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1953-54 Theatre Catalog, 11th Edition, Page 265 (229)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 265
Page 265

1953-54 Theatre Catalog, 11th Edition, Page 265

employ convergence to establish the stereoscopic window, we are either going to have homologous points at infinity spread so far apart that the eyes have to diverge to accommodate for them, or we are going to have to adjust the projected stereoscopic window to a plane far in front of the screen.

It is not difficult to arrive at the correct interocular if we use the simple equation

. . a w e d I inteiax1al) Sf where w 3: width of the image on the film, e : normal human interocular

(21/: inches)

d 2 distance from the camera lens to a plane just in front of the nearest object (plane of convergence),

s 3 width of the projected picture,

f:focal length of the camera lenses.

The establishment of the stereoscopic window is not of great importance in hand-held views, but it must be employed in projection, and properly employed. If it is not, there will be the marginal disturbances that have been mentioned before, and they are hard to look at. There is nothing in natural vision to correspond to them, and since the ideal stereoscopic view is one that should afford complete visual comfort, the appropriate window frame should be calculated in every scene. If it is not, people may have trouble looking at your stereoscopic ttmasterpieces."

Very striking stunt shots can be made stereoscopically. For instance, objects can be made seemingly to float in space between screen and observer provided the object is well inside the margins of the picture areas. Objects should not be photographed so as to appear so near to the person observing the projected images that he will have trouble fusing them. Consideration must be given to the accommodation limits of the eyes; that is, for convergence accommodation limits.

Theoretical accommodation limits of the human eye in convergence are based on normal close reading distance of 15 inches. (Note: This formula does not take into consideration what physiological effect, if any, is introduced when the accommodation muscles are used without correlative focusing.) The angle of convergence of the eyes (interpupilary distance of 2.625 is used) at a distance of 161.4.) inches is slightly more than nine degrees. The displacement of. the disparate images on the screen are given in inches and decimals of an inch.

Formula: Observer distance from screen less 15 inches multiplied by the tangent of half the angle subtended by the eyes gives the maximum separation on the scrccn at a given distance. To obtain the required separation of images on the film, divide the projectit'm aperture width by the screen width and multiply by the separation of the projected images. (tan 4 degrees 30 feet by distance from the screen)


Maximum Separation on Screen in Inches Observer Distance from Screen

4' 2.60 6' 4.48 8' 6.37 10' 8.26 12' 10.15 16' 13.93 20' 17.71 24' 21.48 30' 27.15

An Analysis of Ligh'l' Polarization

Since the phenomenon of light polarization is so closely related to the practice of stereoscopy, it is of benefit briefly to review it.

Let us imagine we are looking head-0n at a beam of light and that we can conceive it as a bundle of rapidly vibrating arrows pointing outward in an infinite number of directions. A polarizing filter can .cause all vibrations to take place parallel to each other.

The polarizer transmits not only the vibrations which are originally parallel to the polarization axis, but all the components of all the infinite number of vibrations at angles to the axis. The amplitude of any vibration along the axis is equal to A1 COSu where ii is the angle between the direction of vibration and the axis.

Since the energy of a vibration is proportional to the square of its amplitude, the relative intensity I.. of light transmitted by two polarizers with axes

at any angle from 0 degree to 90 degrees is given by Iu I L. C0823

when the angle between the polarizing axis is a and L, is the relative intensity of the transmitted light when the angle a is zero.

A graphical representation of this, with L, arbitrarily equal to unity, shows the relative intensity of the light through two polarizers with axes at various angles to each other. This curve is true only for perfect polarizers which would have a transmission of 50 per cent. Actually, the best polarizers have a transmission of only about 40 per cent.


The fundamental requirement of any stereoscopic system is that each eye sees only that member of the stereoscopic pair intended for it and excludes the image belonging to the other eye. The disparate images of the stereoscopic pair must be distributed to the eyes of the audience in a selective manner. To quote from Dr. H. E. Ives:

There are only two places where the distribution of images to eyes can be done; these are at the screen and at the eyes. The number of images at the screen can be reduced to two, if the number of viewing instruments is equal to the number of spectators. The number of viewing instruments can be reduced to zero if the number of images at the screen is made infinite. Any gain in simplification at one point is offset by increase in the complexity or expense at the other.

THE AUTHOR, IOHN A. NORLING, president of Loucks and Norling Studios, and the chairman of tho Stereoscopic committee of the Society of Motion Picture and Television Engineers has pioneered in 3-D.
1953-54 Theatre Catalog, 11th Edition, Page 265