Tables 366 and 367 



TABLE 366. — Sensitometric Constants of Type Plates and Films, Definitions 



341 



Ordinates are density (D) ; abscissae, logs 

 of exposure (log E). 



Density (D) is the absorbing power of the 

 silver deposit. 



If F is the luminous flux incident upon 

 the deposit, 



Fi the luminous flux transmitted, 



T, the transmission, O, the opacity, 



D, the density, then 



T = F 1 /Fo; = i/T = Fo/F 1 



D = logic O = logic i/T = log,o F /Fi 



Leg Ei»po3urft(E)ii 



44. 27 3-0 



Typical Characteristic Curves 



Exposure (£) : E=It (expressed in meter-candle seconds, mes), 1 = illumination 

 (meter-candles, mc) incident on the photographic material during exposure, t = exposure 

 time in seconds. 



Speeds given in the following table were obtained with a light approximately equivalent 

 to mean noon sunlight in spectral composition. 



Gamma (7) : Gamma is defined as the tangent of angle alpha (a). 



Gamma infinity (7^): 7^ is defined as a theoretical limiting value to which gamma 

 approaches as the development time is increased. 1 



_ 7i 



7 »~ I - e -Kh 



Velocity Constant of Development (K)- K= — loge — — 



t 72 — 71 



Time of Development for Gamma of Unity (/ 7 =i.o) : A convenient practical specifi- 

 cation of development rate. 



X°g (F) : Fog is the density produced when material is developed without exposure. 

 Values in the table are when development is carried to a gamma of unity. 



Latitude (L) : L = length of the projection (expressed in exposure units) of the 

 straight line portion on the logic E axis, assuming development to a gamma of unity. 



Inertia (f) : ;'z=the value of exposure where the straight line portion of the char- 

 acteristic curve extended cuts the logic E axis. The inertia is in general a function of the 

 extent to which development is carried. Values of i given in the table were determined for 

 a gamma of unity. 



Speed (S): S = ±X*o. 

 1 



In the determination of the values given in Table 368 a developing solution made up 



according to the following formula was used : 



TABLE 367. — Formula for Laboratory Pyrogallol Developer 



Solution A Solution B 



NasSOrs 70 # NaCO:;, anhyd 75 g 



NaHSCfc, 17 KBr 1 



Pyrogallol 20 Water to 1 liter 



Water to 1 liter 



Temperature 20° C. For use, mix equal volumes of A and B. 



1 Sheppard and Mees, Investigations on the theory of the photographic process. London, 

 Longmans, 1907. 



Smithsonian Tables 



