Patent GB-193448-A (GB)
Title: Improvements in or relating to cameras more particularly for use in aerial photography
IPC: G03B17/34
Filed: 1921-09-22
Abstract: 193,448. Wootton, H. D. Sept. 22, 1921. Aeronautical apparatus; change boxes; plate sheaths.-A camera for aerial photography comprises (1) a series of plates mounted in pile formation in a carrier which may be rotated intermittently in order that the plates may be successively exposed, withdrawn from the front of the pile, and replaced at, the rear; (2) a changebox, removably mounted in the carrier, for holding the plates, and having covers which may be removed and replaced by means within the camera,; (3) sheaths for holding the plates; and (4) a focal-plane shutter, and an auxiliary safety shutter, carried on, and automatically operated by the movement of, a reciprocating member mounted in front of the carrier. In the form shown, the camera comprises a casing 40 with an apertured front wall 41 for the objective, and supported on a fixed member either rigidly, or on a pneumatic cushion, or pivotally so that its inclination may be varied. Within the casing is a carrier 45 having spring-urged members 50 which may be caused by a cam 54 to engage and clamp within the carrier a change box 43 enclosing a pile of plates 42 each contained in a sheath comprising two interlocking parts 131, 132, Figs. 23 and 24, having channeled edges, the plate being held by a U-shaped spring 133 fitted in the part 132. The carrier 45 is mounted on discs 47 rotatable in slides 49 which may be moved by hand or automatically to traverse the carrier first to one side of the casing 40 and then to the other, for the purpose, when the carrier is turned through 90‹ from the position shown in Fig. 2, of removing or replacing the top and bottom covers of the change-box (not shown). The contact of the ends of the change box successively with the opposite sides of the casing causes bolts locking the covers to be released, and the covers to be held by turn-buttons 60 so that they are removed from the change-box as this is moved away. Provision is made to release the turn-buttons and to re-lock the covers when this operation is repeated after the exposure of all the plates. A safety lock on each cover of the change-box prevents accidental withdrawal of the locking-'bolts after the change-box has been removed from the camera. The reciprocation of the carrier may be effected automatically by a pair of levers 81, turning on pivots 82, and loosely engaging at 83 stub-axles 47<a> carried by the disc bearings 47 of the carrier. Cords 84 attached to these levers are wound and unwound successively on drums 84<a> rotated through a friction cone clutch 93, 95 from a pulley 92 driven through gearing from electric motors 85. The clutch is operated through discs 102 connected to the cone 93 by toggle levers 98, 99, the discs being actuated by means controlled by a lever mounted adjacent tq the slides 49, and adapted to be rotated first by hand to commence the movement of the carrier towards one side of the camera casing, and then automatically, by spring stops on the slides, to reverse the movement at each end of the travel of the slides, the lever being finally returned to its original position, in which the clutch is disengaged, when the slides resume their contral position after removal or replacement of both covers. The carrier 45 is rotated by the motors 85 through pinions 160 driving worm gearing 162, 163, Figs. 1 and 3, pinions 165, and toothed wheels 167 mounted on the stub axles 47<a>, which also carry toothed cam wheels 113, 116, each having half its periphery of circular, and the other, half of spiral form (Fig. 1). The wheels 113 mesh with pinions 114 mounted on a vertically slidable member 115, and the wheels 116 with pinions 117 mounted on a vertically slidable member 118, both members being spring controlled, so that, as the carrier rotates, these members are intermittently reciprocated vertically to and from the carrier. The sliding member 115 contains a focal plane shutter 242 mounted on a spring roller 243 and a roller 244 which, as the member 115 moves downwardly is rotated to wind the shutter by the engagement of a pinion 247 with a fixed, inclined rack 248, Figs. 2 and 4, and its spindle 245 is moved axially against a spring 246 until a spring catch 250 enters an annular groove in the spindle; at the same time a pawl on the bracket carrying the roller engages a ratchet wheel 251, and locks the shutter in the wound position. At the end of the upward travel of the member 115, the carrier 45 is at rest in the position shown in Fig. 2, and a pin on the change-box 43 disengages the ratchet 251 and releases the shutter to make the exposure; thereafter, a projection on the shutter releases the catch 256 and permits the return of the spindle 245. The member 115 also carries a safety shutter 261 which is similary actuated on the downward travel, and released by means co-operating with the main shutter on the upward travel of the member 115. The member 118 reaches its lowest position after the carrier has been turned through half a revolution, when the front end of the change-box arrives opposite the member, and catches 144 thereon release spring-controlled latches 140 retaining the plates, engage the topmost plate which has just been exposed, remove it from the changebox, and retain it during the subsequent half revolution of the camera until the rear end of the change-box again arrives uppermost. The member 118 then again reaches its lowest position, and inserts the exposed plate in the changebox, where it is retained by spring-controlled latches 146. To facilitate these operations, the carrier 45 is arrested at every half revolution as follows. The drive wheel 167 and the cam wheels 113, 116 are loosely mounted at each end of the carrier on the stub axle 47<a>, but rotate together. To the axle is secured a disc 120, Figs. 1 and 16, having a reduced ring 121 recessed at opposite ends 122 of a diameter to receive a pawl 123 on the cam wheel 116. When the pawl enters one of these recesses, the carrier turns with the wheel 116 for half a revolution. The pawl is then disengaged by a stop 130, and the wheel 116 completes its revolution without the carrier until the pawl enters the opposite recess, when the carrier is turned again through half a revolution, and so on. Means are provided for arresting the carrier when released by the pawl. A counting mechanism is provided which comprises a graduated dial 199 driven from a star wheel 181 co-operating with, a pin on one of the cam wheels 113, 116. The dial is set initially according to the number of plates in the change-box, and, after the exposure of all the plates, a cam ring 184 in the counter train releases a spring-urged rod 185 carrying a pin which arrests and locks the carrier 45 in position for replacing the change-box covers. The rod 185 also controls the circuit through the motors 85, and disconnects the drive to the wheels 167. The flywheel of the motors 85 serves as a gyrostat for steadying the camera.