This width may be computed roughly as follows:
(a) Multiply the distance of the face of the projection lens from the outer face of the wall of the projection booth (in inches) by 2.00;
(b) Divide the above result by the focal length of the projection lens (in inches);
(c) To this result add 4"
For example:
If the distance is 25"
and
The focal length is 5"
Then:
(A) = 25 x 2.00 : 50.00 inches
(B) = 50.00 / 5 = 10.00 inches
(C) = 10.00 - 4 = 14.00 inches
or the minimum width of the port opening.

In case the light beam passes through the wall of the booth at an angle thereto, this width must be increased to compensate for the angle and the thickness of the wall.

THE SCREEN

The Miracle Mirror Screen delivered with the CinemaScope Package has been designed for maximum light reflection coupled with correct distribution, and will be fabricated and delivered in the over-all sizes required, webbed and grommeted, the latter on 6" centers with an additional grommet at each end of all seams.

There are two types of surface design available, one for projection angles approximately 10 to 12 degrees and greater, known as Type M-5 or tilted pattern, and one for projection angles less than approximately 10 to 12 degrees, and known as Type M-2 or head-on pattern, but a selection of Type can best be judged by first examining the Light Distribution charts and figures included in this manual, consisting of a series of drawings indicating the light reflections from these two types of screens at various angles of projection, and at vertical and tilted positions of the screen.

THE FRAME
(May or may not be included in the CinemaScope Package)

The screen must be mounted in a suitable frame and in a smooth concave curve, the arc of which is the picture throw or as close thereto as possible. In many instances, a cord or tape affixed to the projection booth wall at a point between the two projection ports, may be used as a radius to describe the arc upon the floor

of the stage.

Also included in this Manual is a chart explaining the meaning of the terms chord, arc, rise and radius as they apply to the CinemaScope picture and fixing the unknown dimensions when the length of the projection throw is known to the nearest 10 feet, and the size of the CinemaScope picture has been established.

In addition to the shaping of the aperture, where an angle of projection approximates 14 - 15 degrees and over, some tilt should be given the entire concave screen and frame to overcome keystoning, but in practically every case this tilt should not exceed an approximate 5 - 6 degrees.

Some means of varying the tilt of the screen is desirable, but attention is called to the fact that, as a concave screen is tilted, its outer extremities rise, and this situation should be recognized in the design and construction of the frame.

By reason of the considerable size of the frame itself, and by reason of the various situations arising in theatres, standard forms of frames are not possible in every case. The exhibitor may wish to furnish his own frame in accordance with the diagrams attached to this survey, or a similar one of his own devising, but should he be unable to furnish and erect such a frame, then he should request frame quotations additionally from the supplier.

Since the picture width is computed upon the chord of the screen, the arc of such chord should be computed in order to obtain the width of screen necessary, and the height should be determined from the exhibitors' calculations as respects the size of the CinemaScope picture he desires, the size of the conventional picture he desires, and the size he might require for other methods of projection. Consult the charts for CinemaScope and conventional picture sizes.

THE MASKING
(Not included in CinemaScope Package)

The screen and frame should be masked top and bottom to the established height of the picture, placing the bottom of the CinemaScope picture as close to the floor of the stage as possible, or as low as the sight lines permit.

Since, as has been mentioned heretofore under THE FRAME, the outer ends of the picture projected