Harry L. Shepherd

Recognizing the fact, from the school of experience, that practical information, for the busy amateur on the subject of ortho-chromatic photography is hard to find, I hope in this article to introduce the subject to those who are ignorant of the vast possibilities of color sensitive plates and perhaps to aid others who are struggling with the same plates in a haphazard way.

In trying to make the matter very clear, I may leave myself open to criticism at certain points, but please remember the article is principally for those who wish to get an understanding of the subject without recourse to text books on chemistry and physics.

The first question naturally asked by those unacquainted with the subject is, "Are ortho- or iso-(as they are also called) chromatic plates hard to work?" Now, to set your minds at rest, let me say right here that they are just as easy to " work " as ordinary ones, the only difference being that you must use more care with your dark-room light.

A few words of explanation. The popular idea is that ortho plates give a better rendering of the " color value" of objects than ordinary plates. Now, to set your minds at rest, let me say right here that they are just as easy to " work " as ordinary ones, the only difference being that you must use more care with your dark-room light.

A few words of explanation. The popular idea is that ortho plates give a better rendering of the "color value" of objects than ordinary plates. Now, the term "color values" is to many, misleading. It is not the differences of hue in objects that these plates render more correctly, but rather the "relative brightness " of objects one with another without regard to their color. You must see that you cannot render colors in monochrome. White light, as perhaps you know, is composed really of seven colors, viz.: red, orange, yellow, green, blue, indigo and violet. This you can see for yourself by darkening a room and allowing a ray of sunlight to pass through a narrow slit in the window blind. Let this ray or beam of light fall on a white screen, say a piece of white blotting paper. Now in the path of the ray of light, near the screen, interpose a glass prism and you will get the band of colors, called the spectrum, in the order I have mentioned above. It is an experiment well worth trying.

Besides the visible spectrum two sets of invisible rays exist, one located beyond the violet, called the ultra-violet, the other beyond the red, called infra-red.

The ultra violet rays are those which affect all photographic plates most and are thus said to be "actinically powerful. " The infra-red really has no effect.

Now, the trouble with ordinary plates is this: They are so powerfully, i. e., quickly affected by the ultra-violet, violet and also blue rays, that the green, yellow, orange and red rays do not get time, as it were, to act or impress themselves on the plate. If we give sufficient exposure for the green to red rays, then the blue, etc., are greatly over-exposed.

Try to render blue sky, white clouds and green grass on an ordinary plate. In your print the blue will be rendered as white paper; at any rate, there will not be any distinction between the blue sky and white clouds, and the green grass will be rendered many tones too dark. The reason is that blue affects the plate more powerfully or quickly than the green, and so in the negative the " blue part " is very dense and the " green part" comparatively thin, when to the eye the green grass may be only a shade or two darker than the blue of the sky. To overcome this defect certain dyes are mixed with the plate emulsion, before coating the plates - sometimes ordinary plates are bathed in the dyes - and this gives us ortho- or iso-plates which, according to the dyes used, are made more sensitive to green, yellow, orange and red. This property is strongly increased when in conjunction with the ortho-plates we use a ray screen, also called ray filter, which is usually placed over the lens and which to a great or less degree, according to its depth of color, absorbs the ultra-violet, violet, indigo and blue rays, {, e., holds them back, as it were, thus giving the others a chance to impress themselves on the plate. In fact, it acts as a "compensator," and of course increases the exposure, the increase depending on the depth of color of the ray screen.

All ray screens are for the purpose of absorbing or " holding back " the rays at the violet end of the spectrum. They are made of yellow tinted glass or cells filled with a weak solution of bichromate of potash, and are made light or dark to suit certain work. For ordinary work screens to increase the exposure from three to six times are all that are required. Ortho-plates, i. e., the " fast" varieties, are equal in speed to all ordinary "fast" brands of regular plates. They can be used in snap-shot work just as any other plate, but under ordinary circumstances for snapshot work they are not any better than the regular plates, as the ultra violet rays affect them to too great a degree. If you possess a "fast " lens and say at snap-shot speed and stop f. 16. you get a properly exposed negative; then if you use a screen which increases the exposure four times and open your stop to f. 8, you may go ahead, and you will get the benefit of the ortho-chromatic quality of the plate. You see, you increase the exposure four times by using the screen, but with stop f. 8, you allow four times as much light to pas . Stop f. 8 is four times the area of stop f. 16.

If you wish to "catch" the clouds, use an ortho plate and ray screen, except, perhaps sometimes about sunset, when the yellow tint of the atmosphere acts it-self as a screen.

In flower and fruit studies, in fact any place where we have to deal with colors, ortho-plates are a neces ity if correct results are required. In the case of flowers a ray screen is seldom necessary, except where blue and yellow are together, and then one to increase the normal exposure not more than six times is all that is necessary. If you use too dark a screen you are apt to reverse the color values in your subjects.

In fact, ortho plates should be used in flower and fruit studies, marine, autumn landscapes, clouds, interiors (where color has to be dealt with), portraiture, (subjects with golden hair), copying paintings and faded (yellow) photographs.

So, you see, their use ought to be pretty general.

I will now touch on their manipulation. Calculate your exposure as you would for an ordinary plate, i. e., if your ortho-plate is of" fast " variety, such as Cramer Inst. Iso. If you use a ray screen which increases the exposure say four times, then give the plate four times the exposure you have calulated.

When handling in the dark room I use two thicknesses of orange tissue paper, and I do not allow any more light than necessary to fall on the plate at any stage. Now, don't imagine that you have to work almost in Egyptian darkness. Nothing of the kind; but use care and judgment. As ortho-plates are color sensitive, then they are more sensitive to the dark-room light than ordinary plates. During development I keep the developing tray covered with a piece of card-board.

For developers, Pyro can't be beaten. The solution soon colors and protects the plate, and in the print you get " snap " that personally I can't get with other developers.

In conclusion, take my advice and buy a dozen Instaneous Iso-chromatic plates and a light ray screen to increase the exposure say four times (if the man you buy your screen from is not sure of the increase of exposure necessary you will have to experiment and find out), and expose them against a dozen ordinary plates of the brand you use. Try a flower study, such as pansies with yellow and blue in abundance, a couple of landscapes with clouds, an interior where you have to deal with color, etc., and if you work carefully and systematically your first dozen ortho-plates will convince you that in most cases they are far superior to ordinary plates and the "tales" you have heard of of their " hardness" of working is a myth. - Western Camera Notes.