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

Making a parabola may be easier and cheaper, and the
corrector should be small, like those the Big-Name
telescopes use to 'flatten' their fields.  At f/22 or
whatever f/Snail the Greg is going to be, however, I
don't see the point in flattening a field that's only
half to three quarters of a full moon across.  That's
a flat-enough field for all but the shortest focal
length EP's.

Why put a corrector in front of a Greg, anyway?

Kevin of Eastern Iowa
Seeker of the Darkness

--- John Sherman <atm@johnspics.com> wrote:

> 
> Hi Doug,
> 
> >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. 
> 
> Here's a way that should work:
> http://www.johnspics.com/hi/Greg.gif (5kb). This is
> from an old issue of SciAm. Note that having the
> secondary at the focal point of the primary makes
> for a small secondary. However, every speck of dust
> will be in sharp focus, so it's best to move the
> secondary away from that position. Interesting how
> the secondary obstructs both the primary and the
> tertiary..
> 
> I've heard that making a parabola is easier and
> cheaper than making and collimating a corrector and
> a sphere, but I wouldn't know.
> 
> Good luck,
> 
> John
> 
> 
> 
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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