Re: [ATM] refiguring a 20 inch Pyrex f/2 cassegrain

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Thomas Janstrom wrote:

>Hi Guy,
>
>If optimised for IR work the wavelength of light used to do the figuring
>could have been in the far red (say 700ish plus nm), and so although it
>might have been 1/20 wave at that WL if you now test at say 550nm it
>won't be any where near that good, in fact (although I haven't done the
>maths on this yet) it might even be less than 1/4 wave, which is why it
>appears not to have been figured very well.
>  
>
nah... (1/20)/(550/700) = 1/15.7

>Cheers, Thomas
>  
>
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