbers to what we're talking about
and to point out that one has to be careful about the spider configuration
in drawing conclusions about the relative benefits of small secondaries.
>for me I can detect subtle differences in contrast and brightness
>between my 12.5 and 16 inch telescopes.
For the same features on a planet or something, the MTF of the 16 inch has
a considerably higher contrast value, so I'd expect the differences here to
be obvious if the atmosphere cooperated (a big "if" around my sites).
(snip)
>These things also depend on one's eyesight and acuity. When comparing
>my ability to see dm objects and detect subtle surface features on
>Mars of Jupiter with that of Steve O'Meara we have found we both can
>see nearly the same stuff. However, Steve can see more than me using
>larger apertures. This may be just the age thing. The last time he
>observed with my 16-inch he came away in awe at the high contrast and
>crisp images. That says a lot about fine tuning telescopes.
No doubt this is true. My eyes are not the best by a long shot
anymore---one reason I tend not to use my own subjective experiences as
guides for other people very much. It's useful to me to read experiences
of people with better eyes, but I sometimes have a hard time translating
them to what I would see without putting numbers to things.
Zane
Herm
airplanes..what software package (hopefully under $2k) would you recommend to
try?. How steep is the learning curve on one of these cad programs?
Herm
On Sat, 15 Apr 2000 12:45:26 -0500, Larry Brown <tangoDe...@fuse.net>
wrote:
>
Del Johnson
just the relative obstruction. There are many reasons why one might
have better contrast than the other. Mirror surface roughness for one.
Try this experiment: View a planet through a refractor. Have somebody
suspend a reasonable obstruction. Did the image degrade? Does the
effect repeat?
Del Johnson
In article <38f8abcc...@news.gte.net>,
cecr...@NOWORMS.gte.net wrote:
> I suppose you could also say there isn't a dramatic increase in
> brightness of, say some galaxy, if you were to increase aperture from
> 8 to 10 inches. However, experienced observers will tell you they can
> see the difference. It really comes down to what you call "dramatic."
> for me I can detect subtle differences in contrast and brightness
> between my 12.5 and 16 inch telescopes. In fact the 16 renders
> planets much brighter. However, there is not a dynamic difference in
> aperture or square area between the two scopes.
>
> These things also depend on one's eyesight and acuity. When comparing
> my ability to see dm objects and detect subtle surface features on
> Mars of Jupiter with that of Steve O'Meara we have found we both can
> see nearly the same stuff. However, Steve can see more than me using
> larger apertures. This may be just the age thing. The last time he
> observed with my 16-inch he came away in awe at the high contrast and
> crisp images. That says a lot about fine tuning telescopes.
>
Jeff
in the past few years and the last time I saw some more floaters. My
scopes are stored away and I use the 12-inch Clark at work whenever
the sky is clear. Seeing at work isn't all that great, but at times
is okay. The telescope is a good one, considering how old it is and
the type of lenses, but contrast is good on Jupiter. My eyes tend to
be blue sensitive and the refractor tends to give a yellowish tent, at
least for me. It must be that my floaters are yellow!
My 16 is a fine instrument and am looking forward to
reassembling it. AT times both of the telescopes (12.5&16) would be
operating and I used the smaller one to rest my eyes. Even with both
of them, side by side it is hard to tell if I can see more or less in
each. I know what my mentor would say, have the aperture when you
need it, but I really think 16 inches is about the upper limit for
visual work on the bright planets.
My 12.5-inch f/7 sports a 1.5 -inch secondary and the 16-inch was
designed for 1.83, but someone borrowed it so I use a 2-inch. It
works well. You can go smaller but for other than planetary work or
CCD work it isn't necessary to stretch it too far. Considering that
the field lenses in most of my eyepieces are no more than 1/4inch in
diameter, there is no reason for a larger secondary than would give
that linear image. Also, my CCD is very small and using projection to
increase elf to an image size that fits the chip is about right for
the secondary I use. That is also a consideration when using CCD
chips -- the actual size of the chip relative to the plate scale of
the optics.
Jeff
On Sat, 15 Apr 2000 19:28:39 GMT, zane...@sansnetcom.com (Zane)
wrote:
>cecr...@gte.net (Jeff) wrote:
>
>>I suppose you could also say there isn't a dramatic increase in
>>brightness of, say some galaxy, if you were to increase aperture from
>>8 to 10 inches. However, experienced observers will tell you they can
>>see the difference. It really comes down to what you call "dramatic."
