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Kodak 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 the 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.

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.

COLOR CHARACTERISTICS OF FILTERS
AND FILTER COMBINATIONS FOR BLACK & WHITE PHOTOGRAPHY
Filter or Filter Combination
Light Transmittance Over 10%
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+
Nanometers
400
500
600
< UltravioletInfrared >
Table 1

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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