Re: [ATM] Cassegrain vs. Gregorian (secondary testing)

["Bob May" <bobmay@nethere.com>]

The comment was made that the cass secondary with a e of -4+ would be easier
to build than a gregorian of -.5 would be and in this, I beg to differ.
The methods that I know of for testing a cass secondary are the Hindle test
(large perforated sphere needed), through the back (need to grind and polish
the back to a near ROC of the front surface to minimize the errors from
refraction or run a raytrace to see what happens to the light as it goes
through the back surface and glass) or using a match plate (making a concave
surface to match the curve of the secondary).
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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