Patent GB-657620-A (GB)
Title: Improved single blind roller-blind shutter for photographic cameras
IPC: G03B9/30
Filed: 1948-01-16
Abstract: 657,620. Photographic roller-blind shutters. DUCAEI SOC. SCIENTIFICA RADIO BREVETTI DUCATI. Jan. 16, 1948, No. 1432. Convention date, April 28, 1947. [Class 98 (i)] A single blind shutter in which the blind driving force is varied to obtain different exposures has two or more springs driving one of the shutter blind drums and arranged between the drum and its shaft, the cumulative tension driving the blinds only for the shorter exposures and a single spring only for the longer, one spring having its ends permanently connected between the drum and its shaft while the other spring or springs has one end permanently connected to said shaft and the other end engageable with said drum for the short times only, said shaft being rotatably adjustable to govern the tension of said springs as required. The speed of the blind may also be regulated by the action of an auxiliary mass connected by means of a weak spring to the drum on which the blind is wound ready for release, said mass following exactly at low speeds the movements of the moving parts of the shutter but lagging behind at high speeds. As shown, a shutter blind 101 (Fig. 2) having an aperture equal to the exposure frame for the film is wound on drums 102, 103 rotatable on shafts 134, 108. The shutter is wound, tensioning its driving spring 132 secured between the drum 102 and the shaft 134 and also a releasably-connected driving spring 133 by rotating the film winding knob on a shaft 104 geared to the shaft 108, when a disc 109 (see Fig. 5) on this shaft, carrying on a pivot 111 a lever 110 urged clockwise as seen in Fig. 2 by a spring (not shown), moves the nose 110<SP>1</SP> of the lever into engagement with a tooth 112 on the drum 103 and rotates it clockwise until the rear of the tooth abuts against a stop member 154, the shutter then being set and prevented from unwinding due to a one-way pawl acting on the gear 105 on the shaft 104. A pair of capping blades 124, 125, pivoted at 121, 126 for movement perpendicular to their planes and connected to a rotatable member 120 on the pivot 121, exclude light from the film during setting. On depressing the release button 116, a lever 113 pivoted at 114 rotates clockwise so that a pin 118 on it rotates the member 120 anticlockwise to open the capping blades and a lug 117 on the lever 113 releases the latch between the lever 110 and the tooth 112 on the drum 103. The blind having made the exposure, it is brought to rest without rebound by the tooth 112 on the drum 103 engaging in a slot 160 on the member 154, which is pin-and-slot mounted on the casing, moving it to the left against an increasing resistance afforded by a V-shaped deformation 159 in a fixed leaf-spring 158 bearing against a curved recess 157 in the member 154. For slow exposures only, the spring 132 drives the drum 103 and a cylindrical mass 128 freely mounted on the shaft and connected to the drum by a weak spring 129, rotates with the drum by engagement of a tooth 130 on the mass 128 with a tooth (not shown) on the drum, thereby rendering the motion of the drum more uniform. Different slow exposures are produced by means of an adjustable dashpot retard device carried by a lever 146 pivoted on the casing at 147 and having a spring 152 extending into the path of a pin 153 on the drum 103, said spring yielding to allow clockwise passage of the pin during setting the shutter, the initial setting of the lever 146 and hence spring 152 being controlled by a cam 1431 on the shaft 134 which is rotatable by a speed setting knob 141 having a pin 143 engageable in suitably spaced holes in the casing. For bulb exposures, a lug on the cam prevents rotation of the lever 146 under the engagement of pin 153 with the spring 152, the capping blinds closing the exposure aperture when the trigger is released. For faster exposures, the retard mechanism is held out of action and the spring 133 secured between the shaft 134 and a cup 135 which is freely mounted on said shaft and has a tooth 136 arranged to be engaged by a pin 138 which is carried on a ring also freely mounted on the shaft and engages a radial wall 140 on the drum, so that the tension of the spring 133 is determined by the angular setting of the shaft 134 as determined by the knob 141. To prevent double exposures, the lever 113 which releases the drum 103 is formed with an extension 117 which engages the disc 109, thus preventing actuation of the release except when a complete frame has been wound on and the shutter set, when an arcuate recess 171 in the disc comes opposite the extension 117. Specification 651,221 is referred to.