Hitherto there has not been much demand for the reproduction of films which were to old and shrunken to pass through an ordinary printer. It is true that at various times old films have been reproduced for various commercial purposes, both by optical and by step printers. But the problem did not assume a serious aspect until the use of old films for museum and archival study and research purposes became as significant as it is today.
With the advent of sound, modern film processing became a much more precise procedure than it was in the old days before rigid standards for film dimensions were established. The present trend in film printing has been for the elimination of the old style step or intermittent printer and to substitute for it the much speedier and more precisely constructed continuous printer. However, the step printer had an advantage which the continuous printer does not have. As each frame was printed step by step in the intermittent printer and minute deviation of the negative was independently corrected by a slight shifting of the relation between the negative and the copy film. This correcting shift took place during the period when the printing light was cut off by the shutter and the exposure of the copy film took place subsequent to the correcting shift between the two films. As long as the tolerance of the printer permitted the shrunken negative film to run over the sprockets and to be pulled down by the intermittent mechanism, the resulting print was quite satisfactory for silent projection. Old style step printers are still used to a limited extent for certain purposes, such as the making of master or duplicating prints and for background transparencies, but even when so used they are usually rebuilt for greater accuracy so that they are seldom suitable for films having more than slight shrinkage. Even an old style step printer can not be used for printing badly shrunken films, because there is a very definite limit to the shrinkage which its tolerance limit can accept. Other disadvantages in step printers consist in the variations form old standards which are found in modern sound projectors.
The modern sound projector requires a smaller image or frame in order to allow for the sound-track. A sound projector can be made convertible for silent pictures, but in most cases convertible projectors are not to be found when a silent print is to be run. It is desirable, therefore, in most cases to reproduce an old film to the new standard if its use is not to be very much limited. Not only is the frame size of the present-day standard smaller, but the number of frames per second of projection is 24 instead of 16. Unless extra frames are interpolated to convert the silent film to sound speed, the tempo of the action becomes too fast to be natural. It is not possible to introduce these extra frames when using an ordinary step printer. No doubt a step printer mechanism which would add the interpolated frames could be designed, but this would not solve the problem of reducing the frame size without losing a considerable portion of the image within the frame taken up by the sound-track and the wider frame line.
The obvious solution of the problem is an optical printer especially designed to take care of the contraction of the shrunken film from standard size. This requires more than an ordinary optical reduction printer such as is used for making 16-mm reduction prints from 35-mm negative. Such an optical printer would have to be a modified form of trick optical printer such as is used for process photography.
There are two general types of trick optical printers, one which uses direct optical methods only, and a second type in which the image is projected upon a translucent screen and rephotographed by a camera on the other side. The second type has no advantages over the first for our purpose and is much more cumbersome and bulky than the first type.
The direct optical printer is essentially a small projector adapted to project very small images directly upon a virgin film in a lensless camera. For accuracy the projector, the projector lens, and the camera are all adjustably mounted in line on a light bench. Such a light bench is most economically and accurately made from a lathe bed. Often the other parts of the lathe can be utilized for parts of the apparatus. After the removal of the upper part of the headstock the camera is mounted thereon. The tailstock base can be used to mount the projector lens which must be a photographic objective, preferably
Of four to six inches in focal length and of very good definition. For this purpose the tailstock is removed from the right end of the lathe and placed between the headstock camera mount and the lathe saddle. The lathe saddle is run toward the right end of the lathe and used as the mount for the projector head and lamp house (see fig.)
The lamp house can be quite small, as a single 6-volt head-light lamp will furnish ample illumination. Adjustment for positioning the lamp in relation to the condenser and film aperture is necessary. The lamp house should be ventilated and reasonably light tight. For control of the light intensity the lamp may be connected to a 6-volt storage battery through a sensitive graduated rheostat and a large, finely calibrated voltmeter. As the camera mount is the control end of the machine, the rheostat and voltmeter should be mounted on a small switchboard placed at or near the camera end of the machine. A flexible lamp cord connects the lamp to the instruments on the control board and to the battery.
The line-up of the component parts of the machine must be very accurate. Am imaginary line parallel to the lathe bed and passing through the optical axis of the projection lens determines the positions of the camera, the projection head, the condenser, and the lamp filament, as well as the projection lens. The center of the camera picture aperture must be at right angles to the optical axis with its intersection at the center of the frame; the objective axis coincides with the optical axis of the machine as above stated; the projection head aperture meets the axis at its center and at right angles; the optical axis of the condenser systems coincides with the general axis, and the lamp filament, which must be of small dimension, has its center also on the general axis.
When these conditions are met, a film placed in the projector head can be focused directly on he film in the camera, and by suitable adjustment of the component members of the assembly, the image on the copy film in the camera can be adjusted to any desired proportion of frame size.
These are the essential primary conditions for a direct optical trick printer, so that when the necessary changes are made to permit the projector head to function with shrunken film, the machine can reproduce not only badly distorted film, but it can be used also for an infinite variety of effects such as fades, dissolves, wipes, swishes, multiple exposure, mask work, and many other kinds of process photography.
