Patent ID: 9658428
Date: 2017-05-23
CPC Classifications: G02B,G03B

Claim:
1. An optical instrument, comprising: a plurality of focus lens groups, including first and second focus lenses capable of moving in an optical axis direction, a magnification lens group that is capable of movement in the optical axis direction, for changing image magnification factor of a subject image by varying focal length using movement, a plurality of focus drivers, including first and second focus drivers for respectively independently driving the first and second focus lenses within the plurality of focus lenses, a zoom driver for driving the magnification lens group, a zoom operation input section for supplying operation amount to the zoom drivers, a magnification lens position detector for detecting position of the magnification lens group in the optical axis direction, a memory for storing first and second focus position characteristic data representing relationships between a specified subject distance and positions at which the plurality of focus lens groups reach a focused state, for every position of the magnification lens group, a first focus controller for respectively outputting first and second drive amounts for the focus drivers, based on first and second focus command positions determined based on first and second focus position characteristic data that has been stored in the memory for the magnification lens position detected by the magnification lens position detector, a second focus controller for respectively calculating first and second drive amounts for focus drivers, based on first and second focus command positions determined based on first and second focus position characteristic data that has been stored in the memory for the magnification lens position detected by the magnification lens position detector, to obtain second focus instruction position by different means to the first focus controller, and outputting a third drive amount to the plurality of focus drivers, and a lens controller having a selection section for selecting any one of the first and second focus controllers, wherein: when the lens controller is changing focal length of the magnification lens group in accordance with operation amount from the zoom operation input section, the selection section selects the second focus controller, while when the focal length of the magnification lens group is not being changed in accordance with operation amount from the zoom operation input section the selection section selects the first focus controller; the second focus instruction position is an instruction position derived by adding specified correction amount data to the second focus lens position characteristic data stored in the memory; the correction amount data is obtained when the magnification lens group is moved as a result of driving the zoom drivers; a period until movement to a focal length before image magnification ratio change is determined; and in the period until movement to the focal length before focal length after the focal length change, a correction amount subtraction value is subtracted from the correction amount data every specified period data so that an absolute value of the correction amount becomes smaller.