PHOTOGRAPHIC FILTERS

LEARNING OBJECTIVE: Identify the purpose of photographic filters, the various filter designations, and the filters used in black-and-white and color photography.

Filters are used in all the various steps of the photographic process. Though often neglected in the shooting stage, the use of filters can tremendously enhance the final product in both black-and-white and color photography.

PURPOSE

The purpose of photographic filters is to alter the characteristics of light that reaches the light-sensitive emulsion. As light is transmitted through a filter, at least one of the following alterations occurs: l The color of light is modified. l The amount of light is reduced. . The vibration direction of the light rays is limited.

To use photographic filters properly, you must understand the nature of transmitted light.

White light is composed of three primary colors: red, green and blue. A filter of a primary color will transmit its own color and absorb the other two; for example, a red filter looks red because it transmits red and absorbs green and blue, as shown in figure 11-17.

Secondary colors are mixtures of primary colors. Yellow, for example, is a combination of red and green. Because a filter passes its own color and absorbs others,

Figure 11-18. - Characteristics of a red photographic filter.

Figure 11-19. - Characteristics of a yellow photographic filter.

a yellow filter passes read and green and absorbs blue (fig. 11-18).

In selecting a filter in black and white photography, you can use the color star in figure 11-19 to determine the effect of the filter on the gray scale of the negative and the final print. On the final print, the result will be that a filter will lighten its own color and the colors adjacent to it and darken its complement and the colors adjacent to its complement; for example, a green filter will lighten green (its own color) and cyan and yellow (adjacent colors). It will darken magenta (its

Figure 11-19. - Color star

complement) and blue and red (adjacent colors of the complement).

FILTER DESIGNATIONS

Some filters are designated by a descriptive name, such as neutral density, haze, polarizing and skylight. Color compensating and color print filters have yet another designation system.

The Kodak Wratten filter line uses a numbering system to designate its black-and-white filters, as shown in table 11-1 that filters in the

Table 11-1. - Kodak Wratten Filter

first column lighten colors next to them, and opposite filters darken colors on the print. For example, a yellowgreen No. 11 filter lightens subjects that are yellow-green or yellow and darkens subjects that are violet. A No. 44 cyan filter lightens blue and blue-green and darkens light red and orange.