PHOTOGRAPHY BY POLARIZED LIGHT 



By J. W. McFarlane 



[With 6 plates] 



We are blind to some of the most beautiful phenomena in the 

 domain of light. Our eyes respond naturally to differences in color 

 and in intensity of light, and it is by these differences that we are 

 able to see the world around us. There is another property in which 

 light rays may differ, but our eyes, unaided, cannot see those differ- 

 ences. This property is called jDolarization, and is concerned with 

 the manner in which the Ught ray vibrates. Were we able to see 

 unaided these differences in polarization, we would be conscious of 

 a dark wide band across the sky, normally invisible. We would also 

 see oblique reflections darken, and we would see beautiful color 

 effects in some common transparent materials. 



WHAT IS POLARIZED LIGHT? 



While the nature of light is not entirely understood, many of its 

 effects can be explained by assuming that light is a vibratory motion 

 which goes through space in the form of waves. Among these 

 effects is the polarization of hght. The vibration of a light wave is 

 not along the direction of the ray, as in the case of sound, but is at 

 right angles to the ray and usually in all possible directions, that is, 

 up and down, sideways, etc. It is possible (by various devices 

 generally known as polarizers) to change the light ray so that only 

 one direction of vibration is left. The ray is then said to be polarized, 

 or strictly spealdng, plane-polarized. 



A number of polarizing devices have been known to scientific 

 workers for many years, but they have involved the use of prisms 

 having a very small field and imsuited to photography. The inven- 

 tion which makes the Pola-screen possible is a polarizing substance 

 in sheet form containing countless minute, rodlike crystals which 

 are parallel to each other. The Eastman Pola-screen type I incorpo- 

 rates this sheet material cemented between glass plates. 



The vibration plane of the polarizer is parallel to the vibration of 

 the emerging rays. In the Pola-screen, the direction of the vibration 



' Reprinted by permission from the American Annual of Photography, 1937. 



31508—38 16 225 



