| 摘要 |
PURPOSE:To obtain an accurate correction value with a simple detecting device, by forming the rotational angle of a zoom ring so that the angle can become the logarithmic function of the focal distance. CONSTITUTION:By rotating a zoom ring 14 a cam cylinder 11 is rotated and the movable lens of a zoom lens section A is moved forward and backward by means of the cam grooves 11a and 11b of the cam cylinder 11. Since the zoom ring 14 is marked with the logarithmic function of the focal distance of the zoom lens section A by means of the cam grooves 11a and 11b, the movable lens of the zoom lens section A moves forward and backward in the logarithmic function against the rotation of the zoom ring 14. As the movable lens moves, the position of the zoom lens 14 is detected and squared values of the focal distances of the zoom lens section A and a master lens section B are calculated by inversely transforming the detected value into its inverse logarithmic value by means of a squared value calculating device. The signal of the squared value calculating device is used for driving a driving section 23 which drives the movable lens of the master lens section B in order to adjust the focal distance. |