>
>I agree. I'm not saying that no one can see the difference; I just
>thought it would be helpful to put some numbers to what we're talking about
>and to point out that one has to be careful about the spider configuration
>in drawing conclusions about the relative benefits of small secondaries.
>
>>for me I can detect subtle differences in contrast and brightness
>>between my 12.5 and 16 inch telescopes.
>
>For the same features on a planet or something, the MTF of the 16 inch has
>a considerably higher contrast value, so I'd expect the differences here to
>be obvious if the atmosphere cooperated (a big "if" around my sites).
>
> (snip)
>
>>These things also depend on one's eyesight and acuity. When comparing
>>my ability to see dm objects and detect subtle surface features on
>>Mars of Jupiter with that of Steve O'Meara we have found we both can
>>see nearly the same stuff. However, Steve can see more than me using
>>larger apertures. This may be just the age thing. The last time he
>>observed with my 16-inch he came away in awe at the high contrast and
>>crisp images. That says a lot about fine tuning telescopes.
>
Larry Brown
Herm wrote:
> Larry, I would be interested in doing virtual models of telescopes and model
> airplanes..what software package (hopefully under $2k) would you recommend to
> try?. How steep is the learning curve on one of these cad programs?
>
Herm,
It's difficult to answer your question without knowing what you want
to do
with the models that you will be creating as Cad files.
I use Unigraphics (about 12K per seat), Surfcam (about 10K) and Solidworks
(about 4K per seat) but these are all high-end programs with a learning
curve of
about one year or so (after three years I'm still learning things about
Unigraphics and Surfcam). Uni is owned by General Motors where they use
it to
design cars. I build smaller cars, radio-controlled and other types, for
a toy
company. These platforms are expensive because they contain a machining package.
If you want engineering software, something that will integrate 2D and 3D
models, I think Alias/Wavefront is about the best program out there.
They have
ported it to Windows NT (although it will also run in SGI Irix and Sun Solaris
environments. I recommend NT.) If all you want is an object technology
that will
define parametric objects, there are many things out there. If parametrics
aren't important, try AutoCAD. ArchiCAD runs on windows and MAC, and
will allow
you to do free-form modeling in 3D. Most of these smaller programs have a
six-month or so learning curve. This may sound like a lot but I am
assuming that
you want to learn to use everything the program has to offer. In two
days I
learned enought to use Photoshop, but I don't use it to the extent that a
graphics designer uses it.
Some modeling programs develop surfaces (like Surfcam) others
develop solids
(like solidworks). Which one you use depends on what you want to do with the
file--engineering, manufacturing, or just graphic display.
These are all programs that my company has purchased that I know something
about. There are many more. I suggest getting a magazine called Computer
Graphics World which reviews all this stuff. If you look at a few back issues
I'm sure you can find a program that will work for you. They reviewed a
new 3D modeler in the April issue that sells for about $400 and runs on
Windows and MAC. I don't remember the name of it, but it sounded very
promising. Sorry if I can't give you a
better answer.
Clear skies (I wish they were clear here, I wouldn't be sitting inside
at my
computer). --Larry Brown
Fdeal
you havn't already. You can swap out secondaries on this unit easier than
anything else on the market from what I've seen. All the critical
collimation on the secondary will stay with the diagonal & holder leaving
only gross centering and rotation on the changeout. The spider vanes are
also very thin - I noticed a definite decrease in defraction over my
Astrosystems unit. Give it a look:
http://www3.bc.sympatico.ca/gwolanski/SPIDERS.HTM
Peace,
Fred Deal
Del Johnson <deljo...@my-deja.com> wrote in message
news:8d7ni9$t1h$1...@nnrp1.deja.com...
> I meant why not sell both secondary mirrors to the user so that they
> can change them at will. I do this with my reflector. The extra cost
> is relatively small and I am now optimal for both planetary and deep
> sky viewing (they are both important to me). It takes me about 10
> minutes to swap secondaries and recollimate the telescope.
>
> Del Johnson
>
>
>
>
>
> In article <20000414121535...@ng-ch1.aol.com>,
> mauri...@aol.com (Excelsior Optics) wrote:
> > >Why not offer the larger secondary as a changeout option?
> >
> > Any option (within reason and my mechanical abilities) is
> available, as is
> > indicated on the "Biz" page, but it would seem to be illogical to
> take a format
> > that is intended to deliver the best planetary images, and configure
> it with a
> > less-than ideal secondary.
