Wide-angle photographic lens system with a short overall length

Claim 2

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length satisfying the following conditions (1) through (4), the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by the following formulas (5) when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: 1. 1.2f < f 1 < 1.8f 2. 0.16 < n 2 - n 1 < 0.22 3. 1.8 < - r 4 /r 5 < 2.3 4. 0.4f < - f 3 < 0.8f ##EQU3## wherein reference symbol f represents the focal length of the lens system as a whole, reference symbol f 1 represents the focal length of said first lens component, reference symbol f 3 represents the focal length of said third lens component, reference symbols n 1 and n 2 respectively represent refractive indices of said positive and negative lenses of said first lens component, and reference symbols r 4 and r 5 respectively represent radii of curvature of the front and rear surfaces of said second lens component.

Claim 3

A wide-angle photographic lens systems with a short overall length comprising a first, second and third lens component, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21554 d.sub.1 = 0.1014 n.sub.1 = 1.62299 ν.sub.1 = 58.1 r.sub.2 = -0.38921 d.sub.2 = 0.0174 n.sub.2 = 1.80440 ν.sub.2 = 39.6 r.sub.3 = 0.35753 d.sub.3 = 0.0957 r.sub.4 = 1.08906 d.sub.4 = 0.0493 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.57852 d.sub.5 = 0.1014 r.sub.6 = -0.15688 d.sub.6 = 0.0435 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.36970 ##STR1## E = 0.1235 × 10.sup.2 F = -0.1493 × 10.sup.4 G = 0.1073 × 10.sup.6 H = -0.7535 × 10.sup.6 f.sub.1 = 1.414 , f.sub.3 = -0.567 S' = 0.487 , P = 0.896 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surface, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 4

A wide-angle photographic lens systems with a short overall length comprising a first, second and third lens component, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21554 d.sub.1 = 0.1014 n.sub.1 = 1.62299 ν.sub.1 = 58.1 r.sub.2 = -0.38921 d.sub.2 = 0.0174 n.sub.2 = 1.80440 ν.sub.2 = 39.6 r.sub.3 = 0.35753 d.sub.3 = 0.0957 r.sub.4 = 1.08906 d.sub.4 = 0.0493 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.57852 d.sub.5 = 0.1014 r.sub.6 = -0.15688 d.sub.6 = 0.0435 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.36970 ##STR1## E = 0.1235 × 10.sup.2 F = -0.1493 × 10.sup.4 G = 0.1073 × 10.sup.6 H = -0.7535 × 10.sup.6 f.sub.1 = 1.414 , f.sub.3 = -0.567 S' = 0.487 , P = 0.896 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surface, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 5

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21729 d.sub.1 = 0.1012 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.42111 d.sub.2 = 0.0176 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36445 d.sub.3 = 0.0945 r.sub.4 = 1.12628 d.sub.4 = 0.0491 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.55153 d.sub.5 = 0.1012 r.sub.6 = -0.16558 d.sub.6 = 0.0434 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38325 ##STR2## E = 0.1245 × 10.sup.2 F = -0.5946 × 10.sup.3 G = 0.5206 × 10.sup.5 H = -0.3086 × 10.sup.6 f.sub.1 = 1.590 , f.sub.3 = -0.606 S' = 0.446 , P = 0.910 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 6

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21729 d.sub.1 = 0.1012 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.42111 d.sub.2 = 0.0176 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36445 d.sub.3 = 0.0945 r.sub.4 = 1.12628 d.sub.4 = 0.0491 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.55153 d.sub.5 = 0.1012 r.sub.6 = -0.16558 d.sub.6 = 0.0434 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38325 ##STR2## E = 0.1245 × 10.sup.2 F = -0.5946 × 10.sup.3 G = 0.5206 × 10.sup.5 H = -0.3086 × 10.sup.6 f.sub.1 = 1.590 , f.sub.3 = -0.606 S' = 0.446 , P = 0.910 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 7

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21655 d.sub.1 = 0.1013 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.41052 d.sub.2 = -0.0177 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36066 d.sub.3 = 0.0947 r.sub.4 = 1.12069 d.sub.4 = 0.0492 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.53469 d.sub.5 = 0.1013 r.sub.6 = -0.16428 d.sub.6 = 0.0434 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38422 ##STR3## E = 0.5398 × 10 F = -0.4996 × 10.sup.3 G = 0.4808 × 10.sup.5 H = -0.1629 × 10.sup.6 f.sub.1 = 1.636 , f.sub.3 = -0.596 S' = 0.503 , P = 0.910 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 8

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21655 d.sub.1 = 0.1013 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.41052 d.sub.2 = -0.0177 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36066 d.sub.3 = 0.0947 r.sub.4 = 1.12069 d.sub.4 = 0.0492 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.53469 d.sub.5 = 0.1013 r.sub.6 = -0.16428 d.sub.6 = 0.0434 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38422 ##STR3## E = 0.5398 × 10 F = -0.4996 × 10.sup.3 G = 0.4808 × 10.sup.5 H = -0.1629 × 10.sup.6 f.sub.1 = 1.636 , f.sub.3 = -0.596 S' = 0.503 , P = 0.910 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 9

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.22114 d.sub.1 = 0.1011 n.sub.1 = 1.67000 ν.sub.1 = 57.3 r.sub.2 = -0.42318 d.sub.2 = 0.0144 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.32388 d.sub.3 = 0.0983 r.sub.4 = 1.22274 d.sub.4 = 0.0491 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.64515 d.sub.5 = 0.1011 r.sub.6 = -0.16128 d.sub.6 = 0.0433 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.30438 ##STR4## E = 0.8133 × 10 F = -0.8612 × 10.sup.3 G = 0.6481 × 10.sup.5 H = -0.3608 × 10.sup.6 f.sub.1 = 1.502 , f.sub.3 = -0.741 S' = 0.514 , P = 0.922 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbols S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 10

