TABLE OF CONTENTS This chapter will briefly survey the factors involved in reducing an optical system to practice. A short description of the optical manufacturing 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 section on optical laboratory measurement techniques.
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...
