AFOCAL VARIABLE POWER OPTICAL SYSTEM

Japanese Patent JPH04204616

A

PURPOSE:To suppress a virtual in a visual field arising from variable power and to provide the afocal variable power optical system which is compact and is well corrected in aberration by moving 2nd and 3rd lens groups along the optical axis in the directions varying from each other, thereby executing the variable power. CONSTITUTION:An objective optical system which consists, successively from an object side, of a positive 1st lens group, an erecting prism system and a negative 2nd lens group and an eyepiece optical system which consists of a 3rd lens group constituted of three elements and a positive 4th lens group constituted of one piece are arranged. The variable power is executed by moving the 2nd and 3rd lens groups along the optical axis in the directions varying from each other. Further, only the size of the image is eventually changed in the specified visual field at the time of the variable power and an observing person is enabled to more easily view the way of the variable power by satisfying the following conditions: few/fet<=1.30; 1.70