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HANDBOOK OF PHOTOGRAPHY 



gives the reflection factors as a function of wavelength for several polished materials 

 from which reflectors are constructed. The figures in this table represent the fraction 

 of incident light which is reflected with unity as the ideal limiting figure. It is desir- 

 able that the reflection factors for a given material be as near unity as possible and 

 that they do not vary with wavelength. The nearer the reflection factor approaches 

 unity, the more efficient is the reflector. Constancy of reflection factor throughout a 

 wide range of wavelengths is desirable in order that selective reflection may be avoided 

 and so that reflected beam has the same spectral distribution ("color") as the light 

 incident upon its surface. 



Table X gives the reflection characteristics of several materials suitable for use as 

 diffuse reflectors. Included in this table for purposes of comparison are the character- 

 istics of black velvet (frequently used as an excellent light-absorbing medium) and 

 black carbon in oil. 



The effectiveness of commercially available reflectors for photographic purposes 

 depends greatly upon their shape and the materials out of which they are constructed. 

 As a rough approximation, however, it may be said that with conical reflectors made 

 of white paper, the exposure need be only one-half of that required when no reflector is 



Table X. — Reflection Coefficients 



Substance 



Magnesium oxide 



Paper, white bond 



Paper, white blotting. . 

 Paper, newsprint stock. 

 White porcelain enamel 



Black carbon in oil 



Black velvet 



0.97 



0.64 

 0.38 

 0.77 

 0.003 



Wavelength, m/t 



500 600 



0.98 



0.72 

 0.61 

 0.73 

 0.003 



0.98 



0.75 



0.79 



0.63 



0.72 



0.003 



0.0175 



0.98 



0.70 

 0.78 

 0.70 

 0.003 



