This width may be computed roughly as follows:
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"
If the distance is 25"
The focal length is 5"
(A) = 25 x 2.00 : 50.00 inches
(B) = 50.00 / 5 = 10.00 inches
(C) = 10.00 - 4 = 14.00 inches
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 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
(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
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.
(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