APPENDIX B 



APPROXIMATE RELATIVE VALUES FOR SPECIFYING SPEED OF PHOTO- 

 GRAPHIC MATERIALS 



Note: It is not possible to make exact comparisons between the various systems of rating speeds, 

 and therefore the above table should be considered only as approximations. The data for the above 

 table were obtained from several sources as listed below. In a few of the columns the values were 

 extended in order to have a more complete set of data. 



Recent film speeds published by the Eastman Kodak Co. [see "The Problem of Film Speeds" by 

 Walter Clark, Photo Technique, 1, 12 (1939)] indicate that the Kodak speeds are, numerically, about 

 four or five times the speed as given by the Weston rating. However, the available data are not 

 regarded as being sufficiently complete to warrant listing Kodak film speeds in this tabulation. 



A, C, E, F, H, and J. Jones, L. A., "Photographic Sensitometry." 



B. Compiled by A. T. Williams. 



G. "Wellcome Handbook and Diary" (common fractions have been converted to decimals). 



D and I. Values in columns D and I are representative of the continental ratings, which are always 

 higher than the American ratings. The Scheiner ratings usually are from 3 to 6 units higher than the 

 equivalent American speeds. The values given are from Turner, Brit. J. Phot., July 8, 1938. 



K. "Handbook of Physics and Chemistry," 21st ed. 



L. Turner, Brit. J. Phot., July 8, 1938. 



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