Re: ATM Dummy refractor question...

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

Jerry gives the most common version of a lens setup.  For a Franhoufer, the
first glass is the crown which will be two convex curves.  One of those
curves is about 1.5-2.0 or so times the ROC of the other and that will be
the second surface.  The Flint will be a concave and something else for a
curve.  If the Flint is more ov a mensiscus lens then it may be a Stienhiel
lens setup and that means that the flint is frist and the crown is second
but those tend to be somewhat rare by comparison.  Typically the 4th surface
is nearly flat with a Fraunhoufer lens.
Then there is a more primitive design where the two surfaces on the crown
are equal in ROC and then it doesn't matter which one is the first surface.
A quick look with a spherometer or some cardboard templates cut to the
approximate ROC will probably show which way things go.  Like Jerry says,
the marks are probably intended to make an X when they are put together and
the ROC of the two curves should be about equal (within about 5%) and of
opposite sign and the glass shouldn't touch in the middle or things are
wrong somewhere.
Bob May
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bobmay@nethere.com
NEW! http://bobmay.astronomy.net