| 摘要 |
PROBLEM TO BE SOLVED: To always realize appropriate focusing by correcting the deviation of a focal position caused when the moving speed of both of a 2nd group lens and a 3rd group lens is changed in the case of setting a zoom position by relatively moving both lenses. SOLUTION: In the case of deciding the zoom position by moving a zoom lens by cam shape, a cam inflection point P where the relative moving speed of the 2nd group lens and the 3rd group lens is largely changed is examined from relation between the change (FC change)ΔFC of focal reference FCo being the reference position at focusing time and the zoom position Zp, and is interpolated by the approximate expressions of lines A and B to obtain the FC changeΔFC before and behind the point P with the point P as reference. In the case of photographing, which expression is adopted out of the expressions of the lines A and B is examined in accordance with the zoom position Zp at that time, the FC changeΔFC is calculated based on the adopted expression of the line, and the focal reference FCo is set based on the FC changeΔFC. Based on the focal reference FCo and a distance to an object, lens extending amount is determined to focus a focus lens (1st group lens). |
