Re: [ATM] convex secondary

[Jonathan Lavoie <atm@lavoielactee.net>]

Hi all,

I found a really complete wepbage describing many possible tests for convex
surfaces.
http://www.users.bigpond.com/PJIFL/page13.html

The one that retained my attention is the image just below these words:

"a concave reflecting surface a short distance behind the Cassegrainian
secondary under test"

But for this test we must use optical glass for the 4" secondary. How
expensive is this kind of blank?

Up to now in my quest for a good convex testing method here is what I have:

1-Interference testing: Seem really accurate and easy to interpret but added
difficulty in figuring the hyperbola because in addition of getting the good
K value, the RoC ALSO needs to match perfectly (if I understant correctly)

2-Use a sligthly deformed hindle sphere to null the convex at the good K
value (Still don't know how to compute the K deformation of the Hindle
mirror)

3-Double Pass Refraction Test by Autocollimation referred to in the above
url. (Don't know the cost of 4" optical blank)

Jonathan

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