Differences between mirrors
seeing...@my-deja.com
I am trying to determine what the difference is between mirrors made by
Zambuto, Pegasus, Galaxy, Nova and those made by others like Discovery,
Meade, etc... Will I see a big difference between a mirror of equal
size under identical seeing conditions if one is made by Discovery and
one that is made by Zambuto? Will I regret getting a Discovery dob
rather that a dob with a Zambuto mirror for 2-3x the price? I hope
there is someone out there that may have done some comparisons...
Looking for any and all help/input.
Thanks,
Dave
Sent via Deja.com http://www.deja.com/
Before you buy.
Randy Rogers
usually stays with you for the duration of owning your telescope. As it is
right now, you can only buy a Zambuto mirror with 4 brands of telescopes as
he doesn't sell directly to the public like the other three you mentioned.
The four brands are: Starmaster (my favorite since I'm buying one!),
Starsplitter, Portaball, and Teleport (an excellent choice as well).
You can custom order mirrors with Pegasus, Nova, Galaxy and Swayze. As to
the quality distinction of Zambuto vs. other brands, do a DejaNews search
and type in the key word "Zambuto" and see what you get. There is nothing
like it on the market unless you go to Perkin-Elmer, Kodak, or some other
big professional optics plant. The test of a good mirror is the contrast
the mirror provides for faint (extended) objects against the background
black (hopefully) night sky. The unpolluted night sky has a background
noise level of about 24.5 magnitude. If the mirror's surface is rough
(micro-finish), you will have a low signal to noise ratio, and faint objects
will be lost in the noisier background wash. I have never heard of anybody
getting a poor Zambuto- all reviews have been rave. While the prices of his
mirrors are at a "terrestrial" level, I would recommend getting a Zambuto in
one of the 4 brands listed above. I recommend both the Teleport - a really
compact design custom made by Tom Noe in Wylie TX or else if you want a
larger model (over 10"), go with Starmaster.
My .02 1/2 cents worth,
Randy Rogers
St. Louis
<seeing...@my-deja.com> wrote in message
news:8m6t5u$1b0$1...@nnrp1.deja.com...
Axel
If you're serious about this hobby and intend to do more than casual
observing, go with the best! I bought a Celestron Star Hopper 8" Dob
in March and after a mere three months found out via star testing that
my mirror is seriously under-corrected. Even when perfectly collimated
and cooled down, I never get razor-sharp images. They're not horrible,
I was surprised recently at how good Uranus and Neptune looked at
244x. But the real tests are Jupiter and Saturn because of all the low-
contrast features, and when they were up in the Spring I was not
impressed at high power.
The optics in these mass-produced Dobs are adequate for beginners, but
I quickly graduated to "serious amateur" and the primary mirror will be
replaced shortly. I ordered a Royce 8" f/6 six weeks ago and am
expecting delivery anyday now. The catch is this: the mirror alone is
$700, nearly twice what I paid for the entire Celestron scope!!!
I recommend plunking down the extra change (perhaps 2-3 times what the
cheap Dobs cost) for the premium Dobs like Starmaster. Another MAJOR
consideration is that these premium Dobs come with premium components,
like great focusers, finders, bearings, mounts, mirror cells, spiders,
etc. The extra cost is worth it, IF you intend to spend many fruitful
years pursuing this incredible hobby.
BTW, someone on this newsgroup mentioned that Starmaster's smallest Dob
now is 11". If you can't find a premium small Dob out there, you'll
need to do what I did: buy a cheap Dob and UPGRADE virtually everything
on it!
Ritesh
In article <8m6t5u$1b0$1...@nnrp1.deja.com>,
Jeff Lipsman
--Jeff Lipsman
Randy Rogers wrote:
ste...@binghamton.edu
Are you just starting out? Will spending 2x or 3x faze you or your budget?
How much portability do you want?
I went through this decision-making on getting a 10" dob and, even though I own
a 7" with a Zambuto mirror, ended up going with Discovery. They have a
reputation for good optics--and I just couldn't see spending double or more for
the high-end optics. I also would not have had the room for a 10" f/6 solid
tube dob and a truss dob would have meant $1300 more. And all that would have
put me in the range of a computerized, CCD ready SCT, which would have worsened
my quandary.
