Patent ID: 6930831

Claim:
A vari-focal polar alignment scope comprising; an objective optical system, a relay optical system which relays an image formed through said objective optical system to form a secondary image, and an eyepiece optical system for observing said secondary image, in that order from the object side; wherein said relay optical system comprises an erecting vari-focal viewing optical system, including a positive condenser lens element constituting a first relay lens group, a positive second relay lens group, and a positive third relay lens group, wherein said second and third relay lens groups relatively move in a direction along the optical axis thereof so as to vary the magnification of said polar alignment scope, wherein the following conditions (1), (2) and (3) are satisfied: 6.0 <f o /fe <10.0 (1); −4.0 <M 2L <−1.0 (2); and 0.2 <M 3L <0.6 (3); wherein f o designates the focal length of said objective optical system; fe designates the focal length of said eyepiece optical system; M 2L designates the lateral magnification of said second lens group of said relay optical system at a low magnification; and M 3L designates the lateral magnification of said third lens group of said relay optical system at a low magnification.