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Old November 21st 03, 03:45 PM
Tony Flanders
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Default Is 1/4 wave good enough for a rich field?

donutbandit wrote in message ...

I ran into a great deal on a 6" f/4 parabolic mirror. All the stats on it
look good, except that it is a 1/4 wave mirror.

I was raised believing that no less than 1/8 wave will suffice, but how
about a low power rich field scope? The magnification would never be
greater than 40.


I'm sure that you would never know the difference between 1/4 wave and
1/8 wave at 40X. But this suggests that the mirror wasn't fabricated
very carefully, and there are other defects besides wavefront error
that *would* be noticeable at 40X, particularly turned edge and a
rough surface. Both of those would show up as loss in contrast.

Besides, why restrict yourself to 40X, when a decent mirror could
easily get to 200X? Even if you only used it 5% of the time, it
would be an awfully nice ability to have.

- Tony Flanders