Re: [APML]: SCT CONVERSION

["Mike Wyatt" <mwyatt@mn.uswest.net>]

Hey, if you place a stop of the appropriate size and distance from the
primary it may make a nice lensless schmidt wouldn't it?  Sky and Tel
described on a few years back.  It would cut the aperature by a little bit
but your field would be great I would think starting with an f2 mirror as
the article describes sphere mirrors with f3 being very suitable..
----------
> From: Wil Milan <wmilan@airdigital.com>
> To: astro-photo@nightsky.com
> Subject: Re: [APML]: SCT CONVERSION
> Date: Saturday, January 17, 1998 4:27 PM
> 
> 
> Mike Regish wrote:
> 
> > Don't quote me, because I'm really not sure, but if it's an f10 scope
I'm
> > pretty sure the primary is f5. Somebody told me the secondary is f2
making
> > the end result f10.
> >  Don't know if it's ever been done or if it can be, but I'd be
interested
> > since I now have a 12.5" f6.3 Newtonian with essentially the same focal
> > length as my 8" f10 SCT.
> 
> It's the other way around. The primary is an f/2 or so, the secondary
> multiplies that by 5x or so to get f/10.
> 
> However, just having an f/2 spherical primary and an aspheric corrector
is not
> enough to make a Schmidt camera because the corrector is ground for an
f/10
> SCT, not an f/2 Schmidt camera. Also, the tube is wrong; on an f/10 SCT
the
> corrector is located inside the focus of the primary, whereas on a
Schmidt
> camera the corrector is at 2x the focal length of the primary. That's why
a
> Schmidt camera is so much longer than a typical SCT.
> 
> Still, it would be interesting to investigate what it would take to turn
an
> f/10 SCT into a Schmidt camera. You'd need a longer tube and the
corrector
> would be wrong, so it would be either over- or under-corrected for
spherical
> aberration, but I wonder what the images would look like. And if all it
would
> take is a different corrector maybe someone could be talked into making
them.
> Or perhaps a small corrector lens could be place just ahead of the film;
I
> believe that's what the new Celestron CCD scope does at its f/1.95 focus.
> 
> One other factor: the primary on an f/2 Schmidt camera should be about
1/3
> larger than the corrector aperture in order to capture the divergent
light
> cone from the corrector. Thus an 8" SCT could be used to make a 6"
Schmidt
> camera, and a 10" SCT could make a 7.5" Schmidt camera.
> 
> 
> Wil Milan
> --
> "When I consider your heavens, the work of your fingers, the moon and the
> stars which You have set in place, what is Man that you are
> mindful of him, or the son of Man that you care for him?"  -- Psalm 8
> 
>