My 7" is a marvelous scope--and produces truly wonderful views. But I am
pleased, greatly, with the views through the 10". (The 7" isn't getting the use
it used to.) The real proof of the pudding, though, will await planetary
observations.
Larry Stedman
Vestal, NY
seeing...@my-deja.com
Seeing as dobs are more for looking at faint fuzzies anyway, it seems
better to spend less on a dob, say a discovery, and then get a scope
that is optimized for planets like a refractor or a mak-newt.
BTW, how does your discovery star test?
Thanks,
Dave
In article <stedman-5A0623...@news.binghamton.edu>,
si...@my-deja.com
"Randy Rogers" <star...@email.msn.com> wrote:
As to
> the quality distinction of Zambuto vs. other brands, do a DejaNews
search
> and type in the key word "Zambuto" and see what you get. There is
nothing
> like it on the market unless you go to Perkin-Elmer, Kodak, or some
other
> big professional optics plant
How would one go about ordering a mirror from Kodak or Perkin-Elmer?
Their web sites don't say anything about mirrors.
Bob May
Discovery and maybe get the same quality but there's no proof of it.
The question here really is how much of a gamble you want to make on
getting a really good quality (1/10th wave P/V) mirror. I might note
that anything beyond 1/10th rms (a looser standard than P/V) is often
not used to it's fullest except for a very few days in the lifetime of
the scope if it's well used and you live in an area where you can even
see such a night.
Go buy the better mirror and you won't have to inspect it to verify
even if it's in spec and that's most of the price difference.
--
Bob May
Access1 has gone Chapter 7 so I don't know how long my website is
going to last.
Bob May
Randy Rogers
to use <g>
Randy
<ste...@binghamton.edu> wrote in message
news:stedman-5A0623...@news.binghamton.edu...
Dave S
Recently I set up my Meade 12.5" F/4.8 Dob next to Carl Zambuto and his
12.5" F/5 dob and we made comparisons. Using the exact same eyepieces, his
stars were a little sharper than mine but his scope cost 3X as much as my
Meade! I would say that a beginner probably would not notice the difference
where as an advanced astronomer would easily notice the difference. You
decide if it is worth 3X the cost!
Dave
----------
In article <8m6t5u$1b0$1...@nnrp1.deja.com>, seeing...@my-deja.com wrote:
> Hello,
>
> I am trying to determine what the difference is between mirrors made by
> Zambuto, Pegasus, Galaxy, Nova and those made by others like Discovery,
> Meade, etc... Will I see a big difference between a mirror of equal
> size under identical seeing conditions if one is made by Discovery and
> one that is made by Zambuto? Will I regret getting a Discovery dob
> rather that a dob with a Zambuto mirror for 2-3x the price? I hope
> there is someone out there that may have done some comparisons...
> Looking for any and all help/input.
>
> Thanks,
> Dave
>
>
Paul Roy
seeing...@hotmail.com wrote:
> Hello,
>
> I am trying to determine what the difference is between mirrors made
by
> Zambuto, Pegasus, Galaxy, Nova and those made by others like
Discovery,
> Meade, etc... Will I see a big difference between a mirror of equal
> size under identical seeing conditions if one is made by Discovery and
> one that is made by Zambuto? Will I regret getting a Discovery dob
> rather that a dob with a Zambuto mirror for 2-3x the price? I hope
> there is someone out there that may have done some comparisons...
> Looking for any and all help/input.
>
> Thanks,
> Dave
Dave,
Good question. First of all Dobs are not mainly used for looking
at faint fuzzys. This type of mentality was first implemented at the
conception of the big dob idea. Coulter Optical back in the mid-80's
graced the industry by making avialable large telescopes for little
money. They did as much good as bad. The term 'light bucket' was
first used illustrating an attitude that big telescopes not only were
not good optically, but did need to be as well! After all, buckets are
not made to exacting tolerances as they need not to be, but telescopes
do! The current high-end dobsonian is a highly optimized, awesome
visual observing machine that can in many cases provide views superior
to all other kinds of telescopes due to thier large size. Never forget
that in the end APERTURE is paramont and DIRECTLY determines
resolution. This of course assumes the quality is good as well. By the
way, good contrast (a hallmark of good optics) is not only essential
for planetary viewing, it's equally as essential for deep sky observing
as well!
