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Minimisation Of Errors In Optical And Mechanical Systems

There are some kinds of optical and mechanical system for which particular emphasis is placed on obtaining the best possible geometrical accuracy. In the design of accurate mechanical devices the engineer usually has to choose between two different approaches - should he proceed according to so-called 'kinematic principles', or should he rely instead on 'averaging by over-constraint'? The same kind of choice can arise in the design of many types of optical system, and the virtues of the averaging approach are sometimes over-looked. Illustrations of this dual choice are taken partly from early work on the photographic manufacture of gratings and partly from current work on the optical micrometer.