Ch. VII] 



PHOTOGRAPHY WITH COLOR SCREENS 



237 



v0.4p 



Fig. 141. 



^0.7 1- 



x0.5m x0.6u 



Normal Spectrum Showing the Sensitiveness of Ortho- 

 chromatic OR ISOCHROMATIC PLATES. 



(After Mees; magnification as in fig. 139). 



These plates have practically the same sensitiveness as the ordinary plates 

 except that the sensitiveness is continued through the green and yellow. 

 (Compare fig. 139, 140 and 142.) 



contrast effects it was necessary to devise means for blocking out 

 special parts of the spectrum (§ 368). These selecting media are 

 known as Color Screens or Ray Filters. 



§ 366. 



Color Screens or Ray Filters 

 Color screens or ray filters. — These are transparent, 



colored bodies which select the wave lengths of light which they 

 transmit and absorb the other waves, or they diminish more or less 

 some of the wave lengths and transmit the others w r ith very slight 

 loss. The color of such a screen to the eye will be determined by the 



^0.6/1 



V07ti 



\0.4/i X0.5n 



Fig. 142. Normal Spectrum Showing the Sensitiveness of Panchro- 

 matic Plates. 



(After Mees; magnification as in fig. 139). 



Panchromatic plates have the maximum sensitiveness still in the violet-blue, 

 but it is extended to include the red. (Compare fig. 139-141). 



light which it transmits in the greatest quantity. For example, if 

 the violet-blue light is absorbed the remaining light will appear 



