Projection lens

Claim 2

A projection lens for producing on a screen an enlargement of an image appearing on a cathode-ray tube (CRT), comprising: successively from the screen end, a Gauss type lens system, a positive lens unit contributing mainly to enlarging the aperture ratio and comprising at least one lens; and a negative lens unit contributing mainly to widening the field angle and having a strongly concave surface which faces the screen end, said projection lens satisfying the following conditions: 1.2f<f.sub.1-5 <1.6f (1) 1.4f<f.sub.6 <1.7f (2) 0.1f<d.sub.11 <0.3f (3) -1.4f<f.sub.7 <-f (4) where, f: focal length of the overall system f 1-5 : focal length of the Gauss type lens system f 6 : focal length of the positive lens unit contributing mainly to enlarging the aperture ratio f 7 : focal length of the negative lens unit contributing mainly to widening the field angle d 11 : interplane spacing between the Gauss type lens system and the positive lens unit contributing mainly to enlarging the aperture ratio.

Claim 3

The projection lens according to claim 1, having substantially the following characteristics: __________________________________________________________________________ f = 148.264 mm aperture ratio 1:1.1 magnification of projection × 10.5 f.sub.1-5 = 1.3173f f.sub.6 = 1.4635f f.sub.7 = -1.0979f d.sub.11 = 0.2753f __________________________________________________________________________ first lens unit r.sub.1 = 170.31 mm d.sub.1 = 14.22 mm n.sub.1 = 1.67790 ν.sub.1 = 55.5 r.sub.2 = 981.29 mm d.sub.2 = 0.59 mm second lens unit r.sub.3 = 93.32 mm d.sub.3 = 18.53 mm n.sub.2 = 1.69350 ν.sub.2 = 53.3 r.sub.4 = 259.13 mm d.sub.4 = 0.59 mm third lens unit r.sub.5 = 275.33 mm d.sub.5 = 3.54 mm n.sub.3 = 1.54072 ν.sub.3 = 47.3 r.sub.6 = 61.51 mm d.sub.6 = 56.75 mm fourth lens unit r.sub.7 = - 76.53 mm d.sub.7 = 3.95 mm n.sub.4 = 1.75520 ν.sub.4 = 27.7 r.sub.8 = 4872.80 mm d.sub.8 = 20.46 mm n.sub.5 = 1.69350 ν.sub.5 = 53.3 r.sub.9 = -98.26 mm d.sub.9 = 0.28 mm fifth lens unit r.sub.10 = 291.93 mm d.sub.10 = 18.39 mm n.sub.6 = 1.69350 ν.sub.6 = 53.3 r.sub.11 = -215.90 mm d.sub.11 = 40.82 mm sixth lens unit r.sub.12 = 264.48 mm d.sub.12 = 30.60 mm n.sub.7 = 1.49178 ν.sub.7 = 57.7* r.sub.13 = -172.05 mm d.sub.13 = 44.10 mm * seventh lens unit r.sub.14 = -80.05 mm d.sub.14 = 3.95 mm n.sub.8 = 1.49178 ν.sub.8 = 57.7* r.sub.15 = ∞ d.sub.15 = 16.92 mm n.sub.9 = 1.45 r.sub.16 = ∞ d.sub.16 = 11.62 mm n.sub.10 = 1.50 r.sub.17 = -2350.00 mm __________________________________________________________________________ Aspherical coefficient K AD AE AF AG __________________________________________________________________________ twelfth surface: -1.4213 -0.1833 × 10.sup.-7 0.8328 × 10.sup.-11 -0.6460 × 10.sup.-15 0.1536 × 10.sup.-18 thirteenth surface: 1.3146 -0.3321 × 10.sup.-7 0.2188 × 10.sup.-11 0.1849 × 10.sup.-14 -0.8994 × 10.sup.-19 fourteenth surface: 0.6996 -0.1432 × 10.sup.-6 0.3929 × 10.sup.-10 0.6206 × 10.sup.-15 -0.2109 × 10.sup.-18 __________________________________________________________________________ where r 1 , r 2 , r 3 , . . . represent radii of curvature of the lens surfaces successively from the screen end; d 1 , d 2 , d 3 , . . . represent thicknesses and spacings of the lenses; n 1 , n 2 , n 3 , . . . represent refractive indices at line d of the lenses; ν 1 , ν 2 , ν 3 , . . . represent Abbe's numbers at line d; f represents the focal length of the overall system; f 1-5 represents the focal length of the Gauss type lens system comprising the first to fifth lens units; f 6 represents the focal length of the sixth lens unit; and f 7 represents the focal length of the seventh lens unit; the * marked surfaces represent aspherical surfaces which are in the shape of a revolution-symmetric aspherical surface represented by the following equation in a rectangular coordinate system with the X axis extending in the direction of the optical axis, provided r is a vertex radius of curvature, k is a conical constant, and AD, AE, AF and AG are aspherical coefficients: ##EQU2## n 9 represents the refractive index of a medium filled in the space between the seventh lens unit and the face plate of the cathode-ray tube; and F represents the face plate of the cathode-ray tube.

