International photographer (Jan-Dec 1941)

l6MM. dEpARTMENT FILTERS — THEIR USE AND MISUSE As bad as never using a filter at any time for any purpose whatsoever is the practice of using a filter just to be using one. In fact, the latter is probably worse. Present day films are so balanced when panchromatism is introduced that for any ordinary scenes the omission of a filter results in a far more natural result — and pleasing result — than the promiscuous use, or, rather, thoughtless use, of the filters at hand. To begin with, filters have many different uses. Primarily, they were — and are — , used to bring the response of the emulsion : used more nearly to that of the eye. All films are more sensitive to blues than to ' any of the other colors, and unless the strength of the blue rays entering the lens , is lessened the exposure necessitated is such that the other colors do not have a chance j to act completely upon the emulsion, with the result that they are not photographed in their true relationship. Perhaps it would be better to first look into the action of filters. Actually, if we . have a red filter — pure red — this filter • would pass only the red rays of the spec; trum, and hold back all the others. This , would also be true of all the other color ■ filters. An important point to remember, however, is that this is true only of a filter ' that is known to be true in color, such as ; the primary tri-color filters A, B, and C i used in making three-color-separation negatives. (In actual practice, however, such ; filters are rarely used except for making separation negatives and in special cases 1 for black and white work.) Going back to the operation of the filters, a yellow filter would hold back the blue sky, which I would photograph as white without correction, and permit a normal exposure of the foreground while the sky would be photographed in a normal tone. Hence, any clouds appearing in the sky would photograph as clouds instead of being lost in the mass of white that would represent the sky. Distortion of color response would be true wherever a noticeable amount of blue were present, and could be corrected by the introduction of a light yellow filter to hold back the blue a little, giving the other colors a chance to act normally upon the emulsion, without burning up the blues because of the greater sensitivity of the film to that color. A scene photographed in this manner would result in a pleasing picture, with the tones represented naturally — as they really are. When a deep blue sky is present, very little correction is needed. Should the heavier filters be used, overcorrection will result which will render it unnatural, and if any clouds are present, they will take on the aspect of storm clouds. On the other hand, if the sky is a hazy one, such as seems to be present over Hollywood so much of the time, ( San Franciscans and Chamber of Commerce please note! ) then a much greater amount of correction will be found necessary in order to keep the sky from going "bald." The foreground will still be overcorrected, but this effect will not be so noticeable because of the natural appearing sky. The ideal way to deal with a condition of this sort — and this used professionally— is to use a graduated filter, where the top portion covering the sky may be a 23A or 25 ( light and heavy red, respectively) which blends down into an Aero 1 or 2 (very light yellows) covering the ground. While this is one of the most common uses of a filter, it is only one use. Filters have the ability of changing the contrast existing in the scene. Used in scenes where there are strong contrasts in the form of strong highlights and fairly deep shadows, the 3N5 and 5N5 will soften the scene down. On the other hand, filters like the 21, G, (both deep yellow) the 23A and the 25 (reds) will make a rather flat looking scene photograph with a much greater contrast. It must be emphasized that this change of contrasts will be effected at the expense of true rendition of colors, and must be used with this thought in mind. To bring home a point, let us consider for a moment a haystack against a blue sky in which there are clouds, and where the rest of the field is a fairly deep green. Photographed without a filter of any kind, the yellow haystack would go very light because of the high sensitivity of the panchromatic film to yellows; the blue sky would go white because of the unnatural sensitivity of the film to blues, while the green would photograph quite naturally. The introduction of a light yellow filter (such as the Aero 1) would hold the sky back to a neutral tone sufficiently to permit the clouds to stand out, without permitting the yellow haystack to build up too strongly because of the high yellow sensitivity of a panchromatic film, and would not hold too much blue back to make the grass go too dark. Green, you will remember, is a combination of yellow and blue. If a heavy filter were used here, we would have a sky that would be too dark, clouds looking like storm clouds, a white haystack, and green green grass or other foliage that would go too dark, almost black, in fact. On the other hand, if the sky were not a deep blue but rather hazy and flat in character, then the heavy filter would be called for. It would take a deep filter to give character to the sky and make it appear a natural blue; the haystack could be printed down a little deeper to keep it from going white; and the added exposure that would be necessary for such a light condition would enable the foliage to build up to a value to keep from going black. There are conditions where a red filter would not result in a picture giving the appearance of being overcorected by adding the proper amount of contrast to an otherwise flat scene. A filter little used, but none the less very useful, is the neutral density filter. This filter has no color corrective properties, but is merely of a grayish tint for the purpose of holding back some of the light. It is particularly useful where there is a strong glare "kicking back" from sidewalks, streets, and objects of highly reflective natures, and when shooting with the sun coming from behind the subject. It is also of great value when it is desired to work with the larger lens apertures on close-ups to give the background a softness that results when the depth of focus is made smaller by using a wider stop. Frequently, too, one finds when using the fast films that the aperture indicated is smaller than is physically possible with the equipment at hand, such as when shooting in bright sunlight and where the lens will not stop below f:16, and the shutter is not of the adjustable variety. The only solution here is the use of the neutral density filter. Night effects can be simulated in bright daylight by the proper use of filters. An excellent combination is the 23A and 56, where the film is not too red sensitive, such as the regular panchromatic. The extreme red sensitivity of the faster films makes the use of the 72 and 80 more desirable. The most satisfactory and pleasing is the use of the infra-red number 88, used with infrared film, but this is something that should not be attempted by the novice because of the nature of infra-red film, and the problems its use will poise. Filters should not be used indoors with incandescent lighting, unless they are used for special effects, and under special conditions. The spectrum of a standard nitrogen filled bulb is such that the light is equivalent to a light yellow filter, and the use of a filter would result in a distortion similar to overcorrection. True, there are times when deep blue eyes would be lost and go white unless the blues would be held back a little by means of a light yellow filter. And there are times when certain types of blond hair would go white in a close-up without the use of a light blue filter. But these are problems for the expert, and unless the amateur has reached that stage of proficiency where he can deal with them accordingly, his efforts will result in failures. The use of filters for color photography requires an entirely different approach. The sole use of filters with Kodachrome is for the maintenance of a given specific color temperature, and never to correct the film response to the visual response, nor to correct for contrasts. In using filters with Kodachrome, a color temperature meter is (Continued on page 28) International Photographer for October, 1941 27