There are many other factors other then optical quality that controls
how well a telescope will perform. Most rookie astronomers do not know
this yet, but soon find out only after they purchased the cheaper
model. Thes factors include optical support, secondary optical quality
and support, EYEPIECES (very important 1/3 you're image in any
Newtonian) ventilation for the optic, COLLIMATION..etc..
Mirror quality is very important, however the above must be consistent
in quality as the mirror in order for the optic to show it's stuff.
Zambuto seems to be the hot item now in Newtonian mirrors. I
personally have observed through 2 telescopes that employed Zambuto
mirrors, both were excellent however,the others you list above are just
as capable of producing an equally quality optics. Mirror fabrication
is not a 'cult', or magic show, it's a learned discipline that can be
mastered by many who are willing to take the time to learn it, and have
the attitude and motivation to maintain a specific high QC level.
Trends can affect any market, this industry is by no way an exception.
Zambuto, Pegasus, Galaxy, Nova, all gurantee their optical quality,
this is what is important. I've seen outstanding examples from all of
the listed mirror fabricators. Good Newtonian optics are becomming
more available all the time. Good telescopes are not..especially in
the dob market where the big '3' companies continuesly see the dob as a
low end product.
Save you're money a get the premium dob. A premium dob holds it's
value very well unlike the others. So financially speaking you'll
never really lose money, and besides, the stars ain't goin' anywhere
soon. I'm sure they will be ready for you when you're ready for them!
Have fun!
Paul
mag...@arnprior.com
>I am trying to determine what the difference is between mirrors made by
>Zambuto, Pegasus, Galaxy, Nova and those made by others like Discovery,
>Meade, etc... Will I see a big difference between a mirror of equal
>size under identical seeing conditions if one is made by Discovery and
>one that is made by Zambuto? Will I regret getting a Discovery dob
>rather that a dob with a Zambuto mirror for 2-3x the price? I hope
>there is someone out there that may have done some comparisons...
>Looking for any and all help/input.
I just had my Discovery-made, plate, 8-inch mirror recoated, and asked
for an evaluation along with the recoat. In Foucault testing, it met
1/8 wave at the wavefront, and was good out to the edge. In
star-testing, it shows no vices--no zones, turned edge, obvious SA.
However, it is slow to cool down, and shadow breakout often takes
awhile to get below 2:1. When it does, images are very good. When the
seeing gets good, planetary detail can be surprising. It's hampered a
little by my scope's thick spider vanes, and 25% secondary, and closed
tube--things that are going to change.
I'm not sure about the smoothness, and would like to compare it
side-by-side to a Zambuto. I'm willing to believe that any careful
craftsman can produce good glass, and a few artists can come up with
masterpieces, but I don't believe in magic scopes.
As to whether it's worth spending 2-3X the money, that's up to you.
Other aspects of the scopes may be as important (smooth motion,
focuser, cell). If you live in an area of very good seeing, then I'd
say go for it. If you're in the Jetstream zone, you're only going to
get a few nights a year that the better optics will make a difference.
Of course, those infrequent, stunning views are what keep us going the
rest of the year.
Doug Hoy
seeing...@my-deja.com
Ok, lets look at my quandry this way, would it
be better to get an 8" Zambuto or spend the same
amount on a 12.5" Discovery?
Thanks,
Dave
In article <8m6t5u$1b0$1...@nnrp1.deja.com>,
seeing...@hotmail.com wrote:
> Hello,
>
> I am trying to determine what the difference is between mirrors made
by
> Zambuto, Pegasus, Galaxy, Nova and those made by others like
Discovery,
> Meade, etc... Will I see a big difference between a mirror of equal
> size under identical seeing conditions if one is made by Discovery and
> one that is made by Zambuto? Will I regret getting a Discovery dob
> rather that a dob with a Zambuto mirror for 2-3x the price? I hope
> there is someone out there that may have done some comparisons...
> Looking for any and all help/input.
>
> Thanks,
> Dave
Les Blalock
>I just had my Discovery-made, plate, 8-inch mirror recoated, and asked
>for an evaluation along with the recoat. In Foucault testing, it met
>1/8 wave at the wavefront, and was good out to the edge. In
>star-testing, it shows no vices--no zones, turned edge, obvious SA.
>However, it is slow to cool down, and shadow breakout often takes
>awhile to get below 2:1. When it does, images are very good. When the
What is _shadow breakout_ ?
