Lens device and position detection method of movable optical element

A lens device having a movable optical element, the lens device comprising:

• a rotary member which rotates in accordance with a movement of the movable optical element;
• a first magnetic recording scale and a second magnetic recording scale which are recorded with magnetic signals having different wavelengths, respectively, the first magnetic recording scale and the second magnetic recording scale being fixedly disposed on an outer periphery of the rotary member to extend along a peripheral direction of the rotary member;
• a signal detecting unit which detects a first signal corresponding to a magnetic signal having a first wavelength recorded in the first magnetic recording scale and a second signal, of which a phase is shifted from that of the first signal by a predetermined amount from the first magnetic recording scale, and detects a third signal which corresponds to a magnetic signal having a second wavelength which is different from the first wavelength and is recorded in the second magnetic recording scale and a fourth signal, of which a phase is shifted from that of the third signal by the predetermined amount from the second magnetic recording scale;
• and
• a position detecting unit which detects a position of the movable optical element based on the signals which are detected by the signal detecting unit,
• wherein the position detecting unit includes:
• a phase difference calculating unit which calculates a phase difference between the first signal and the third signal, based on the first signal, the second signal, the third signal, and the fourth signal for one cycle which are detected by the signal detecting unit;
• a phase average calculating unit which calculates an average of the phase differences respectively calculated for n (n is a natural number of 2 or larger) cycles by the phase difference calculating unit;
• and
• an absolute position detecting unit which detects an absolute position of the movable optical element based on the average which is calculated by the phase average calculating unit,
• wherein the lens device further comprises:
• an error data storing unit which stores, as error data, a difference between a movement average for every n phase differences which is obtained by moving the movable optical element from end to end within a movable range and a designed value of the movement average for every n phase differences, and
• wherein the absolute position detecting unit compares the average obtained by the phase average calculating unit and the error data to correct the average based on the error data and detects the absolute position based on the corrected average.