A New System For Obtaining Natural Depth
By EDWARD P. HOLDEN, JR.,
Smith-Dieterich Corporation
from the American Cinematographer February, 1942 p.56/57
FROM the first feeble and eye-wracking “flicker” of the primitive movie, to the present time, three cardinal improvements were always in the minds of
the scientist and engineer,—Sound, Depth and Color.
The first of these—Sound—was finally introduced to motion picture audiences against practically universal opposition on the part of the producer. Even though far from perfect at its inception, once audience reaction became evident, all silent pictures were but remnants of an ancient era, gone forever.
Color, after vast expense in its development, and much complication even today in its production, coupled with more or less satisfactory results, has at length become a recognized feature of motion pictures.
But what of so-called Depth, which was said by no less an authority than the great Thomas A. Edison, to be the next important step forward in cinematography? Efforts without number have cluttered the files of the Patent Office with vast reams of paper; monstrous cameras have been built on concrete bases; the shape and surface of the screen has been modified; the unfortunate audience has been saddled with spectacles and eye-glasses, all with what result? A bad imitation of the ancient stereoscope found on the sitting-room tables of our grandparents. No depth effect in its true sense, which is nothing more than clear, natural vision.
That was the condition prevailing up to some fifteen years ago. At that time, the late distinguished scientist and engineer, Dr. Ludwig M. Dieterich, A.S.C., attracted by this problem, gave up his entire time to research, study and practical experiment looking toward its solution. His efforts were directed not in the direction of stereoscopy, which he was well aware was not the true solution he sought, but even if mechanically and optically possible of accomplishment in motion picture practice, would cause such intense “eye-strains” that a stereoscopic picture or couple could not be viewed for upward of three minutes continuously, without blurring of vision. The basis of Dr. Dieterich’s theory was simple; its execution one of the most complex and important optical discoveries of all time.
The theory—can a lens be so designed and constructed as to automatically accommodate itself, as does the eye of man, to focus clearly at every perceptible distance and at the same time not change the size of the various images at different distances from the viewer? This theory and its solution, and the construction of such a lens, was pronounced optically impossible by most of the scientific brains of the time. The good doctor, in no way discouraged by such depressing commentary, persevered in study and experiment, using his own funds and those of some friends who believed in him; stopping from time to time as such funds were exhausted, until the coffers could be replenished.
At one period of this saga, the doctor, with such limited funds and still more limited scientific apparatus, took 3,300 photographic hand tests, of which three were successful, and thus demonstrated to himself the correctness of his theory, and that with the necessary refinement and development, his lens would indeed become a photographic eye.
At this time patents were applied for in most of the important countries of the world. So novel was his theory, and so revolutionary its accomplishment, that several of the patent offices refused to allow his claims, as impossible of performance, until furnished with the actual film showing the definite and unquestioned result to the doubting Thomases of the scientific and optical world.
Thereafter, Dr. Dieterich equipped several Bell and Howell and Mitchell cameras with “Detrar” lenses, all of which performed satisfactorily, each model an improvement over its predecessor.
Shortly before Dr. Dieterich’s death, a young sound engineer, P. Stanley Smith, who had been working on the same idea, knowing nothing of Dr. Dieterich or his patents, discovered the latter in the course of his research. He then realized that he was precluded by these patents from further progress. As sometimes, but rarely, happens in scientific research, these “twin” ideas did not fight each other, but chose to collaborate.
As a result, Mr. Smith applied for his patents on electrical operating mechanism applicable to the Dieterich “Detrar” lenses and a combination was made of all such patents, and the Smith-Dieterich Corporation of New York was formed. Further extensive studies and experimental tests were made over a period of years, which resulted in the birth of the present Smith-Dieterich Electroplane Camera.
What is it and what does it do?
The “Detrar” lens operates on the principle of the human eye, that is, automatically adjusts its focus without changing the size of the image, thus producing on the film the same illusion of depth as seen by the human eye.
The lens itself is composed of four cells, or elements, one cell of which oscillates along the axis of the system, without tilting or distortion of motion, for a maximum distance of 3/10 mm. The lens presently employed is a 50 mm lens, f:3.75, coated, effectively f:3.2 and so calibrated. Calculations covering the basic focii of a wide range of lenses of various focal lengths have been completed and checked by Smith-Dieterich engineers.
The present “Detrar” lens, like Dr. Dieterich’s earlier objectives, is made by the Bausch & Lomb Optical Co., to the highest American standards.
The “Detrar” oscillating lens permits the moving of the plane of sharpness from an arbitrary point four feet from the camera, through the field to the infinity position, thus registering a sharp image of every object in that field in front of the camera, and resulting in uniform focus throughout.
In the Electroplane Camera, the oscillation occurs a multiplicity of times during the exposure of a single frame of film, thus eliminating the necessity of synchronizing the lens movement with the camera shutter and intermittent. This motion makes possible the change of equivalent focus of the system, without change of image size, so that, when operated in a motion picture camera a multiple of cycles, during the exposure of a single frame of film, registers an in-focus image of every object before the camera.
The lens in early Dieterich cameras was mechanically operated by a cam attached to the balance wheel of the film driving mechanism. This cam, in turn, transmitted motion through a series of levers and shafts to a sleeve in which the moving lens was mounted.
The current model of the Smith-Dieterich Electroplane Camera, the electrical operating control of which was designed and patented by P. Stanley Smith, is an adaptation of a standard Mitchell motion picture camera, fitted to a special base designed to receive the “Detrar” lens and its actuating motor. This lens-actuating “motor” is very much like that of the voice coil and exciter field of a dynamic loudspeaker. However, it is designed to meet precision of motion requirements. The development of this latter has required months of experimentation. It involves the use of a specially formed diaphragm on which the moving coil and the “B” lens second from the left in the drawing) are mounted coaxially with respect to the other lens-elements of the system.
A very important feature in this respect is that the “B” lens and its driving and locating components have no frictional contact, and therefore can be described as a “floating” structure. Said structure is rubber and air damped. The lenses are in accordance with the Dieterich specification in U. S. Patent No. 1,927,925. The exciter field is operated by direct current. The moving coil is actuated by (1) alternating current, or (2) direct current, or (3) a combination of both in achieving (1) the maximum oscillation of the lens, which is .3mm; (2) the biasing action, or (3) a combination of oscillation and biasing.
Mr. Smith’s first considerations in his investigations concerned the possibility of moving a large mass or body at the rate of as high as 300 cycles per second, at the same time conforming to the limitations of designing a structure which would fit into but not interfere with standard accessories for both camera and sound-recording equipment.
The control instrument or console, which can be operated remote from the camera, supplies to the lens motor alternating and direct current, or both blended, which
(a) Causes registry of all objects before the camera;
(b) Operates the camera as a standard limited focus camera;
(c) Causes an extension of the in-focus area, permitting, at the same time and if desired for artistic purposes, extreme background or extreme foreground out-of-focus with a selected range intermediate between the two extremes, in-focus.
Any one of these three conditions is producible by the simple throwing of a switch and without interruption or stoppage of the camera filming- mechanism. All power for the lens unit is received from the control console, which in turn operates on 110 volt, 60 cycle alternating current.
In other words, automatically and exactly, any focus or depth of focus the cinematographer may wish to use is available instantly, with predetermined accuracy.
While the motion picture industry is a promising potential field for the Electroplane Camera, its principle readily lends itself to television, a field which is now definitely in its infancy, but which holds much promise. It is also adaptable to most forms of photography.
END.