Shrinkage of photographic film is extremely complex. Several different 

 processes are going on at once, and each is affected in a different manner by 

 heat and moisture, and other factors. It is not always easy to predict how a 

 given film will react when subjected to unknown conditions of storage and 

 handling. 



Recommendations 



Film choice . 



The film which shows the least amount of processing and storage 

 change should be used. This, at present, is the Type A .cellulose acetate 

 butyrate base. When it becomes available for aerial film, Du Pont "Cronar" 

 should show some improvement over other bases. 



The two rolls intended for stereophotography should be chosen from 

 the Seune emulsion lot. 



Making the photographs 



Dimensional errors in aerial negatives caused by humidity or 

 thermal expansion may be reduced by printing (or measuring the negatives) 

 in an air conditioned laboratory, preferably at about 70°F, and 50 percent 

 relative humidity, and by thermostating the cameras at the sanne tennpera- 

 ture. Ideally, the negative should be in equilibrium with air of the same tem- 

 perature and relative humidity at the time of printing or measurement as at 

 the instant of exposure. Film is in equilibrium with air at approximately 

 55-60 percent relative humidity when packed in air-tight (taped) cans, and will 

 change very little in the camera if exposures are made in rapid succession; 

 however, temperature changes inside the camera cannot be prevented except 

 by some method of automatically controlled heating. Completely air-con- 

 ditioned cameras, which provide both temperature and relative humidity con- 

 trol, have been used quite successfully, in the recent past. Dimensional 

 errors have been reduced considerably by this method, as well as markings 

 by static electricity. 



Processing 



Film should be processed at normal temperatures ~ 68-70°F. It 

 should be subjected to as little tension as possible, especially while wet, and 

 should be dried at a relative humidity of about 50 percent, and temperature 

 not in excess of 85°F. 



Handling 



Film should be handled gently, and, insofar as possible, both rolls 

 intended for stereo photography should receive identical treatment. 



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