APPLICATION OF FILTERS.
Taking pictures of old paintings, appliances, colorful furniture, porcelain and documents (e.g. for counterfeit detection), you need to use many types of filters with different colors and shades.
However, in the daily practice of a press photographer, portraitist or amateur, you can limit yourself to one or two filters. One yellow-green or yellow filter is needed under these conditions, extending the exposure time by about three times and one contrasting one, preferably light orange, quadrupling the exposure time.
For everyday use, these two filters are sufficient. Only for special purposes you need to try to get other filters. And so, when shooting in high mountains, the ultraviolet filter gives great services, almost colorless, not extending the exposure time, which removes excess ultraviolet rays from the sun. Using a normal yellow filter under these conditions would be too strong, namely, it would almost completely eliminate the blue of the sky, giving an image of the sky in black, and other parts of the landscape in colors too bright.
An orange or bright red filter is also used for distant panoramas, it reduces haze in the distance and allows distant objects to be reproduced more clearly.
If we wanted to use the two brighter ones we had in order to obtain a particularly strong filter effect (e.g. light and dark yellow or two light yellow), we can put one on top of the other and then the extension of the exposure time is calculated by multiplying the coefficients of both filters together. However, this method is not indicated, because we get too many reflections and it is possible to deteriorate the sharpness of the image.
Modern panchromatic films are already perfect enough, that under normal conditions they give quite good results even without a filter.
Filters on sale are made of colored glass. They have a frame to put on the lens (PZO) or for screwing into the thread of the front lens element (Panchromar). Because 35mm SLR lenses generally have standardized frames, one filter is usually suitable for lenses with different focal lengths or different brightnesses, both for application, as well as for screwing. The latter are more convenient to use, because they do not scratch the frame.
Covering the filter surface with an anti-reflection layer (T layer) offers no particular advantage. Studies of light loss by reflection (reflections) showed, that they are small, they are therefore out of the question for normal membrane tolerance. they take out, depending on the color, a few percent of the total light passing through the filter. On the other hand, harmful reflections reflected from the surface of the filters, and that could affect image clarity are so weak, that they do not leave traces of the image on the emulsion at all.
Despite all the perfection of modern emulsions, filters are an indispensable part of photographic equipment, and both correction filters, used in everyday professional and amateur practice, and contrast filters, intended for special purposes. Many experienced photographers even put a yellow filter on the lens twice, removing it only in exceptional cases (night photos, use a different filter, portrait that does not require the use of a filter).