Re: ATM Lensless Schmidt Camera/telescope

[Anthony Stillman <atmer@flash.net>]

>The idea of the long tube, and the
>ring light-blocker is to fix the problems of a spherical mirror (coma,
>antigsman or something like that).
>
>Well, anyone built a telescope/camera like this? any ideas?


Asaf,

Many many years ago I built a lensless Schmidt camrea using a curved film
holder at the prime focus.  It worked well, providing wide fields.  I moved
on though, as I was diasapointed with the short focal length (small image
size) and image fogging.  In retrospect I probably should have played with
it more.  Alas I was an impatient teenager in a hurry to get on with it.
What ever "it" was, I still don't know.

Regarding the design, as there is only a spherical surface in the system,
there is no coma.  As the aperature is at the radius of curvature of the
system, all rays are on axis, hence there is no stig.  This leaves
spherical abberation and field curvature.  The later is delt with by using
a curved film holder and the former can be ignored for photography so long
as the Airy disk is small enough (0.025mm)

As for an f/3 mirror.  Salid bowls, fish bowls, f/ash trays or what ever
they are called are quite easy to make, except for hogging, as it is
amazingly hard to figure anything but a very good sphere.

Anthony