Patent GB-833745-A (GB)
Title: Photographic camera
IPC: G03B9/18
Filed: 1956-05-12
Abstract: 833,745. Focal plane shutters. CHATANI, K. May 12, 1956, No. 14860/56. Class 98(1) The focal plane shutter of a photographic camera comprises two pairs of rigid blades adapted to move in sequence across the exposure aperture so to to effect an exposure through a slit between the blades of pre-set width which is constant during a particular exposure, the blades being pivoted and balanced on levers, the other ends of which engage slides which co-operate with cams which are free to be rotated so as alternately to load and operate the shutter. As shown in Fig. 1, the shutter is disposed behind the camera exposure aperture 4 and comprises two pairs of shutter blades la, 1b and 2a, 2b, the blade of each pair being pivotally interconnected by levers 7, 14 and 8, 15 of which the levers 7 and 8 are pivotally mounted on balancing slides 5, 6 on a rail 11. Pins projecting from the slide 5 and from a spring plate attached to slide 6 are provided for engagement with spiral cam grooves 18, 19 on a rotor 20 so that, as the latter rotates counterclockwise, the slides 5, 6 are moved downwardly on the rail 11 and, due to a phase difference between the spiral cams, a slit is formed between the two pairs of blades to effect an exposure. To prevent double exposures, it is arranged that, during the shutter setting operation, the slide 6 is carried upwards by the slide 5, as the rotor 20 is turned clockwise, so that there is no slit between the pairs of shutter blades, the pin projecting from the attached spring plate of slide 6 riding over the rotor surface. This setting of the shutter is effected by rotating clockwise a knob 54, Figs. 1 and 6, on an axially movable shaft 26 which is cross-pin connected to a gear 28, meshing with a gear 29 so as to windup the shutter spring 25, gear 29 also being meshed with a gear 27 so as to turn the rotor 20 for moving the slides 5, 6 upwardly. Shaft 26 is also cross-pin connected with a sleeve 35 for frictionally rotating a film reel 34, the sleeve having a toothed flange meshing with a film sprocket so that the film is wound on one frame as the shutter is set. Release of the shutted is effected by depression of a button 55, housed in the knob 54 and connected to the shaft 26, to disengage the cross-pins and allow counter-clockwise rotation of rotor 20, under the force of spring 25, to move slides 5, 6 downwardly. The width of the exposure slit formed between the two pairs of shutter blades may be varied from zero to that of exposure aperture 4 by rotating a knob 84 on a shaft 74, Fig. 8, on which a sleeve 72b is axially movable and at the same time rotatable with the shaft. This sleeve 72b is threaded on a sleeve 72a from which projects a pin 79 riding in a spiral slot in a fixed sleeve 75 so that, as shaft 74 rotates, the sleeves 72a, 72b move up or down. These sleeves carry a pin 70 which projects through symmetrical cam slots 68, 69 in relatively rotatable parts 20a, 20b, which together form the rotor 20 and respectively house the cam grooves 18, 19 for slides 5, 6 and so, as shaft 74 rotates, the parts 20a, 20b rotate in opposite directions to vary the phase difference between the grooves 18, 19 and thus the width of the exposure slit that is formed. Rotation of shaft 74 until pin 70 enters a straight part in each slot 68, 69 ensures an exposure slit of the width of aperture 4. The shaft 74, also has secured thereto a cam wheel 86, Fig. 12, on the part circular outline of which a follower 88 rides during the rotation of shaft 74 necessary to provide for the maximum exposure slit. If a larger exposure is required, shaft 74 is rotated further so that the follower moves on to the involute outline of cam 86 and positions one limb 89b of a pivoted lever 89, connected to a slow speed governor in the path of a pin 94 on the gear 29, the exposure then being dependent upon the position of follower 88 on the involute part of cam 86. When the shutter is released, the gearing 27, 28, 29 rotates at normal speed until the shutter blades 1a, 1b have moved upwardly to open the exposure slit, and then, while the exposure is being made, at a slow speed only, due to the engagement by pin 94 and limb 89b and the operation of speed governor 93, and finally, when pin 94 moves off the limb 89b, at normal speed again to cause shutter blades 2a, 2b to move upwardly and terminate the exposure. In order that the speed of the shutter blade movement may vary inversely with the exposure time, the end of spring 25 remote from the gear 29 may be connected to a shaft, which is geared to the lower end of the shaft 74, so that turning of shaft 74 through an increasing angle to set the shutter blades for long exposures results in a decrease in the spring tension. An involute spring is provided to maintain shaft 74 in adjusted position.