| 摘要 |
PURPOSE:To obtain the large variation of a focal distance inspite of the small refractive power difference of a variable refractive power element by constituting an optical system of a lens group for varying the power of the whole system and a lens group consisting of the variable refractive power element. CONSTITUTION:A lens group A consists of a fixed lens group A1 and a lens group A2 movable in the optical axis direction and the power of the whole system can be varied the power by moving the lens group A2 by a helicoid or the like. The lens group B consists of the variable refractive power element 1 and an electromagnet driving circuit 9 controls current flowing into an electromagnet 6 to control the refractive power of the surface 5 of an elastic body. The position of the lens group A2 which is detected by a position detecting means 7 consisting of a potentiometer or the like, i.e. the variable power state of the whole system, is outputted to a nonvolatile memory ROM8. The ROM8 outputs a signal to the circuit 9 in accordance with the previously stored information so that the image forming surface of the whole system is set up to a prescribed position to keep the position of the image forming surface of the whole system always constant independently of the state of variable power. |
