Patent GB-550675-A (GB)
Title: Improvements in and relating to apparatus for testing photographic shutters
IPC: G04F13/02
Filed: 1941-11-28
Abstract: 550,675. Testing photographic shutters. KODAK, Ltd. Nov. 28, 1941, No. 15376. Convention date, March 5. [Class 98 (i)] [Also in Group XL] A photo-electric apparatus for testing photographic shutters comprises a light-sensitive cell subjected to illumination through the shutter during the period of its operation and a relay circuit operated thereby to charge a condenser during the same period, the charge thus acquired being measured by a meter and compared with the charge which should have been produced for the time indicated by the shutter graduation. As shown, light from a lamp 10 passes through lenses 17, 12 and a chopper 18, 19 to the shutter 13 and thence through a lens 14 and a diffusing screen 16 to a cell 15. This cell is connected to a circuit comprising a voltage amplifier 20, an adjustable gain control 21, a power amplifier 22, and a rectifier unit 23. This unit includes a diode 24 for converting the alternating current into direct current and a second diode 25 for feeding the direct current to the measuring network. In addition, the output of the amplifier 20 is connected to a power amplifier 44 which controls a relay 46 in the measuring network through a diode rectifier 45, a glow tube 51 being provided across the relay to limit the potential on the relay. The measuring network comprises two condensers 26, 36 adapted to be charged through two adjustable resistances 27, 37 and two valve voltmeters 33, 34, 35 and 39, 40, 41 for indicating the voltage to which the condensers are charged all connected as shown with switch 57, and resistances 53, 54 controlled by contact member 47 of relay 46. Electric power for the several parts comes from a supply 50. The operation is as follows : The shutter is first closed to pass no light and the pointer 30, which serves to adjust both resistances 27, 37 simultaneously, is set at the checking position CHK; the resistances 34, 40 are then adjusted until both meters 33, 39 register 100. Next, the shutter is opened to the maximum amount desired, and the gain control 21 is adjusted until the maximum output voltage for which the apparatus is designed is obtained from the rectifying unit 23 ; this voltage may be measured by a voltmeter 55 across the load resistance 56 of the rectifying unit, or by one the meters 33 or 39 switched in circuit for this purpose. The apparatus having been thus prepared, the pointer 30 is set to the shutter speed to be tested, the condensers 26, 36 are fully discharged by temporarily closing the switch 57, and the shutter 13 then tripped at the speed to be tested. The relay 46, 47 closes for the time during which the shutter is open, and during that time the condenser 36 is charged from the constant voltage source 50, so that its voltage at the end is a measure of the time during which the shutter remained open. During the same time, the other condenser 26 is charged from the voltage delivered by the rectifying unit 23 which depends on the amount of illumination passed by the shutter ; hence the voltage attained by the condenser 26 is a measure of the equivalent exposure produced by the shutter.