This section is from the "Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1912" book, by Aristo Motto. Also see Amazon: Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1912.
If you don't just understand what is meant by color contrast, hunt around for a bright red label with black printed matter on the red, and try to make a negative that will show the label as you see it with your eyes. You can't do it with an ordinary plate. The bright red looks lighter than the black, but you can't get the plate to see it that way. The red will photograph as black as the black letters, so there is no contrast in the negative.
This may seem an extreme case to you, but such things come up every day in Commercial Photography, and if the man in the small town expects to make the most of his opportunities, he must not only be prepared to do an occasional job of commercial work, but he should encourage it. This can only be accomplished by doing good work. And to do good commercial work you must know something about making photographs of colored objects.
To begin on this subject of color, you must know first of all, that you cannot make red, or any color containing red, appear in a photograph as light as it appears to the eye unless you use a Panchromatic Plate. This is very simple to understand, as the ordinary plate is not sensitive to red; consequently red objects photograph much darker than they look.
The only way to overcome this trouble is to use a plate that is sensitive to red, the best plate of this kind being the Wratten Panchromatic. As the name implies, this plate is sensitive to all colors, and as it is not possible to make a plate which is not more sensitive to blue than to other colors, it is necessary to use with this plate a yellow screen or filter in front of the lens to cut out some of the rays of blue light. Then all colors may be photographed in the same tone and contrast to one another that they have to the eye. This gives a true orthochromatie result.
For example, if you had four cards, one blue, one yellow, one green and one pink, all being equally dark in tone, they would photograph alike on the Panchromatic Plate, using the correct yellow filter (K 3).
Now suppose you have a florist bring in a beautiful bouquet of red roses in a mass of green foliage, and he asks you to make a photograph of these flowers. What are you going to do? Use an ordinary plate and the flowers and foliage will both be very dark. Use a Panchromatic Plate and yellow (K 3) filter, and they will both be lighter, but still the result will not be satisfactory. Right here is where what is known as a "Contrast Filter" saves the situation. This filter would be of no use without the Panchromatic Plate, for it is red in color and the plate must be sensitive to red. By placing this filter before the lens, the roses will photograph much lighter than the green leaves, and a very satisfactory negative is secured. It would be just as easy to make the green leaves photograph light and the roses dark, by using a green filter. This method is known as over-correction towards red or green - making color contrast where there is no contrast in tones.
From A Zelta Print By Elias Golden sky Philadelphia, Pa.
The red filter, or to be more correct, orange-red (A) filter, is especially valuable if used with the Panchromatic Plate in photographing pieces of mahogany furniture. Another contrast filter which is very valuable when used with the Panchromatic Plate is the strong yellow (G) filter. This filter brings out the grain of oak and all yellow woods in a surprising manner, and is also valuable in making copies of old prints which have become stained. If you have to copy an old print which has a bad yellow stain, the ordinary plate will emphasize the stain and make it almost black. The Panchromatic Plate and correct Orthochromatic Filter (K 3) will show the stain just as dark as it looks to the eye. The Panchromatic Plate and strong yellow Contrast Filter (G) will make the stain absolutely invisible and you will be enabled to secure a copy that will, as a rule, be much better than the original.
Naturally the Panchromatic Plate being sensitive to red can not be developed by a red light, but is very conveniently handled in the plate tank, or may be developed in a safely covered tray.
The Wratten & Wainwright color filters are prepared by coating glass with gelatine to which the necessary dyes have been added. After drying, the gelatine is stripped from the glass and carefully examined, tested and compared, that it may give scientific color separation. "We can supply the gelatine film, but most photographers prefer to have these filters protected by being cemented in optical glass. A complete set of filters is furnished, neatly packed in a case, and these filters will all be found of great value to the commercial photographer. Single filters may be had when the entire set is not wanted.
The effect that will be secured on the Panchromatic Plate with any of these filters may be very quickly seen by examining the object through the filter. The colors will photograph on the Panchromatic Plate in the same tone and contrast to one another that they have to the eye in viewing them through the filter. This makes it very easy to secure the result desired in difficult colored subjects.
The Wratten & Wainwright Orthochromatic and Contrast Filters are as follows:
Orthochromatic Filters, K 1, K 2 and K 3.
The K 1 is a light filter, requiring on a Wratten Panchromatic plate only about 1/4 times the unscreened exposure, therefore it is very suitable for quick view work.
The K 2 is the most generally useful filter, increasing exposure on a Wratten Panchromatic plate about 3/4 times, and giving excellent color rendering.
The K 3 filter gives absolutely correct color rendering and requires about 5 times the unscreened exposure on the Wratten Panchromatic plate. It is not suitable for use with other plates.
The Contrast Filters are as follows: G, F and the Tri-Color Filters A, B and C.
G. A strong yellow filter, valuable in photographing oak and other yellow woods, stained prints, etc.
F. A deep red filter used in photographing very dark mahogany, blue prints, etc.
A. An orange-red filter for photographing mahogany and other red woods. Used in giving strong contrast between reds and other colors.
B. A green filter used in photographing blue or purple typewriting, carpets, rugs, etc.
C. A blue filter for three-color work.
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