Photographing apparatus and interchangeable lens control method

A photographing apparatus comprising:

• a focus adjustment lens which is provided within a lens barrel containing a photographing lens and is movable in an optical axis direction;
• a ring member disposed rotatably with respect to the lens barrel in an angle range from a first end point to a second end point;
• a storage unit to store a first relationship between a rotation angle of the ring member and a value related to a subject distance, and a second relationship between a position of the focus adjustment lens in the optical axis direction and a value related to a subject distance to be focused corresponding to the position of the focus adjustment lens in the optical axis direction;
• a rotation angle detection unit to detect a rotation angle of the ring member periodically;
• and
• a control unit to set a position of the focus adjustment lens in the optical axis direction according to the rotation angle of the ring member, wherein the control unit (1) judges that change of the rotation angle has started responsive to a determination that a number of times a difference between a previously obtained rotation angle and a subsequently obtained rotation angle exceeds a predetermined range exceeds a predetermined threshold, (2) calculates a value related to a subject distance corresponding to (i) the rotation angle of the ring member according to the rotation angle of the ring member, that is obtained when the determined number of times is determined to have exceeded a predetermined threshold, in accordance with judging that the change of the rotation angle has started and (ii) the first relationship, and (3) sets the position of the focus adjustment lens in the optical axis direction according to the value related to the subject distance and the second relationship.