Projection lens for high definition TV

Claim 2

A projection lens for projecting on a screen an enlargement of an image appearing on a cathode ray tube (CRT), comprising, successively in a direction from the screen end to the CRT end: a first lens having a positive optical power and a convex surface facing the screen; a second lens having a positive optical power and a meniscus shape; a third lens having a negative optical power and bi-concave surfaces; a fourth lens having a positive optical power; a fifth lens having a positive optical power and bi-convex surfaces; and a sixth lens having a negative optical power and an aspheric concave surface facing said fifth lens, wherein the projection lens satisfies the following condition: 2.5≦f.sub.a /f≦5 0.45≦d.sub.8 /d.sub.10 ≦1.0 ν.sub.2 ≧50 ν.sub.3 ≦38 where: f is a focal length of the overall projection lens system; f a is a combined focal length of the first, second and third lenses; d 8 is a distance between the fourth and fifth lenses; d 10 is a distance between the fifth and sixth lenses; and ν 2 and ν 3 are respectively Abbe numbers of the second and third lenses.

Claim 3

The projection lens according to claim 1, further satisfying the following condition: 1.25≦f.sub.4 /f≦1.8 0.5≦f.sub.4 /f.sub.5 ≦1.0 where f 4 is a focal length of the fourth lens and f 5 is a focal length of the fifth lens.

Claim 4

The projection lens according to claim 1, wherein said fifth lens has an aspheric surface.

Claim 5

The projection lens according to claim 1, wherein said fifth lens is a plastic lens.

Claim 6

The projection lens according to claim 1, wherein said sixth lens is a plastic lens.

Claim 7

The projection lens according to claim 1, wherein a space between the sixth lens and a face plate of the CRT is filled with a transparent medium.

Claim 8

The projection lens according to claim 6, defined substantially as follows: __________________________________________________________________________ f = 260.076 mm FNO = 1.45 β = -18.0 ω = 24.6° f.sub.a = 920.865 mm f.sub.4 = 350.273 mm f.sub.5 = 440.981 __________________________________________________________________________ mm r.sub.1 = 304.091 d.sub.1 = 17.50 n.sub.1 = 1.59143 ν.sub.1 = 61.25 L.sub.1 r.sub.2 = 2791.969 d.sub.2 = 1.00 r.sub.3 = 172.476 d.sub.3 = 23.50 n.sub.2 = 1.68082 ν.sub.2 = 55.52 L.sub.2 r.sub.4 = 638.510 d.sub.4 = 23.76 r.sub.5 = -1583.198 d.sub.5 = 8.50 n.sub.3 = 1.76168 ν.sub.3 = 27.53 L.sub.3 r.sub.6 = 184.524 d.sub.6 = 59.22 r.sub.7 = 261.306 d.sub.7 = 17.50 n.sub.4 = 1.59143 ν.sub.4 = 61.25 L.sub.4 r.sub.8 = -974.879 d.sub.8 = 59.53 r.sub.9 * = 302.376 d.sub.9 = 29.50 n.sub.5 = 1.49383 ν.sub.5 = 57.70 L.sub.5 r.sub.10 * = -753.190 d.sub.10 = 83.65 r.sub.11 * = -100.754 d.sub.11 = 5.00 n.sub.6 = 1.49383 ν.sub.6 = 57.70 L.sub.6 r.sub.12 = ∞ d.sub.12 = 23.83 n.sub.7 = 1.40000 ν.sub.7 = 50.70 r.sub.13 = ∞ d.sub.13 = 16.00 n.sub.8 = 1.54000 ν.sub.8 = 50.70 P r.sub.14 = 4000.000 __________________________________________________________________________ Aspheric surface coefficients 9th surface (r.sub.9) 10th surface (r.sub.10) 11th surface (r.sub.11) __________________________________________________________________________ K = 1.19206 × 10.sup.-1 K = -2.16641 × 10 K = -5.91635 × 10.sup.-1 AD = 0 AD = 0 AD = -2.64843 × 10.sup.-8 AE = 0 AE = 0 AE = 5.16019 × 10.sup.-12 AF = 0 AF = 0 AF = 0 AG = 0 AG = 0 AG = 0 __________________________________________________________________________ where: L 1 -L 6 , G and P denote the first through sixth lenses, the transparent medium and the face plate of the CRT, respectively, which are elements for constituting the projection lens; FNO is F number; β is magnification factor of an projected enlarged image; ω is a semi-field angle; f 4 is a focal length of the fourth lens; f 5 is a focal length of the fifth lens; r 1 -r 14 are radii of curvature of successive surfaces of the elements in the direction from the screen end to the CRT end; d 1 -d 13 are axial distances between the surfaces; n 1 -n 8 are refractive indices with respect to e-line of the elements; ν 1 -ν 8 are Abbe numbers of the elements; K is a conic constant; AD, AE, AF, and AG are coefficients of respective aspheric surfaces each being indicated by ?.

