Why So Few Schmidt Newtonians?
weird_al
One of the scopes Tod Gross reviews on his web site is the Meade 6" f/3.6
Schmidt-Newtonian "Comet Tracker" (not to be confused with Celestron's
popular 5.5" Comet Catcher, which is also a Schmidt-Newtonian). Todd
commented in his review that Meade really should think about re-releasing
the Comet Tracker. He also noted that Meade used to make 6" f/5 and 8" f/4
Schmidt-Newtonian scopes. I have one of the 6" f/5 ones and I think it
performs very well for wide field deep sky viewing and astrophotography,
and is better on planets than I expected when I bought it (used).
Given how well the scope is working for me, I am wondering why the
Schmidt-Newtonian design has not been more popular (commercially) over the
years? Among scope designs, it has a few things going for it:
1. It has somewhere between 40% and 50% less coma than a pure Newtonian
at the same f-ratio (e.g. at f/5 it's essentially coma free over a full
35mm film frame).
2. The reflective optical surfaces (a sphere and a flat) are easy to figure.
(The Schmidt correct plate is also easy to manufacture commercially.)
3. The lack of secondary support vanes means nice round star images without
the diffraction spikes you get with a pure newtonian.
Yet there have been very few commercial Schmidt-Newtonian scopes over the
years. All I can remember are the three Meades I mentioned above, Celestron's
5.5" Comet Catcher and an 8" scope once sold by JMI. Why isn't this scope
design more popular?
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weird_al
In article <358742...@telcocom.com>, r...@telcocom.com says...
>
>Probaably a longer tube than a SC and thus, no fork mount that is
>extremely compact. The SC design is VERY compact and does a lot of good
>work and is hard to beat.
Agreed, the SC's extemely compact tube is undoubtedly one of the main
reasons the design is so popular. Yet the tubes of Meade's 6" f/5 and
8" f/4 SNs, while not quite as short, are still reasonably compact
(e.g. the 6" model's tube is 24" long). And both of these SN scopes used
fork mounts. In fact, in the case of the 6" f/5, the fork arms are
identical to those used now on Meade's 8" LX10 SC (although mounted
closer together). The fork assembly rotates in the same polar housing
used on Meade's equatorial Starfinder scopes. In the case of the 6"
f/5 the result is very stable and reasonably compact. It's compact
enough for me, in any case.
weird_al
"Rick" said...
>
>Alen Koebel wrote in message <3586F0...@electro.com>...
>>Chris Marriott wrote:
>>
>>> Orion Optics here in the UK make a range of Schmidt-Newts.
>>
>>Do they have a web site?
>
>You bet: http://www.orionoptics.co.uk/
Thanks. Looks like they have two SNs there: a 8" f/4 (as various
models with different EQ mounts) and a Vixen 5" advertised as being
f/8 (although it looks too short to be f/8). I wonder if the 8" is the
same OTA that JMI used to sell?
PS. Did you notice they call the Vixen 8" Cassegrain a catadioptric?
Stephen Tonkin
Weird Al <?@?.?> wrote:
>>>> Orion Optics here in the UK make a range of Schmidt-Newts.
>I wonder if the 8" is the
>same OTA that JMI used to sell?
Unlikely. The Orion Optics 8" SN is made by them in the UK.
--
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weird_al
In article <AwHD4WAf...@aegis1.demon.co.uk>, Stephen says...
>
>Weird Al <?@?.?> wrote:
>>>>> Orion Optics here in the UK make a range of Schmidt-Newts.
>[...]
>>I wonder if the 8" is the
>>same OTA that JMI used to sell?
>
>Unlikely. The Orion Optics 8" SN is made by them in the UK.
It's possible JMI imported it from Orion. Unlikely, but possible.
But if Orion didn't make the JMI Schmidt-Newt, who did? And is there
anyone out there who owns one?
(Is there anyone else out there reading this thread?....Is there
anyone out there?...CQ, CQ ... :-)
Jonas Carlsson
Hi,
I bought one of the Orion Optics 8"/f4 Schmidt-Newtonians about 1 1/2 year
ago through an agent here in Scandinavia and is very happy with it. I bought
the tube assembly only and mounted it on my home made GEM.
