Patent GB-180360-A (GB)
Title: Improvements in photographic printing processes and in copying cameras therefor
IPC: G03B27/68
Filed: 1920-12-18
Abstract: 180,360. Janzer, C. Dec. 18, 1920. Enlarging, copying, and reducing.-In a process for correcting perspective in reproducing from negatives which at the time of exposure were not parallel to the subject, the negative is progressively projected through a slit fixed at right-angles to the optical axis of a projection apparatus. A narrow strip only of the receiving- surface is thus exposed at a time, correlated movements of certain of the elements comprising the negative, the slit, the projection lens, and the receiving-surface causing this strip to move across the receiving surface, whilst at the same time the ratio of enlargement is continuously varied in such a way as to correct the perspective effect, and the negative, lens, and receiving-surface are kept in correct focal relation one to another. Fig. 6 shows diagrammatically one arrangement, in which the negative 1 is projected by a lens 4 through a slot 5 immediately in front of a receiving-surface 3. In the position shown, one edge of the negative, on which lie the points 8, 9, is being projected on to the receiving-surface through the slit 5, and in order to effect the complete exposure the negative is moved perpendicularly to the optical axis in the direction of the arrow 10 whilst the surface 3 receives a corresponding movement in the opposite direction, as shown by the arrow 11. To correct the distorted perspective, so as to reproduce the converging lines 8-12, 9-13 on the negative as parallel lines on the surface 3, the lens 4 and negative 1 are at the same time moved along the optical axis 2 away from the surface 3 so that the ratio of enlargement increases as the strip of the negative under exposure passes toward the points 12, 13. Figs. 9, 10, and 11 show diagrammatically a copying-apparatus for carrying out the process, Fig. 9 showing the mechanism for correlating the movements of the receiving-surface and negative transverse to the optical axis, whilst Figs. 10 and 11 show mechanisms for correlating the longitudinal movements of the lens and receiving surface with the transverse movements and with one another. The receiving-surface is held in a carrier 3b which, by means of a driven shaft 18 and a pinion and chain gear 15, 16, is moved transversely on a carriage 3<a>, on which carriage is also supported the slit bearer 5. The negative 1 is held in a cradle 41 carried by a transversely sliding member 37 to which motion is given by the mechanism shown in Fig. 9. This comprises a shaft 22 driven from the shaft 18 and carrying a sliding gear wheel (not shown) which engages a rack 23<a> operating a slide 27 carried by a turntable 24. A pin 35 on this slide engages one arm of a slotted lever 33 which is pivoted at 34 and imparts transverse motion to the slide 37. The frame 28 of the turntable is longitudinally adjustable on bearers 30, by which adjustment, combined with an angular adjustment of the turntable, the correct relative transverse motions of the negative 1 and of the carrier 3b may be obtained corresponding to the degree of correction necessary in the negative. The mechanism for adjusting the lens box 4<a> along the optical axis comprises a bell-crank lever, one arm 19<a> of which is engaged by a finger attached to the casing 3<b>, whilst the other 19b engages a pin 21 on a rod 20 attached to the lens box, which is thus moved proportionately to the transverse motion of the carrier 3<b>. The arm 20 is adjustable transversely according to the degree of correction required. To maintain the receiving-surface 3 in correct focal position the carriage 3<a> on which it is mounted is adjustable longitudinally and a right-angled bell-crank lever 43, 44 pivoted at 42 on the lens box 4<a> engages pins 45, 47 carried by arms 46, 48 attached respectively to the negative-carrier 41 and the carriage 3<a>, the distances x being equal to one another. Methods in which the receiving-surface is arranged at an angle to the optical axis equal to that between the axis of the lens and the ground at the time the negative was taken are also described. The slit may also be arranged in other positions, and may be movable transversely across the receiving-surface. As regards the longitudinal motions, either the negative, lens, or receiving surface may be fixed, the other two being movable.