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Table of Contents

Selection of Lenses.—Upon the proper selection of lenses depends very much the quality of the picture. The size of the picture, under given circumstances, depends entirely upon the focal length of the objective. With a given distance between lens and screen there is practically but one size of picture obtainable. If we wish to obtain a picture of another size by the use of the same lens, this can be done only by sacrificing the definition and had better not be attempted.

Very large pictures are desirable only in large halls in which portions of the audience are very far from the screen. Such a picture requires very much light and, on account of its size, shows many imperfections to those who sit in the front rows. It is better to limit the size of the picture to one which can be easily illuminated, and thus avoid such imperfections.

TABLE II. MOTION PICTURE LENSES. TABLE SHOWING SIZE OF SCREEN IMAGE WHEN MOVING-PICTURE FILMS ARE PROJECTED.

Size of Mat opening 11-16 × 15-16 inch.
E.E. In.	15 ft.	20 ft.	25 ft.	30 ft.	35 ft.	40 ft.	45 ft.	50 ft.	60 ft.	70 ft.	80 ft.	90 ft.	100 ft.
2	1⁄8	4.	8	6.	4	8.	0	9.	6	11.	3	12.	9	14.	5	16.	1	...	...	...	...	...
6.	5	8.	7	11.	0	13.	2	15.	4	17.	6	19.	8	22.	0	...	...	...	...	...
2	1⁄2	...	5.	4	6.	8	8.	2	9.	6	10.	9	12.	3	13.	7	16.	4	...	...	...	...
...	7.	4	9.	3	11.	2	13.	1	14.	9	16.	8	18.	7	22.	4	...	...	...	...
3		...	4.	5	5.	7	6.	8	8.	0	9.	1	10.	3	11.	4	13.	7	16.	0	...	...	...
...	6.	2	7.	7	9.	3	10.	9	12.	4	14.	0	15.	6	18.	7	21.	8	...	...	...
3	1⁄2	...	...	4.	9	5.	8	6.	8	7.	8	8.	8	9.	8	11.	7	13.	7	15.	7	...	...
...	...	6.	6	8.	0	9.	3	10.	6	12.	0	13.	3	16.	0	18.	7	21.	4	...	...
4		...	...	4.	2	5.	1	6.	0	6.	8	7.	7	8.	5	10.	3	12.	0	13.	7	15.	4	...
...	...	5.	8	7.	0	8.	1	9.	3	10.	5	11.	6	14.	0	16.	3	18.	7	21.	0	...
4	1⁄2	...	...	...	4.	5	5.	3	6.	2	6.	8	7.	7	9.	1	10.	6	12.	2	13.	7	15.	4
...	...	...	6.	2	7.	2	8.	4	9.	3	10.	5	12.	4	14.	5	16.	6	18.	7	21.	0
5		...	...	...	...	4.	8	5.	4	6.	1	6.	8	8.	2	9.	6	10.	9	12.	3	13.	7
...	...	...	...	6.	5	7.	4	8.	4	9.	3	11.	2	13.	0	14.	9	16.	8	18.	7
5	1⁄2	...	...	...	...	4.	3	4.	9	5.	6	6.	2	7.	4	8.	7	9.	9	11.	2	12.	4
...	...	...	...	5.	9	6.	7	7.	6	8.	4	10.	2	11.	9	13.	6	15.	3	17.	0
6		...	...	...	...	...	4.	5	5.	1	5.	7	6.	8	8.	0	9.	1	10.	3	11.	4
...	...	...	...	...	6.	2	7.	0	7.	7	9.	3	10.	9	12.	4	14.	0	15.	6
6	1⁄2	...	...	...	...	...	...	4.	7	5.	2	6.	3	7.	3	8.	4	9.	6	10.	6
...	...	...	...	...	...	6.	4	7.	1	8.	6	10.	0	11.	4	13.	0	14.	5
7		...	...	...	...	...	...	4.	4	4.	9	5.	8	6.	8	7.	8	8.	8	9.	8
...	...	...	...	...	...	6.	0	6.	6	8.	0	9.	3	10.	6	12.	0	13.	3
7	1⁄2	...	...	...	...	...	...	...	4.	5	5.	4	6.	4	7.	3	8.	2	9.	1
...	...	...	...	...	...	...	6.	2	7.	4	8.	7	10.	0	11.	2	12.	3
8		...	...	...	...	...	...	...	...	5.	1	6.	0	6.	8	7.	7	8.	5
...	...	...	...	...	...	...	...	7.	0	8.	1	9.	3	10.	5	11.	6

Example: With a lens of 5¹⁄₂ inch focus at a distance of 35 ft. the screen image will be 4.3×5.9; at 40 ft., 4.9×6.7; at 45 ft., 5.6×7.6; etc.

Note: When ordering lenses, give size of picture wanted, and distance from machine to screen.

TABLE III. STEREOPTICON LENSES. TABLE SHOWING SIZE OF SCREEN IMAGE WHEN LANTERN SLIDES ARE PROJECTED.

