Digital Camera: Black and White (or Contrast)Filters in Photography

The black and white emulsion is panchromatic , sensitive to all colors, and therefore the visible brightness is registered on the film independent of it's original color. In a scene, the different zones are highlighted by there brightness and color. In black and white we loose color contrast and, in many cases, the contrast of the print doesn't exactly respond to what we were seeing. If we photograph two zones of different color and same brightness, we can find ourselves with a black and white image were one zone barely stands out over the other.

With a colored filter we can noticeably alter the contrast of the black and white image when the scene is composed of different tones. Actually, with a contrast filter we select a determined tone, and therefore we go on to working only with some of the regions of the visible spectrum . Now, the tone is important, because it implies a different exposure level of the different zones of the frame according to it's greater or smaller color of light intensity of the filter being used. The zones of the scene that are rich in the tone of the filter will appear registered on the negative with a certain density; the zones that

barely contain that color of light will have minimum or void density. Working the concept of complementary colors we can lighten or darken determined zones of the frame. If we foresee that two zones of the image are going to be registered on the negative with similar densities, and we don't want this to occur, we can always vary the contrast with an adequate filter.

Some examples: we want to photograph a plant of green leaves and red flowers, and we want that contrast to be reflected on the monochrome image; without a filter, the density of both tones in the negative will be similar; on the other hand, with a red and green filter, we can lighten a zone regarding another. This is what happens on the previous photograph: there are red and green peppers, but without a filter this difference will not be seen in the image.

When we want the clouds in a landscape to be highlighted on the blue sky, it's necessary to use a yellow or orange filter, which has the effect of darkening the sky (yellow is the complementary of blue) in the positive image, while the clouds remain registered as lighter gray, because they are also rich in the filters tone.