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1945 Theatre Catalog, 4th Edition, Page 317 (293)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 317
Page 317

1945 Theatre Catalog, 4th Edition, Page 317

Recent Developments in Projection Optics

Orthoscope System and Heat-Filtering Glass Top the New Advances in the Theatre Field

The application of hard, durable 10wreflection films to the optical parts of motion-picture-projection lens systems is, without question, one of the greatest advances in optical science in recent years. Because of its significance in the optics world, and its inevitable adoption as standard practice by manufacturers of projection lenses, there is presented in these pages a complete account of the subject, in fact it is believed that this is the first truly complete and scientifically accurate account ever to be presented in a publication of this nature.

But the war years saw other developments* in the field of optics as applied to motion pictures and the theatre. Such will be discussed at this point, together with other pertinent information to promote a better understanding of the use and purpose of optical equipment.


K The constant cry on the part of the exhibitor has always been for two properties of projection lenses: (1) An image as free from aberration as possible, and (2) a bright image.

The first condition was gradually brought about by improvements of lens formulae. The second condition, however, was still not satisfactorily met until manufacturers of lighting devices hit upon new ideas, such as the high-intensity lamp.

Since the light output has a direct relationship to the size of the light source, the old, small, tfquarter-size,i lenses (with diameters between 1-11/16 and 2% inches) became more and more incapable of taking advantage of the increased amounts of light available. This is the reason why the diameter of the modern lens is fixed around 2% inches, outside diameter.

As for the nquarter-sizei, and ifhalfsizeii, these terms go back to the turn of the century, when projection lenses were specified not by focal length but by the extent to which a standard 8X10 plate was covered with light. This means that a half-size lens, theoretically, would cover a 5x8 plate and the quarter-size a 4x5 plate. In order for a projection lens to cover a 5x8 plate, it would normally be of a certain diameter, say three inches. As changes were made in lens formulae, it became possible to produce a lens whose diameter was not three inches but 11/2 inches, and still covering the 5x8 size. The final result of these developments was that, instead of both these lenses being called half 'Concui'ning some developmentsisuch as, for example, the Garutso optical balancereditorial comment and discussion is Withheld until such a time as the inventors and proponents of these devices either make a complete scientific disclosure or make a demonstration which is entirely conclusive to competant scientific and technical critics. Since these things have not been done, the eidtors have no alternative but to consider that there is no case.


size, since they covered a half plate, nomenclature degenerated to the point where barrel diameter alone was the governing factor. Thus, the first 3-inch diameter was half size, and the ll/g-inch diameter lens was quarter size.

The trade has all but discontinued the use of this nomenclature, adopting instead the more optically accurate focal distance as the criterion of size. Anya how, exhibitors now realize that lenses with larger diameters are required in order to make use of improved lamp equipment and to obtain brighter screen images.

Exhibitors sometimes ask concerning the longevity of a projection lens. This question can hardly be answered, for there is no way of accurately estimating the useful life, which is wholly dependent upon the care that it is given. Some lenses have been known to be ready for the junk pile after a mere six months in the hands of a careless operator, while lenses have been as good as new after ten or fifteen years of use by a skilled operator.


The new Orthoscope auxiliary lens system* consists of two high-precision elements, a negative and a positive,

*This material has been prepared by Hal Huff. exploitation manager of the H and H Optics' theatre division, through whose cooperation and that of the International Projectionist and the

ground to individual theatre requirements, and highly polished. They are made of quartz to endure any amount of heat.

The Orthoscope might be called the 6(missing link", for the very important work it does. It replaces no part of the existing optical system, but is a supplementary set of lenses inserted between the light source and the film.

The mirror arc can do, and does do, a great job, but it has its limits. This can be readily understood, for at a glance you can see, by looking at a short focallength objective lens and a long focallength objective lens, a great deal of diEerence in the diameter of the rear lenses. Does it not stand to reason, then, that the mirror cannot fill each objective lens with light when they vary in size, as they have to, to meet different focal-length requirements.

This is where the new Orthoscope comes in. They are designed so that the correct curve is placed on them, in order that the light is placed evenly and directly on the film, and to fill the pupil of the objective lens with light, no matter what the diameter of the lens is. In filling an order for the new Orthoscope there is required the following information: type of lamp, name of mae chine, and the focal length, F value,

National Theatre Supply Division of NationalSimplex Bludworth, Inc., the illustrations have been used.

TYPICAL OF THE PROJECTION LENSES perfected as the result of war research and development is the Snaplite Series II, shown here, of the Kollmorgen Optical Corporation. The new Series II Snoplite has been redesigned to produce increased illumination with a quality of image outstanding in contrast, definition, flatness of field, and freedom from color fringes. Speed of f/2.0 is maintained in all focal lengths up to 5 inches. Durable Iowreflection coatings are regularly supplied. The rugged mounts are sealed for lasting trouble-free performance.
1945 Theatre Catalog, 4th Edition, Page 317