Patent ID: 7206129

Claim:
A real image type zoom finder, comprising, in order from an object side thereof, an objective optical system for forming an intermediate image-formation plane, an image-erection optical system for erecting the intermediate image-formation plane formed by said objective optical system, and an eyepiece optical system for viewing said intermediate image-formation plane, wherein: said objective optical system comprises, in order from an object side thereof, a first lens group of negative refracting power, a second lens group of positive refracting power, a third lens group of negative refracting power and a fourth lens group of positive refracting power, and upon zooming from a wide-angle end to a telephoto end of the zoom finder, said first lens group and said fourth lens group remain fixed, said second lens group moves toward the object side of the zoom finder at the wide-angle end rather than at the telephoto end of the zoom finder, and said third lens group moves toward an image side of the zoom finder at the telephoto end rather than at the wide-angle end, wherein said first lens group consists of one single lens of double-concave shape, which satisfies the following condition: 0<SF1<0.65 where SF1=(r 1 +r 2 )/(r 1 −r 2 ) provided that r 1 is an axial radius of curvature of an object side-surface of the double-concave lens in the first lens group, and r 2 is an axial radius of curvature of an image side-surface of the double-concave lens in the first lens group, wherein a surface located nearest to the object side in said first lens group is an aspheric surface axially concave on an object side thereof, said aspheric surface being configured in such a shape as to decrease in refracting power with distance from an optical axis of the objective optical system.