Abstract: A magnification changing device in an imaging optical system comprises a magnification changing lens system including first and second lens groups disposed in series on the optic axis of the imaging optical system, a cylindrical cam member rotatable about a rotational axis extending along the optic axis and having first and second cam grooves spirally formed in the circumference thereof, the first cam groove being formed through the peripheral wall of the cylindrical cam member, a cylindrical movable member coupled to the first lens group, the movable member being fitted to the outer periphery of the cylindrical cam member and coupled to the second cam groove to be slid in the direction of the rotational axis while the cylindrical cam member rotates, the peripheral wall of the cylinder of the movable member being partly cut away by a groove extending along the rotational axis from one end opposed to the second lens group, a bar member fitted to the inner periphery of the cylindrical cam member, and a coupling

Abstract: In a torque adjuster including a rotary shaft, a first handle or knob fitted to the rotary shaft for rotating the same shaft, a stationary member, and a first friction member provided between the first knob and the stationary member, the first knob being movable axially of the rotary shaft to vary the force with which the first knob urges the friction member, thereby adjusting the torque of the first knob, the diameter of the rotary shaft is made uniform over a predetermined range thereof so that the first knob is freely movable axially of the rotary shaft. A second friction member is provided to couple the first knob and the rotary shaft with a friction force greater than the friction force created between the first knob and the stationary member by the first friction member so that the rotation of the first knob is transmitted to the rotary shaft without any loss.