Choosing The Right Filter For Black and White Photography

Choosing the right Filter for black and white photography

  • All filters act by removing some of the light that strikes them. Although it is true that a yellow filter absorbs blue and transmits green and red, a red filter absorbs blue and green and transmits red, and so on, this information gives the novice only a poor idea of how to choose a color filter for differentiating tones in black and white photography.

  • Although incorrect in strictly physical terms, there is a very useful rule of thumb for choosing a filter to use with panchromatic films. The rule is based on the complementary color wheel we all learned about in school. In such a color wheel the three primary colors - red, yellow, and blue - are spaced around the edge of the wheel at 120˚ intervals. Between them are the secondary colors - orange, green, and violet. Each secondary color can be obtained, with paints, by mixing approximately equal amounts of the primary colors found on either side of the color wheel; thus, red and yellow mix to make orange, yellow and blue mix to make green, and blue and red mix to make violet. Mixing unequal quantities of the primaries will make intermediate shades of the secondary colors. With red and yellow, if red predominates the result will be a reddish orange, and if yellow predominates the result will be a yellowish orange, and so on. The color wheel, as used for paint mixing, is a description of what happens in an additive system in which a color or hue is achieved by mixing pigments; whereas color filters are subtractive: wavelengths, or colors, of light are selectively absorbed from an existing mixture of all visible wavelengths.

  • Although the theory of the color wheel does not accurately describe the color filtering process, if you look through a color filter the color tones will appear to change with respect to one another roughly in accord with a color wheel. Thus, the rule of thumb is simple: in black and white photography, to darken the tone of gray that represents a color, use a filter of the complementary color. A deeper or lighter hue of the filter will provide a correspondingly greater or lesser filter effect.

  • Looking at the subject through a filter will give you a fairly good idea of how it will affect the image as recorded on panchromatic film. You will see a monochromatic scene, with the relative brightness similar to those of the final print. Although it will be seen in shades of the filter's color, rather than in shades of gray, as in the print, a little practice will allow you to predict the final results reasonably well.

  • A failure of the color wheel system becomes apparent when you are photographing broad leaved green vegetation. Such leaves have an internal structure that causes them to reflect strongly in the red and infrared regions of the spectrum. Thus, if a red filter is used with panchromatic film (or with infrared film), the greens do not darken as expected, but lighten instead. (In infrared photography, such vegetation prints as very light or even white.) This is called the Wood effect.

  • Fortunately, the failures of the color wheel system become obvious when you view through the filter you have decided to use. Therefore, if you are aware of these drawbacks they do not pose real problems. Although theoretically somewhat inexact, this system is a very useful way to start looking for the correct filter in most situations.

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