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116 RICHARDSON'S BLUEBOOK OF PROJECTION
straight arc, reflector type, high intensity or high intensity reflector arc. (b) Exact width of the picture at the center of its vertical length if there is any projection angle, (c) Projection angle, (d) Exact distance from the center of the screen to projection lens center, (e) Make of projector, (f) Width of projector aperture, in thousandths of an inch. The aperture width may be procured from the manufacturer of the projector, or it may be measured with the proper tool. If an exact measurement cannot be made, nor the lens sent, then tell the lens manufacturer the exact type of aperture used, (g) Specify lenses without jackets.
Range of Focal Lengths
(64) Projection lenses of the following standard focal lengths are carried in stock by manufacturers and by some dealers. Figures represent equivalent focus.
Quarter Size Series I: 3, 3%, 3A, 3# ; 4, 4#, *A, Wa\ 5, 5%, 5%, 5H; 6, 6A, 6/2, 634 ; 7, 7 A ; 8.
Half She Series II: 5, 5&, 5V>, SV4; 6, 6A, ^A, &A\ 7, 7 A; 8, 8A \ 9.
Super Cinephor Lenses Mounted in quarter size barrels: 2, 2^4, 2^2, 23^; 3, 3%, 3A, ^VaMounted in half size barrels: 4, 4%, 4A, 4?4 ; 5, 5%, S]/2.
The above data — used merely as an illustration — covers Bausch and Lomb lenses only. Statement of focal lengths, etc., can be secured direct from other lens manufacturers upon request.
The so-called "quarter size" projection lenses are manufactured in focal lengths from 3 to 8 inches. E. F. Beyond 7 E. F. they may be had only in two sizes : 7l/2 and 8 inches E. F.
The new anastigmatic projection lenses, such as the Super Cinephor, are available in one-quarter inch focal length from 2 to 5^2 inches E. F. The expressions "quarter and half sizes," of Series I and II, are no longer used in describing the Super Cinephor lenses. Every effort is being made in this line to approximate constant speed, as in the anastigmatic photographic lens