Thanks,
Les Blalock
Odessa, Tx
Randy Rogers
phone numbers listed on some of the pages... Get ready to grab your
pocketbook on these two though.
Randy
<si...@my-deja.com> wrote in message news:8m7m22$lbj$1...@nnrp1.deja.com...
> In article <OKHxbX$#$GA.233@cpmsnbbsa07>,
> "Randy Rogers" <star...@email.msn.com> wrote:
> As to
> > the quality distinction of Zambuto vs. other brands, do a DejaNews
> search
> > and type in the key word "Zambuto" and see what you get. There is
> nothing
> > like it on the market unless you go to Perkin-Elmer, Kodak, or some
> other
> > big professional optics plant
>
> How would one go about ordering a mirror from Kodak or Perkin-Elmer?
> Their web sites don't say anything about mirrors.
>
>
Paul Roy
seeing...@my-deja.com wrote:
> Thanks everyone for your insight and advice.
>
> Ok, lets look at my quandry this way, would it
> be better to get an 8" Zambuto or spend the same
> amount on a 12.5" Discovery?
>
> Thanks,
> Dave
David,
I would say that the better choice would be the 12.5" Discovery IF
you are willing to deal with the additional size and weight. A well
designed, good 12.5" scope will still outperform an outstanding 8"
scope, ( one simple observation of a globular cluster will illustrate
this immediately)remember, all things considered aperture wins. Just
be sure that by you being the buyer you beware, and ensure that a
gurantee is provided and is unambiguous in nature.
Good Luck!
Paul
>
> In article <8m6t5u$1b0$1...@nnrp1.deja.com>,
> seeing...@hotmail.com wrote:
> > Hello,
> >
> > I am trying to determine what the difference is between mirrors made
> by
> > Zambuto, Pegasus, Galaxy, Nova and those made by others like
> Discovery,
> > Meade, etc... Will I see a big difference between a mirror of equal
> > size under identical seeing conditions if one is made by Discovery
and
> > one that is made by Zambuto? Will I regret getting a Discovery dob
> > rather that a dob with a Zambuto mirror for 2-3x the price? I hope
> > there is someone out there that may have done some comparisons...
> > Looking for any and all help/input.
> >
> > Thanks,
> > Dave
> >
Randy Rogers
of four different brands of scopes). Carl sells only to: Starsplitter,
Starmaster, Teleport, and Portaball. No sales to the general public.
Randy
<seeing...@my-deja.com> wrote in message
news:8m9rev$8j5$1...@nnrp1.deja.com...
> Thanks everyone for your insight and advice.
>
> Ok, lets look at my quandry this way, would it
> be better to get an 8" Zambuto or spend the same
> amount on a 12.5" Discovery?
>
> Thanks,
> Dave
>
Randy Rogers
steel. Somebody better snap up that baby before I sell one of my kidney's
on the black market.
Randy
"Paul Roy" <pro...@my-deja.com> wrote in message
news:8m9t5a$a2k$1...@nnrp1.deja.com...
> In article <8m9rev$8j5$1...@nnrp1.deja.com>,
> seeing...@my-deja.com wrote:
> > Thanks everyone for your insight and advice.
> >
> > Ok, lets look at my quandry this way, would it
> > be better to get an 8" Zambuto or spend the same
> > amount on a 12.5" Discovery?
> >
> > Thanks,
> > Dave
>
> David,
>
> I would say that the better choice would be the 12.5" Discovery IF
> you are willing to deal with the additional size and weight. A well
> designed, good 12.5" scope will still outperform an outstanding 8"
> scope, ( one simple observation of a globular cluster will illustrate
> this immediately)remember, all things considered aperture wins. Just
> be sure that by you being the buyer you beware, and ensure that a
> gurantee is provided and is unambiguous in nature.
>
> Good Luck!
> Paul
> >
Les Blalock
Les Blalock
http://www.cableone.net/les/astro/
West Texas Astronomers
http://www.apex2000.net/nonprof/wta/
On Thu, 03 Aug 2000 21:52:04 GMT, mag...@arnprior.com wrote:
>On Wed, 02 Aug 2000 13:50:40 -0500, Les Blalock
><l...@NOSPAMector911.org> wrote:
>
>>What is _shadow breakout_ ?
