American cinematographer (Jan-Dec 1926)

June. 1926 AMERICAN CINEM ATOGR APHER Twenty -five . power, that it is no more soluble in hydroquinone or pyro developers, and that the persistency of the stain is about the same. As is indicated by its absorption spectra, Fig. 3, its stain has a greater tendency to retard printing than phenosafranine stain, but in the amount present in an ordinary fixed and washed negative such an effect is inappreciable. 7. durantia. Aurantia has been recommended by Lumiere and Seyewetz,s especially for use with Autochrome plates. Its desensitizing power is far less than that of phenosafranine, it stains badly, and washes out slowly. Unlike most other desensitizers it can be added to a concentration as much as 1-500 without precipitating and for this reason may have some use in special cases. 8. Miscellaneous Dyes. A large number of dyes are known15* in' 20 which desensitize photographic emulsions but which are not practically useful because they produce some undesirable effect such as fog, stain, destruction of the latent image, or retardation of development. Notable among such substances is methylene blue which is a more powerful desensitizer than pinakryptol green, but which fogs-1 very badly. It has been stated 15 that methylene blue can be used in connection with another dye such as acoridine yellow which retards the fogging action and still permits desensitizing. Other combinations suggested are rholuline blue or rholuline violet with acridine yellow. The methylene blue-acridine yellow mixture was tested and found to desensitize well without serious fog when carefully used. However, it has no advantage over other common desensitizers, as Luppo-Cramer7 has also shown, and a mixture is certainly less desirable than a homogeneous substance. Pinakryptol green was selected for studying the limits of safety in the use of a typical desensitizer because it appeared to be the most satisfactory in all respects of any desensitizer available at the time of this investigation. . IV. Methods Used for Testing Desensitizing Action 1. Tablet Exposures. A step tablet was prepared which had 25 steps covering a density range from 0.14 to 3.40. Over this were placed narrow strips of the dyed gelatin filters corresponding to the Wratten safelights Series 00, 0, 1,2, and 3. The strip on which white light measurements were made was covered with a neutral density of 2.30 in order to bring the exposure within the same range as those through the safelight filters. Tests were made by soaking a strip of film in the solution to be tested, removing excess liquid by drawing it quickly across a piece of chamois stretched over a bottle, and exposing while wet through the tablet. Exposures were made in a cabinet lined with black cloth 50 cm. from a 200 W. tungsten lamp which had a candle power of 176 as used. Exposures for desensitized film were 5 minutes and for untreated film 10 seconds. The strips were developed for 10 minutes in an elon-hydroquinone tank developer- (NQ-80 tank), fixed, and washed. From the last visible step on each strip relative exposure values necessary to produce a visible density were calculated. Comparison with the value for untreated film showed the relative sensitiveness for each treatment. With one exposure through the tablet, values could be obtained for white light and for each of the safelights mentioned CLASSIFIED ADVERTISING Rates: Four cents a word. Minimum charge one dollar per insertion. All copy must be prepaid and must reach us before the 15th of the month preceding publication. CLASSIFIED ADVERTISING American Cinematographer, 1222 Guaranty Building, Hollywood, California WANTED: MOTION 1'KTIRK CAMERA AKELEV Camera Outfit. State price anil equipment. Len H. Roos. Bank of New South Wales. George Street. Sydney, Australia. X. S. W. FOR SAJLE: LENSES ONE three-inch Dahlmeyer P.l:9, mounted for Mitchell; one two-inch Bauach & l.omb F.2:7: one Dahlmeyer Pentac 37 mm. F. 2:9. George Benoit. 845 Crescent Heights Blvd.. Hollywood, Calif. FOR RENT: CAMERAS BELL, & HOWELL. Victor M'lner, 2221 Observatory Ave.. Los Angeles, California. 500-044. MITCHELL, and Bell ,<• Howell Cameras. F.2:3; F.2:7; F.3:5 Lenses — 4 0-5 0-75 mm. Complete equipment. J. R. Lockwood, 523 North Orange St., Glendale. California. GLendale 3 3 6 1 W. E. BURTON STEENE. Bell & Howell, and Akeley. Complete Camera Equipment. Latest models. Address American Society of Cinematographers, Hollywrood, Calif. BELL & HOWELL. Frank M. Cotner, 6273 Selma Ave., Hollywood, California. Hollywood 504G. above. By this method the measurements were made on an intensity scale instead of a time scale. The values obtained were subject to an error at least equal to the difference in exposure represented by one step on the tablet, which would be about 50</t • Considering the enormous range in sensitivity covered, a difference of 100% would not be serious, however, as this would only mean that a film might have, for example, either 0.1% or 0.2% of its original speed. For practical use a margin of safety much greater than this should be allowed. 2. Direct Exposure to Safelights. In order to relate the results of the tablet exposure to practical darkroom conditions, the time required to fog desensitized film when exposed directly to the safelights was determined. Strips of film 10 cm. x 25 cm. (4"xl0") were dipped by stages into a desensitizing bath so that the different areas were in the solution 5, 3, 2, 1, and J/2 minutes with an untreated portion left on the end. The strip was then wiped with a chamois, placed under the safelight to be tested, and an opaque slide moved across it in such a way that each of the above areas were exposed 1 S. A. and L. Lumiere and A. Seyewetz. "Experiments on Desensitizers," B. J. Phot. 6S, 351 and 370. (1921). 19. E. Stenger and Hans Stammreich, "Contribution to the Knowledge of Desensitizing Silver Bromide-Gelatin Emulsion." Zeit. wiss. Phot. 23, 11, (1924). 20. J. G. F. Druce. "Notes on the Action of Desensitizers In Photographic Development." Science News. Nov. 1924. p. 2. 21. .1. Eggert and J Reitstotter, "The Photographic Effect of Methylene Blue as an Adsorption Effect," Kolloid Zeit. 36, 298, (1925). 22. J. I. Crabtree, 'The Development of Motion Picture Film by the Reel and Tank System," Trans. Soc. M. P. Eng. 16, 163, (1923).