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Message: <blockquote data-quote="henry link" data-source="post: 1279362" data-attributes="member: 6806">Thanks for posting the link, Kevin. The new information there for me is the bit about contrast loss at the roof faces that both reflect and transmit in a Schmidt-Pechan. I had always assumed that the TIR occurred at the surface of the glass even when it was coated. Just one more strike against the S-P.Interesting to note how the future brought unforeseen changes in Swarovski designs. A few years after this paper the SL Porro line was discontinued while the older Traditional Porros still hang on today. The internal construction of the SL might have looked like the wave of the future, but the actual binoculars were not so attractive. Focus was at the front of the bridge and was very slow, probably because the large waterproof moving eyepiece tubes needed a high gear ratio to be easily moved. Only the 8x56 had adjustable eyecups. The field was very narrow in the 7x42, 8x56 and 7x50. The coatings had a strong yellow tint. They never went over with birders.The basic optical design of the early SLC models (8x30/7x30) illustrated in the paper is still retained in the current 8x30 which uses a moving objective for focusing, but the later SLCs would use internal focusing lenses. I think in 1991 only the Leica Trinovids used a focusing lens and a little later the Zeiss Night Owls. Phase coating is certainly essential for decent image quality, but I suspect that the quality of the phase coating varies in different binoculars and that in cheap phase-coated binoculars it's not very good. I noticed that the phase coating of an inexpensive roof prism bin I tested recently did not appear to be completely effective. I tested it by sighting my LCD computer screen through the objective end while rotating a polarizing sunglass lens in front of the objective. One half of the illuminated circle got very dark as I rotated the lens which I think indicates incomplete correction. This test can also be done without the LCD screen by using two polarizing lenses, one behind the eyepiece and one in front of the objective. There's an obliging retailer nearby so the next time I visit her store I hope to try this test on a number of binoculars.Henry</blockquote>

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