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Kodak Wratten Filters for Black & White Photomicrography

The absorption and transmission characteristics of Kodak Wratten filters are published in the Kodak Photographic Filters Handbook (Publication No. B-3), which includes tabulations of spectral data at various wavelengths. A typical visible light absorption spectrum for one of these filters, the Wratten number 34a, is illustrated in Figure 1. In this figure, absorption (diffuse density) is plotted as a function of wavelength from 300 to 700 nanometers.

The 34a filter has a strong absorption band at 370 nanometers, in the ultraviolet region of the spectrum, and another centered at 560 nanometers in the green-yellow transition region of the visible spectrum. This filter passes or transmits wavelengths whose diffuse density is less than 0.1, so the wavelength ranges transmitted by the 34a filter are 410 to 470 nanometers (blue light) and 660 to 700 nanometers (red light).

The transmission bands of filters are conveniently represented as a bar graph, such as the one illustrated in Figure 2. The darker areas represent regions of transmission by a filter that exceed 10 percent, and the lighter areas represent wavelengths blocked by the filter. This type of graph provides a simple index for comparing a set of filters to quickly determine the suitable filter for any particular application.

Color Characteristics of Filters for Black & White Photography
Filter or Filter Combination Light Transmittance Over 10 Percent
 47B (deep blue) 400-470  
 47B + 2E (pale yellow)  420-470  
 47B + 3  440-470  
 47 (blue)  410-500  
 47 + 3  440-500  
 47 + 4  460-500  
 47 + 8 (yellow)  440-500  
 45  450-510  
 47A (light blue) 380-520    
 47A + 4  460-520  
 47A + 8 (yellow)  480-520  
 44 (blue green)  440-540  
 44 + 8 (yellow)  480-540  
 44 + 12 (deep yellow)  500-540  
 64  440-560  
 61  500-560  
 58 (green)  500-580  
 58 + 15 (deep yellow)  520-580  
 57  480-580  
 57 + 12  500-580  
 57 + 15  520-580  
 92  630+
 29 (deep red)  610 +
 25 (red)  590 +
 22 (deep orange)  560 +
 15 (deep yellow)  520 +
 12 (deep yellow)  510 +
 8 (yellow)  480 +
 Wavelength (Nanometers) 400 500 600
< Ultraviolet         Infrared >

Table 1

A compilation of bar charts for the common Kodak Wratten color filters are listed in Table 1. Use this table as a reference in choosing filters to enhance contrast in stained specimens using black & white photomicrography.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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