Re: [ATM] schmidt Correctors

["Bob May" <rmay@nethere.com>]

Steve, I did a corrector for a 6" F1.95 primary and had to do
both sides with half each..  I was pulling 12" of vacuum or so
*been a while) and had troubles with cracking corrector plates.
The glass was really getting bent with that much vacuum tho.
Consider grinding with just the 5 micron grit and see if the ring
quickly disappears into a fully ground surface.  At that point,
start polishing.
It is generally better to polish out both sides with the curve as
this means that you don't need to have as much vacuum in the pan
to do the proper curve on the glass.
When you're done, you'll wonder if you did anything so just put
it in front of a spherical mirror and see the surface profile
change.  Don't bother measuring it as it isn't the right way to
measure the curve for correctness, you have to do an
autocollimation test with a large flat and the tester at the
focal plane to check it out for being correct.
When you get it done, you will bne proud of what you managed to
get into that little piece of glas!!!
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Steve Renden <stevey0303@yahoo.com>
To: <atm@atmlist.net>
Sent: Tuesday, March 11, 2008 5:33 AM
Subject: [ATM] schmidt Correctors


> Hello,
>
> I am a bit new to the list, and wish to say hello.
>
> I have a question on schmidt correctors. I have spent about
three days on the internet looking for everything i can about
them, and have found a lot of useful information. such as the
excel spreadsheet by Dave Rowe.
>
> There are a few questions I have now for anyone that has done a
corrector.
>
> 1. did you use the spread sheet?
>     * if so, how do i calculate using my sphearometer what the
initial dip is? because it really doesnt change based on if i use
the corrector for one side or two sides.
>      * when i initially pull vacuum, what should be the
measurment on the sphearometer, before I start to polish, and
after polishing? where should i stop grinding?
>  2. Is there a benefit using two sides correction verse one? or
is it simply easier than making one side an optical flat.
> 3. if i do both sides how do i know when to stop polishing?
> 4. what type of stroke is it to grind and polish the corrector
plate?
>
> I have been looking for quite some time and these are the
questions i can not answer, and suggestions would be very greatly
welcome.
>
> Thanks!
> Steve
>
>
>
>
>
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