American cinematographer (Feb-Dec 1929)

September, 1929 AMERICAN Cl NEMATOGRAPHER Thirty-nine A. S. C. Resourcefulness Here we see another useful article devised by an A. S. C. member. Frank M. Cotner is seen in his automobile, on the running board of which he has fstened a special "auto tripod" for his camera. The picture explains everything and tells its own story without verbal description. Cotner says the device has proven itself very useful in chase shots. up to the point when the time required to clear the emulsion is greater than a definite limit. This varies according to the particular emulsion to be fixed, the active capacity being much less in the case of slow fixing emulsions than in the case of rapid fixing emulsions which are usually more fine grained. 3. The staining limit of the bath. That is. the quantity of emulsion fixed before the bath stains the film with average manipulation. Staining in a fixing bath may be a result of (a) insufficient fixation or (b) lack of agitation especially in the presence of free developer. If the film is insufficiently fixed any residual silver thiosulfate ultimately decomposes producing a brown stain. Also, if the bath becomes alkaline because of developer carried into it by films, the free developer reduces the silver thiosulfate in the film to finely divided metallic silver in situ causing dichroic fog.2 4. The cost of fixing bath. Although with negative motion picture film a 40% solution of ,eiss lessar^ No camera can be Letter tnan its lens. Alt Carl Zeiss Tessars ensure perfect definition and brilliancy/ even at full aperture,, and results will not be impaired by flare. Tkese are only a few reasons wny Carl Zeiss Tessar Lenses have universal endorsement CARL ZEISS, INCORPORATED 435 Fifth A vevNew York 728So. Hill Stv Los An8eles hypo gives the most rapid fixation as compared with 30% solution for positive motion picture film, the question arises as to whether the extra cost of the more concentrated solution is justifiable by the slightly shorter time of fixation. For average use, a 25% solution of hypo is satisfactory for fixing both positive and negative motion picture film though if time is the most valuable consideration a 40% solution for negative film is desirable. (To be Continued) REFERENCES 1. A Non-turbid Fixing Bath containing Alum by A. Lainer. Phot. Korr. 26: 311 (1899). 2. Stains on Negatives and Prints by J. I. Crabtree. Amer. Ann. Phot. 25: 204 (1921): B. J. Phot. 68: 294 (1921). 3. Chemistry of the Acid Fixing and Hardening Bath by S. E. Sheppard and A. Ballard. J. Frank. Inst. 200: 537 ( 1925). 4. The Development of Motion Picture Film by the Rack and Reel Systems by J. I. Crabtree. Trans. Soc. Mot. Pict. Eng. 1 6: 163 ( 1923). 5. Rapid Fixing Baths by E. J. Wall. Amer. Phot. 366 ( 1923 ). 6. Chemistry of the Acid Fixing Bath by S. E. Sheppard, F. A. Elliott, and S. S. Sweet. J. Frank Inst. 196: 45 ( 1923). 7. High Temperature Development of Film and Paper by J. I. Crabtree. B. J. Phot. 64: 555 ( 19 1 7). 8. On Convection Effects in Photographic Bathing Operations by E. R. Bullock. B. J. Phot. 69: 110 (1922): Amer. Phot. 16: 162 (1922). 9. The Fixation of Photographic Plates by A. Lumiere and A. Seyewetz. Bull, soc. franc, phot. 1 1: 66 ( 1924). 10. The Time of Fixation by C. Wclborne Piper. B. J. Phot. 60: 59 ( 19 13). 11. Investigations, on the Theory of the Photographic Process ( 1907) p. 123. Longmans Green W Co., London. 12. The Fixing Bath and Time of Fixation by P. Strauss. Phot. ind. 911 (1925). 13. Fixing Baths and their Best Utilization by E. Lchmann and L. Busch. Kinotech. Jahrbuch 1 14 ( 1925-1 926). 14. The Recovery of Silver from Exhausted Fixing Baths by J. I. Crabtree and J. F. Ross. Amer. Ann. Phot. 14 (1927).