>
>Oh, it's when the central obstruction first begins to become obvious
>as you defocus a star image. You make a mark on your focuser when the
ste...@binghamton.edu
much more use than my 7" Starmaster (with Zambuto). The difference between
12.5" and 8" would be even greater. . .
On the other hand, if you're thinking about a 12.5" *solid* tube dob, then it's
another ball game. That will be a monster, big and bulky; by contrast most 8"
scopes are manageable even by mere mortals (i.e., people other than Hercules or
the Incredible Hulk). The larger scope also won't fit in many cars,
particularly compact ones, so you'd be limited to backyard observing.
The solution? The 12.5" discovery truss.
P.S. Dave, you asked about the star test on the 10" Discovery. Ha! I live in
upstate New York; given the jet stream, forget star testing. On the rare nights
where seeing is okay, I'd rather be observing than trying to learn how to star
test. What I need to do, but haven't yet, is the artificial star testing which
I could master at my leisure.
Randy, take a number! :-) Ever since I mentioned it's getting less use, I've
been getting suggestions about new homes for the 7"! At one level, I really
hoped the 10" was going to be a dog (no offense to "fellow" Lassie lovers or
PETA members); that way I could have relished the 7" forever.
Yet, there's something wonderful about the scale of the 7"; the most
ergonomically friendly scope I've ever used. And the images are amazing for a
7" scope.
Larry Stedman
Vestal, NY
tfla...@my-deja.com
> Ok, lets look at my quandry this way, would it
> be better to get an 8" Zambuto or spend the same
> amount on a 12.5" Discovery?
I agree with everyone else that a 12.5" Discovery would
give you more for the money, with a few important provisos.
First, there is the question of portability and cooldown.
Given identical designs, there is a *huge* difference in
portability and cooldown time between an 8" and a 12.5".
This may or may not be a major issue for you.
Second, there is the question of field of view. All other
things being equal, the max FOV of a 12.5" Dob is 2/3 the
max FOV of an 8" Dob, and the difference can be *very*
significant at those particular apertures. For instance,
it is the difference between fitting M31 entirely in the FOV
and not, or of getting a good view of the North America Nebula
and not. I don't think this is enough to balance the vastly
greater performance of 50% extra aperture on most DSOs, but
it is nothing to sneer at either.
Third, in my experience Zambuto mirrors have not only
better resolution than average but (surprisingly) better
contrast. I think this is a question of surface smoothness,
which is not one of the measurements often listed for a
mirror -- more or less independent of wavefront error.
The superior contrast is really noticeable for things like
seeing the E and F stars in the Trapezium -- anywhere where
you have to pick out a faint object right next to a very
bright object. There is also an esthetic aspect to this --
a big part of what makes people love refractors, and why
people say that high-quality Newts provide "refractor-like
views."
Finally, I do not really agree with your statement that
Dobs are not optimized for planetary views. Aside from the
matter of tube currents, Newts are every bit as good for
planetary work as Mak-Newts (why shouldn't they be?) and
clearly superior to Mak-Cass's of the same aperture. And
not far behind refractors of the same aperture, and far
ahead of refractors in the same price range. There's
plenty of dedicated planetary observers for whom Newts
are the instrument of choice. Fit your Dob with a drive,
and you will have a planetary instrument second to none.
Having said all of that, I am sure that a 12.5" Discovery
would be a fine telescope, giving superior views to an
8" with Zambuto mirror of all objects that fit in the FOV
if you luck out and get a mirror in the top 25%, and of
most objects if you have bad luck and get a mirror in
the bottom 25%.
--
- Tony Flanders
Cambridge, MA
Paul Roy
Dave,
Just thought I would let you know, and others who may find this
interesting but, John Hall; president of Pegasus optics, was Carl
Zambuto's mentor. Zambuto, like Hall, aheares to the same more
stringent optical tolerance envelope then the standard Rayleigh
limit.(unlike most others who just comply witht the Rayleigh limit for
primary optics) Adhearence to this specific envelope creates higher
STREHL ratio's in which focus more of the reflected mirror's light
energy into the airy disc. Most more common commerical telescope
mirror makers are only concerned with complying with the Rayleigh limit
in which usually results in a total system error exceeding the 1/4 wave
criteria.
