Opto-mechanical design of optical instruments is a tightly integrated process involving many technical disciplines. It begins when the requirement for a particular hardware item is established by the potential user, such as military, other governmental organizations, or commercial representatives who seek ways to expand sales with a new or improved product. Once approved, funded, and staffed, the design effort proceeds through a logical sequence of major steps and concludes only when the instrument is awarded a pedigree establishing its ability to meet all its technical specifications and capable of being produced, within cost limits, in the required quantity—whether that is as a one off (such as the highly successful Hubble Space Telescope [HST]) or as a large number of a much simpler item (such as a new spotting scope with an integral digital camera for nature study).