| 摘要 |
PURPOSE:To prevent deviation from occurring in the detected position of the absolute position of a focusing lens even though ambient temperature changes in the case of detecting the absolute position of the focusing lens by a photointerrupter in a rear focus system zoom lens. CONSTITUTION:A light projecting element 8a constituting the photointerrupter has negative temperature characteristic, so that a current is decreased and luminance becomes low when the temperature is low. Therefore, a temperature- sensitive resistance or a thermistor 8d having positive temperature characteristic is connected to the element 8a, and the current applied to the element 8a is increased, for example, when the temperature is low, so that the luminance of the element 8a is kept constant in spite of the change of the temperature. |
