From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


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
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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