Patent GB-487647-A (GB)
Title: Improvements in or relating to photographic shutters
IPC: G03B9/34
Filed: 1937-10-21
Abstract: 487,647. Photographic shutters. KODAK, Ltd. Oct. 21, 1937, No. 28718. Convention date, Oct. 21, 1936. [Classes 98 (i) and 98 (ii)] In a focal-plane shutter having a separate power drive for each shutter member or blind, each drive is controlled by a latch and a lost motion means is provided whereby one latch may be released after the other, said means comprising a plurality of coaxially mounted discs carrying lugs selectively engaged by a movable member to permit any desired extent of lost motion to be obtained. The invention is described with reference to a stereoscopic camera having a pair of shutters, but may be applied to a single shutter. As shown in Fig. 2, the shutter comprises a leading blind 31 carried on a spring roller 32 and connected by tapes 33 to drums 34, 34a fixed to a shaft 35. The following blind 28 is carried at one end on a spring roller 30 and at the other on a roller 28 free on the shaft 35. Gears 36, 37 are provided to wind the shutter, a lug 39 on the drum 34 engaging a lug 40 on the roller 29 to wind both shutters. The shutter is maintained wound by engagement of an arm 42, Fig. 6 attached to a shaft 43 with a notch in a disc 45 on the roller 29. Pivoted on the shaft 43 is a detent 51 having an end 52, Fig. 10 engaging a disc 54 carried on the drum 34a and having an extension 55 in the path of a release lever 49 carried on a second shaft 46. The two blinds are thus independently held by the latches 42, 51. Slidably attached to a flattened portion 61, Fig. 9, of the shaft 43, is a trip lever 60 having a slot 62 engaging a pin 63 carried on a lever system 64, 65, 66 which carries a pin 67 engaging a spiral slot in cam disc 69 rotatable by an external knob. The end of the lever 60 lies in the path of the projections 75a, &c., of a number of discs 75, 76 ... &c., Figs. 6, 7 carried on the shaft 35 and comprising the lost motion device determining the time at which the following blind is released. A lug 75a on the first disc engages a slot 53 in the disc 54. The operation of the shutter is as follows. When the blinds have been wound and the lever 60 moved along the shaft 43 by the disc 69 to an appropriate position the lever 49 is depressed thereby raising the lever 51 and releasing the roller 34, 34a of the leading blind, the following blind still being held by the lever 42. The engagement of the disc 54 with the disc 75 causes the two to rotate together and at given intervals to " pick up " successively the disc 76, 77 &c. Eventually one of the projections raises the lever 60 to rotate the shaft 43 and lever 42 thereby releasing the following blind to complete the exposure. The time at which the second blind is released depends on the position of the lever 60 along the shaft 43 so that for long exposures the lever should be to the right, Fig. 6. When the shutter is rewound the discs 75, 76... &c., are automatically spaced at the appropriate angular positions. To enable " Bulb " exposures to be made, the shaft 46 carries a pivoted lever 85, Fig. 9, having a claw 85a adapted to engage a shoulder 86 on a disc 78 of the lost motion device, but normally held out of engagement by a spring 87. The disc 69 is rotated to an extreme position for a " Bulb " exposure and a projection 88a, Fig. 6, on this disc engages a block 88 to slide it along the shaft 46 and to cause an extension 89 of the block 88 to engage a flat portion of the lever 85 to lock the lever to the shaft 46. Depression of the lever 49 to effect exposure releases the leading blind, but as the discs rotate the lever 85 engages and holds the disc 78 thereby stopping the motion of the leading blind. On release of the lever 49 the shaft 46 rotates under the action of a spring 50, the disc 78 is released and the leading blind completes its motion. The engagement of a lug raises the lever 60 to release the following blind to complete the exposure. Instead of being separate the discs of the lost motion device may be rigidly connected together with the lugs at appropriato angular positions.