> >
> > Best,
> >
> > Maurizio
> >
> >
>
>
Del Johnson
ideal secondary mirror size.
Del Johnson
In article <vDoK4.784$rk.3...@news.uswest.net>,
"Fdeal" <fd...@uswest.net> wrote:
> You guys should take a look at Gary Wolanski's spider/diagonal
assemblies if
> you havn't already. You can swap out secondaries on this unit easier
than
> anything else on the market from what I've seen. All the critical
> collimation on the secondary will stay with the diagonal & holder
leaving
> only gross centering and rotation on the changeout. The spider vanes
are
> also very thin - I noticed a definite decrease in defraction over my
> Astrosystems unit. Give it a look:
> http://www3.bc.sympatico.ca/gwolanski/SPIDERS.HTM
>
> Peace,
>
> Fred Deal
>
Tim Parker
Jeff wrote:
> How's the f/23 Cass coming along? I have further
> refinements for you from the old days when I made my first 12.5-inch
> f/30.
It's coming! I put a 20" long 1.5" ID PVC baffle tube in it after we last
talked (20" from the backplate behind the mirror). This was the size my
graphical approach (combined with a little from the Novak "Cassegrain Notes"
called for. Do you think I should try a smaller ID tube? (they're cheap,
at least!). Tossed the thing together and got LOTS of glare on the moon (no
real surprise). So next evening, I sanded the tube inside and out and
painted it flat black. Could still see sky through the focuser without an
eyepiece, so I "measured" it's width (percent of field of view through
baffle), and made an aperture stop to fit the end of the tube. It's about a
1 3/8" ID stop. Now I can just see the edge of the secondary from the
focuser, but not the sky. Put it all back together and gee-whized Jupiter
and Saturn with it. Seems pretty good, but the seeing isn't good enough to
be sure, and they both drop too low before it gets dark to evaluate the
contrast anyway. The moon was behind clouds that night, and the next couple
it was behind the house. I haven't tried a glare stop at the mirror end
yet, because the seeing has continued to be awful. Now it's raining, and we
don't expect blue sky until Thursday, at least. And then there's that
bathroom door in the way in the middle of my shop that I'm refinishing...
...but that's another story. A delay, at any rate.
Next thing I need to do is beef up the saddle attachment to the tube. Then
I need to build a tube for the 6" f/10 Jaegers lens and one for the 3" f/15
Edmund lens. I also still need to add a finder to the Cass, as I've been
sighting along the corner of the nonagonal tube all this time. Works, but I
waste a little time unecessarily, and I do have a nice old 8x50 finder with
a helical focuser to put back to use. Depending on how well the Jaegers
works, I may not add the Newtonian secondary option to the Cass. I can
gee-whiz through the 6".
> Don and I worked out a 22-inch f/50 for Chick once and the
> optics are still around somewhere. The surface was so rough we gave
> up on it and went for 16-inch F/50's using a 1.5-inch secondary.
That would be neat! is the perforation in the primary also that small? (be
neat to see that 22" refigured, too).
> While using the UH24 Cass, the 24-inch f/75 that Tombaugh designed, I
> found that t he near zip obstruction in that machine produced very
> high contrast images, much much more so that the Air Forces Cass next
> door with their 20% obstruction. Oh well, who cares about actual
> experience, huh?
Yeah. My Cass has a 20% obstruction. Ed Beck talked me out of the 2"
secondary, which would have given me a f/27 system. I did keep the
perforation in the primary down to 2", so I could add the smaller secondary
at a future date, I suppose. That'd give me a 16% obstruction.
planetarily,
-Tim.
Jeff
>Do you think I should try a smaller ID tube?
I used a 1.25-inch diameter. Also, maybe a couple glare stops in the
tube. Like a refractor needs some stops. The last thing I tried was
flocking paper. That cured most of the glare problems.
>That would be neat! is the perforation in the primary also that small? (be
>neat to see that 22" refigured, too).
Yeah, the mirror was one of those conical shaped affairs with a
1.25-inch hole in it. Never got around to fitting it into the Cass
mode. We just put in a Newt secondary to see how the mirror was and
stopped right there. The thing had dog bisques from the center to
about the 70% zone and figured like a $ sign. Sent the mirror back
with a thanks but no thanks.
