The two reflected images Carl is talking about can interfere, and in a
dark room using a laser source, one can see quite a nice set of 'Newton's
Rings' reflected from a meniscus lens. I wrote up something on this in
the May 1974 AJP.
--
Mike Moloney, Physics & Optical Engineering Department
Rose-Hulman Inst of Tech, 812 877 8302
moloney@rose-hulman.edu http://www.rose-hulman.edu/~moloney