CH. VIII} 



PHO TO- MICROGRAPHY 



217 



Fig. 182. Bull's eye lens and. holder. {Bausch & Lomb Opt. Co.) 

 COLOR-CORRECT PHOTOGRAPHY 



From the fact that the different wave lengths of light affect the photographic 

 plate with different degrees of vigor, the ordinary photographic print of a many 

 colored object or landscape is not satisfactory. All objects whose light is of short 

 wave lengths, as blue, etc., will appear too light and those which are red, yellow 

 and green will be too dark relatively. To obviate this difficulty two methods have 

 been adopted, and for the most complete success they must be combined. 



( A) The use of ortho- or iso- chromatic plates and (B) the use of a color screen 

 or light filter. 



i 355- Orthochromatic or Isochromatic Plates. — These are plates which have 

 been rendered much more sensitive than ordinary plates to the long waves of red, 

 orange, yellow and green, they therefore give a much more natural rendering to 

 many-colored objects than ordinary plates. As they are sensitive to red, orange, 

 etc. , one must be very careful in exposing them in the dark room even to the light of 

 the developing lantern. The more nearly the plate can be kept from all light, 

 except that acting during the exposure in the camera, the more satisfactory will 

 be the resulting negative. 



These color-correct plates are not very enduring, and must be used while they 

 are fresh, or only weak, foggy negatives will result. 