Claim 9

The projection lens according to claim 6, defined substantially as follows: __________________________________________________________________________ f = 259.729 mm FNO = 1.45 β = -20.0 ω = 25.0° f.sub.a = 900.418 mm f.sub.4 = 369.449 mm f.sub.5 = 395.394 __________________________________________________________________________ mm r.sub.1 = 304.403 d.sub.1 = 18.00 n.sub.1 = 1.59143 ν.sub.1 = 61.25 L.sub.1 r.sub.2 = 3129.676 d.sub.2 = 1.00 r.sub.3 = 173.581 d.sub.3 = 24.00 n.sub.2 = 1.68082 ν.sub.2 = 55.52 L.sub.2 r.sub.4 = 666.633 d.sub.4 = 22.05 r.sub.5 = -1577.059 d.sub.5 = 9.00 n.sub.3 = 1.76168 ν.sub.3 = 27.53 L.sub.3 r.sub.6 = 184.935 d.sub.6 = 56.84 r.sub.7 = 314.512 d.sub.7 = 15.00 n.sub.4 = 1.68082 ν.sub.4 = 55.52 L.sub.4 r.sub.8 = -1231.735 d.sub.8 = 67.33 r.sub.9 * = 280.976 d.sub.9 = 33.50 n.sub.5 = 1.49383 ν.sub.5 = 57.70 L.sub.5 r.sub.10 * = -614.804 d.sub.10 = 78.35 r.sub.11 * = -96.269 d.sub.11 = 5.00 n.sub.6 = 1.49383 ν.sub.6 = 57.70 L.sub.6 r.sub.12 = ∞ d.sub.12 = 22.27 n.sub.7 = 1.40000 ν.sub.7 = 50.70 r.sub. 13 = ∞ d.sub.13 = 16.00 n.sub.8 = 1.54000 ν.sub.8 = 50.70 P r.sub.14 = 4000.000 __________________________________________________________________________ Aspheric surface coefficients 9th surface (r.sub.9) 10th surface (r.sub.10) 11th surface (r.sub.11) __________________________________________________________________________ K = 7.03666 × 10.sup.-1 K = -5.60962 K = -8.98400 × 10.sup.-1 AD = 0 AD = 0 AD = -2.09391 × 10.sup.-8 AE = 0 AE = 0 AE = 3.26864 × 10.sup.-12 AF = 0 AF = 0 AF = 0 AG = 0 AG = 0 AG = 0 __________________________________________________________________________ where: L 1 -L 6 , G and P denote the first through sixth lenses, the transparent medium and the face plate of the CRT, respectively, which are elements for constituting the projection lens; FNO is F number; β is a magnification factor of an projected enlarged image; ω is a semi-field angle; f 4 is a focal length of the fourth lens; f 5 is a focal length of the fifth lens; r 1 -r 14 are radii of curvature of successive surfaces of the elements in the direction from the screen end to the CRT end; d 1 -d 13 are axial distances between the surfaces; n 1 -n 8 are refractive indices with respect to e-line of the elements; ν l -ν 8 are Abbe numbers of the elements; K is a conic constant; AD, AE, AF and AG are coefficients of respective aspheric surfaces each being indicated by *.

Claim 10

A high resolution projection lens for projecting on a screen an enlargement of an image of a resolution of more than 525 lines appearing on a high resolution cathode ray tube (CRT), comprising, successively in a direction from the screen end to the CRT end: a first lens of a positive optical power having a convex surface facing the screen; a second lens of a positive optical power having a meniscus shape; a third lens of a negative optical power having bi-concave surfaces; a fourth lens of a positive optical power; a fifth lens of a positive optical power having bi-convex surfaces; and a sixth lens of a negative optical power having an aspheric concave surface facing the fifth lens.

Claim 11

A high resolution projection lens for projecting on a screen an enlargement of an image of a resolution of more than 525 lines appearing on a high resolution cathode ray tube (CRT), comprising, successively in a direction from the screen end to the CRT end: a first lens of a positive optical power having a convex surface facing the screen; a second lens of a positive optical power having a meniscus shape; a third lens of a negative optical power having bi-concave surfaces; a fourth lens of a positive optical power; a fifth lens of a positive optical power having bi-convex surfaces; and a sixth lens of a negative optical power having an aspheric concave surface facing the fifth lens.

Claim 12

The projection lens according to claim 9, satisfying the following condition: 2.5≦f.sub.a /f≦5 0.45≦d.sub.8 /d.sub.10 ≦1.0 ν.sub.2 ≧50 ν.sub.3 ≧38 where: f is a focal length of the overall lens system; f a is a combined focal length of the first through third lenses; d 8 is a distance between the fourth and fifth lenses; d 10 is a distance between the fifth and sixth lenses; and ν 2 and ν 3 are respectively Abbe numbers of the second and third lenses.

Claim 13

The projection lens according to claim 10, further satisfying the following condition:

Claim 14

25≦f 4 /f≦1.8 0.5≦f.sub.4 /f.sub.5 ≦1.0 where f 4 and f 5 are focal lengths of the fourth and fifth lenses, respectively.

Claim 15

25≦f 4 /f≦1.8 0.5≦f.sub.4 /f.sub.5 ≦1.0 where f 4 and f 5 are focal lengths of the fourth and fifth lenses, respectively.

Claim 16

The projection lens according to claim 9, wherein the fifth lens has an aspheric surface.

Claim 17

The projection lens according to claim 9, wherein the fifth lens is a plastic lens.

Claim 18

The projection lens according to claim 9, wherein the sixth lens is a plastic lens.

Claim 19

The projection lens according to claim 9, wherein a space between the sixth lens and a face plate of the CRT is filled with a transparent medium having a refractive index which is almost the same as that of each of the sixth lens and the face plate of the CRT.