Re: ATM startest 20 inch

["Jan van Gastel" <jhm.vangastel@wanadoo.nl>]

Temperature doesn't have that much effect on my 12 incher. Is the difference
between Pyrex and Zerodur (the 12") that big?

Jan
http://www.geocities.com/janvangastel/
----- Original Message -----
From: "Mel Bartels" <mbartels@efn.org>
Cc: "ATM" <atm@shore.net>
Sent: Friday, April 13, 2001 8:05 PM
Subject: Re: ATM startest 20 inch


>
> >>>
> I did a little more startesting on polaris with 540x after
> two hours of cooling with two fans. I am not an experienced startester
> and
> find it very difficult to interpret. The most obvious think I saw was
> undercorrection. I don't know how much. The other thing I saw (maybe has
> to
> do with the undercorrection): nice visible rings inside focus and rings
> almost unvisible outside focus. Even when turned far outfocus, much
> farther
> then 10-12 waves, the rings were almost unvisible and there where
> clearly
> visible spikes of light acros the diffraction pattern. Is it possible
> for
> someone to shine some light on this?
> <<<
>
> Sounds like the mirror needs to match ambient air temperature better.
>
> I like to leave them out all night and test about 4am
>
> Mel Bartels
>
>