Patent GB-222675-A (GB)
Title: Improvements in or relating to photographic processes for the production of images in relief
IPC: G03B35/24
Filed: 1923-10-06
Abstract: 222,675. Pocock, L. W. Oct. 6, 1923. Statuary and solid objects, reproducing; relief photographs.-Photographs in which the scale of density of the image bears a definite relation to the contours of the object are obtained by illuminating the object by light admitted through a narrow aperture and photographing through the same or another aperture from a position from which the visible width of the illuminated zone of the object at any part thereof is proportional to the distance of said part from a selected datum plane, and traversing or virtually traversing the aperture or apertures across the path of the light so that the exposure at all parts of the plate is proportional to the distance of the corresponding part of the object from the said datum plane. The photographs are used more particularly for producing images in relief or intaglio, for example swelled bichromate images which may be reproduced by casting or making an electrotype therefrom. In one example, Fig. 1, a screen a, preferably of blackened, slightly inclined, parallel strips b, Fig. 4, about a quarter of an inch in width and spaced apart a like distance, is placed vertically near the object c and parallel to its median plane e, which is also the datum plane. The light source f, camera d, and screen a are so arranged that no light from the datum plane e reaches the camera,. Narrow light strips h of irregular width illuminate the object. During the exposure the screen a is oscillated to-and-fro. To eliminate the effect of unequal reflecting power or uneven colour, the photograph obtained is combined with one taken with the arrangement of Fig. 2, in which the screen a is at about twice its previous distance from the object c so that the zones g of light cast by the slits on to the datum plane e are visible from the camera d. The conditions of lighting and the differences in density due to contour are now reversed but those due to colour &c. remain the same. By making a positive transparency from this negative and printing with both in register the differences in density due to contour are reinforced, while those due to colour &c. are eliminated. Alternatively the positive may be made from the first negative, or one of the photographs may be taken without the screen. in a modification, Fig. 5, the projection lantern j and camera d are mounted on a common baseboard k, and their lenses l, l<1> are of the same focal length and have a common lensboard m and focusing means n. Two screens are employed, one screen a in the focal plane of lens l, and the other a<1> as near as possible to that of lens l<1>, in front of plate-holder q. The screens, which may be made by cementing opaque strips on glass, are mounted in a carrier o movable transversely by means of screw p. The screens are arranged so as to produce on the object the lighting effect shown in Fig. 1, and means r are provided for adjusting the lens l<1> to a second position in which the effect shown in Fig. 2 is obtained. Alternatively, the lens l or one or other of the screens a, a<1> may be adjustable to enable the two effects to be obtained, or two cameras may be employed close together to obtain the two effects simultaneously.