BOTANICAL PHOTOGRAPHY 175 



tween the object being photographed and the background or whether 

 it is desired to obtain the maximum detail within the object. For the 

 beginner, perhaps the most confusing part of the procedure comes in 

 choosing the proper fiUer. The yellow and orange filters will probably 

 be the ones most frequently used, for when they are used with a good 

 orthochromatic or panchromatic plate or film the result will be an 

 approximately correct rendering of the color values in black and 

 white. It is not possible to state just which filters will serve for each 

 set of conditions but certain rules will aid in determining. To obtain 

 the greatest amount of contrast between the specimen and the back- 

 ground use a filter or a combination of filters which transmits only that 

 part of the spectrum completely absorbed by the specimen. This will 

 cause the specimen to appear black in the picture. If the result is 

 unsatisfactory because detail within the specimen has been sacrificed 

 in favor of contrast between the background and the specimen, try a 

 filter or a combination of filters whose spectral transmission is not 

 exactly limited to the part of the spectrum absorbed by the object. 

 To eliminate the contrast between the object and the background use 

 a filter or combination of filters transmitting that portion of the spec- 

 trum which is also transmitted by the object. After a little experience 

 one will be able to estimate the probable photographic result by mak- 

 ing a visual examination with first one and then another of the filters 

 in place. 



We started with the assumption that a photograph was to be made 

 of a part of a vascular bundle in a section that had been stained with 

 safranin and anilin blue. If the photograph were to be made without 

 a light filter and on an ordinary uncorrected plate or film which is 

 oversensitive to the blue portion of the spectrum and completely in- 

 sensitive to the red part, the picture would not be satisfactory. The 

 red-stained part of the specimen would appear black and the parts 

 stained in anilin blue would hardly appear in the photograph. This 

 effect would result from the insensitiveness of the ordinary plate or 

 film to red and the oversensitiveness to blue which gives blue almost 

 the value of white light. Instead, a good color-corrected plate or film 

 should be used and a combination of filters such as the Wratten "B" 

 and "E" filters. This combination of filters will increase the contrast 

 of the part of the specimen stained in blue since the spectral trans- 

 mission of the combination is included within the absorption band of 

 anilin blue. While these filters will not give the maximum contrast for 



