Re: Schmidt Corrector Plates
PFAFF2@delphi.com
Sun, 09 Jul 1995 23:48:10 -0400 (EDT)
>
> Anyway, the vacuum method is only effective for moderate f/ratios - the
> shape will be only an approximation of a complex curve. Also, it is
> useless if your blank is thick (like my Wright - almost 1/2" for a
> 6"). Another thing is that it won't be good for high quality work
> (say, visual scope) because you will grind/polish in all the errors of
> a vacuum pan (something finished on a lathe hardly qualifies as an
> optical surface !).
>
> Bratislav
>
>
I am not qualified to debate the math of corrector plates but the
vacuum method is the method that Bernard Schmidt used.
As for making the vacuum pan it can be made on the lathe to .001".
The pan seal rim can be laped grinding against a piece of plate glass
to less then .0001". If the pan is thick and kept at a near constant
temperature like in the house it should keep its shape. After the plate is
half corrected on one side you turn the plate over and remount it 90 deg.
with respect to first side to cancel any residual astigmatism.
The vacuum method does lend itself to zone free plates. They could be
over or undercorrected in which case the correction can added to the primary.
I am sure the process is not perfect but it does work. Meade uses this process
for there corrector. Yeah they have problems but it is more then correctors.
Why a 1/2" thick plate for a 6" scope? I used a 1/2" plate for a 16" plate.
Nothing like a little telescope talk to keep the blood flowing. :-)
Bob Pfaff