Patent GB-679734-A (GB)
Title: Improvements relating to photographic shutters
IPC: G03B9/34
Filed: 1949-10-31
Abstract: 679,734. Photographic roller blind shutters. WRAY (OPTICAL WORKS), Ltd., and EDWARDS, C. A. Oct. 30, 1950 [Oct. 31, 1949], No. 27875/49. Class 98 (i). In a double blind roller blind shutter, the trailing blind winding means is driven by a hand-operated winding member which also winds the leading blind through a friction drive and drives a rotatable member carrying a dog engageable with one of a series of steps in an adjustable exposure determining member to limit the winding, of the trailing blind, the winding of the leading blind being limited by a fixed stop engaging with a stop driven from the leading blind, the winding mechanism being held in a " set " condition by a detent which engages a member driven by the trailing blind winding roller and which is disengaged to make an exposure. As shown, each of the leading and trailing blinds 5, 9 is attached to a separate roller as 6, freely mounted on a fixed adjustable shaft 28 to which it is connected by a driving spring 32 and both blinds are tensioned by rotating the winding shaft 39. A drum 11 for the trailing blind is secured to this shaft, and pulleys 8 for the tapes 7 of the leading blind are freely mounted on flanged bushings 44, themselves rotatable on the shaft 39 and provided on the outer flange face with ratchet teeth 43 engaged by pins 41 on the hubs 40 of the drum 11 from which the pulleys are driven by friction clutches, each comprising deformed spring discs 47 on opposite sides of the pulley engaged by a lock-nut 46 and a shouldered inner flange face of the bushing. The movement of the blind 5 is limited by a gear 33 on its roller driving a gear 34 carrying a peg 36 which in turn engages opposite faces of a fixed stop 37 so as only just to cap and uncover the exposure gate 4 during winding and release. The winding shaft 39 is rotated by gearing 48, 49 from a gear 51 on the shaft 52 of a manual knob, one revolution anticlockwise of the gear 51 bringing a lug 59 on a disc 57 against the right-hand face of a fixed stop 60 and causing winding of the blind 9 to produce the largest slit. Secured to the gear 51 and extending just beyond its teeth is a disc 90 (Fig. 9, not shown) against which bears a ratchet 53, the disc being cut away so that the ratchet engages the gear 51 and holds the shutter set for all exposure settings. The blind 5 being held against the pull of its spring 32 by the friction clutches 47 carried by the locked shaft 39. To release the shutter the plunger 72 is depressed, when the nose 76 of a member secured to a clockwiseurged pivoted lever 75 moves clockwise, a lever 70 pivoted on a slidable plate 61 and disengages the pawl from the gear 51. Faster instantaneous exposures are selected by rotating a knob on the shaft of a disc 65 carrying a pin 64 engaging in a slot 63 in the plate 61 which has a series of steps 62 which arrest the lug 59 at positions corresponding to different slit widths, the lever 70 being positioned so that the nose 76 engages the edge 77, permitting only a small movement of the lever 75 so that its finger 84 remains clear of the lugs 85, 86 on the disc 57. A further rotation of the disc 65 moves the step 78 into the path of the nose 76, so that on releasing the shutter the finger 84 moves into the path of the lug 85 and arrests the shutter as soon as the blind 5 has cleared the aperture 4, but before the blind 9 has reached it, so that a bulb exposure is effected, the shutter closing only on releasing the trigger. For a time exposure, the disc 65 is rotated still further, bringing the step 79 into the path of the trigger nose 76 and causing the finger 84 to engage with the lug 86 when the shutter is wide open. Release of the trigger, however, merely causes the finger 84 to move inwardly and engage the side 88 of the lug 85 so that it again stops the disc 57 by engaging the face 89 of the lug, and the gear is not released to close the shutter until the release is again depressed, moving the finger 84 outwards behind the lug 86. A winding knob and ratchet mechanism, releasable by a hand-operated detent, may be provided for increasing the tension of the trailing blind take-up roller.