The ordinary plate is sensitive to blue, violet and ultra-violet. The orthochromatic plate is sensitive to these same colors, and in a certain degree to green and yellow, while the panchromatic is sensitive to all the colors of the spectrum.

All plates, however, are supersensitive to blue, violet and ultraviolet, so it is necessary with orthochromatic and panchromatic plates to use a yellow filter which will cut out all the ultraviolet and enough of the blue and violet light to bring these colors into proper relation to the other colors to which these plates are sensitive. These yellow filters could be done away with if plates could be made less sensitive to blues and violets - but this is not possible.

Yellow filters then are used to cut out the surplus of blue light, but they in no way increase the sensitiveness of the plate to other colors. They make an increase of exposure necessary only because they cut out the greater portion of the light to which the plate is most sensitive.

With the orthochromatic plate this allows bright green, yellow, blue and violet objects to make an impression on the plate more nearly in proportion to the impression they make upon the eye, so a K2 filter and orthochromatic plate can be said to give an approximately correct rendering of these colors.

They are no more sensitive to red, however, than an ordinary plate, so, regardless of the filter used, red objects will photograph as black in an orthochromatic plate. A panchromatic plate must be used to secure a truthful rendering of red, orange or any color of which red is a part.

Examples of results secured by using panchromatic plates are usually compared with results secured on ordinary plates, and while the difference does not exaggerate the rendering of red objects it may seem an exaggeration to those who use orthochromatic plates and color filters. For this reason we show two examples of the best results that could be secured on orthochromatic plates with a filter and the results on Wratten Panchromatic Plates with K3 filter.In the first example (A) the center of the rug is a brilliant red, the design showing in black.

One sees at a glance that the orthochromatic plate does not show any contrast between the red and black, the design being entirely lost. The background of the outer border is buff and this is rendered very well by the orthochromatic plate. With an ordinary plate this would also be dark. The various colored figures in the outer border are also fairly well rendered except the reds.

The result could not be called satisfactory, however, as the prints would not give a good idea of the appearance of the rug, and if the prints were to be colored those from the panchromatic negative would be very satisfactory, while those from the orthochromatic negatives would be impossible.

The second example (B) shows a rug with black design on a dull red ground, the smaller figures in lighter colors being outlined with black. The orthochromatic plate picks out the blues, yellows, greens and whites, but the black design, which is of greatest importance, is entirely lost. The panchromatic plate gives a satisfactory rendering, the result being what the eye sees as nearly as can be shown without coloring the print.

Correct rendering with panchromatic plates requires only the use of the correct yellow filter (K3) which absorbs the surplus of blue light. There are instances, however, where only

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(A) PIROT RUG Orthochromatic Plate, with Filter

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THE SAME RUG Wratten Panchromatic, K3 Filter

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(B) Orthochromatic Plate, with Filter

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Wratten Panchromatic, Ks Filter an incorrect rendering of colored objects will give a satisfactory result in a photograph. For example, a carpet or rug may have a dark green ground with an orange or red figure that is of a tone as dark as the ground, the only contrast being in the colors. A perfectly correct rendering would make both colors appear in the photograph in so nearly the same shade of grey that there would be no contrast.

In such a case one of the colors must be over-corrected or made lighter. A green filter will absorb red, allowing the green to photograph lighter and an orange filter will absorb green, allowing the red to photograph lighter, the nature of the subject determining which of the colors should be made lighter to secure the most satisfactory result, but these results can only be secured on a panchromatic plate.

Within certain limits ortho-chromatic plates will give excellent results - beyond those limits only panchromatic plates can give satisfactory results.

You can be sure your developing light is safe if you use a Wratten or Kodak Safelight Lamp

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By Morrall-Hoole Studio Rochester, N. Y.