Motion-Picture Projector Objective

an optical system for the projection onto a screen of an enlarged image from a frame of motion-picture film. A main characteristic of the quality of such an objective is the resolution, which is evaluated by the number of separate lines per millimeter that are visually distinguishable in the image of a test pattern. An objective’s resolution may be up to 100 lines per mm in the center and 50–60 lines per mm at the edge of a frame, with a light transmission coefficient of 0.8–0.85, depending on its design. Such objectives provide a uniformity of screen illumination of 0.6–0.7.

Among the main technical characteristics of motion-picture projector objectives are the focal length f’, the aperture ratio 1:n, and the angles of vision 2w; the first two characteristics are engraved on the smooth rim of the objective, together with its name and serial number.

A distinction is made among objectives for showing conventional films (four-lens and six-lens anastigmats with f’ = 50–180 mm, an aperture ratio of 1:2 to 1:2.5, and 2w = 30°-8°), wide-screen films (six-lens anastigmats with f’ = 80–140 mm, and an aperture ratio of 1:2; as well as anamorphic attachments), wide-gauge films (six-lens anastigmats and complex optical systems consisting of an objective and a spherical attachment with f’ = 70–120, an aperture ratio of 1:2, and 2w= 42°-25°), 16-mm films (four-lens and six-lens anastigmats with f’ = 35–50 mm and an aperture ratio of 1:1.2 and with f’ = 65 mm, and an aperture ratio of 1:1.4 and 2w = 20°-11°), and amateur 8-mm films (three-lens aplanats with f’ = 18 mm, an aperture ratio of 1:1.4, and 2w = 19°); there are also objectives whose f’ is variable between 15 and 25 mm, with an aperture ratio of 1:1.4.