PHOTOGRAPHY BY POLARIZED LIGHT— McFARLANE 



231 



subject by diffusely reflected light. This fact, which is extremely 

 important, permits many applications. The use of Pola-screens in 

 front of the lights, illuminates the subject with polarized light. 

 Another such device at the camera lens permits photographing by 

 diffusely reflected light alone. This is desirable in many cases, be- 

 cause the specularly reflected light obscures more or less the detail 

 which it is desired to record. If the Pola-screen at the camera is 

 rotated, some of the specular light is allowed through, so that the 

 amount of reflections permitted is under the control of the photog- 

 rapher. When the camera Pola-screen is rotated so that its vibration 

 plane is actually parallel to that of the specular ray, the ray is trans- 

 mitted even more freely than is the diffuse ray, so that the subject 



LIGHT DirrOSELY RETLtCTED 



LIGHT SPCCOLAR.LY " 



CAMERA. 



Figure 4.— Photography by diffusely reflected light, using Eastman Pola-screens. Light reflected speeu- 

 larly retains its polarized form; it may therefore be cut out by a Pola-screen at the camera. I indicates a 

 Pola-screen, type I; II indicates a large Pola-screen, type II. The indexes on the two Pola-screens show 

 their planes of vibration. 



appears to have even brighter reflections and more glass than it 

 actually does have. The most important point about reflection 

 control with Pola-screens at both lens and lights is the freedom in 

 photographing-angle. The use of a Pola-screen at the lens alone 

 restricts the reflection control to surfaces oblique to the camera axis, 

 but the technique just described imposes no such restriction. 



Possibly the most valuable application of this technique is in copy- 

 ing photographs and other subjects whose surfaces up to now have 

 been considered unsuitable for photographing. Much of the light 

 reflected from the blacks of a matte or rough-surfaced photograph, 

 for instance, is specularly reflected, and, therefore, can be cut down 

 by the Pola-screen technique, resulting in a much deeper black, as 

 shown in plate 6. Such photographs, when viewed or copied by polar- 

 ized light, are startling in their changes. The surface texture, which 



