| 摘要 |
1465380 Automatic exposure control NIPPON KOGAKU KK 5 Dec 1974 [6 Dec 1973] 52659/74 Heading G2A S.L.R. camera has a pentaprism view-finder attachment A which incorporates light metering and automatic timing circuitry that is powered by the camera body B, receives a starting signal therefrom and transmits like to a shutter closing command. The body also includes a manually set, electronically controlled, shutter timer and can be switched to respond either to the attachment or to its built-in timer. In a first embodiment, Fig. 2 a photo-conductive element 1 logarithmically varies its resistance to alter the bias on capacitor 3 and the manually operated resistor 5 is set to represent film speed and aperture. When the shutter release is actuated switch SW1 opens and the potential stored across 3 alters the charging current presented to capacitor 10 such that the current is proportional to the linear light value. The constant of proportionality is controlled by 5 via linear expanding circuitry 7, 8 and thus the charging rate of 10 integrates both inputs. The voltage across 10 is compared with a reference in Schmitt trigger circuitry 11-13, the reference being calibrated by resistor 25. When the shutter release is operated in the camera, magnet Mg opens the shutter and current continues to flow via C6 to hold the shutter open until the exposure period is terminated as described above. A timing circuit 17-20 is also provided in the body and is set manually by 15. This may be operable by switching to "M" In a second embodiment (Fig. 4) the stored e.m.f. representing the light intensity is presented to a differential amplifier and the film speed/aperture setting value is used to provide a variable amplitude reference signal that is also input to the differential amplifier. The output from this amplifier charges a timing capacitor, the e.m.f. across which controls the duration of the "shutter open" signal which is fed to the body as before. This embodiment includes a light value indication. |