Claim 4

The projection lens according to claim 1, having substantially the following characteristics: __________________________________________________________________________ f = 149.128 mm aperture ratio 1:1.15 magnification of projection × 10.5 f.sub.1-5 = 1.4815f f.sub.6 = 1.5188f f.sub.7 = -1.2940f d.sub.11 = 0.1300f __________________________________________________________________________ first lens unit r.sub.1 = 293.62 mm d.sub.1 = 11.20 mm n.sub.1 = 1.67790 ν.sub.1 = 55.5 r.sub.2 = ∞ d.sub.2 = 0.58 mm second lens unit r.sub.3 = 94.42 mm d.sub.3 = 15.58 mm n.sub.2 = 1.69350 ν.sub.2 = 53.3 r.sub.4 = 176.36 mm d.sub.4 = 1.49 mm third lens unit r.sub.5 = 195.87 mm d.sub.5 = 11.73 mm n.sub.3 = 1.54072 ν.sub.3 = 47.3 r.sub.6 = 62.58 mm d.sub.6 = 67.78 mm fourth lens unit r.sub.7 = -70.29 mm d.sub.7 = 3.89 mm n.sub.4 = 1.75520 ν.sub.4 = 27.7 r.sub.8 = 5129.85 mm d.sub.8 = 20.69 mm n.sub.5 = 1.69350 ν.sub.5 = 53.3 r.sub.9 = -88.89 mm d.sub.9 = 1.14 mm fifth lens unit r.sub.10 = 271.21 mm d.sub.10 = 27.21 mm n.sub.6 = 1.69350 ν.sub.6 = 53.3 r.sub.11 = -244.09 mm d.sub.11 = 19.38 mm sixth lens unit r.sub.12 = 292.07 mm d.sub.12 = 33.23 mm n.sub.7 = 1.49178 ν.sub.7 = 57.7* r.sub.13 = -173.30 mm d.sub.13 = 63.57 mm * seventh lens unit r.sub.14 = -94.90 mm d.sub.14 = 3.89 mm n.sub.8 = 1.49178 ν.sub.8 = 57.7 r.sub.15 = ∞ d.sub.15 = 17.10 mm n.sub.9 = 1.45 r.sub.16 = ∞ d.sub.16 = 11.62 mm n.sub.10 = 1.50 r.sub.17 = -2350.00 mm __________________________________________________________________________ Aspherical coefficient K AD AE AF AG __________________________________________________________________________ twelfth surface: -0.2401 -0.1110 × 10.sup. -7 0.1044 × 10.sup.-10 -0.2219 × 10.sup.-15 0.4493 × 10.sup.-19 thirteenth surface: -0.6534 0.4773 × 10.sup.-8 0.8093 × 10.sup.-11 0.9191 × 10.sup.-15 -0.8274 × 10.sup.-19 __________________________________________________________________________ where r 1 , r 2 , r 3 , . . . represent radii of curvature of the lens surfaces successively from the screen end; d 1 , d 2 , d 3 , . . . represent thickness and spacings of the lenses; n 1 , n 2 , n 3 , . . . represent refractive indices at line d of the lenses; ν 1 , ν 2 , ν 3 , . . . represent Abbe's numbers at line d; f represents the focal length of the overall system; f 1-5 represents the focal length of the Gauss type lens system comprising the first to fifth lens units; f 6 represents the focal length of the sixth lens unit; f 7 represents the focal length of the seventh lens unit; the * marked surfaces represent aspherical surfaces which are in the shape of a revolution-symmetric aspherical surface represented by the following equation in a rectangular coordinate system with the X axis extending in the direction of the optical axis, provided r is a vertex radius of curvature, k is a conical constant, and AD, AE, AF and AG are aspherical coefficients: ##EQU3## n 9 represents the refractive index of a medium filled in the space between the seventh lens unit and the face plate of the cathode-ray tube; and F represents the face plate of the cathode-ray tube.

Claim 5

A projection lens for producing on a screen an enlargement of an image appearing on a cathode-ray tube (CRT), comprising: successively from the screen end, a first lens unit which is a positive lens; a second lens unit which is a positive meniscus lens having a convex surface facing the screen end; a third lens unit which is a negative meniscus lens having a convex surface facing the screen end; a fourth lens unit which is a negative meniscus lens having a strongly concave surface facing the screen end and having a cemented surface; fifth and sixth lens units which are both positive lenses; and a seventh lens unit which is a negative lens having a strongly concave surface facing the screen end, said projection lens satisfying the following four conditions: 1.2f<f.sub.1-5 <1.6f (1) 1.4f<f.sub.6 <1.7f (2) 0.1f<d.sub.11 <0.3f (3) -1.4f<f.sub.7 <-f (4) where, f: focal length of the overall system f 1-5 : focal length of the system from the first to fifth lens units f 6 : focal length of the sixth lens unit f 7 : focal length of the seventh lens unit d 11 : interplane spacing between the fifth and sixth lens units.

Claim 6

A projection lens for producing on a screen an enlargement of an image appearing on a cathode-ray tube (CRT), comprising: successively from the screen end, a first lens unit which is a positive lens; a second lens unit which is a positive meniscus lens having a convex surface facing the screen end; a third lens unit which is a negative meniscus lens having a convex surface facing the screen end; a fourth lens unit which is a negative meniscus lens having a strongly concave surface facing the screen end and having a cemented surface; fifth and sixth lens units which are both positive lenses; and a seventh lens unit which is a negative lens having a strongly concave surface facing the screen end, said projection lens satisfying the following four conditions: 1.2f<f.sub.1-5 <1.6f (1) 1.4f<f.sub.6 <1.7f (2) 0.1f<d.sub.11 <0.3f (3) -1.4f<f.sub.7 <-f (4) where, f: focal length of the overall system f 1-5 : focal length of the system from the first to fifth lens units f 6 : focal length of the sixth lens unit f 7 : focal length of the seventh lens unit d 11 : interplane spacing between the fifth and sixth lens units.