734. Reproducing Colored Objects

Reproducing Colored Objects. The nature of the illuminant for reproducing colored objects is immaterial.

Exactly as good results can be produced with artificial light as with daylight and, in fact, if any preference is given, it should be in favor of the artificial light, for the reason that there is more latitude in the exposure. For our next subject, we have selected a double-stained slide, which represents protoplasm. The colors range from a slight pink to a deep red with some blue. It is evident that if sufficient exposure were given to obtain detail in the dark parts of the image, the lighter or more delicate portions would be entirely obliterated. In order to overcome this obstacle and produce the colors in their relative values, we used a yellow color-screen, as previously explained and as illustrated in Fig. 1 (J), Illustration No. 124. This screen is placed before the microscope as shown in Fig. 1, Illustration No. 122.

735. With the screen in position the focusing and other manipulations are exactly the same as previously instructed. You will observe, when focusing the image upon the ground-glass, the light being diffused through this screen, that the image does not appear as strong, but the outline is more clearly defined and the relative values are more apparent than if the screen were eliminated entirely. When using the screen, whether for daylight or artificial light, the exposure is again prolonged. Usually, from three to six times the exposure is required, all depending upon the density of the screen. The lighter the color of the screen, the shorter will be the required exposure, but, at the same time, the greater will be the loss in color values. The darker the screen the longer the exposure and the better the color values produced. Therefore, a medium color-screen should be employed, one that can be used universally for all purposes - usually a three, or even a four-times screen is selected. A screen dyed according to instructions given in the previous chapter will supply you with the right color.

736. Plates To Use

Plates To Use. Having retained the relative color values upon the focusing screen, your next endeavors must be devoted to recording these same values upon the sensitive plate. As previously stated, we have learned that the ordinary plate is not corrected to a variety of colors. Therefore, we must employ specially prepared plates which are sensitized and corrected expressly for the preserving of color values. Such a plate will be found, to a certain degree at least, in the orthochromatic, and for the best results the orthochromatic slow plate is recommended. However, the rapid orthrochromatic plate may be employed. In Fig. 3, Illustration No. 129, we present the results which were made on a rapid orthochromatic plate, used in conjunction with a color-screen, giving an exposure of six seconds.

737. Opaque Illumination

Opaque Illumination. In Fig. 4, Illustration No. 129, we present the results of an opaque illumination. For this subject we selected a strip of linen, stretched it across the stage and held it firmly by means of the nickel clips. When viewing this linen by light transmitted from the mirror through the linen, an interlaced, rope-like effect, with bright spots of light, is seen. If a picture of the linen were made with transmitted light, as above explained, the photograph would not show the texture of the fabric but each thread would be represented by shadow outlined with light, which was admitted between the threads when reflected through the goods into the camera. By changing the position of the mirror, so that no light is transmitted through the opening in the stage, and by elevating the bull's-eye condenser, adjusting it to the light so as to throw the rays downward and directly upon the object on the stage, we obtained a good view of the surface.

738. In order to give an even illumination to the goods, we employed a back reflector, as previously described and illustrated in Fig. 1, (H), Illustration No. 124. This reflector, receiving the full rays of light coming from the illuminant, reflects back upon the object, thus giving double illumination. Now, upon again viewing the image on the ground-glass, we find a very pretty effect and an accurate rendering of the fabric. Instead of the dark lines, as would be the case if transmitted light were used, we obtained an interlaced white rope-like effect with dark spots, which gives it a magnified natural appearance. For this subject we employed a non-halation or double-coated plate, the object being to avoid halation. The linen being white, unless a non-halation plate were employed, the results would be quite harsh, lacking in roundness, while with the non-halation plate we preserved all the half-tones and soft detail.