I have started doing some astrophotography with it but have had some
problems with focusing with the Meade 2" focuser that was mounted on it by
the agent. (The original focuser is a 1 1/4" and I wanted a larger.) Since I
mounted another, all-metall, 2" focuser it haven't been weather for
photographing with the telescope.
I am no specialist in judging optics but compared to a friends 8"/f6, it
only has slightly more coma on the outer edge but it nothing disturbing.
The tube is made of rolled aluminium and the only thing I would like to
change in the overall design is the very exposed wing nuts for adjusting the
primary mirror. If one isn't careful, they can easily be moved when handling
the tube assembley. (A good thing is of course that they are easy to reach
when you need collimating the scope.)
Hope this answers some questions.
Regards
Jonas
Weird Al skrev i meddelandet <6mbqfe$m...@pdrn.zippo.com>...
Stephen Tonkin
Weird Al <?@?.?> wrote:
>It's possible JMI imported it from Orion. Unlikely, but possible.
Simple way to check if it bothers you: ask Barry Pemberton at Orion
Optics -- his email is Barry Pemberton <sa...@orionoptics.co.uk>
--
Stephen Tonkin
(N50.9105 W1.829)
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
The Astronomical Unit - <http://www.aegis1.demon.co.uk/astunit.htm>
David Nakamoto
There is a 5.7 inch Maksutov-Newtonian, advertised very seldom in Sky
and Telescope. I just scanned through a dozen issues without seeing
the ad. The company offers it in f/6 and f/4 focal lengths. It
seems like a fine optics system; it better be at nearly $2000 for
just the optic assembly alone!
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>From: David Nakamoto <d...@blankreg.jpl.nasa.gov>
>Date: Thu, 18 Jun 1998 09:56:15 -0700
>Organization: Jet Propulsion Laboratory - Pasadena CA
>There is a 5.7 inch Maksutov-Newtonian, advertised very seldom in Sky
>and Telescope. I just scanned through a dozen issues without seeing
>the ad. The company offers it in f/6 and f/4 focal lengths. It
>seems like a fine optics system; it better be at nearly $2000 for
>just the optic assembly alone!
You are thinking of Peter Ceravolo's instruments. The price is
reasonable considering the optical quality. I suppose that, if he's
busy, he doesn't run the advertisement.
* SLMR 2.1a * Astronomy is Looking Up!
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Joseph O'Neil
On 18 Jun 98 23:32:04 , Jim.Van...@sjpc.org (Jim Van Nuland)
wrote:
>>There is a 5.7 inch Maksutov-Newtonian, advertised very seldom in Sky
>>and Telescope. I just scanned through a dozen issues without seeing
>>the ad. The company offers it in f/6 and f/4 focal lengths. It
>>seems like a fine optics system; it better be at nearly $2000 for
>>just the optic assembly alone!
>
> You are thinking of Peter Ceravolo's instruments. The price is
>reasonable considering the optical quality. I suppose that, if he's
>busy, he doesn't run the advertisement.
I've looked through several of Peter's Mak-Newts, side by side
with Astro-physics refractors, and the mak-Newts are comparable in
every way to image quaility in the A-P's.
Two sizes, 6 and 8 inch, they sell for I believe $2000 and
$3500 US, tube asembly alone.
The reason they do not advertise much anymore is he has almost
a 3 year backorder on scopes, all just from word of mouth, and the
orders just keep comming in.
joe
Michael J Edelman
As Meade discovered, most telescope buyers shy away from unfamiliar design.
Meade hs to sell large numbers to pay for their tooling and such. A
Schmidt-Newtonian is neither as compact as an SCT nor as cheap as a
Newtonian, and thus was a difficult item to market without a lot of
consumer education.
Meade's success has been built on following paths trod by others. They
followed Celestron's pioneering inexpensive SCTs. When APO refractors
became popular, they made a cheap, good quality "semi-APO". They traded on
the reputation of the Questar to make their ETX.
Their Schmidt-Newtonian was an excellent unit, but they don't know how to
sell unique products.