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.22114 d.sub.1 = 0.1011 n.sub.1 = 1.67000 ν.sub.1 = 57.3 r.sub.2 = -0.42318 d.sub.2 = 0.0144 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.32388 d.sub.3 = 0.0983 r.sub.4 = 1.22274 d.sub.4 = 0.0491 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.64515 d.sub.5 = 0.1011 r.sub.6 = -0.16128 d.sub.6 = 0.0433 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.30438 ##STR4## E = 0.8133 × 10 F = -0.8612 × 10.sup.3 G = 0.6481 × 10.sup.5 H = -0.3608 × 10.sup.6 f.sub.1 = 1.502 , f.sub.3 = -0.741 S' = 0.514 , P = 0.922 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbols S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 11

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens component, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21735 d.sub.1 = 0.1017 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.37831 d.sub.2 = 0.0145 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36612 d.sub.3 = 0.0988 r.sub.4 = 0.99655 d.sub.4 = 0.0494 n.sub.3 = 1.62374 ν.sub.3 = 47.1 r.sub.5 = -0.45257 d.sub.5 = 0.1017 r.sub.6 = -0.16614 d.sub.6 = 0.0436 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.46848 ##STR5## E = 0.8003 × 10 F = -0.7941 × 10.sup.3 G = 0.6248 × 10.sup.5 H = -0.3443 × 10.sup.6 f.sub.1 = 1.719 , f.sub.3 = -0.524 S' = 0.493 , P = 0.902 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 12

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens component, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed as an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21735 d.sub.1 = 0.1017 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.37831 d.sub.2 = 0.0145 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36612 d.sub.3 = 0.0988 r.sub.4 = 0.99655 d.sub.4 = 0.0494 n.sub.3 = 1.62374 ν.sub.3 = 47.1 r.sub.5 = -0.45257 d.sub.5 = 0.1017 r.sub.6 = -0.16614 d.sub.6 = 0.0436 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.46848 ##STR5## E = 0.8003 × 10 F = -0.7941 × 10.sup.3 G = 0.6248 × 10.sup.5 H = -0.3443 × 10.sup.6 f.sub.1 = 1.719 , f.sub.3 = -0.524 S' = 0.493 , P = 0.902 ______________________________________ wherein reference symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 4 respectively represent Abbe's numers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and the image plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 13

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed by an aspherical layer provided on a spherical surface and having an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21171 d.sub.1 = 0.1013 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.41978 d.sub.2 = 0.0177 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36454 d.sub.3 = 0.0947 r.sub.4 = 1.14089 d.sub.4 = 0.0492 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.54446 d.sub.5 = 0.1013 r.sub.6 = -0.16634 d' = 0.00029 n' = 1.491 ν' = 57.8 r' = -0.17051 d.sub.6 = 0.0431 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38811 ##STR6## E = 0.42555 × 10 F = -0.49109 × 10.sup.3 G = 0.47535 × 10.sup.5 H = -0.21743 × 10.sup.6 f.sub.1 = 1.535 , f.sub.3 = -0.688 S' = 0.514 , P = 0.911 ______________________________________ wherein referece symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbol ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.

Claim 14

A wide-angle photographic lens system with a short overall length comprising a first, second and third lens components, said first lens component being a cemented doublet lens consisting of a positive lens and negative lens, said second lens component being a positive lens, and said third lens component being a negative meniscus lens, said wide-angle photographic lens system with a short overall length having numerical values as given below, the surface r 6 on the object side of said third lens component being formed by an aspherical layer provided on a spherical surface and having an aspherical surface expressed by formulas given below when the direction of the optical axis is represented by x axis and the direction perpendicular to the optical axis is represented by y axis: ______________________________________ r.sub.1 = 0.21171 d.sub.1 = 0.1013 n.sub.1 = 1.62280 ν.sub.1 = 57.1 r.sub.2 = -0.41978 d.sub.2 = 0.0177 n.sub.2 = 1.83400 ν.sub.2 = 37.2 r.sub.3 = 0.36454 d.sub.3 = 0.0947 r.sub.4 = 1.14089 d.sub.4 = 0.0492 n.sub.3 = 1.66672 ν.sub.3 = 48.3 r.sub.5 = -0.54446 d.sub.5 = 0.1013 r.sub.6 = -0.16634 d' = 0.00029 n' = 1.491 ν' = 57.8 r' = -0.17051 d.sub.6 = 0.0431 n.sub.4 = 1.51633 ν.sub.4 = 64.2 r.sub.7 = -0.38811 ##STR6## E = 0.42555 × 10 F = -0.49109 × 10.sup.3 G = 0.47535 × 10.sup.5 H = -0.21743 × 10.sup.6 f.sub.1 = 1.535 , f.sub.3 = -0.688 S' = 0.514 , P = 0.911 ______________________________________ wherein referece symbols r 1 through r 7 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 6 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 4 respectively represent refractive indices of respective lenses, reference symbol ν 1 through ν 4 respectively represent Abbe's numbers of respective lenses, reference symbol S' represents the distance between the lens surface in the lens system closest to the image and plane, reference symbol P represents the telephoto ratio, and reference symbols E, F, G and H respectively represent coefficients in the above formulas.