Re: ATM Mak... Schmidt Correctors

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

The calculations for the corrector are relatively tolerant of an error of
the RI of the glass so anything in the area of 1.517 will do just fine.
Much more important is knowing the thickness of that glass and that it
doesn't have any wedge in it.
Window glass of any kind also has a problem in that the glass is not
necessarily homogoneous and thus will often have changes in refractive index
in waves through the glass.  If you are doing a single sided corrector, you
can usually work that error out on the flat side by inspecting and changing
the shape of that flat surface.  This is why most end up going and getting
some BK-7  (BSC-2) or other optical glass just to insure that the piece of
glass is a good glass inside.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net