20% for a Cass isn't so bad. The first secondary I had in the
12.5-inch was for f/16 and was kind of large. We did up a 2-inch for
f/30 and that was probalby too big. I think my Cass image was 4
inches or so. hey, using 1.25-inch eyepieces all I needed was a half
inch or so. The nice thing aobutr the long FL Cass is the depth of
focus. I could put in a 32mm Pl and focus it in and out more than a
half inch before it would begin to fuzz up. It was really nice with a
camera on it. Using Don's "seeing monitor" an image could be fine
focused to a nat's butt.
A good Classical Cass can be a really nice instrument. If one can
keep the obstruction down it is nearly as good as Newt. ad far as
contrast goes.
Jeff
Tim Parker
I would be interested in seeing your updates to Cass designs. I'm far from
committed to this 1.5" ID baffle tube, so I could try a 1.25" that's shorter (so
as not to truncate the cone from the secondary. I do worry that the 1.5" ID
tube (about 1.875" OD) may be giving me an effective obstruction of the primary
cone to the secondary that might be greater than 2.5", but I'll have to draft it
up to see for sure. I'm using a 1/2" wide focal plane to determine the "spread"
of the light cone back to the primary in my graphical approach.
Jeff wrote:
> >Do you think I should try a smaller ID tube?
>
> I used a 1.25-inch diameter. Also, maybe a couple glare stops in the
> tube. Like a refractor needs some stops. The last thing I tried was
> flocking paper. That cured most of the glare problems.
>
> >That would be neat! is the perforation in the primary also that small? (be
> >neat to see that 22" refigured, too).
>
> Yeah, the mirror was one of those conical shaped affairs with a
> 1.25-inch hole in it. Never got around to fitting it into the Cass
> mode. We just put in a Newt secondary to see how the mirror was and
> stopped right there. The thing had dog bisques from the center to
> about the 70% zone and figured like a $ sign. Sent the mirror back
> with a thanks but no thanks.
>
> 20% for a Cass isn't so bad. The first secondary I had in the
> 12.5-inch was for f/16 and was kind of large. We did up a 2-inch for
> f/30 and that was probalby too big. I think my Cass image was 4
> inches or so. hey, using 1.25-inch eyepieces all I needed was a half
> inch or so. The nice thing aobutr the long FL Cass is the depth of
> focus. I could put in a 32mm Pl and focus it in and out more than a
> half inch before it would begin to fuzz up. It was really nice with a
> camera on it. Using Don's "seeing monitor" an image could be fine
> focused to a nat's butt.
This was a really pleasant surprise for me, coming from an 8" f/6. On the other
hand, it made finding the focus in daylight really challenging when I was first
putting the thing together!
> A good Classical Cass can be a really nice instrument. If one can
> keep the obstruction down it is nearly as good as Newt. ad far as
> contrast goes.
That's certainly my hope. Of course, it's still pretty wet and cloudy around
here. Maybe a few sucker holes tonight and tomorrow night, but another storm is
due in by Friday! Rats!
-Tim.
Jeff
Jeff
On Tue, 18 Apr 2000 14:12:11 GMT, cecr...@gte.net (Jeff) wrote:
>
>>Do you think I should try a smaller ID tube?
>
>I used a 1.25-inch diameter. Also, maybe a couple glare stops in the
>tube. Like a refractor needs some stops. The last thing I tried was
>flocking paper. That cured most of the glare problems.
>
>>That would be neat! is the perforation in the primary also that small? (be
>>neat to see that 22" refigured, too).
>
>Yeah, the mirror was one of those conical shaped affairs with a
>1.25-inch hole in it. Never got around to fitting it into the Cass
>mode. We just put in a Newt secondary to see how the mirror was and
>stopped right there. The thing had dog bisques from the center to
>about the 70% zone and figured like a $ sign. Sent the mirror back
>with a thanks but no thanks.
>
>20% for a Cass isn't so bad. The first secondary I had in the
>12.5-inch was for f/16 and was kind of large. We did up a 2-inch for
>f/30 and that was probalby too big. I think my Cass image was 4
>inches or so. hey, using 1.25-inch eyepieces all I needed was a half
>inch or so. The nice thing aobutr the long FL Cass is the depth of
>focus. I could put in a 32mm Pl and focus it in and out more than a
>half inch before it would begin to fuzz up. It was really nice with a
>camera on it. Using Don's "seeing monitor" an image could be fine
>focused to a nat's butt.
>
>A good Classical Cass can be a really nice instrument. If one can
>keep the obstruction down it is nearly as good as Newt. ad far as
>contrast goes.
>
>>That would be neat! is the perforation in the primary also that small? (be
>>neat to see that 22" refigured, too).
>>