Patent GB-191509955-A (GB)
Title: Improvements in and relating to Focal Plane Shutters.
IPC: G03B9/34
Filed: 1915-07-08
Abstract: 9955. Prout, G. F., and Houghton- Butcher Manufacturing Co. July8. Shutters, roller-blind.-Relates to the type of shutter described in Specifications 27,461/10 and 6121/13, and consists in the provision of a geared fan which is brought into engagement with the shutter roller on winding up, and also in the provision of mechanism for enabling the shutter to be set by a single turn of the winding- knob for " instantaneous," " time," or " bulb " exposures. The shutter is of the focal-plane roller-blind type, in which the instantaneous exposures are obtained by varying the extent of the winding and thereby the width of the slit. The roller blind 1<a>, Fig. 1, is wound by turning the knob 3 clockwise, the instantaneous exposures being obtained in the ordinary way as long as the winding is stopped before the pin 4 on the gear-wheel 2 reaches the lever 9<b>. A slower instantaneous exposure is obtained by winding the wheel 2 still farther, whereupon the pin 4 turns the lever 9<b>, 8 about the pivot 9<a> and thus puts the fan 6 in gear with the shutter mechanism, so that its running-down is retarded. The exposure is made by depressing the lever 24 which operates the lever 15, which in turn operates the lever 29 pivoted at 29<a>, which forces out the pawl 25 to release the wheel 2. During the running-down of the wheel 2, the lever 9 is retained in its engaged position by means of the pin 14 on the left side of the catch 13, which forms part of a bellcrank lever attached by a link 12 to the lever 8, 9<b>, 9. When the pin 4 is wound past the point 9<c>, it pushes the plate 21 to the right and consequently moves the link 5 to the right, the link 5 being connected to the plate 21 by the pivoted link 20. When the shutter is then released, the pin 4 returns only as far as the detent 5<a>, the pin 16 holding the detent 5<a> in position by its interposition to the left of the lever 21<a>, which forms part of the plate 21. On releasing the lever 24, the detent 5 is permitted to return to its normal position out of the path of the pin 4, and the pawl 25 reengages with the wheel 2, so that the shutter is held open. On pressing the lever 24 again, the pawl 25 is forced out and the shutter closes. Time exposures are thus obtained. For bulb exposures, the knob 3 is wound slightly farther, until the pin 4 engages with the projection 26b of the plate 26 and moves this plate downwards over the pin 26<c>. The lower end of the plate is pivoted to the bell-crank 27<a> provided with a hooked end 27. On releasing the shutter by depressing the lever 24, the pin 28 on the lever 29 is retained by the hook 27 so as to hold the pawl 25 out of engagement with the wheel 2, while the shutter runs down till the pin 4 reaches the detent 5<a>. On releasing the lever 24, the pin 16 frees the lever 21<a> and consequently the detent 5<a>, and the pawl 25 being still held out of engagement by the hook 27, the shutter completes its running-down movement. To obtain the slowest instantaneous exposure, the knob 3 is wound still farther, till the pin 4 forces out the plate 21 and its connected links 20, 5 so far that the projection 30<a> of the link 20 engages with the fixed pin 32 and is tilted upwards. The links 5, 20 then slip to the left, the slot 30 moving over the pin 31, so that the detent 5<a> is not then in the path of the pin 4. On pressing the lever 24, the shutter runs down completely.