Re: [APML] Ash Lurie Schmidt alternative

[Robert Reeves <reeves10@swbell.net>]

> > I have had a Celestron Schmidt for over 20 years and I have never had a
> >  problem with vignetting.  The manual that came with it says it
> theoretically
> >  vignets 15%, but I have never seen it.
>
> A ray trace shows 15% vignetting 0.5" off-axis with an 8" primary and 33%
> vignetting at an off-axis distance of 1" (for a 50 mm film holder).  I've
> found with TechPan that 25% vigetting is quite noticeable and hard to
remove,
> but with color film it's not much of a problem.  So I guess it depends on
the
> size of the film and the type of film.
>
> Dave Rowe

All I have ever used is a 35 mm film holder so it would keep vignetting to
the minimum figure.  Kent is the only person I know using the 10 degree film
holder with a Celestron type Schmidt.  I imagine he has a bit more
vignetting than I do, but then he has better darkroom skills by an order of
magnitude than I do, so getting rid of vignetting may not be too much
trouble for him.  I have a bunch of his Tech Pan Schmidt prints that I used
in my book Wide-Field Astrophotography and I can't see any vignetting.
Whatever he does to get rid of vignetting with the Vehrengerg film holder...
it works!

Robert Reeves                      reeves10@swbell.net
520 Rittiman Rd.                   www.robertreeves.com
San Antonio, Texas 78209    210-828-9036
USA                                     29.484  98.440  200 meters


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