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Re: [ATM] 16" RCC primary



--- Attila Schné <yolo@chello.hu> wrote:


>           The Ross-null, I tried it before to make
> parabs but I founded
>           messy,maybe because I didn't know the
> exact dadas of my
>           Ross-null lens. 

Well,assuming the secondary will be of pyrex,you will
exactly know the RC of the convex side from the
concave tool.Getting the index of pyrex for any
wavelenght is easy off the web.Pyrex does work as a
material for this test.You do have the slight extra
work of getting a good spherical shape on the convex
side but given the multiple benefits of the Ross it's
worth the trouble.

I've done a 18" f/2.8 primary and the secondary for
this cass scope using the Ross and will never go back
to the uncertainty of masks and the Foucault test.

Ric
Toronto

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