COPYING. A term applied in photography to the reproduction of paintings, engravings, manuscripts, maps, etc. A copying camera is usually employed, but any form of camera, where the distance between the lens and plate can be made sufficiently great, may be used for this pur pose. The lens should be rectilinear. with a tol erably wide angle of aperture. and slow plates are considered preferable. Care should he taken in developing to use a sufficient restrainer and camera, and suitable color-screens.
It is important that the work or surface to be copied should be placed in a strong light, and exactly at right angles to the axis, of the lens, which should be furnished with a small stop. These three conditions, it will be seen, are such as are calculated to insure density in the blacks of the negative, freedom from distortion, and sharpness at the edges of the picture. The copy ing of oil-paintings seems to the amateur, at first sight, to present almost insuperable difficul ties. on account of the reflected from the 'varnish passing through the lens, and producing black patches on the negative. Thin may, how ever, be completely avoided by the employment of a lens of long focus, which admits of the oblique pencils of light passing off without entering the camera, and suitable coloĽ-screens.
In copying transparent negatives, a somewhat. different arrangement it required, as will appear from considering the following facts. Every ob ject to be copied may be regarded, for the sake of illustration, as an assemblage of bright points, from each of which divergent pencils of rays are reflected, and suffer refraction on passing through the lens: an engraving or oil-painting is, in fact, in its relation to the sensitive surface, the source of light. In a negative, however,.
many of the parts of which are transparent. glass, it is manifest the case is different, for if we suppose the sun or a luminous background to be placed behind the negative, that will act as the source of light, and any rays coining there from will pass almost directly through those parts of the negative which are bare glass, to the lens: thus producing the same effect as if the transparent parts were opaque, but luminous, and emitted divergent pencils of light. It is nec essary, therefore, that the rays should be made to converge at those points where bare glass ex its, and this may be accomplished by employing what is called a condensing lens, by which means negatives may be most successfully copied, by placing an artificial light behind it, or still bet ter. by reflected sunshine through it.
Negatives are sometimes copied on glass by di rect superposition in the ordinary printing frame, such as is used for printing photographs on paper, being exposed to a gas-flame or other source of light, and then developed in the usual way. See PHOTOGRAPHY.