Patent GB-990943-A (GB)
Title: Photoelectric exposure control means
IPC: G03B7/085
Filed: 1963-05-02
Abstract: 990,943. Photo-electric exposure control systems. EASTMAN KODAK CO. May 2, 1963 [May 2, 1962], No.17313/63. Heading G2A. Inconsistency in the response of an electromagnetic relay used in a photo-electric exposure control system, due to magnetic hysteresis in the iron relay core is eliminated by pre-determining the magnetic history of said core before each exposure. An electromagnetic control relay 10 has soft iron core 12 with coil 14, and two resilient soft-iron armatures 22, 24 which may control diaphragm vanes 40, 50, adjustable limit members 17, 19 being provided. A manual control actuates arm 64 to close contacts 66, 68 thereby passing maximum current through coil 14 and saturating the magnetic circuit: both armatures are then drawn inwardly to give the smallest aperature. Further depression of arm 64 breaks contacts 69, 70 to introduce photo-resistance 56 into the coil circuit, and the magnetizing current is then controlled in dependence on the prevailing light conditions. The armatures comprise springs of different stiffness and are therefore released from core 12 at different times as the coil current is reduced when light intensity decreases. Three different apertures settings are therefore available. Further depression at arm 64 rocks a member 72 to release the shutter; the arm is then released to restore the initial conditions. A single armature and vane may be used to give only two aperture settings. In a modification, the armatures are heavier and are pivoted at their centres of gravity, adjustable non-magnetic leaf-springs urging them away from the relay core. The calibration of the system is therefore not upset by different camera positions. The relay may be used with a cine camera having a rotating disc type shutter or whose shaft is mounted a cam which actuates a pivoted arm controlling contacts 66, 68 and 69, 70 such that the photo-cell 56 is switched into the coil circuit while the shutter is open. The relay may also set both aperture and shutter speed if one armature in Fig. 1 is used to move the speed selecting lever of the shutter. Armature-sensing system. In the modification shown in Fig. 16 the position of the armatures 22<SP>1</SP>, 24<SP>1</SP> of the gravity balanced relay referred to above, is sensed by a manually movable mechanism coupled to the diaphragm. Vanes 110, 112 form an aperture 124, 126 and have slots 118, 120 engaging pin 132 for vertical movement, and are pivotally secured to arm 114 rocking about shaft 116 on manually operated arm 128 pivoted at 129 and spring loaded at 130. Vane 110 has a saddle position 107 with unequal arms 106, 108 which engage the armature 22<SP>1</SP> and 24<SP>1</SP> whichever has been released. Arms 206,107 are urged towards the armatures by spring 127, but are held disengaged by the more powerful spring 130 which pulls arm 128 clockwise and hence pulls vane 112 upwards by the engagement with the arm of the ear 133. Manual depression of arm 128 allows the armature sensing operation to proceed and the aperture to be set; further depression of arm 128 trips shutter release 136. Vane 110 may have a projecting ear to set a shutter speed controlling member. The relay is calibrated by illuminating the photo-cell at the light intensity required for the transition from the smallest to the next size aperture and the appropriate armature spring is then adjusted to just allow the armature to release. The illumination is reduced to the lowest value required and the other spring is adjusted. In another embodiment, a common armature spring 142 is used with the gravity balanced relay, and two values of threshold current are obtained by adjusting the air gaps between armatures and core by means of non-ferrous screws 150,152 whereby the magnetic forces on the armatures are made different. Agreater range of aperture settings becomes available if spring 142 is mounted on line 151 and so exerts different torques on the armatures. Fire adjustment automatic control system. Soft-iron armature 164 pivots at shaft 162 carries a diaphragm vane 166 with aperture 168, and is connected by link 172 to second vane 176 pivoted at 180 and having aperture 178. Fixed cantilever spring 212 co-operates with ear 169 and urges the armature anti-clockwise against stop 165 for maximum aperture. The relay core comrpises soft-iron bell-crank 202 mounted on bracket 208 pivoted at 162 and spring-loaded at 204, with adjustable non-ferrous spacing screws 210 abutting ear 171 of the armature. The other end 200 of bell-crank 202 has a bifurcated tip co-operating with shoulder 198 of actuating member 192 sliding  in sleeve 193 and having at its lower end a disc 190 which engages a spring-loaded lever 188 pivoted at 162 whose pawl co-operates with ratchet 182 integral with vane 176. Depression at member 192 frees lever 188 and allows pawl and ratchet 184,182 to engage, while further depression of member 192 rocks bell-crank clockwise about shaft 162, armature 164 following until spring 212 overcomes the magnetic attraction of the bellcrank when the armature separates and is retained in position by the pawl and ratchet whereby the setting of the aperture vanes is preserved. Further depression of member 192 trips shutter release 191, and when the member is raised the initial conditions are restored. The response of spring 212 is controlled by means of the adjustable curvature of fixed backing member 220. Another form has two main armatures each with two open and one closed position, and a third armature whose release permits the first two armatures to move to their fully open positions.