American cinematographer (Feb-Dec 1929)

Thirty-eight American Ci NEMATOGRAPHER September. 1929 TRUEBALL TRIPOD HEADS For follow-up shot* are known for their smoothness of operation, equal tension on all movements and being unaffected by temperature. The Model A is made for Amateur motion picture cameras and also fits the Standard Still tripods. Trueball tripod heads are unexcelled for simplicity, accuracy and speed of operation. Model A The Hoefner four-inch Iris and Sunshade combination is also a superior product. FRED HOEFNER 5319 SANTA MONICA BOULEVARD CLadstone 0243 LOS ANGELES, CALIF. Some Properties of Fixing Baths (Continued from Page 19) (2) The nature and degree of exhaustion of the fixing bath. (3) The temperature of the fixing bath. (4) The degree of agitation of the film. (1) In general, course-grained emulsions fix much more slowly than those composed of finer grains. For example, under any given conditions Eastman motion picture positive film fixes in about one-fifth the time required for Eastman negative motion picture panchromatic film. A thickly coated emulsion obviously fixes more slowly than one of less thickness. (2) The times of fixation for various concentrations of sodium thiosulfate at 55° F., 65° F., and 75° F. for Eastman motion picture positive and negative panchromatic film are shown in Fig. 2. The negative film fixes most rapidly in a 40% solution which corresponds with the results of Piper 10 and Lumiere film, while with Eastman positive motion picture film a 30% solution gives the most rapid fixation. Some workers have contended that the hardening of a gelatin film does not affect the rate of fixation while others maintain that it does. Sheppard and Mees11 found that formalin hardening does not affect the time of fixation and state that in the case of hardened film which does not melt at 212° F. as compared with a film melting at 105° F., the time of fixation is the same in both cases. Experiments by the authors have indicated that although an excessive quantity of the hardener constituents retards fixation, for all practical purposes when using normal hardening baths with motion picture film, the hardener does not materially affect the time of fixation. Strauss12 and Lehmann and Busch" have observed that the accumulation of potassium iodide in a fixing bath used for fixing bromo-iodide emulsions has a considerable retarding effect on the rate of fixation. Experiments by Crabtree and Ross" indicate that the addition of 3 grams per liter of potassium iodide to a 30% hypo solution doubles the time to clear a negative emulsion at 70° F. (3) The effect of temperature on the time of fixation is likewise shown in Fig. 2. With positive motion picture film an increase in temperature from 55° to 75° F. changes the time of fixation from 50 seconds to 30 seconds in a 30% hypo solution, while with negative film the same temperature change alters the time of fixation from 3 to 2 minutes in a 40% hypo solution. For maximum efficiency it is therefore necessary to maintain the temperature of the fixing bath not lower than 65° F. (4) The effect of agitation on the rate of fixation is shown in the following table: TABLE I Hypo Cone. 35 %« 35% 10% No Agitation 1 20 sec. Agitation every 30 Seconds 1 20 sec. Continuous Agitation 105 sec. Brush Treatment 90 sec. Nature of Film Eastman Panchromatic Negative Eastman Motion 3 5 sec. 3 5 sec. 3 0 sec. Picture Positive Eastman motion 150 sec. 1 20 sec. 90 sec. 75 sec. Pictuie Positive ^Crystalline hypo was used. A 35% solution was preoared by dissolving 3 5 grams in water and then adding water to make 100 c.c. of solution. It is seen that with motion picture negative film a very thorough renewal of the fixing bath at the surface of the film by brushing causes the emulsion to clear in 90 seconds at 65° F. as compared with 120 seconds with no agitation in a 35% hypo solution. Conditions of agitation analogous to those produced by brushing rarely exist in practice. With positive motion picture film agitation has little effect under the same conditions although with a 10% hypo solution the time of fixation is cut in half by brush treatment. The rate of agitation produced in the average processing machine corresponds approximately to that produced by hand agitation. V. The Efficiency of Acid Hardening Fixing Baths The practical efficiency of a fixing bath is governed by the following factors: 1 . The absolute times oi fixation when the bath is fresh and when exhausted. In practice with motion picture negative emulsions a fixing bath is considered exhausted when the time required to clear the film is excessive, the limit being usually from 10 to 15 minutes; that is, it is considered better economy to prepare a fresh bath than to waste time waiting longer than 20 to 30 minutes for the film to fix, although at this point the bath is not actually exhausted because an emulsion could be satisfactorily fixed by prolonged treatment. (In practice the rule "time of fixing = twice the time to clear" is usually observed.) 2. The quantity of emulsion fixed during the active life of the bath. The active capacity may be defined as the quantity of film fixed \