HUNTINGTON] 



LANDSCAPE NATURE, II 



197 



chromatic," and by other trade names. These plates, however, 

 are not equally sensitive to the different primary colors, but are 

 most sensitive to the violets and the blues. A given "ray filter" 

 absorbs definite amounts of these two colors, but transmits the 

 full amount of yellow, orange and red that strike it, and greens, 

 yellows and orange appear in the photograph as grays of proper 

 values, and not as blacks. 



These filters are made in different grades, each of which offers 

 a certain amount of resistance to the passage of the blue and 



Fig. 3. Swamp and forest". Note direction of shadows of trees. 

 Mineral Springs, Ind., September, 1915. Aperture F-8, time 2 seconds, bright light. 



violet rays; they are usually graded so that a No. i filter absorbs 

 half of the violets and blues, and so necessitates proportionate 

 increase in the time of exposure; a No. 2 absorbs two-thirds of the 

 blues and violets, and the time of exposure must be tripled; and 

 since a No. 3 absorbs three-fourths of the blues and violets, the 

 exposure must be quadrupled. 



The No. 1 filter is the most practical for nature photography 

 since it only requires a doubling of the time of exposure. A No. 2 

 will give better values if the long exposure it requires can be given. 



