COPYING Copying should present no serious difficulty provided suitable precautions are taken, and correct exposures given. It is essential that the print to be copied should be held perfectly flat on a board which is parallel with the sensi tive plate. If this condition is not observed, a dis torted image will result. The arrangement shown at A (p. x45) is simple, inexpensive, and answers well for copying and also for other photographic work. The direction of lighting is important. A direct front light minimises the effect of the grain of the paper, while a strong side light accentuates it. On the other hand, a direct front lighting cannot be adopted for glossy surfaced prints on account of the reflections. To avoid the sheen of the glossy surface, lighting from one side, slightly in front, is necessary.
For copying pictures under glass, the camera front should be covered with a black cloth, and a black or dark cloth should be hung up close behind the camera to avoid reflections. A side lighting is desirable for the same reason ; but where the original is liable to show a grain, the lighting should be from two sides. (For copying oil paintings or water-colour drawings, see " Paintings, Photographing.") For copying an ordinary silver print, or any strong photographic print with a glossy surface, a rapid plate will give the most truthful rendering of the gradation. If the print is faded or yellow an isochromatic plate should be used. For copying a line engraving or drawing, or a wash drawing, or a photographic print with very little contrast on matt-surfaced paper, ts slow plate specially made for copying, such as a " process " plate or ts fine grain ordinary plate, will give the most satisfactory negative. In all cases the plates should be backed. Correct exposure is most important, and the best method of deter mining this is by using a meter, which should be placed flat against the picture that is being copied and the time that is required for matching the standard tint noted. Using a plate of which
the speed is 200 H. & D., the exposure for copying a glossy silver print the full size of the original, and using the aperture marked 1116 on the diaphragm scale, will be from one-fourth to one half the meter tint if a Wynne meter is used, and from one-eighth to one-fourth with a Watkins meter. A dark or red-toned photograph will require longer exposure than a light or cold toned print. For copying a line drawing, one half the meter tint for a Wynne meter, and one fourth for a Watkins will be the correct exposure for a slow plate, 4o H. & D. For a black-and white drawing in wash, these exposures should be doubled.
The above exposures are for making a copy the same size as the original. For other proportions, the following will be the relative exposures, the lens aperture being the same throughout :— In process work, the art of copying has been brought to great perfection for photo-mechanical processes, where the reproduction has generally to be made from a print or drawing. The essen tials that are carefully studied are : The light ing of the subject ; the parallelism of the original to the sensitive surface ; the sharpness in defini tion of the image ; and the opacity and dearness of the respective parts of the negative. The first condition is generally secured by electric arc illumination. The second is secured by the use of stands on which are rails, the camera and copyboard running on these rails to and from each other ; also by rigid and accurate construction of the camera. The third is secured by the choice of suitable lenses such as are specially made for process reproduction. The fourth is secured by the adoption of suitable plates or processes, the wet collodion process being gener ally considered the best for such work. Further, it is very important to avoid vibration (see "Copying Stand").