Carl Zambuto's mirrors, as well as John Halls typically come out with
wavefront errors not exceeding 1/8th wave. This is why these mirrors
look better then others..more of the mirror's light is being focused
into the airy disc resulting in sharper, more contrasty images.
Paul
> Hello,
>
> I am trying to determine what the difference is between mirrors made
by
> Zambuto, Pegasus, Galaxy, Nova and those made by others like
Discovery,
> Meade, etc... Will I see a big difference between a mirror of equal
> size under identical seeing conditions if one is made by Discovery and
> one that is made by Zambuto? Will I regret getting a Discovery dob
> rather that a dob with a Zambuto mirror for 2-3x the price? I hope
> there is someone out there that may have done some comparisons...
> Looking for any and all help/input.
>
> Thanks,
> Dave
>
mag...@arnprior.com
<l...@NOSPAMector911.org> wrote:
>What is _shadow breakout_ ?
Oh, it's when the central obstruction first begins to become obvious
as you defocus a star image. You make a mark on your focuser when the
star is perfectly focused. Then you defocus one direction (in or out),
and make another mark. Then you go back to best focus and continue on
in the other direction until you just see the shadow appear, same as
the other side. Make a mark. If there is minimal spherical abberation,
the shadow appears, or breaks out, at the same distance on both sides.
On most scopes. or uncooled ones, you'll notice that you have to
defocus farther on one side to get the same appearance. The amounts
vary depending on the focal ratio and the percentage obstruction, but
H.R. Suiter came up with a rule of thumb that a ratio of 2:1 on a 33%
obstructed scope was about equal to 1/4 wave of spherical abberation,
or 'diffraction-limited' optics. It's hard (impossible?) to accurately
measure SA by eye, but this trick is a quick way to see if the optics
are even passable. Check Suiter's book for details.
A few caveats:
A mirror changes shape as it cools, so don't be surprised at higher
ratios until things settle down (maybe hours later).
You may have to increase the obstruction artificially with a paper
disk stuck to the diagonal. You can even introduce one to a refractor,
taped to a fishing line spider over the objective.
It's not that easy to tell exactly when the shadow is appearing,
especially with the finicky focusing of a fast scope at high power.
Practice under different conditions.
It's easy to do, and a great way to ensure the scope is cooled to its
best figure, even if the rings are looking good otherwise.
Doug Hoy
APM
>Finally, I do not really agree with your statement that
>Dobs are not optimized for planetary views. Aside from the
>matter of tube currents, Newts are every bit as good for
>planetary work as Mak-Newts (why shouldn't they be?)
Tony,
I own now a 8" Portaball and a 12.5" as well as a 16"F/5
Newtonian with closed tube and optical window. I can tell you
that my Zambuto optics not 1% worser than my 16" , I expect
maybe even better. But I can tell you that under normal
conditions we using over the year ( I dont speek about the few
magic nights on excotic places) espacialy the Dobs siffers from
stable images, due all that open tubes. Even now in summertime
my bodyhead destroy most seconds the stable image. If air leave
my mouth the image starts bluring, so for observing douplestars
or Planets with my dob I must wear dressing which does not allow
to leave my body head towards the dob and must shut my mouth for
30 seconds to see the very stable image.
The Dob have its open parts and the spiders which cause in
additional damage. All this problems I dont have by using a
Maksutov Newtonian. Even in an 10" or my 16" close system I dont
have this problems, the image is just stable.
I have been already on several US starpartys and must say that I
was very lucky with excellent seeing, but talking about overal
good nights, a MN do most time a clear shoot out of an 3~4 times
larger Dob on planets.
Another impression is, that I never saw that contrast in an Dob
which I have in an MN.
and
>clearly superior to Mak-Cass's of the same aperture. And
>not far behind refractors of the same aperture, and far
>ahead of refractors in the same price range. There's
>plenty of dedicated planetary observers for whom Newts
>are the instrument of choice. Fit your Dob with a drive,
>and you will have a planetary instrument second to none.
A Planetary optimized Newtonian and an Dob is a very big
diffrence. The Planetary optimized Newtonian again have an close
tube. Show me Planetary Newtonian owner with an truss tube, you
will not find it.
Markus
>>
>--
> - Tony Flanders
> Cambridge, MA
>
>
>Sent via Deja.com http://www.deja.com/
>Before you buy.
>
>
-----------------------------------------------------------
Got questions? Get answers over the phone at Keen.com.
