文档介绍：Chapter
15
Optics in Practice
This chapter will briefly survey the factors involved in reducing an
optical system to practice. A short description of the optical manufac-
turing process will be followed by a discussion of the specification and
tolerancing of optics for the shop. The mounting of optical elements
will be considered next, and the chapter will be concluded with a sec-
tion on optical laboratory measurement techniques.
Optical Manufacture
Materials. The starting point for quantity production of optics is most
frequently a rough molded glass blank or pressing. This is made by
heating a weighed chunk of glass to a plastic state and pressing it to
the desired shape in a metal mold. The blank is made larger than the
finished element to allow for the material which will be removed in
processing; the amount removed must (at a minimum) be sufficient to
clean up the outer layers of the blank which are of low quality and may
contain flaws or the powdery fireclay used in molding. Typically a lens
blank will be about 3-mm thicker than the finished lens and 2-mm
larger in diameter. A prism blank will be large enough to allow
removal of about 2 mm on each surface. These allowances vary with
the size of the piece and are less for a clean blank. When the blank is
of an expensive material, such as silicon or one of the more exotic
glasses, the blanking allowances are held to the absolute minimum to
conserve material.
Although most blanks are single, a cluster form is frequently eco-
nomical for small elements. A cluster may consist of five or ten blanks
connected by a thin web which is ground off to free the individual
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550 Chapter Fifteen
blanks. If molded blanks are unobtainable, either because of the small
quantity involved or the type of material, a rough blank may be pre-
pared by chipping or sawing a suitable shape from stock material.
Rough blanks can be checked fairly satisfactorily for the presence of
strain (which