630 HANDBOOK OF PHOTOGRAPHY 



Table II. — Measurements on Color-separation Negatives 



1 The meaning of this factor will be explained later. 



attention, however, must be paid to the nieasureiiient of exactlj' the same spot in the 

 three negatives. 



To illustrate the use of this information the portrait of a young woman will be 

 chosen as subject. The densitometric measurements are given in Table II. Here 

 the transmission values of the No. 1 step in the three negatives are 5, 6.3, and 4.1 per 

 cent, respectively. Taking the ratio of the magenta and yellow with respect to the 

 blue-green, it is found that the magenta bromide should receive 0.8 and the yellow 

 1.22 times the exposure of the blue-green. 



The correct exposure of the blue-green is found empiricallj', and it depends obvi- 

 ously on the type of enlarger and on the intensity' of its light source. It depends also 

 on the aperture of the lens diaphragm and the degree of enlargement. 



With an enlarger having a diffused light source, a scale of magnification will be 

 found very valuable. 



A verj' valuable adjunct to the darkroom is the Kodak enlargement exposure 

 calculator (correct onlj- for enlargers having a diffused light source). ^ 



With the above equipment it is solely necessary to determine once and for all the 

 exposure necessary to produce the faintest silver deposit on the blue-green bromide, 

 which corresponds to the maximum density of the red-filter negative. The informa- 

 tion thus obtained can be jotted down and kept for future information. For instance: 



Red-filter negative maximum density, 1.3; transmission, 5 per cent; exposure, 12 sec, 

 //8; magnification, 3X; Paper, Illingworth normal; development, IV^ min. in Amidol. 



The printing time of another set of color-separation negatives of which the red- 

 filter negative has a maximum density of .say 1.6 (transmission 2.52 per cent) can be 



' This calculator is based on the forniula: 



K(m + 1)2 = £r 



where E is the resulting exposure, 



m is the scale of magnification or reduction, 

 K is a eoiisant determined for m = 1 . 



