Optical system for use with a viewfinder

Claim 2

An optical system for use with a viewfinder in a single-lens reflex camera, which optical system has a finder screen side and an eyepoint side and comprises, in order from the finder screen side, a first lens unit comprising a positive lens element and a second lens unit comprising a negative lens element, said optical system satisfying the following conditions: -2<SF1<0 (1) 0<SF2<3 (2) where SF1 is the shape factor of the first lens unit, SF2 is the shape factor of the second lens unit and with the shape factor of each lens unit being defined by: ##EQU2## where R S is the radius of curvature of the surface of each lens unit on the finder screen side, and R E is the radius of curvature of the surface of each lens unit on the eyepoint side.

Claim 3

An optical system according to claim 1 wherein at least one of the four surfaces delineating said first and second lens units is aspheric.

Claim 4

An optical system according to claim 2, wherein said aspheric surface is of a shape expressed by: ##EQU3## where X is the distance measured from the apex along the optical axis in the direction in which rays travel, Y is the height from the optical axis, R is the radius of curvature of a reference spherical plane, K is the shape factor of a rotating quadratic curved plane, and A 2m is the asphericity coefficient of a higher degree.

Claim 5

An optical system according to claim 1, which further satisfies the condition: 0.05<(d.sub.1 +d.sub.2 +d.sub.3)/f<0.3 where d 1 is the thickness of said first lens unit in the direction of an optical axis of said system, d 2 is the distance between said first and second lens units on the optical axis, d 3 is the thickness of said second lens unit in the direction of said optical axis, and f is the composite focal length of the optical system.

Claim 6

An optical system according to claim 2, which further satisfies the condition: 0.05<(d.sub.1 +d.sub.2 +d.sub.3)/f<0.3 where d 1 is the thickness of said first lens unit in the direction of an optical axis of said system, d 2 is the distance between said first and second lens units on the optical axis, d 3 is the thickness of said second lens unit in the direction of said optical axis, and f is the composite focal length of the optical system.

Claim 7

An optical system according to claim 1, wherein said first lens is made of an acrylic resin and said second lens made of a polycarbonate resin.

Claim 8

An optical system according to claim 1, wherein said first lens unit consists of said first lens element and said second lens unit consists of said second lens element.

Claim 9

An optical system according to claim 1, which further satisfies the condition: 1.0<f.sub.F /f<1.3 where f F is the distance from the finder screen to the first lens surface of the first lens unit, and f is the composite focal length of the optical system.

Claim 10

An optical system according to claim 2, which further satisfies the condition: 1.0<f.sub.1 /f<1.3 where f F is the distance from the finder screen to the first lens surface of the first lens unit, and f is the composite focal length of the optical system.

Claim 11

An optical system according to claim 1, wherein said first and second lens units are cemented together.

Claim 12

An optical system according to claim 2, wherein said first and second lens units are cemented together.

Claim 13

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 15.534 6.476 1.49186 57.4 -0.23684 -7.74061 × 10.sup.-8 2 -28.357 2.154 -7.37018 3 -53.238 1 1.58547 29.9 4 18 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder voverage: 95% f=70.229 Magnification: 0.740X (52/70.229) SF1=-0.292 SF2=0.495 (d 1 +d 2 +d 3 )/f=0.137 f F /f=1.153

Claim 14

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 14.489 6.224 1.49186 57.4 -0.34447 -7.28882 × 10.sup.-8 2 -34.501 2.005 -11.6694 3 -146.305 1 1.58547 29.9 4 15 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=69.961 Magnification: 0.743X (52/69.961) SF1=-0.408 SF2=0.814 (d 1 +d 2 +d 3 )/f=0.132 f F /f=1.158

Claim 15

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 13.231 8.203 1.49186 57.4 -0.275 -1.30316 × 10.sup.-7 2 -24.387 1.231 -9.80573 2.4702 × 10.sup.-8 3 -110.535 1 1.71736 29.3 4 15 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=67.03 Magnification: 0.776X (52/67.03) SF1=-0.297 SF2=0.761 (d 1 +d 2 +d 3 )/f=0.156 f F /f=1.208

Claim 16

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 14.678 7.6 1.49186 57.4 -0.38849 -9.08487 × 10.sup.-8 2 -28.267 2.153 -9.04108 3 -333.815 1 1.80518 25.4 4 18 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=67.314 Magnification: 0.772X (52/67.314) SF1=-0.316 SF2=0.898 (d 1 +d 2 +d 3 )/f=0.160 f F /f=1.203

Claim 17

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coveraqe is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 13.944 7.548 1.49186 57.4 -0.43628 -9.28391 × 10.sup.-8 2 -31.306 1.94 -12.3174 3 136.934 1 1.80518 25.4 4 15 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=66.927 Magnification: 0.777X (52/66.927) SF1=-0.384 SF2=1.246l (d 1 +d 2 +d 3 )/f=0.157 f F /f=1.210

Claim 18

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 12.472 7.237 1.49186 57.4 -0.49027 -8.40087 × 10.sup.-8 2 -69.886 1.944 -53.6169 3 30.528 1 1.80518 25.4 4 11.288 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=65.58 Magnification: 0.793X (52/65.58) SF1=-0.697 SF2=2.173 (d 1 +d 2 +d 2 )/f=0.155 f F /f=1.235

