PAINTINGS, PHOTOGRAPHING The general principles to be observed in photo graphing paintings are given under the heading Copying," but the arrangement for holding the original and the camera so that the picture and the sensitive plate are parallel cannot often be employed. Carefully ruled pencil lines on the focusing screen, forming perfectly true rectangles, will assist in avoiding inaccuracy. Glass should always be removed from glazed paintings, if possible, it being so difficult to kill reflections entirely. When the glass may not be removed, a black screen should be hung immediately behind the camera, and the last-mentioned should be covered with a black cloth ; or the screen should be hung close in front of the camera, with a small aperture through which the lens may project. Folds or undulations in the surfaces of screen and cloth should be avoided, so that the picttire reflects only a uniformly dark mass. A lens of long focal length is preferable, it being then easier to avoid the sheen on an oil painting interfering with the rendering. In the case of water-colour draw ings, the chief consideration is that the lens should cover the plate with crisp definition, and the proportion of focus to plate is immaterial.
After the image has been focused, the lens and focusing screen should be removed and the picture examined through the lens opening from the back of the camera. In the case of an oil painting without glass this examination deter mines whether sheen on the surface is visible ; in the case of a picture under glass, it shows whether reflections are destroying the image. Sheen or reflections at the top of a picture can frequently be avoided by raising the camera ; those at either side can be obviated at times by means of a screen.
Isochromatic plates should be used for this work, together with a yellow screen or light filter. A green screen is an advantage with some subjects. (See also " Monochrome, Ren dering Colours in.") The screen should be used behind the lens when possible, and the final focusing should be done with the screen in position.
The exposure must be gauged by the aid of a meter held with its back flat against the picture. For an oil painting in good, bright con dition, using a plate of the speed of 20o H. and D., and a lens aperature of f/i6, the exposure. should be half the time necessary for matching the meter tint in the case of a Wynne meter, or one-fourth the meter tint in the case of a Watkins meter. For an old or very dark pic ture, from twice to three times this exposure will be necessary. For a water-colour drawing the exposures will be shorter. For a very dark or solidly painted picture the exposure will be about one-third the meter tint of a Wynne meter, and one-sixth that of a Watkins, using the same plate and lens aperture as given above. For a light and delicate sketchy drawing these expo sures may be reduced to one-eighth of the Wynne meter tint, and one-sixteenth of the Watkins. All the above exposures are those necessary without a colour screen or light filter ; and they must be multiplied by the number of times extra exposure that the screen necessitates. They are all given for copying the same size as the original, the lens aperture being that marked f/i6 on the diaphragm scale, and not calculated from the extra extension. Proportionate exposures for other scales will be found under the heading " Copying."