Re: [ATM] Large Schmidt Camera?

[Joe <nss@mwt.net>]

As  something to play with could do a lensless schmidt,,

Joe

Dominic-Luc Webb wrote:

>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
>
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