1918 ' Ovebton and Barpee, Bird Photography. 75 



variegated detail. But an autochrome may he used as a lantern 

 slide, and herein lies its greatest field of usefulness. It is more 

 dense than an ordinary slide, hut a good lantern will project an 

 autochrome photograph upon the screen with nearly all the bril- 

 liancy that the plate exhibits when held in the hand and looked 

 through by daylight. The colors will he slightly affected by the 

 color of the light in the lantern, hut not to a greater degree than the 

 colors of a painting are affected when seen in an artificial light. 



An autochrome plate differs from an ordinary photographic plate 

 chiefly in that a single layer of transparent, microscopical starch 

 grains, dyed orange-red, green, and violet, and mixed in even pro- 

 portion, is interposed between the glass and the sensitive coating 

 or film. This coating is extremely thin, and is made of a panchro- 

 matic emulsion. The plate is exposed in the camera with the glass 

 side toward the lens, so that the rays of light must pass through the 

 colored starch grains before reaching the emulsion. Each starch 

 grain is about gffljQ of an inch in diameter. An autochrome thus 

 bears some resemblance to a half-tone plate, but the dots upon it 

 are only about one fifth as large as the smallest dots upon the 

 best half-tone plate. The density of the plate is due to the fact 

 that the starch grains intercept a considerable amount of light. 



Any plate camera may be used in taking an autochrome, and a 

 special yellow screen, fitted to the lens, is the only extra piece of 

 apparatus needed. If a screen is not used, the photograph will 

 show a dominant purplish tone, owing to the excessive actinism of 

 the violet and blue rays of ordinary light. 



The main difficulty of autochrome photography lies in the length 

 of exposure required, which is 100 times as long as is necessary for 

 an ordinary plate. This is owing to the absorption of light rays 

 by the color screen and by the colored starch grains. An auto- 

 chrome of a wild bird is taken in the same way that an ordinary 

 negative would be made of the same bird, except that the exposure 

 is greatly prolonged. The fastest time in which we have taken a 

 bird autochrome is one quarter of a second, which would corre- 

 spond to 2rgi5 of a second with an ordinary plate. On the other 

 hand, a brooding Blue Jay in a dark thicket has posed for as long as 

 tun minutes. 



The development <>l an autochrome is not especially difficult, 



