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1954-55 Theatre Catalog, 12th Edition, Page 303 (267)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 303
Page 303

1954-55 Theatre Catalog, 12th Edition, Page 303

Astrolite Reflection Theory

Complete Study of the Theory Behind the Development of the Astrolite Screen, and Its Adaptability to the New Systems

Reflective type surfaces for use in the projection of motion pictures are classified broadly into three optical categories. 'Those which spread the reflected light from the projector in all directions and which obey Lambertls Law are called diffusing type reflectors, while projection screens which have mirror-like qualities and obey the law of specular reflection are called specular reflectors. In addition to these two general types, there is a. third class of screen surface which co'mbines the principles of both diffusing and specular screens, and it is in this latter or third type of optical surface that the Astrolite screen may be best classified.

BRIEF: This article contains much valuable information about that very important subject . . . screens . . . With the wider pictures . . . 3-D . . . and other new projection systems . . . the need for bigger and better screens is quite apparent . . . In order to properly understand the needs of his theatre . . . the exhibitor should know some of the fundamentals behind the construction . of motion picture theatre screens . . . The author of this article . . . therefore . . . performs a valuable service by explaining many of these basic facts and theories . . . in a clear and simple fashion . . . The reader will have a much better grasp of the entire subject after reading this feature.

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The most distinguishing feature .of the Astrolite screen, and the one which sets it apart from other surfaces, is the fact that it is of a lenticular type. This word, lenticle, is perhaps new to the vocabulary of the motion picture industry, and so deserves some further description. In the sense that it is used in this paper, a lenticle is an embossed or curved small mirror which has the property of spreading the reflected light in a controlled manner uniformly in all directions. The manner in which this function is performed will be the basis for much of the following discussion.

Need for High Efficiency Surface

The Astrolite projection surface was first presented to the exhibitor at a time when the industry was confronted with two new concepts of motion picture display, each requiring a special type screen. The first of these processes was CinemaScope with its 2.55 to 1

FIGURE 1 is a photometric comparison of light reflectivity between a vacuum coated sample and one coated in a plastic carrier.



Research Director. Glowmeter Corp.

aspect ratio, Since the screen area was almost doubled over the conventional 1.33 to 1 ratio, means were sought whereby additional illumination could be obtained, either by using higher wattage projectors or by developing new high intensity carbons for the arcs. Both of these methods met with some success. However, the ultimate solution came with the great increase in efficiency of the screen surface itself. Not only was it required that the brightness of the image by maintained along the center of the theatre, but also from side to Side with no appreciable dropping off in image brightness at either ex treme side of the theatre. Only a lenticular surface with its built-in optics, such as Astrolite, could perform such a function and thereby enhance the artistic value of CinemaScope productions. The second process which demanded a special type screen was the 3-D concept of picture presentation. Here two problems presented themselves insofar as the type of screen surface was concerned. The first of these was the necessity of using a metallic reflector to preserve the state of polarization of the two beams and secondly, a method to combat the high loss of efficiency resulting from the means required to separate the two images. Calculations predict that a perfect filter will allow 50 per cent transmission and the viewer will permit only 50





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1954-55 Theatre Catalog, 12th Edition, Page 303