Size of Mat opening 23⁄4 × 3 inches.
E.F. In.	15 ft.	20 ft.	25 ft.	30 ft.	35 ft.	40 ft.	45 ft.	50 ft.	60 ft.	70 ft.	80 ft.	90 ft.	100 ft.
5		8.	0	10.	8	13.	5	16.	3	19.	0	...	...	...	...	...	...	...	...
8.	8	11.	8	14.	8	17.	8	20.	8	...	...	...	...	...	...	...	...
5	1⁄2	7.	3	9.	8	12.	3	14.	8	17.	3	19.	8	...	...	...	...	...	...	...
7.	9	10.	7	13.	4	16.	1	18.	8	21.	6	...	...	...	...	...	...	...
6		6.	6	8.	9	11.	2	13.	5	15.	8	18.	1	20.	4	...	...	...	...	...	...
7.	3	9.	8	12.	3	14.	8	17.	3	19.	8	22.	3	...	...	...	...	...	...
6	1⁄2	6.	1	8.	2	10.	4	12.	5	14.	6	16.	7	18.	8	...	...	...	...	...	...
6.	7	9.	0	11.	3	13.	6	15.	9	18.	2	20.	5	...	...	...	...	...	...
7		5.	7	7.	6	9.	6	11.	6	13.	5	15.	5	17.	5	19.	4	...	...	...	...	...
6.	2	8.	3	10.	5	12.	6	14.	8	16.	9	19.	0	21.	2	...	...	...	...	...
7	1⁄2	5.	3	7.	1	8.	9	10.	8	12.	6	14.	4	16.	3	18.	1	...	...	...	...	...
5.	8	7.	8	9.	8	11.	8	13.	8	15.	8	17.	8	19.	8	...	...	...	...	...
8		...	6.	6	8.	4	10.	1	11.	8	13.	5	15.	2	17.	0	20.	4	...	...	...	...
...	7.	3	9.	1	11.	0	12.	9	14.	8	16.	6	18.	5	22.	3	...	...	...	...
8	1⁄2	...	6.	2	7.	9	9.	5	11.	1	12.	7	14.	3	16.	0	19.	2	...	...	...	...
...	6.	8	8.	6	10.	3	12.	1	13.	9	15.	6	17.	4	20.	9	...	...	...	...
9		...	5.	9	7.	4	8.	9	10.	5	12.	0	13.	5	15.	1	18.	1	21.	1	...	...	...
...	6.	4	8.	1	9.	8	11.	4	13.	1	14.	8	16.	4	19.	8	23.	1	...	...	...
9	1⁄2	...	5.	6	7.	0	8.	5	9.	9	11.	4	12.	8	14.	2	17.	1	20.	0	...	...	...
...	6.	1	7.	6	9.	2	10.	8	12.	4	14.	0	15.	5	18.	7	21.	9	...	...	...
10		...	5.	3	6.	6	8.	0	9.	4	10.	8	12.	2	13.	5	16.	3	19.	0	21.	8	...	...
...	5.	8	7.	3	8.	8	10.	3	11.	8	13.	3	14.	8	17.	8	20.	8	23.	8	...	...
12		...	...	5.	5	6.	6	7.	8	8.	9	10.	1	11.	2	13.	5	15.	8	18.	1	20.	4	...
...	...	6.	0	7.	3	8.	5	9.	8	11.	0	12.	3	14.	8	17.	3	19.	8	22.	3	...
14		...	...	...	5.	6	6.	6	7.	6	8.	6	9.	6	11.	6	13.	5	15.	5	17.	5	19.	4
...	...	...	6.	2	7.	3	8.	3	9.	4	10.	5	12.	6	14.	8	16.	9	19.	0	21.	2
16		...	...	...	...	5.	8	6.	6	7.	5	8.	4	10.	1	11.	8	12.	5	15.	2	17.	0
...	...	...	...	6.	3	7.	3	8.	2	9.	1	11.	0	12.	9	14.	8	16.	6	18.	5
18		...	...	...	...	5.	1	5.	9	6.	6	7.	4	8.	9	10.	5	12.	0	13.	5	15.	1
...	...	...	...	5.	6	6.	4	7.	3	8.	1	9.	8	11.	4	13.	1	14.	8	16.	4
20		...	...	...	...	...	5.	3	6.	0	6.	6	8.	0	9.	4	10.	8	12.	2	13.	5
...	...	...	...	...	5.	8	6.	5	7.	3	8.	8	10.	3	11.	8	13.	3	14.	8
22		...	...	...	...	...	...	5.	4	6.	0	7.	3	8.	5	9.	8	11.	0	12.	3
...	...	...	...	...	...	5.	9	6.	6	7.	9	9.	3	10.	7	12.	0	13.	4
24		...	...	...	...	...	...	...	5.	5	6.	6	7.	8	8.	9	10.	1	11.	2
...	...	...	...	...	...	...	6.	0	7.	3	8.	5	9.	8	11.	0	12.	3