RE: [APML] Sort of OT: New Meade Ritchey-Chretien

[Radu Corlan <rcorlan@pcnet.ro>]

On Tue, 4 Jan 2005, Lane, Jason R wrote:

> Hi Chuck,
> 
> I wasn't sure about the OT and figured I was better off safe than sorry :)
> 
> I hope they can produce them in quantity and quality, too.  Most will
> agree that Meade does do a good job on their optics.  An RC design at
> that price is really really cool..although it still costs more than my
> car :(
> 
> The optician and I here at work have been talking about it...he thinks
> the corrector doesn't do much more than replace the spiders and protect
> for dust, and that you can't do much for astigmatism out there but I'm
> not so sure.  I think maybe you can play some tricks with the extra
> variables.  I'm not sure if you have to reduce astigmatism all that much
> for astrophotography anyways, since if that's all you got then you'll
> still get nice round star images (just a little bigger...but would it be
> noticeable with film grain and atmospherics anyways?).  I might play
> with a basic RC design I have in Zemax to see what adding a corrector
> does.  So maybe this is a Schmidt-Ritchey-Chretien? :)  In either case,
> it will definitely give better views and photos than the SCT's (just
> don't tell that to my LX90).

My bet is that the primary mirror is spherical, secondary is hyperboloidal 
(like is should be on a R-C). So basically, you have an aplanatic SCT 
(which is a good thing). They may get lower astigmatism due to the fact 
that the entry pupil is at the corrector.

> 
> I would be surprised if those spot diagrams were not along a curved
> focal plane (to eliminate the effects of field curvature when comparing
> diagrams)...you would have to get a field flattener like you do for
> SCT's (this would make sense because f/8 is still kind of slow for
> astrophotography).  You should be able to get really nice star images
> all across your frame.  The "typical Cassegrain" diagram looks a lot
> like one for a Dall-Kirkham.

Field curvature is a first order effect in a cassergrainian (which means 
that for a given secondary magnification, it will only loosely depend on 
the configuration (SCT, classical cassergrain, RC etc). If the tube is the 
same relative length as a SCT (which would imply f/2 primary and 4x 
secondary magnification), it will have a little less curvature than a SCT, 
but not a lot less). Besides, if it were a flat-field design, Meade's 
marketing machine would let us know ;-).

Nevertheless, the same affects a regular R-C, and this looks like a fine 
telescope. Adding a field flattner is not that big of a deal.

Radu

> 
> What interests me as well is what sounds like the improvements in the
> mounts and mechanical design.  Especially in the worm blocks (which
> gives me a headache on my LX90) and the fixed primary and the much
> improved focusing method.  IMO those have been Meade's weak points
> (although their worm block design is really good, it's still a lot of
> trouble).  I don't know about the tripod, tho.  No cross-supports or
> whatever you call them.
> 
> Steve:  I just saw your post pop up while I was typing this.  RC's
> inherently have rather large field curvature.  Astigmatism is also a
> problem, but you don't have to be concerned with it as much because they
> also don't have any coma so you get nice round star images.  The stars
> will be bigger at the edges than center due to astigmatism (but are they
> big enough to be a problem on film?).
> 
> -Jason
> 
> 
> 
> -----Original Message-----
> From: astro-photo-bounces@seds.org
> [mailto:astro-photo-bounces@seds.org]On Behalf Of Chuck Vaughn
> Sent: Tuesday, January 04, 2005 8:27 AM
> To: Discussion of Film Astrophotography
> Subject: Re: [APML] Sort of OT: New Meade Ritchey-Chretien
> 
> 
> Jason,
> 
> Not OT in the least! Astrophotographers need telescopes. :-) I hope 
> they can produce them in enough quantity to meet the demand and 
> maintain quality. Nothing like some competition in the market to rein 
> in prices!
> 
> The astigmatism corrector is a good idea. The only thing I don't see is 
> a field flattener.
> 
> Happy New Year,
> 
> Chuck
> 
> -------------
> 
> > Hi folks,
> >  
> > http://www.meade.com/rcx400
> >  
> > Don't know if anybody's seen this yet or cares, but I thought it 
> > looked pretty interesting...especially since it's an affordable RC 
> > design.  Thought I'd share since it was apparently designed for the 
> > astrophotographer.
> >  
> > Cheers,
> > Jason
> 
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-- 

-------------
Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan@pcnet.ro  str. Argentina nr. 28, Romania

   You can still escape the "Gates" of Hell!   
                 Use Linux!                       


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