Re: [ATM] convex secondary

["Jonathan Lavoie" <atm@lavoielactee.net>]

----- Original Message ----- 
From: "Jonathan Lavoie" <atm@lavoielactee.net>
To: <atm@atmlist.net>
Sent: Tuesday, March 01, 2005 9:11 AM
Subject: Re: [ATM] convex secondary


> Thanks to Jim and Richard, I decided to refigure the 16 inch and go for 
> the Ritchey-Chrétien design. Since I have to repolish the big mirror, I 
> will be able to use it as a Hindle sphere for testing the secondary. I 
> know it will not illuminate the edge of the secondary but I have no 
> problem to shorten its RoC a bit to make the Hindle test then grind back 
> to the good RoC.
>

Bad news about my idea of shortening the 16" RoC to use it in a Hindle test 
then grind it back to it's good focal length: I forgot that it's current RoC 
is twice the F length so if I want to use it as a Hindle there is a lot of 
glass that will be removed. So this idea becomes impraticable.

I heard of another test for convex but can't remember where. The idea was to 
test from the back through a liquid of similar refraction index that is in 
contact with the back surface, and just do standard foucault measurement. 
Anyone heard of it?

Jonathan 

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