US2220882A - Film treatment - Google Patents

Description

Nov. 12, 1940. c, D, BEN-gas 2,220,882

FILM TREATMENT Filed May 5, 1959 Patented Nov. 12,1940 it rmu rnmrnmu'r Charles D. Bennes, Los Angclca, Cali!., assignor to Technicolor Motion. Picture Corporation, Los Angcles, CaliL, a corporation of Maine Application May 5, 1939, Serial No. 271,945

3 Claims. (01. 956) In the art of photography it is often desirable to increase the eifective speed of photographic emulsions as much as possible, particularly in color photography where the exposure light must 5 be divided between a plurality of films or layers vof emulsion and/or some of the exposure light is lost by absorption. To this end the present invention comprises a method of increasing the effective speed far beyond the inherent speed of 10 the emulsion, however fast the emulsion may be as aresult of original compoundingor subsequent hypersensitizatlon. Objects of the invention are to providesuch a method which is applicable after the film has 15 been exposed to form latent images therein;

which'is applicable to film responsive to all or part of the visible range to which photographic.

emulsions may be sensitized, which can be applied quickly and cheaply, in which the tendency 2 to produce oblectional fog is slight and readily controlled, which can be readily and accurately controlled to regulate the degree of increase of efiective speed, which can therefore be used to control the color balance between the difi'erent 25 color component records of pictures in natural.

35 treating the film of photographic emulsion comprises exposing the film to form a latent image and subsequently developing the latent image, characterized in that the latent image, before 7 being developed, is intensified by flashing the 40 film with infra-red radiation. Evidently the infra-red radiation acts upon the silver halide of the latent image to render it-more readily reducible, so that a. developed image of predetermined density can be obtained with a lesser ex- 45 posure than is possible without the infra-red flashing.

For the purpose of illustration a suitable way of applying the infra-red treatment to cinemato-, graphic film is shown in the accompanying draw- 50 ing in which Fig. 1 is a front elevation of a flashing machine; and

Fig. 2 is a section on line 22 of Fig. 1. a The particular ma chine chosen for the purpose 5 of illustration comprises a frame I, a lamp house 2, a feed-reel I, a take up reel 4 and a drum 5 over which film is fed from the feed-reel to the take-up reel. In the bottom of the lamp housing an opening 6 is provided in line with the periphery of the drum 5 so that rays from the lamp 5 I may radiate to the film passing over the drum 5. Mounted in the opening 6 is a filter 8 which transmits infra-red rays but absorbs substantially all of the visible light. The filter 8-is preferably a Corning No. 254 infra-red filter. By making the housing 2 light-tight the machine may be operated in a dark room without enclosing the film. To ventilate the housing 2 a fan 9 draws air into the housing through light-bailied openings 10 at the sides of the housing and forces it out through a light-bellied opening I I.

The drum 5 is driven at constant speed through shaft l2 leading to a source of power (not shown), the periphery of the drum preferably being covered with rubber to prevent slipping of. the film. The feed-reel 3 is prevented from overrunning by the usual brake (not shown) and take-up reel 4 is driven by shaft l3 somewhat faster than the drum 5 through the usual friction clutch so as to take up the film as rapidly as it is delivered by the drum 5. With a 1000 watt Mazda lamp .of the concentrated filament type about 8" from the film, a light opening about 3 long, and a Corning No. 254 filter approximately 1 mm. thick, high-speed negative film may be run as fast as 130' per minute with excellent results, which results in an exposure of somewhat more than 6 second. g

The aforesaid Corning filter No. 2'54, which is the best filter readily available, transmits a slight 5 amount of red light which would produce objectionable fog if the exposure is too long. Thus the maximum flashing exposure may readily be determined by gradually increasing the exposure until the fogging effect becomes objectionable. By increasing the thickness of the filter, the proportion of red transmission may be reduced because the transmission for red light falls off faster with increasing thickness than that for infra-red radiation. By wholly eliminating the red component the magnitude of the flashing exposure maybe further increased, still further to increase the efiective speed of the film. The slight decrease in contrast of the developed plcture may ii desired be' counteracted by a slight so increase in development time. ,1

While some increase in effective speed may be obtained by flashing with visible light,"infra-- red radiation is far superior in many ways. It not Only increases the effective speed to a higher order of magnitude than visible light but it has less tendency to fog any film except the few special films which are sensitive to infra-red radiation. It is superior in that the contrast of the resulting picture is affected far less; flashing with visible light decreases the slope of the H 8! D curve to a marked extent. It is also superior in that it penetrates emulsions better than visible light so that the effect is more uniform throughout the depth of the emulsion. In comparison with visible light the efi'ect of infra-red radiation is relatively independent of the color sensitivity of the film, so that approximately the same eifect may be obtained with the same treatment in treating film having difi'erent color sensitivity. This is particularly important in treating sets of color-separation film of different color sensitivity, such as three negatives predominantly sensitive to red, green and blue respectively. Where the color-selective emulsions are all carried by the same support, either in superposed layers or intermingled, this advantage is even more important, particularly where all emulsions are to be afiected in approximately the same degree.

Furthermore, the infra-red treatment herein described is not to be confused with so-called incubation; that is a small elevation of temperature for long periods of time. The treatment herein described and claimed is not only much more effectiye than incubation but can be applied in a fraction of a second instead of requiring hours or even days. Incubation is also inferior in that it shrinks the film, which is particularly serious in color-cinematographic processes where shrinkage interferes with the registration of the diiIerent color components of the pictures.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

-I claim:

1, In forming a picture in a film of photographic emulsion, the method which comprises forming a latent image in the film by exposure to visible light, flashing the film with infra-red radiation, and developing the latent image.

2. In forming a picture in a film of silverhalide emulsion which is substantially insensitive to infra-red radiation, the method which comprises forming a latent image in the film by exposure to visible light, rendering the exposed silver-halide particles more easily reducible by flashing the latent image with infra-red radiation, and then reducing the exposed silver halide to form a picture.

3. In forming pictures in a cinematographic film of photographic emulsion, the method which comprises forming latent images. in the film by exposure to visible light, continuously feeding the film past a source of infra-red radiation to intensify the latent images by flashing with infra-red radiation, and developing the latent image. I

CHARLES D. BENNES.

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