OPN July 1998
Cover Story
Extrapolating HST Lessons to NGST

Richard G. Lyon, J.M. Hollis, John E. Dorband, and Timothy P. Murphy
TO CORRECT FOR PROBLEMS WITH THE ORIGINAL HST OPTICAL SYSTEM, NASA SCIENTISTS USED PHASE RETRIEVAL TECHNIQUES. HOW THAT WAS DONE AND HOW RESULTS FROM THIS RESEARCH LED TO NASA'S DECISION TO USE IT WITH NGST ARE DISCUSSED. more>>
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Reciprocity in Classical Linear Optics
Masud Mansuripur
A recent informal survey of some
optical science colleagues and
students revealed that the notion of reciprocity in optics is not widely appreciated. One colleague even justified the prevailing ignorance by drawing a parallel between reciprocity in optics and the correspondence principle in quantum mechanics: "Both are true statements, which have little, if any, practical value in their respective domains." This column
is an attempt at explaining the
concept of reciprocity, clarifying
some associated misconceptions, and pointing out its practical applications. more>>
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SGML
Bob Jopson
Thus warned, we embark on a
short article in a Society journal
about Standard Generalized Markup
Language (SGML). Although you
may have never heard of it, SGML is an integral part of your professional life. It's used to print and archive OSA's and other AIP journals; many government and academic organizations use it to disseminate and archive documents. One SGML application,
hypertext markup language (HTML), underlies most of the Web pages you view. more>>
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Wide Angle Shift Lens for 35-mm Format
J. Brian Caldwell
If a tall building is photographed
by pointing a camera upward, the
vertical lines of the building converge. Large format photographers have long known that it is possible to avoid this problem by shifting the lens vertically upward while keeping the image plane parallel to the building. To do this, the lens must have an image circle that is larger in diameter than the diagonal of the film format. While this is the norm for large format photography, in the realm of the 35-mm system a special lens called a shift lens is required. In addition to having a larger than normal image circle, shift lenses have a special mechanical structure that enables the shifting motion. This mechanical structure requires that the back focal distance be even greater than that normally required for 35-mm SLR lenses. Needless to say, the combination of a larger than normal image circle and back focal distance places great demands on the optical design, and, as a result, shift lenses tend to be a little slower and a lot more expensive than non-shift lenses with the same focal length. more>>