236 



PHOTOGRAPHY WITH COLOR SCREENS 



[CH. VII 



FIG. 139. SENSITIVENESS OF THE EYE TO THE SPECTRUM WITH MODERATE 



ILLUMINATION. 



(Base Line = Wave lengths x 250,000 times). 



As shown in this curve the normal human eye with moderate illumination 

 has its maximum sensitiveness at about wave length Xo.55/i, that is, in the 

 green next the yellow. With very brilliant light the greatest sensitiveness is 

 in the yellow, while with dim light it moves along well into the green. (See 

 406 for designation of wave lengths in microns, etc.). 



Ultra-violet Short radiation invisible to the eye. Compare the sensitive- 

 ness of the photographic plate to this radiation (fig. 140-142). 



Violet-blue Radiation at the blue end of the spectrum. 



Green Radiation in the middle of the spectrum. 



Red Radiation at the red end of the spectrum. 



Infra-red Long radiation invisible to the eye. 



G Y Borderland between green and yellow. 



B G Borderland between blue and green. 



(2) But as all of these color-sensitive plates are more sensitive to the 

 violet-blue than to the other colors, it is necessary to use some means 



Green 



I 

 |GY| 



Red 



X0.7, 



X0.4/* xo.5/i XQ.6/1 



FIG. 140. NORMAL SPECTRUM SHOWING THE SENSITIVENESS OF ^ORDINARY 

 PHOTOGRAPHIC PLATES. 



(After Mees, and magnified as in fig. 139). 



As shown in this curve, the ordinary photographic plate is sensitive only 

 in the blue end of the spectrum including the ultra-violet, the maximum 

 sensitiveness being at about wave length \o.4$[j.. It is insensitive to all wave 

 lengths longer than about Xo.52/i. (Compare with fig. 139, 141-142). 



for reducing or blocking out part of the violet-blue light without 

 interfering with the action of the other colors ( 367). For gaining 



