Re: Re:ATM An Old TMs Simple Query

["Dwight K. Elvey" <dwightk.elvey@amd.com>]

>From: "Richard Schwartz" <richas@earthlink.net>
>
>OK, I have a few schmidt questions...
>
>If I have a schmidt, I will end up with a lot of little round pieces of
>film.  What is a good way to cut the film to the requires shape and size?

Hi Richard
 To trim, you might look at large Greenly chassis hole punches.
These are intend for metal but if they are sharp ( new ) they should
work like shears. The only problem is that they are originally
designed to have a bolt through the middle that both aligns
and it used to pull them through the chassis. To do what you
want, it would be a good idea to fix them to two plates on a slide
so that they stay aligned.

>What is a good way to identify the films, index them, and store them?

 Envelopes.
 
  What
>is a good way to take measurements off of them?  What is a good way to warp
>the film to match the curved focal plane? 

 A dished surface with a layer of fine filter paper. Then use a
vacuum to pull it down.

  If a field flattener lens is
>used, what is a good way to remove distortion from the image, and to correct
>measurements on the distorted image (assuming the exact center of the image
>is not located).

 I'm not sure there is a way, inless you also projected a grid into
your telescope with a small lens that you knew had no distortion,
when used to project at infinity. This could be done with a LED,
grid mask and a lens. The grids image on the film could be used
as a reference. Controlling the brightness of the grid, you should
be able to keep it from washing out the stars.

>
>I think the science value is greatly enhanced when the images can be located
>in time and space, and stored in a non-destructive way.   There is more to
>working with schmidts than just building the optics.
>
>What I really would like is (1) some kind of field flattener lens, and (2)
>something like a Hasselblad camera back that automatically records date,
>time, and approximate RA and Dec.

 Just add that to the grid! The same lens that you used to project
the grid can be used with a digital readout.
Dwight

>
>. . . Richard
>
>
>----- Original Message -----
>From: "Jerry Hudson" <hudsonjk@pacbell.net>
>To: <atm@shore.net>
>Sent: Wednesday, January 22, 2003 11:16 AM
>Subject: Re:ATM An Old TMs Simple Query
>
>
>>
>> To ol' Coyote -
>>
>> Your formula,
>> >  a*rho^2+b*rho^+b*rho^4...
>> giving the shape of the Schmidt plate, is
>> exactly opposite in sign to the wavefront
>> aberration describing an uncorrected spherical
>> mirror.  The glass introduces just enough extra
>> path length where it is thicker to compensate.
>>
>> A straightforward way to see how this all works
>> out, if you have the patience and either a
>> good calculator or BASIC, is to start
>> at the desired focal point of the sphere and
>> trace a ray, bouncing it off the sphere, and
>> taking it out to where it intersects a plane
>> positioned where you want the plate to go.
>> Figure out the path distance along that ray,
>> and subtract off the path distance for the
>> central ray.  THat's your "wavefront aberration."
>> If you plot this against radial distance of
>> the ray from the axis, you will get a 4th order
>> looking curve.
>>
>> Note that adding the rho^2 term simply re-focuses
>> the wavefront - you have this degree of freedom
>> to try to make the overall power of the plate
>> to be zero (avoiding all but a trace of color).
>>
>> I hope this helps.
>>
>> BTW, I'd enjoy a direct off-list exchange with
>> you about Schmidts - an interest of mine.  I've
>> only made one: a Wright-type Newtonian.  And, yes,
>> Edgar Everhart's articles were a great help to me!
>> He was a smart guy and a great glass-pusher!
>>
>> - Jerry Hudson
>>
>>
>>
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