| 摘要 |
1531888 Exposure control in cameras KONISHIROKU PHOTO INDUSTRY CO Ltd 12 July 1976 [21 July 1975] 28969/76 Heading G2A A camera has an array of photodiodes PD 1 PD 2 ... PDn located in or near the image plane, means for determining the maximum, minimum and average logarithmic outputs and means for controlling exposure time or aperture in dependance on one of said outputs. As shown, the photodiode outputs are logarithmically amplified to provide signals P 1 , P 2 ...P n . Circuits PH, VH and MH respectively store P max , P min and P av and amplifiers OP 1 , OP 2 respectively calculate P max -P min and (P max + P min )/2. A comparator CP1 compares P max - P min with a reference value #, and the following possibilities arise: (i) P max -P min # #. This means the speed of signals P 1 ... P n is small, so a switch AS 3 is turned on and the signal P av is used to control exposure. (ii) P max -P min > #. This means that the spread is large and is provided by a light or dark subject against a dark or light background. To determine the nature of the background, a second comparator CP2 compares (P max + P min )/2 with P av . If P av is the smaller, the background is dark, a switch AS, is turned on and the signal P max is used to control exposure. If P av is the larger, switch AS2 is turned on and the signal P min is used. |
