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an optical system for projecting onto a screen images of opaque objects, such as hardware, technical drawings, illustrations, and photographs.
The basic optical diagram of an episcope is shown in Figure 2 in PROJECTOR. In an episcope, the object whose image is being projected reflects diffusely the light rays striking it; thus, only a small amount of the reflected light enters the projection lens. The brightness of the image is enhanced by using one or more powerful light sources as well as high-transmission projection lenses with relative apertures of up to 1:1.5–1:2. Since the focal lengths of episcope lenses are usually shorter than those of diascope lenses, the magnification produced by an episcope is lower. A mirror located above or behind the projection lens of an episcope inverts the image so that it is right side up when it appears on the screen (see: Figure 1). A special cooling system is required in an episcope because of the intense heat that is generated.
An episcope may be a component of the optical system of the alterable projectors known as epidiascopes, which can project images of both opaque and transparent objects onto a screen.