| 摘要 |
When a photographic film cassette is loaded in a camera and a rear lid of the camera is closed, a current adjusting circuit supplies a light emitting element of a photo-sensor with a drive current while stepwise increasing the value of the drive current and comparing a maximum value of the output signal from the photo-sensor with a predetermined maximum level. The value of the drive current, at which the maximum value of the output signal reaches the predetermined maximum level, is stored as an optimum current value. Thereafter, photographic film is advanced from the cassette to position each exposure frame in an exposure aperture of the camera, with reference to the position of perforations formed in association with the exposure frames. The position of each perforation is determined based on a rising edge of the output signal from the photo-sensor while driving the light emitting element at the optimum current value.
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