Patent GB-190302-A (GB)
Title: Improvements in or relating to photographic camera shutters
IPC: G03B9/32
Filed: 1921-10-15
Abstract: 190,302. Bettles, A. E. Oct. 15, 1921. Shutters, roller-blind.-In a focal plane shutter of the kind in which the exposure is made through a gap between the rear edge of a blind which is being rolled up and the front edge of a companion blind which is being unrolled, means are provided for varying the size of the aperture and for making possible instantaneous, bulb, and time exposures. The blinds 14, 19, Fig. 2, are brought into the " set " position by means of cogs 12, 17 engaging teeth 2, Fig. 1, of a mutilated spur-wheel mounted on a setting-disc 1, a shoulder 55 of a segment 56 on the disc engaging with a pin 54 on a spring-actuated detent 50 to keep the mechanism in the " set " position. This trigger-mechanism is operated to effect the exposure from a primary slide 44 (which in some cases operates the mirror of a reflex camera) by a pin 51 actuating a lever 52 to strike a pin 53 on the detent 50, when the blind springs come into action and effect the exposure. To allow of variation of the aperture the cog 17 is connected tu its spindle 18 through a clutch operated by a cranked lever 24, which when pressed into engagement with a slide 21 by the nose 29 of a lever 30 disengages a tooth 28 from the cog 17 and thus releases the spindle 18 from this cog and holds the spindle and its attached blind 19 stationary while the other blind 14 is being wound up. When the lever 24 is released, the cog 17 is clutched to its spindle 18 and the blind 19 is unwound at the same speed as the other blind. The lever 30 is held in the position at which it operates to keep the clutch free by a spring-pin 32 engaging the outside of a gapped cylindrical guard 5, Fig. 7, mounted adjustably on the setting-disc 1, and is released when the gap in the guard 5 comes opposite the pin, a spring 35 then operating to retract the lever 30. The guard 5 is adjusted to effect the adjustment of aperture by a cog 8<a> on the setting-disc, which may be provided with a pointer. When the first blind is completely rewound and the setting-disc is stationary, the cog 17 of the second blind is in the gap of the mutilated spur-wheel 2 so that its unwinding is completed under the action of its own spring. The mechanism so far described constitutes an instantaneous shutter. To provide for bulb and time exposures, a lever 57 pivoted at 58 and carrying a slotted arm 60 working over a stud 61 on the primary slide 44 is added and a stud 43 is provided on the primary slide so that as this slide is pressed down a tumbler 41 connected by a link 45 to the lever 30 is pressed outwards and returns as the stud 43 passes the nose 49. For bulb exposure the lever 57 is arranged in the position shown in Fig. 15 and the end 62 of the slotted arm 60 engages and presses down a pin 38 on a subsidiary slide 39 so that a second pin 36 on this slide engages the tail of the lever 24 and so holds the clutch 21 in the free position so long as the slide 44 is depressed thus keeping the second blind from unrolling and giving a bulb exposure. When the slide 44 is raised the second blind is released. For time exposure the lever 57 is positioned as in Fig. 13 so that when the slide 44 is depressed the pin 38 catches underneath the end of the tumbler 41 and remains there when the slide is raised. A second depression of the slide 44 moves the tumbler 41 outwards and releases the pin 38 so that the lever 24 rises and terminates the exposure.