| 摘要 |
PURPOSE:To increase the accuracy of focusing operation by changing the driving speed of a focusing lens group according to focal lengths. CONSTITUTION:A stationary lens group 1, a movable lens group 2 for variable magnifications, a lens group 3 for correction, a focusing lens group 4 and a film plane 5 are provided. The lens grouPs 2, 3 are moved along grooves 6, 7 respectively by zoom operation, and the lens group 1 is immobile. The focusing lens group 4 is moved by a pulse motor 12, and a driving circuit 11 outputs forward run pulses or reverse run pulses according to the states of front focus and rear focus by the signal from a focus detector 10. The generation of pulses is stopped by the focusing detection signal, by which the movement of the lens group 4 is stopped. The frequency of the output pulses of the circuit 11 is changed by the output signal of a focal length detecting means 9, and according to the varying lengths of the focusing distance, the driving speed of the lens group 4 is changed. |
