Optical projection systems

(optics) An optical system which forms a real image of a suitably illuminated object so that it can be viewed, photographed, or otherwise observed. Also known as optical projector; projector.

Optical projection is the process whereby a real image of a suitably illuminated object is formed by an optical system in such a manner that it can be viewed, photographed, or otherwise observed, Essential equipment in an optical projection system consists of a light source, a condenser, an object holder, a projection lens, and (usually) a screen on which the image is formed (Fig. 1). For some important applications of optical projection .See also Cinematography.

A simple optical projection system.

The luminance of the image in the direction of observation will depend upon (1) the average luminance of the image of the light source as seen through the projection lens from the image point under consideration, (2) the solid angle subtended by the exit pupil of the projection lens at this image point, and (3) the reflective or transmissive characteristics of the screen. Usually it is desirable to have this luminance as high as possible. Therefore, with a given screen, tens, and projection distance, the best arrangement is to have the light source imaged in the projection lens, with its image filling the exit pupil as completely and as uniformly as possible.

The object is placed between the condenser and the projection lens. If transparent, it can be inserted directly in the light beam; however, it should be positioned, and the optical system should be so designed that it does not vignette (cut off) any of the image of the light source in the projection lens. If the object is opaque, an arrangement known as an epidiascope (Fig. 2) is used.

An epidiascope, or system for projecting an image of an opaque object.