60 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



sensitive to the blues, and more sensitive to the other colors of the 

 spectrum. They do not show more than half of their color value, 

 however, until the ray filter of greenish yellow color is placed on the 

 lens. It prevents many of the blue rays of light from reaching the or- 

 thochromatic plate and allows the other colors to be registered more 

 nearly as they appear to the eye. Some stunts in photography may be 

 performed by the selection and use of proper filters and plates; red 

 can be photographed so it appears as white, blue as black, and green, 

 yellow and brown may be readily differentiated. 



By selecting the proper filter, the colors which ordinarily give no 

 great amount of difference in monochrome on the ordinary plate 

 become widely different in appearance when a spectrum or ortho- 

 chromatic plate is used in place of the ordinary plate. There are a 

 number of makes of color filters on the market : the most complete set, 

 which is inexpensive, is made by The G. Cramer Dry Plate Company. 

 With regard to photo dry plates I have finally settled on five or six 

 different kinds of the Seed brand, because they give much clearer and 

 snappier negatives than any of the many other makes I have used. 

 Some of the others apparently give slightly better color differentiation 

 but they also have faults which more than overbalance their good 

 qualities. There are many things to be considered, especially little 

 details which are ordinarily overlooked. 



The difference in the distance of the plate and ground glass screen 

 from the lens, often gives indistinct out-of-focus negatives; coarse 

 ground-glass or lack of care in focusing; the use of large stops when 

 small ones should be used; incorrect exposure; or overdeveloped neg- 

 atives and many other things must all be considered. Extremely 

 fast lenses often prove undesirable, because of their lack of depth of 

 focus. Theoretically lenses of the same focal length, but of different 

 speed, when stopped down to the same aperture, should have the 

 same depth; but in practice the speed lens fails. 



With regard to prisms for photographic use, I have been advised by 

 expert engravers and lens makers, not to use a prism, because even in 

 the best prisms, there is always a certain amount of aberration which 

 cannot be eliminated and it often makes part of the image appear in- 

 distinct. This defect occurs in prisms costing as much as $1800, and 

 in using the cheaper kinds, many slightly indistinct photographs are the 

 result. When the plates vary considerably in thickness the same 

 trouble will be experienced. The use of impure chemicals or solutions 

 will also give the worker all kinds of trouble. 



I use pyro for developing plates as it is a flexible developer which 

 gives negatives with excellent detail, without any of the dense, harsh, 

 contrasty effects which always attend the useof hydrochinon. Acetone 



