أنواع المرشحات -١- كتاب فن التصوير الفوتوغرافي

Types of filters

Color filters for black and white photography can be classified according to their purpose, and these purposes are:

Correction filters.
2- Contrast filters.
3- Aberration filters
4- Neutral filters, or filters that reduce exposure.

1- Correction filters:

Although panchromatic films respond to all colors that the eye can see, they do not respond to all colors with the same relative value that the eye responds to. For example, the eye sees blue and violet as darker than green, while the film is very sensitive to blue and violet and records them at a lighter value than green.
By using an appropriate filter, the film's response to colors can be corrected and recorded at the same relative values ​​as seen by the eye. For example, to overcome the film's increased sensitivity to blue, a filter that absorbs some of this color must be used. The K2 filter is the appropriate filter for use with ordinary panchromatic film.

2- Contrast filters:

Contrast filters are used to darken or lighten some colors in a subject, by introducing differences or contrast between two colors.

The eye distinguishes between things by means of two types of contrast: the contrast in value (tone), and the contrast in color. As for the black and white image, it has one contrast, which is the value contrast. Sometimes it is necessary to translate the color contrast into a contrast in value when taking a picture of colored objects. There are cases in which exaggeration or softening of this discrepancy is required. For example, a black and white photo of a red apple with its green leaves, in which the two colors appear to be a gray of the same value, because the color contrast between red and green is absent in black and white photography, and the contrast remains the gray value. And this is what picture 1 shows, for two cups of
Plastic: The upright is green and the horizontal is red. The result is a single gray image of the two cups. In order to create a contrast in value, the color contrast of the two cups as seen by the eye, one must be made lighter than the other. If we use a red filter (picture 2), the red (horizontal cup) appears lighter, and the standing cup is darker, because the red filter allows all the light of the red cup to pass through and absorbs a large part of the green light. Thus, we have returned the basic visualization. The same result can be obtained with regard to contrast, by using a green filter (photo 3), where the green cup (upright) appears lighter, and the red cup (horizontal) is darker. As for the use of any of the filters, that is up to the choice of the photographer.