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HANDBOOK OF PHOTOGRAPHY 



plane-polarized light (from flooring, windows, etc.) causing undesirable glare or 

 reflections. Although the use of polarizing plates in front of the camera lens is often 

 effective in reducing some undesirable reflections, it is most effective for glare and 

 reflections within a fairly narrow angle around 35° from the central axis of the camera. 

 It is not a cure-all for all reflection and glare troubles. 



The commercially available polarizing disks give an appearance of being a fairh^ 

 dark-gray color. These disks cut down the amount of light being transmitted through 

 them. For this reason the exposure time must be increased when these disks are used. 

 The exposure will probably be two to five times that required when no polarizing 

 filter is used, although the factor provided by the manufacturer of such devices should 

 be used in determining the increase in exposure. 





K 



K 



rx 



X 



* — #- 





fx 



N 



Fig. 7. — Unpolarized light, coming from the extreme left, is polarized to vibrate in a 

 vertical plane after passing through the first polarizing plate. When the polarizing axis 

 of the second plate is rotated with respect to that of the first, more or less light is permitted 

 to pass. When the axes of the two plates are at right angles, no light passes through the 

 second plate. 



With cameras having ground-glass screens, the polarizing filter is placed over the 

 lens and rotated about its own axis until the desired effect is obtained. In the case 

 of reflex cameras having a taking as well as a viewing lens, the effect of the polarizing 

 filter can be seen bj^ placing this on the viewing lens, and rotating until the proper 

 effect is obtained. The polarizing filter is then transferred to the taking lens without 

 changing its angular rotation, and the exposure is made in the usual way, except for 

 increase in exposure. For cameras having an eye-level or reflecting type of view 

 finder, the lens can be held up to the eye and rotated about its own axis until the 

 desired reflections are reduced to a minimum. The filter is then placed over the lens, 

 without rotating it, and the exposure made. Polarizing filters for photographic use 

 are provided with marks indicating the direction in which the crystals of the polarizing 

 material are aUgned; the relative position of these marks may be used to indicate 

 whether the polarizing filter has been turned or not. For those cameras in which 

 focusing is accomplished by rotating the front lens component, the focusing must 

 obviously be completed before the polarizing filter is attached to the lens. Depending 