--
Michael Edelman http://www.mich.com/~mje
Telescope guide: http://www.mich.com/~mje/scope.html
Folding Kayaks: http://www.mich.com/~mje/kayak.html
Airguns: http://www.mich.com/~mje/airguns.html
gser...@vgdirect.ca
For those interested in having a Schmidt-Newtonian, you should
consider using a sub-aperture corrector lens instead of the full
aperture meniscus, as in the S-N. The sub-aperture corrector can do
all the same work (correcting for off-axis aberrations) without the
bother of producing such a large piece of optics, will be relatively
impervious to dewing, weigh far less, and can be added to an existing
Newtonian without significant modifications. Best of all, you can buy
this corrector ready-made. It's called a Paracorr.
Regards,
Gary in Vancouver
(NOTE: Remove "VG" from e-mail address to reply.)
weird_al
In article <358a8f2c...@news.direct.ca>, gser...@VGdirect.ca says...
>For those interested in having a Schmidt-Newtonian, you should
>consider using a sub-aperture corrector lens instead of the full
>aperture meniscus, as in the S-N. The sub-aperture corrector can do
>all the same work (correcting for off-axis aberrations) without the
>bother of producing such a large piece of optics, will be relatively
>impervious to dewing, weigh far less, and can be added to an existing
>Newtonian without significant modifications. Best of all, you can buy
>this corrector ready-made. It's called a Paracorr.
Vixen also used to make (still do?) a corrector for their 8" f/4
Newtonian that was suposed to be pretty good.
weird_al
In article <rjfi1.446$FV.1...@nntpserver.swip.net>, "Jonas says...
>I bought one of the Orion Optics 8"/f4 Schmidt-Newtonians about 1 1/2 year
>ago through an agent here in Scandinavia and is very happy with it. I bought
>the tube assembly only and mounted it on my home made GEM.
>I have started doing some astrophotography with it but have had some
>problems with focusing with the Meade 2" focuser that was mounted on it by
>the agent. (The original focuser is a 1 1/4" and I wanted a larger.) Since I
>mounted another, all-metall, 2" focuser it haven't been weather for
>photographing with the telescope.
I also had to modify the focuser on the Meade 6" f/5. It's a 2"
helical, not so convenient for general observing but fine for
astrophotography. Problem was, Meade made the "drawtube" much too
long. With the camera focused properly the drawtube extended into
the optical path of the mirror. The focuser was none too stable, either.
It had only a single set screw attaching the assembly to the OTA and a
single thumb screw at the eyepiece opening. It was OK under the weight
of a typical eyepiece but not for a camera and off-axis guider. I
fixed all that and it works great now. Leave it to Meade to screw up
the details.
Rene Carlos
gser...@VGdirect.ca wrote:
> For those interested in having a Schmidt-Newtonian, you should
> consider using a sub-aperture corrector lens instead of the full
> aperture meniscus, as in the S-N. The sub-aperture corrector can do
> all the same work (correcting for off-axis aberrations) without the
> bother of producing such a large piece of optics, will be relatively
> impervious to dewing, weigh far less, and can be added to an existing
> Newtonian without significant modifications. Best of all, you can buy
> this corrector ready-made. It's called a Paracorr.
You're absolutely right. One day I plan on making
myself a subcorrector Mak-Newt, maybe 10" f/5.
But for small apertures, the size/cost tradeoff is
small. And it's in these small apertures that a
sealed tube comes in most handy. After the 10",
i'd like to try a rich-field 3" or 4", with a
window figured into a weak Mak corrector, and an
undercorrected primary.
--
Rene Carlos
necr...@merle.acns.nwu.edu Northwestern University
r.v.c...@larc.nasa.gov Langley Research Center
bratislav
Rene Carlos wrote:
>
> gser...@VGdirect.ca wrote:
> > The sub-aperture corrector can do
> > all the same work (correcting for off-axis aberrations) without the
> > bother of producing such a large piece of optics,
>
> myself a subcorrector Mak-Newt, maybe 10" f/5.
>
The subcorector Maksutov is only good on/close to axis. It _can_ be
designed to correct coma as well, but astigmatism and curvature of
the field in particular, are excessive. Visually, OK. Photographically,
forget it.
Bratislav