TABLES 307-309. 



PHOTOGRAPHIC DATA. 



TABLE 307. Numerical Constants Characteristic of Photographic Plates. 



263 



Abscissae of figure are log E = leg // (meter- 

 candles-seconds); 



Ordinates are densities, D = i/T ; 



E exposure = / (illumination in meter-can- 

 dles) X t seconds; 



D, the density of deposit = i/T, where T is the 

 ratio of the transmitted to incident intensity on de- 

 veloped plate. 



* = inertia = intercept straight line portion of 

 curve on log E axis. 



S = speed = (some constant)/ i; y gamma = 

 tangent of angle a. 



L = latitude = projected straight line portion of 

 characteristic curve on log E axis, expressed in ex- 

 posure units = Anti log (b a). 



The curve illustrates the characteristic curve of a 

 photographic plate. 



TYPICAL CHARACTERISTIC CURVE otf PHOTOGRAPHIC PLATE. 



TABLE 308. Relative Speeds of Photographic Materials. 



The approximate exposure may be obtained when the intensity of the image on the plate is known. Let L be the 

 intensity in meter-candles; E, the exposure in seconds; P, the speed number from the following table; then E = 

 i,35o,ooo/(L X P) approximately. 



TABLE 309. Variation of Resolving Power with Plate and Developer. 



The resolving power is expressed as the number of lines per millimeter which is just resolvable, the lines being 

 opaque and separated by spaces of the same width. The developer used for the comparison of plates was Pyro-soda; 

 the plate for the comparison of developers, Seed Lantern. The numbers are all in the same units. Huse, J. Opt. Soc. 

 America, July, 1917. 



SMITHSONIAN TABLES. 



