improved by deemphasiziiig the role of the accessory pigments. 

 This can be done by increasing the step width to 20-50-nm in- 

 crements in the region wherein they absorb. (Preliminary 

 results with a much larger algal set indicate that only two vectors 

 accoiuit for most of the variation. The 400-.')80-nm region was 

 sampled in 20-nm steps. The 600-700-nm region was sampled 

 in 5-nm steps.) 



The usefulness of the method lies in its ability to produce 

 visible absorption spectra of a large number of samples which 

 must be examined simultaneously. The number of samples that 

 can be examined simultaneously is only a function of film dimen- 

 sion and image size, the inter- and intralayer diffusion of the dyes 

 in the film providing a lower bound to image size. Camera and 

 lens combinations establish an \ipper bound to film dimension. 



Subjects in which a visible change occurs with time are es- 

 pecially amenable to this treatment. Instead of correlating 

 film densities of photographs of a number of different subjects, 

 one would be dealing with varying concentrations of the same 

 subject. Once spectrophotometrically calibrated it would not be 

 necessary, for example, to remove the subject from a transparent 



enclosure. The film furthermore provides an accurate record of 

 any visible change. An important advantage gained by the 

 method is that the photograph can be taken in a fraction of the 

 time needed for a .spectrophotomntric scan. Times of the order 

 of O.OI sec are usual. This permits surveillance of fast changing 

 stationary subjects. If the scale of reproduction desired in the 

 photograph is too large to permit a single photograph to be made, 

 smaller areas may be photographed in a fraction of the time it 

 would take to scan them spectrophotometrically. The photo- 

 graphic technique has obvious advantages and is important in 

 aerial surveillance, since it is possible to preserve a degree of 

 micro-variation over wider areas. 



We thank LeRoy DeMarsh of Eastman Kodak Research 

 Laboratories for his continuing assistance with this work. 



This work was supported by the National Science Foundation 

 (#G B-708S)and the AtomicEnergy Commission [#AT-(401)-3845]. 



References 



1. J. L. Simonds, J. Opt. Soc. Amer. 53, 968 (1963). 



2. C. S. Yentsch, Limnol. Oceanogr. 7, 207 (1962). 



2568 APPLIED OPTICS / Vol. 8, No. 12 / December 1969 



31-4 



