Encoder for exposure controller of motorised aperture diaphragm in camera

摘要

The encoder (100) has a rotatable shaft (58a), a disk (58) rotating with the shaft and having a light modulating pattern e.g. a series of slits (S1-Sn) or reflective areas, and a photosensor (56) to detect the pattern e.g. via transmission or reflection. The pattern is provided around less than the entire circumference of the disk to provide one angular range (58b) where the photosensor output does not vary during rotation and another (58c) where the output varies at intervals in accordance with the pattern. When used in a camera having a lens shutter, a controller sets the shutter diaphragm as closed at an initial position in the first angular range and controls the degree of opening of the diaphragm according to the signals from the photosensor produced in the second range. The pattern spacing may vary to increase the sensitivity at small apertures.