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1953-54 Theatre Catalog, 11th Edition, Page 264 (228)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 264
Page 264

1953-54 Theatre Catalog, 11th Edition, Page 264

Non-Stereo System

A system which has recently been described as producing a three-dimensional effect is the Cinerama development of Fred Waller. This method, requiring a multiplicity of cameras and projectors, presents a dramatic panoramic View of the scene photographed. But it is not three-dimensional at all, since it does not present a mutually exclusive image to each eye, the basic requirement on any three-dimensional system.


For successful stereoscopic projection, it is important to know the size to which the picture is to be projected, for upon this knowledge depends comfortable viewing or maximum effectiveness, or both. Distortion of the subject for the spectator depends on his viewing distance and the angle at which he views the picture, but as in conventional movies, distortion due to the spectators viewpoint is not serious unless he is very far off screen center or extremely close to or very far away from the screen.

Stereoscopic Terms

There are certain terms used in stereo< scopy. These are:

The Stereoscopic Window

The ffframef behind which the scene apparently exists in space. In some cases, elements of the scene may extend in front of the window. These are special effects, and do not belong in a discussion of basic principles. The symbol is Sw.

Interocular (In)

The distance apart of the human eyes. We may select two and one-half inches as the interocular.

Interaxial (I)

The distance apart, or horizontal spacing of the stereo camera lenses, more truly the spacing apart of the central axes of the picture area.

Major Distance (D) The distance from the lenses to the farthest object.

Minor Distance (d)

The distance from the lenses to the closest object. This is often the plane at which the stereoscopic window is planned to exist. In most cases, the nearest



i PLANE ' ALWAYS \ , l , PAleArlHLEL $6 ' . IMAGE \ Firm? } Puma . /



I ARC mnoueu WHICH CAMERA a \ LENS swmc

object will be a slight distance in back of the nearest plane.

Width of Image (w)

Refers to the width of that part of the negative which is to be used in the final prints. For standard 85mm theatrical nlm, this is .825 inch, for 16mmfour-tenth inch, for Stereo-Realist slides -.875 inch.

Focal Distance (F)

Refers to the distance from the principal node of the lens to the film, and does not refer to the equivalent focal length of the lens, although in most cases the stated focal length may be considered the focal distance. It is only for extreme close-ups that a differentiation must be made.

Parallax Index (P) ' This refers to the parallactic difference between disparate members of the stereoscopic pair when projected. The parallactic difference is determined by the following factors: 1. The distance to the nearest plane in the subject. 2. The distance to the farthest plane in the subject. 3. The ratio between image width and focal distance of the lenses used. 4. The interaxial used. Parallax index can be expressed by the equation

PF D r d

This equation was derived from the accompanying diagram, which represents the geometry of the system of taking stereoscopic photographs. Calculations are simplified if We consider one of the lenses collinear with the far and near points.

'TPoints D and E represent the positions of the two lenses. The distance DE is the interaxial til". Distance DA or EA is the lens to film distance, and its symbol is HF". F and G are points on the nearest and farthest planes in the subject. DF is ftd" and DG is "D". BC is the horizontal shift on the image plane created by points F and G, and this distance has the symbol "S".

It will be seen that if the nearest point is superposed on the screen that the farthest point will be separated by an amount determined by the interaxial used in taking the picture. The maximum value of the distance of homologous


points on .the screen should not exceed two and one-half inches to avoid visual discomfort. To the observer, homologous points back of the stereoscopic window which are two and one-half inches apart should appear to be at virtual infinity. Some individuals can tolerate three and one-half to four inches, but it is best not to use ffsuper infinitylf if it can be avoided. Homologous points that superpose on the screen will seem to lie in the plane of the stereoscopic window.

The minimum distance at which observers can look at a picture comfortably when it has a two and one-half inches maximum separation of points is about six feet. In general, the maximum horizontal displacement should not exceed 1/30 of the viewing distance. This requirement exists because in viewing projected stereo pictures, the observer must ffuncouplei, the facilities of convergence and accommodation of the eyes.

In viewing, it is desirable that the parallax index be 24 or greater.

Parallax index P may be stated as

- D. P T I

where D, is the viewing distance and L. is two and one-half inches.

Thus where D, Z 60 inches, P = 24; where DV 2 120 inches, P = 48, etc.

General Rules

1. A general rule can be laid down for the photography and projection of stereoscopic Views: The projected view should have the same angular dimension. for the viewer as the scene taken, by the camera. This is the ideal, but never attainable in practice except for just one person at the prescribed distance from the screen and viewing the screen along the projection axis.

2. The apparent depth of the stereoscopic view should be the same as the real depth of the scene. To attain the right apparent depth, the correct interaxial must be employed. The required interaxial varies over a Wide range and for projected views must be given much more serious consideration than for handheld views. If we plan to project on an 18 foot wide screen, we must not use as wide an interaxial as we can use on a six foot screen, because if we do. and

DIAGRAM (LEFT) OF one type of camera for

making lenlicular slereograms. (RIGHT) Diagram

of one method employing the beam splitter principle with addition of slit diaphragms.



1953-54 Theatre Catalog, 11th Edition, Page 264