ABSTRACT
A slide projector or home movie projector has an optical arrangement as illustrated in Fig. 17.1, and uses a special lamp as shown in Fig. 17.2, with a tungsten filament coiled over the area of a small square. Behind the tungsten filament, outside the lamp, but sometimes inside it, a small metallic spherical mirror is placed. The purpose of this mirror is to reflect back the light to the lamp, forming an image of the filament on the same plane. Ideally, the mirror should be aligned so that the image of the filament coil falls in the filament spaces, not over them. Unfortunately, this mirror is easily misaligned, making it completely useless.
