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1953-54 Theatre Catalog, 11th Edition, Page 268 (232)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 268
Page 268

1953-54 Theatre Catalog, 11th Edition, Page 268

THIS IS A CLOSEUP OF THE SELSYN MOTORS which were attached to each machine a! StanleyWarner's Aldine, Philadelphia, to synchronize their projectors for showing three-dimensional pictures.

should be kept as far from the end of the projection lens as possible. The farther away, the longer the filter will last and the better will be picture detail. However, it should not be stuck against the port glass because the glass may become heated and depolarize the light.

Cleanliness is important. Finger prints and oil should be kept off the filter but the filter can be cleaned easily with carbon-tetrachloride and kleenex (use with ample ventilation).

One of the most needed developments is a polarizing projection filter mounted in B-glass and supplied with a permanent holding fixture so that the filter can be easily slipped out or swung away when not needed and so that it can be

readily cleaned. (Some are already being marketed. ED.)


For projectionists, theatre managers and for directors of production and directors of photography in studios the paper framed viewing glasses may be inconvenient. These professionals could well acquire permanent 3-D spectacles. For those who wear corrective lenses most of the time anyhow it would be best to have their corrective lenses especially made with the polarizing material inserted as a sandwich. Manufacturers of corrective lenses should be able to do this job with no difficulty and should be, instructed to properly orient the viewing filter material for :l-D.

SCREENS Projection screens for il-D must be metallic-surfaced to avoid depolarizing the filtered light coming from the projector. Brand new 3-D screens should give ideal results provided the coating does not contain minute particles of now

metallic filler material between the tiny bits of metal that make up the surface.

Refinishing on the spot with aluminum paint may be satisfactory, provided the paint is made of pure aluminum

and is free from non-metallic filler, provided further that the painter uses just exactly the right technique. Plugged-up perforations for instance will have a disastrous effect on the sound and seams are apt to appear as distracting dark lines. Light distribution may become so directional that vision from the sides is extremely poor.

For years most screen development was directed toward making the surface absolutely flat and dead white, and as perfectly diffusing as possible so the screen would not impose unwanted directional redections or unwanted color upon the picture. With the introduction of direct projection systems of theatre television and their limited picture brightness much effort went into developing screens that put less light on the side walls and ceiling and more down where the audience could see it. From this work screen manufacturers got some good basic training in the control of screen light distribution.

There are all-purpose screens for both conventional 2-D and for 3-D but whether they will work as well with the wide pictures will depend not only on the directional characteristics of the surface but equally upon wide-screen curvature, if any. This question can be answered only after detailed requirements for the wide picture systems are clearly specified.


Matching of the focal lengths of the two projection lenses is one detail that must be controlled for good :i-D results. If it is not, one eye will see a larger picture than the other. Motion picture

technical people agree that the normal focal length variations of around two per cent between lenses that carry the identical marked numbers on the barrel is too much. For every two per cent difference of actual focal length, there will be a two per cent difference in the measured width of the picture at the screen. For example, if one lens projects a 25-foot wide picture another lens of two per cent shorter focal length will project a 251/2-foot picture.

If the difference in size affected only the width of the picture, it would not be very serious because your eyes can adjust to reasonable sidewise errors without noticeable difficulty but they cannot adjust to up-and-down errors in size or alignment without terrific discomfort so lenses must be matched some say to onequarter of one per cent, others say within one per cent is satisfactory.

There is so far no exact final limit but extensive studies of this particular problem have been in process in an eastern college for quite some time and some authoritative information should soon be available.


Projectors that run interlocked for 3-D must be carefully aligned so both pictures will just fill the screen. Horizontal lines in both pictures will need to be level with each other and parallel with the bottom masking. This means, of course, that framing adjustments of both films must be exactly alike otherwise the patron, wearing his special viewing glassesy will have to look slightly higher with one eye than with the other. To compensate for framing errors in that way is extremely difficult for one's seeing apparatus, and most discomforting, although the act of accommodating is not a conscious one.

The Motion Picture Research Council has developed a 35mm Test Film for aligning the projectors to show all 3-D pictures now available or about to go into release. Prints of this test film can be obtained from either the Society of Motion Picture and Television Engineers or directly from the Motion Picture Research Council in Hollywood. Actual shifting or shimming-up of the machines to make the projected images coincide, is not difficult, but use of the test films is a little tricky until you get on to it. From the way 3-D pictures are photographed and printed, the left picture may have the emulsion facing one way and the right picture facing the other. In any case the test film is made to work equally well in either direction. It should be run rightside up or upside down so that its emulsion position will match the emulsion position of the particular 3-D film to be run next on that machine. The following instructions prepared by engineers at the Research Council and packed with the films, covers these details quite simply.

Instructions for Use of Target Alignment Loops

This lineup should be made without polarizingr filters in the projector light beams.

l. Two loops of the target alignment

film are provided, each 10 feet in length.

1953-54 Theatre Catalog, 11th Edition, Page 268