Optical system of the real image type for finders having aspheric surfaces

Claim 2

A finder optical system of the real image type comprising four identical non-spherical lenses consisting, in the direction of incident light rays therethrough, of an objective lens, a front lens of an erecting lens system, a rear lens of said erecting lens system, and an eyepiece; said lenses being arranged on a single common optical axis in spaced relation therealong, with the spacing between adjacent lenses being correlated with the optical functions of the respective lenses and corresponding to substantially twice the focal length of the respective lenses, each lens having the following parameters: Focal Length 17.8 mm. Diameter of Entrance Pupil 2 mm phi . Radii of CurvatuRe ra 20 mm. rb 15 mm, Epsilon b -1.9. Lens Thickness d 2 mm. Refractive Index with N 1.4913. Respect to the d Line of Lens Abbe Number with Respect to V 58.8. the d Line of Lens

Claim 3

A finder optical system of the real image type comprising four identical non-spherical lenses consisting, in the direction of incident light rays therethrough, of an objective lens, a front lens of an erecting lens system, a rear lens of said erecting lens system, and an eypeiece; said lenses being arranged on a single common optical axis in spaced relation therealong, with the spacing between adjacent lenses being correlated with the optical functions of the respective lenses, and corresponding to substantially twice the focal length of the respective lenses; the finder optical system having the following parameters: Magnification of the Finder 1 Entrance Pupil 16.8 mm from the front surface of the objective lens. Diameter of Entrance Pupil 2 mm phi . Eyepoint 16.8 mm from the rear surface of the eyepiece. Radii of Curvature r1 to r8 (stated below). Coefficients of the Secondary epsilon 2, epsilon 3, epsilon 6, epsilon 7 (Stated Rotary Curved Surface below). Distances between Lens d1 to d 7 (stated below). Surfaces on the Optical axis Refractive Indexes of the N21 to N24 (Stated below). Lenses with Respect to thed Line Abbe Numbers of the Lenses V21 to V24 (Stated below). with Respect to the d Line r1 20 mm d1 20 mm N21 1.4913 V21 57.8 r2 - 15, epsilon 2 -1.9 d2 34.2 r3 15, epsilon 3 -1.9 d3 2 N22 1.4913 V22 57.8 r4 -20 d4 33.5 r5 20 d5 2 N23 1.4913 V23 57.8 r6 -15, epsilon 6 -1.9 d6 34.2 r7 15, epsilon 7 -1.9 d7 2 N24 1.4913 V24 57.8 r8 -20

Claim 4

A finder optical system of the real image type comprising four identical non-spherical lenses consisting, in the direction of incident light rays therethrough, of an objective lens, a front lens of an erecting lens system, a rear lens of said erecting lens system, and an eypeiece; said lenses being arranged on a single common optical axis in spaced relation therealong, with the spacing between adjacent lenses being correlated with the optical functions of the respective lenses, and corresponding to substantially twice the focal length of the respective lenses; the finder optical system having the following parameters: Magnification of the Finder 1 Entrance Pupil 16.8 mm from the front surface of the objective lens. Diameter of Entrance Pupil 2 mm phi . Eyepoint 16.8 mm from the rear surface of the eyepiece. Radii of Curvature r1 to r8 (stated below). Coefficients of the Secondary epsilon 2, epsilon 3, epsilon 6, epsilon 7 (Stated Rotary Curved Surface below). Distances between Lens d1 to d 7 (stated below). Surfaces on the Optical axis Refractive Indexes of the N21 to N24 (Stated below). Lenses with Respect to thed Line Abbe Numbers of the Lenses V21 to V24 (Stated below). with Respect to the d Line r1 20 mm d1 20 mm N21 1.4913 V21 57.8 r2 - 15, epsilon 2 -1.9 d2 34.2 r3 15, epsilon 3 -1.9 d3 2 N22 1.4913 V22 57.8 r4 -20 d4 33.5 r5 20 d5 2 N23 1.4913 V23 57.8 r6 -15, epsilon 6 -1.9 d6 34.2 r7 15, epsilon 7 -1.9 d7 2 N24 1.4913 V24 57.8 r8 -20