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

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

Bob May wrote:
> What are we discussing here?  I thought that we were discussing the
> differences between making a Gregorian secondary compared to a Cass
> secondary for the same primary!
> Bob May
> http://nav.to/bobmay
> bobmay@nethere.com
> NEW! http://bobmay.astronomy.net

Not quite.  The discussion started comparing the Gregorian and
Cassegrain scopes with equal characteristics.  The original
designs I presented had the same instrument length, back focus,
aperture and focal length.  The primaries were quite different.

When I looked at those designs, however, the secondary size was
larger than some would prefer, so I came up with designs that
were based upon the secondary size, back focal length, aperture
and focal length.  I didn't publish the Gregorian, as the
secondary was something like f/1.7, I think.

But that still came down to the problem of how to test the
Cassegrain secondary.  I've seen methods that use a larger
spherical mirror and methods that attempt to use transmission
through the secondary.  This seemed to be an alternative, so
I was asking about its utility.


-- 

Rick S.

http://users.rcn.com/rflrs

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