Claim 19

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 16.589 5.989 1.49186 57.4 -0.88321 -1.00077 × 10.sup.-7 2 -38.051 3.144 3 -142.669 1 1.58547 29.9 4 18 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=70.066 Magnification: 0.742X (52/70.066) SF1=-0.393 SF2=0.776 (d 1 +d 2 +d 3 )/f=0.145 f F /f=1.156

Claim 20

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 4i denotes a biquadratic asphericity coefficient of the ith surface and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 15.091 6.814 1.49186 57.4 2 -24.665 1.820 -6.00198 -8.98476 × 10.sup.-6 3 -31.262 1 1.58547 29.9 4 20.510 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=70.273 Magnification: 0.740X (52/70.273) SF1=-0.241 SF2=0.208 (d 1 +d 2 +d 3 )/f=0.137 f F /f=1.152

Claim 21

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 4i denotes a biquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81.004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 13.991 6.168 1.49186 57.4 2 -51.422 2.250 3 -86.065 1 1.58547 29.9 58.9175 -5.27521 × 10.sup.-5 4 18 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=69.757 Magnification: 0.745X (52/69.757) SF1=-0.572 SF2=0.654 (d 1 +d 2 +d 3 )/f=0.135 f F /f=1.161

Claim 22

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 81 004 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 12.463 6.502 1.49186 57.4 2 -73.265 1.886 3 -60.334 1 1.58547 29.9 4 18.165 4.40044 -4.80934 × 10.sup.-7 __________________________________________________________________________ Distance from the screen to the first surface: 81.004 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=68.342 Magnification: 0.761X (52/68.342) SF1=-0.709 SF2=0.537 (d 1 +d 2 +d 3 )/f=0.137 f F /f=1.185

Claim 23

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, A 4i denotes a biquadratic asphericity coefficient of the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 74.6 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i A.sub.6i __________________________________________________________________________ 1 12.818 8.5 1.49186 57.4 0.22455 -5.72694 × 10.sup.-6 -8.00138 × 10.sup.-8 2 63.022 0 3 63.022 1.5 1.58547 29.9 4 18 4.08541 -2.04666 × 10.sup.-7 __________________________________________________________________________ Distance from the screen to the first surface: 74.6 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=65.211 Magnification: 0.797X (52/65.211) SF1=-1.511 SF2=1.800 (d 1 +d 2 +d 3 )/f=0.153 f F /f=1.144

Claim 24

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a refractive index of the jth lens (optical material) at the d-line, v j denotes an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, A 4i denotes a biquadratic asphericity coefficient of the ith surface, and denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 95% and the distance from the finder screen to the first surface is 74.6 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i A.sub.6i __________________________________________________________________________ 1 15.175 8.5 1.49186 57.4 0.51174 -6.7107 × 10.sup.-6 -4.61234 × 10.sup.-8 2 737.592 0 3 737.592 1.5 1.58547 29.9 4 25.562 7.51188 -2.60332 × 10.sup.-8 __________________________________________________________________________ Distance from the screen to the first surface: 74.6 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 95% f=68.746 Magnification: 0.756X (52/68.746) SF1=-1.042 SF2=1.072 (d 1 +d 2 +d 3 )/f=0.145 f F /f=1.085

Claim 25

An optical system according to claim 1, satisfying the following data table, in which SN denotes a surface number starting from the finder screen side, r i denotes a radius of curvature (in millimeters) of the ith surface, d i denotes a distance (in millimeters) between the ith and (i+1)th surfaces, n j denotes a the d-line, v j denote's an Abbe number of the jth lens (optical material), K i denotes a shape factor of a rotating quadratic curved plane for the ith surface, and A 6i denotes a triquadratic asphericity coefficient of the ith surface, and wherein the distance from the fourth surface to the eyepoint is 15 mm, the effective finder coverage is 92% and the distance from the finder screen to the first surface is 75.013 mm: __________________________________________________________________________ SN r.sub.i d.sub.i n.sub.j ν .sub.j K.sub.i A.sub.6i __________________________________________________________________________ 1 19.175 5.70 1.49186 57.4 -0.781 -1.523 × 10.sup.-8 2 -82.5 2.10 3 82.5 1.5 1.49186 57.4 4 18 __________________________________________________________________________ Distance from the screen to the first surface: 75.013 Distance from the fourth surface to the eyepoint: 15 Effective finder coverage: 92% f=70.719 Magnification: 0.735X (52/70.719) SF1=-0.623 (d 1 +d 2 +d 3 )/f=0.132 f F /f=1.061

Claim 26

In a finder system having a hollow pentaprism for passing light from a screen to an eyepoint, the improvement wherein said finder system further comprises a positive first lens element and a negative second lens element in order from the screen side, wherein both of said first and second lens elements are made of an arcylic resin.

Claim 27

In a finder system having a hollow pentaprism for passing light from a screen to an eyepoint, the improvement wherein said finder system further comprises a positive first lens element and a negative second lens element in order from the screen side, wherein both of said first and second lens elements are made of an arcylic resin.