| 摘要 |
PURPOSE:To enable best focusing regardless of the temperature difference between the outside and the inside of a device, the temperature characteristic of an optical system, or the variation in a visual field by providing a gate pulse setting circuit, a differentiation circuit, a peak value detecting circuit, etc. CONSTITUTION:A gate pulse setting circuit 19 is provided which controls the timing when only an object signal is extracted from the output of one of detecting element groups constituting a linear array detector 4. A differentiating circuit 18 which differentiates the extracted object signal and a peak value detecting circuit 20 which detects a peak value of the output of the circuit 18 are provided, and a focusing mechanism 11 is so controlled that the output of the circuit 20 is always maximum. In case of focusing, the mechanism 22 is driven in a preliminarily determined direction by initial driving, and the peak value of the differentiated output is detected in every scanning of a scanning mirror 3 and is stored. The driving direction of the mechanism 11 is inverted only when the result of successive comparison indicates the direction of reduction, thereby always controlling the device to an in-focus position. |
