Motion picture projection; an elementary text-book (1921)

Record Details:

Title:
Motion picture projection; an elementary text-book
Date:
1921
Publisher:
New York, Theatre Supply Co.
Volume:
Motion picture projection; an elementary text-book
Leaf #:
000133
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Date Added:
July 19, 2022
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132 MOTION PICTURE PROJECTION same amount of light spread over a larger surface will be weaker. For comparison we give the following examples: Size of Picture Surface Area Magnification 9x12 108 sq. ft. 158.88 diameters 12x16 192 sq. ft. 211.84 diameters 15x20 300 sq. ft. 264.80 diameters The Projection Lens This we have already mentioned as being the ratio between the diameter and focal length and this determines the amount of light transmitted by lenses of all kinds. Obviously there must be a physical limitation to this and in practical optics this is 1 — 2, so the diameter cannot be more than half the focal length. Even to attain this result is an achievement, it involves making lenses with strong curves, each made separately with the utmost care and great precision in mounting and the adjustment of the components of the complete lens in relation to each other. This means the distance from the optical center of the lens to the point where it defines a sharp image when focused for infinity and this measurement can be made accurately only by optical means. Commercially we grade the focal lengths in quarter inches in engraving the cells but we mark the exact focal length in hundredths of an inch on the wrapper and use this measurement in filling orders. To cite an instance a 16 ft. picture at 99 ft. requires a lens of 5.60 focus. A lens of exactly 5^2 inch (5.50) focus would make the picture oversize and 534 focus would be too long. To meet this con