698 HANDBOOK OF PHOTOGRAPHY 



The primary control instruments of laboratory processing are the sensitometer and 

 the densitometer, which are described elsewhere in this volume. The usual form of 

 sensitometer available in motion-picture laboratories operates on the time-scale prin- 

 ciple and utilizes a calibrated light source to impress on a strip of film a graduated 

 series of exposures, in exposure times multiplied successively by ^2 (1.414), so that 

 21 steps will produce an over-all range of exposures of 1024 to 1. The density of the 

 sections of such a record may be determined in two ways: (1) on a direct-reading 

 densitometer of the optical comparison type, in which a single source furnishes light 

 for the area under measurement and the comparison beam ; or (2) on an electric densi- 

 tometer, in which a modulated light source excites a constant type of photocell feeding 

 a constant-gain amplifier which actuates an indicating instrument of the rectifier type 

 through a calibrated attenuator. In this case the attenuator setting required to give 

 a reference reading is a measure of the density. Both types of densitometer in their 

 conventional forms read diffuse density in the range to 3. 



The reader is assumed to be familiar with the theory of H and D and time-gamma 

 curves. The distinction between gamma and contrast, however, may well be reiter- 

 ated in this section. Gamma affects contrast but is not its sole determinant. Con- 

 trast depends on the range of light intensities in the scene, as well as on 

 gamma regarded as a function of the emulsion, the developing solution, and the time 

 of development. Contrast therefore is the broader term; it has to do with a photo- 

 graphic result, a mingling of high lights and shadows affecting the eye. Picture nega- 

 tives of the same scene on the same material, developed to the same gamma, will still 

 show varying contrast if the conditions of illumination under which they were exposed 

 were different. It follows that a sensitometric strip merely gives information on the 

 degree of development, the gamma, and not on the contrast of variously exposed 

 negatives going through the same bath in the same time. 



There are two methods of motion-picture laboratory operation in common use, 

 known respectively as the " time-and-temperature " or "constant-time" system, and 

 the "test" system. The time-and-temperature system is based on the maintenance 

 of a constant laboratory condition to which the cameraman is expected to adjust his 

 exposures. The chemical formula of the solution, the temperature, the time of devel- 

 opment, the turbulency, and consequently the gamma are assumed to be fixed within 

 permissible limits of tolerance. The cameraman relies on his negative going through 

 the same bath each day at the same footage speed; consequently the only variations 

 in the product should be those which he purposely aims for in lighting and exposure. 

 The method is essentially a scientific one, based on the same premises as other applica- 

 tions of technology in mass production, and it offers similar advantages of impersonal 

 operation, standardized procedure, and rationalization. At the same time it should 

 not interfere with any artistry of which the cameraman is capable, since he is free to 

 move the camera, to shoot from any angle with any filters and lenses he may choose, 

 and to dispose his lights as he sees fit. 



The test system, as the name implies, involves the exposure of test strips 5 to 15 ft. 

 in length at the end of each scene, all conditions remaining the same as during the 

 takes. These test strips are furnished to the laboratory and developed in 2- or 3-ft. 

 sections at the time which has been found to give the desired results for the run of 

 normally exposed negative. A visual inspection is made of each developed strip by a 

 timer or supervisor. If the strip is correctly developed the takes go through at the 

 normal footage speed. If it appears that a higher or lower speed would be desirable, 

 or, in the case of seriously xmder- or overexposed negative, necessary, appropriate 

 adjustments are made. What usually happens is that the bulk of the day's footage 

 goes through at the normal speed, but a few scenes may deviate, sometimes by several 

 minutes' development more or less. 



