Re: [ATM] Baffling a Gregorian and corrector plate fabrication.

[Jarvis Krumbein <jkoptic@juno.com>]

Hi Doug,

The Gregorian optical system was once the favored type for terrestrial
telescopes during the 18th century.  The only baffle used was a stop
located at the exit pupil of the eyepiece.  Properly sized and located,
this is very effective.  I don't know where you will find further info on
this though.

Jarvis Krumbein

On Tue, 23 May 2006 15:10:38 -0400 Douglas S Angle
<Douglas.S.Angle@can.dupont.com> writes:
> I'm contemplating building a Gregorian, and I've been looking at 
> different 
> design considerations.  I've browsed through the archives, read 
> Rutten & 
> van Venrooij on the subject.  One thing I can't figure out is how to 
> 
> baffle such that stray light can't get from the entrance aperture to 
> the 
> eyepiece.  There's an article in ATM about a newt-cass-gregorian 
> telescope, but the article doesn't address baffling at all, and the 
> 
> pictures don't look like there's any attempt to baffle.  I did a 
> full size 
> drawing, and I can't see how to catch more than about 1/2 the stray 
> light. 
>  For reference, my design was:
> primary diameter 16"
> primary focal length  64   f/4
> secondary  diameter 4"
> distance of focus behind primary 15"
> 
> I would be interested in hearing from anyone who has built a 
> gregorian, or 
> advice on how to solve the baffling problem. 
> 
> I also considered a shorter focal length primary combined with a 
> corrector 
> plate.  I understand the principle of the Schmidt camera, where the 
> 
> corrector is placed at the center of curvature, and can be made 
> using the 
> vacuum pan method.  If I were to move the corrector plate towards 
> the 
> primary, is it true that the I can't use the vacuum pan method 
> anymore, 
> because the shape is now different?  For that matter, is there any 
> difference between a corrector plate as used in a schmidt camera, vs 
> one 
> used in a compound telescope so that the primary can be left 
> spherical?
> 
> Thanks all.
> -Doug
> 
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