The changes in the projector head, to make it able to accommodate shrunken film, are not many. The feed and take up sprockets must be made easily interchangeable with other sprockets which will accommodate shrunken film. The side guides of the gate can be spring mounted on one side so that whatever variation occurs in the film width, the opposite side guide will meet the opposite edge of the film and eliminate side weave.
The best intermittent movement for this type of machine is the finger or pin draw-down such as was employed in the older type cameras and step printers. Any type of round cam or bell-crank intermittent movement can easily be altered so that a slight shift of the cam or crank on its drive axis will change the throw of the pins to fit any degree of contraction between the perforations. Those types having a harmonic cam can have an adjustable circular cam substituted. Change from a harmonic cam to a circular cam changes the relation of the pull down period to the rest period. The decrease in the rest period is not a disadvantage, because the slow pull-down in more suitable for gentle transport of brittle film, and makes for greater accuracy in registration. Any decrease in exposure time is easily compensated by a slight increase in the lamp brilliancy by use of the rheostat control.
Pilot pin registration for shrunken film is not considered practical. Pilot pin registration requires that the perforations be exactly uniform and that the pilot pin fit each perforation exactly. While it is theoretically possible to make spring pilots with rigid positioning in two directions such a provision would not take care of damaged sprocket holes. With slow operation and gentle spring pressure in the gate, the film will have sufficiently good registration, unless both sprocket holes engaged by the draw-down pins are damaged.
Unless a large proportion of the sprocket holes are damages, these alterations in the projector head will take care of almost any shrunken film that has enough tensile strength to be run through the machine. Even very brittle film can often be conditioned and certain repairs made before insertion in the machine. The conditioning of old film is a subject in itself and will not be considered here.
It is assumed that the projector head has an adjustment for a slight amount of framing. This adjustment needs to be only enough to take care of off standard frame line or less than a quarter of an inch, so that the picture can be threaded in frame. Of course the old film must previously be inspected and all misframes removed before duplication. Of standard frame line is automatically transformed to standard in the camera, as the frame line of the copy depends on the camera mechanism.
Partial discolorations in the image of the old film can be almost entirely eliminated in the optical printer by using modern duplicating stock or panchromatic copy film and suitable filters between the lamp house and the projector head. Generally speaking, this requires a filter the color of which is nearly complimentary to that of the discolored image. Where the image has partially faded, other treatment, such as chemical restoration of the image, may have to be used. Emulsion stains, on the other hand, require filters of the same color as the stain.
Very often considerable improvement in the quality of the image may be obtained by optical copying. It is very easy to increase contrast in flat images or to reduce contrast in harsh films by suitable choice of copy film and controlled development. On the other hand, scratches and abrasions on the film are likely to be accentuated. Cleaning with carbon tetrachloride will often help to clean up dirt and adherent imperfection, and varnishing with clear varnish which does not contain celluloid or gelatine solvents will fill up scratches to a considerable extent.
Details of the interconnections between the camera and the projector movements and the varied arrangements for he different adjustments do not need to be given here. Special optical printers are usually made to order and designed to perform certain special functions. Almost any mechanical shop accustomed to the building of motion picture apparatus can construct a suitable machine for the optical reproduction of old and shrunken films.
The mere possession of such a machine does not alone solve the problem. At least one highly skilled operator must bet rained to operate the machine. Besides the mechanical dexterity required for operation, a wide range of photographic knowledge is required in order to be able to choose the different types of emulsions which will give the best results and to process the copies after exposure.
Most old films requiring rectification and reproduction are silent films taken at the rate of q6 per second; these may be "stretched" to 24 frames per second by repeating the exposure of alternate frames of the original in the camera, so that each foot of the original film results in a foot and a half or 24 frames of copy film. Also, the image size is reduced to fit the sound frame aperture of the copy camera.
This brief summary old printers for the reproduction of old and shrunken films has dealt with the problem of printing copies for preservation. It would take a respectably sized volume to go into detail covering all the minutiae which deal with printer design and use, without even touching upon the various physical, chemical, and mechanical treatments which might prove of value in the restoration of the images on old and shrunken film to render it more suitable for reproductive processes.
The committee feels that the adoption of the standards and practices as set forth in this report would give additional insurance against natural losses of wear and tear generally sustained in handling of film as well as losses from deterioration and fire in storage of film. The interest in printers for old film is less wide spread that that found in the other subjects discussed. Nevertheless, since such equipment does have an important application in the ultimate perpetuation of film records, the Committee has submitted it for reference, and invites constructive criticism.
J.G. Bradley, Chairman J.E.Abbott R.Evans T.Ramsae J.I.Crabtree M.E.Gilette V.B.Sease A.S.Dickinson C.L.Gregory W.A.Schmidt
(From the SMPE Journal , December 1940, Volume XXXV, Report of the Committee on Preservation of Film,pp. 599-605)
Reprinted through courtesy of SMPTE. No unauthorized duplication without approval.