GB1326060A - Flash device for a camera - Google Patents

Abstract

1326060 Electronic flash units CANON K K 1 Dec 1970 [1 Dec 1969(2) 2 Oct 1970(2)] 57048/70 Heading G2A [Also in Division H2] An electronic photographic flash unit comprises a flash lamp and a main, electrolytic capacitor adapted upon triggering to be discharged through the lamp, and comprises a temperature sensitive component adapted to simulate changes in the capacitance of the capacitor caused by changes in temperature and to indicate compensatory changes in the required exposure of a photographic film. In the embodiment shown in Fig. 2, a thermistor 117 is disposed in the base-emitter of transistor 114, the thermistor adapted to have a similar temperature charateristic to an electrolytic capacitor 106 charged via diode 113, from a source 107, to discharge upon triggering into a lamp 101. The output of the transistor 114 is connected in parallel with a photo-resistor 130 in series with an ammeter 128 which may be operationally connected with the iris of a camera lens and changes in the output impendence of the transistor 114 owing to temperature changes of the thermistor are monitored as changes in the lens aperture setting. The thermistor 117 may be connected in alternative ways with respect to the transistor 114 or an S. C.R. may be used, Fig. 3 (not shown). Alternatively, a thermistor 117, Fig.4, may be connected in series with an ammeter 201 across the terminals of a power supply P, the ammeter being adapted to display directly values of light intensity empirically determined for the tube/capacitor combination at various temperatures as simulated by the thermistor, and a manual adjustment of a camera may be made in the light of the reading. In a further alternative, Fig. 5 two neon lamps 300, 301 are connected, one between a junction of resistors R1, R2 and the other, R4, R5 respectively. A thermistor 117 is in parallel with R3 in series with R1, R2 and at normal temperatures, the voltage drop across R5 is greater than that across the R2, R3, 117 combination and lamp 301 ignites, at colder temperatures, the reverse is true. The lamps may be adapted to illuminate different points on a lens aperture scale. Similar apparatus is depicted in Fig. 7 (not shown), however a thermistor with a negative coefficient is connected in series with lamps (501), (502) which are consequently illuminated only when the capacitor (106) is charged to a higher potential when at lower temperatures, compensating for the larger voltage drop across the thermistor and for the decrease in capacitance of the capacitor (106). A similar embodiment employing a positive coefficient device is given in Fig. 8 (not shown). In the alternative of Fig. 9 (not shown) a bi-metal strip is adapted to rotate an exposure indicator dial according to temperature changes.