[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] Large Schmidt Camera?
On Sun, 23 Apr 2006, Michael Peck wrote:
> At 14:51 4/22/06, David Sleeter wrote:
> >Hi Folks:
> >
> >I have a 16-1/2" dia. F-2.5 spherical Cassegrain-style (hole in the middle)
> >mirror, and I'm wondering if there are any off-the-shelf combinations of
> >field flattener and CCD camera with which it could easily be used as a
> >Schmidt camera?
>
> Is no one else going to make the obvious reply? To make a Schmidt
> camera you need a Schmidt corrector plate. That's going to be the
> hard piece to acquire or make. A field flattener by itself isn't
> going to help with the 25 waves or so of spherical aberration your
> spherical mirror has.
>
> Mike Peck
You are of course right Mike. I worry that even the "lensless"
Schmidt config may not work, unless maybe the aperture is
stopped way down (which I sometimes do on smaller spherical
mirrors)?
Getting to basics, could the poster confirm that he actually does
have an actual "spherical" mirror and not some other (parabola,
hyperbola, etc). It makes all the difference in the World here,
and we recognize that Cassegrains have different configs. Also,
please confirm that the mirror (and not the optical system) is F/2.5.
>From there, I would likely go with the corrector plate. For the
image surface, I use the glass tool used to grind out a mirror
with the appropriate corresponding diameter and curve, and then
film. This can be made very quickly with items you already
possess for making mirrors. I made my first one in a couple of
hours by testing the concave surface with water sprayed on its
surface and looking where the light from a lamp came to focus.
I just assumed the tool had an equivalent convex curve. I recall
that on mine the curvature across a 35 mm stretch diverged from
flat by less than the thickness of film, which made me question
how important the flattener was. This of course depends on your
system.
Dominic-Luc Webb
_______________________________________________
ATM mailing list http://www.atmlist.net/