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Mike Spooner
APM <ludesN...@ur.pils.de.invalid> wrote in message
news:26498e43...@usw-ex0105-038.remarq.com...
> to leave my body head towards the dob and must shut my mouth for
> 30 seconds to see the very stable image.
But Markus! If you don't breathe the lack of oxygen will have you seeing
hallucinations and we won't *really* know if those are gaps in Saturn's
rings or just blackouts. <big Grin>
Seriously this body heat problem is why I put focusers on the downside of
prevailing wind for when my scopes are positioned for viewing planets. Would
it be different in the southern hemisphere? :)
BTW, how much magnification did you use to show Zeta Hercules as double with
that fantastic Zambuto 8"?
Thanks,
--Mike Spooner
Dan Chaffee
<ludesN...@ur.pils.de.invalid> wrote:
>A Planetary optimized Newtonian and an Dob is a very big
>diffrence. The Planetary optimized Newtonian again have an close
>tube. Show me Planetary Newtonian owner with an truss tube, you
>will not find it.
Markus,
Well, almost...I have found that the most critical parts of a
newtonan OTA that need covering to take care of thermal
current problems are the area around and immediately
in front of the primary--and-- the area near where the
observer stands/sits. My two newtonians, both used strictly
for high-res work, have been empirically designed and
built with this in mind, such that while they are not truely
a pure truss arrangement, they are not closed tubes either.
What this means is they are tube assemblies that have
been carefully carved with large windows that are not
in a position to take in unwanted currents, yet the critical
locations are reasonably well shielded. The views are
substantially more stable than my experiences with
solid tubes, and I breath normally:-)
I was intially concerned about the convective
currents coming off the GEM, but it does not seem to be
a problem. The scopes cool down noticeably faster.
If you like, I can privately email you a drawing of Saturn
I did with my 150mm f/8.4 that is so constructed, done
on a good, but not excellent night last winter.
Dan Chaffee
Mike Barrs
news:398ba38d...@news.primary.net...
> On Fri, 04 Aug 2000 12:00:31 -0700, APM
> <ludesN...@ur.pils.de.invalid> wrote:
>
> >A Planetary optimized Newtonian and an Dob
> >is a very big diffrence. The Planetary optimized
> >Newtonian again have an close tube. Show me
> >Planetary Newtonian owner with an truss tube,
> >you will not find it.
That's just ridiculous. In South Florida where the local seeing is very
good, the best visual planetary scopes are tracking Dobs with excellent
optics in the 15"-18" size. They have truss tubes for practicality, and this
works just fine on planets.
Markus, come out to the southern Everglades with me some night, and I'll
show you my "planetary optimized" tracking 18" f/4.5 scope, with an Ed Beck
mirror. Bring lots of mosquito repellant... it's not like WSP. :-)
The main thermal issue with scopes of this size isn't "tube currents", it's
dealing with the thin layer of hot air in front of a cooling mirror, which
can be reduced (if not eliminated) with active, side-blowing fan systems.
You're going to hear more about this from various sources, soon. And guess
what... this is best done with an open truss and open mirror box system (if
not a completely open, minimalist mirror box with an exposed mirror), where
you can easily exhaust the air from the mirror scrubbing system. Closed
tubes only trap heat. The trick is to get rid of the heat as quickly and
efficiently as possible, and you can't do that in a closed tube.
Professional observatory scopes are designed to equilibrate the entire
system to ambient temperature, and that's the goal we should be shooting
for.
Mike Barrs
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Jeff Morgan
<star...@email.msn.com> wrote:
> mirrors are at a "terrestrial" level, I would recommend getting a Zambuto in
> one of the 4 brands listed above. I recommend both the Teleport - a really
> compact design custom made by Tom Noe in Wylie TX or else if you want a
> larger model (over 10"), go with Starmaster.
I was looking for a web site for Starmaster, didn't find one. Do you know
the address? And since I am being lazy, how about an url for Teleport?
Thanks!
--
Jeff Morgan
email: substitute mindspring for nospam
Randy Rogers
(soon to be revised)
and Tom Noe's email address:
tom...@wt.net
Regards,
Randy
"Jeff Morgan" <jeffm...@nospam.com> wrote in message
news:jeffmorgan-11...@user-33qt9th.dialup.mindspring.com...