Color corrected projection lens

Claim 2

A color corrected projection lens for producing on a screen an enlargement of an image appearing on a cathode-ray tube (CRT), comprising, sequentially from the screen end: a first unit for correcting spherical aberration, coma and distortion, which is made of bi-convex element having a positive power at least one surface of which is an aspheric surface, the surface of said first unit directed toward the screen end being strongly convex; a seond unit for mainly correcting longitudinal chromatic abberation, which i made of a bi-concave element having a negative power and disposed at or in the vicinity of an entrance pupil position of said lens; a third unit for correcting astigmatism and distortion, which is made of a bi-convex element having a positive power; and a fourth unit having a negative power and having a concave surface directed toward the screen end which is strongly concave, at least said strongly concave surface of said fourth unit being an aspheric surface.

Claim 3

A color corrected projection lens as set forth in claim 1, wherein the following conditions are satisfied: 1.2<f.sub.1 /f.sub.3 <1.6 -1.4<f/f.sub.4 <-1.1 0.35<d.sub.6 /(d.sub.2 +d.sub.3 +d.sub.4)<0.75 0.2<d.sub.2 /(d.sub.2 +d.sub.3 +d.sub.4)<0.45 -1.1<(f.sub.1 +f.sub.3)/f.sub.2 <-0.7 20<ν.sub.1 -ν.sub.2 where: f is focal length of said lens; f 1 , focal length of said first unit; f 2 , focal length of said second unit; f 3 , focal length of said third unit; f 4 , focal length of said fourth unit; ν 1 , Abbe number of said first unit; ν 2 , Abbe number of said second unit; d 2 , a distance between said first unit and said second unit; d 3 , a thickness of said second unit; d 4 , a distance between said second unit and said third unit; and d 6 , a distance between said third unit and said fourth unit.

Claim 4

A color corrected projection lens as set forth in claim 1, wherein the following conditions are satisfied: 0.1<d.sub.5 /f<0.25 1.7<f.sub.12 /f<2.5 -6.5<r.sub.3 /f<-1.8 where: f is focal length of said lens; f 12 , total focal length of said first and second units; d 5 , a thickness of said third unit; and r 3 , a curvature radius of a surface directing to the screen end of said second unit.

Claim 5

A color corrected projection lens as set forth in claim 1, wherein said first and fourth units are made of plastic, and said third unit is made of glass.

Claim 6

A color corrected projection lens as set forth in claim 1, substantially described as follows: 4-130.320 mm, aperture ratio=1.10, magnification=-0.07, half angle of view=28°, __________________________________________________________________________ r.sub.1 = 92.508 d.sub.1 = 30.00 n.sub.1 = 1.49294 ν.sub.1 = 57.0 first unit r.sub.2 = -416.197 d.sub.2 = 23.39 r.sub.3 = -773.490 d.sub.3 = 4.00 n.sub.2 = 1.81264 ν.sub.2 = 25.3 second unit r.sub.4 = 420.502 d.sub.4 = 38.11 r.sub.5 = 146.358 d.sub.5 = 23.00 n.sub.3 = 1.68081 ν.sub.3 = 55.2 third unit r.sub.6 = -172.647 d.sub.6 = 42.44 r.sub.7 = -56.576 d.sub.7 = 4.00 n.sub.4 = 1.49294 ν.sub.4 = 57.0 fourth unit r.sub.8 = 332.193 d.sub.8 = 11.30 r.sub.9 = ∞ d.sub.9 = 11.30 n.sub.5 = 1.50701 F r.sub.10 = -2350.000 __________________________________________________________________________ Coefficient of aspheric surface K AD AE AF AG __________________________________________________________________________ first surface: -2.98371 × 10.sup.-1 -1.13396 × 10.sup.-7 -5.18819 × 10.sup.-12 -3.11515 × 10.sup.-15 -5.31172 × 10.sup.-19 second surface: 0.0 7.61591 × 10.sup.-8 -1.19864 × 10.sup.-11 -1.70684 × 10.sup.-15 1.99136 × 10.sup.-19 seventh surface: -6.09498 × 10.sup.-1 -3.65481 × 10.sup.-6 1.52899 × 10.sup.-9 -4.34740 × 10.sup.-14 -5.57238 × 10.sup.-19 eighth surface: 0.0 -2.26468 × 10.sup.-6 6.93637 × 10.sup.-10 -5.96819 × 10.sup.-14 -2.25483 __________________________________________________________________________ × 10.sup.-18 where: r 1 , r 2 , r 3 . . . are curvature radii of surfaces sequentially from the screen end; d 1 , d 2 , d 3 . . . , thicknesses of and distances between said units from the screen end; n 1 , n 2 , n 3 . . . , refractive indexes with respect to wavelength of 546 nm of said units from the screen end; ν 1 , ν 2 , ν 3 . . . , Abbe numbers with respect to wavelength of 546 nm of said units from the screen end; F, a face plate of said CRT: the shape of each aspheric surface indicated by asterisk (*) being a rotationally symmetrical aspheric surface expressed as follows, supposing r to be a curvature at the apex of said spheric surface, K to be a conical constant, and AD, AE, AF, AG to be higher order constants in an orthogonal system of coordinates with X-axis in the direction of optical axis: ##EQU2##

Claim 7

A color corrected projection lens as set forth in claim 1, substantially described as follows: f=131.430 mm, aperture ratio=1:1.08, magnification=-0.07, half angle of view=25°, __________________________________________________________________________ r.sub.1 = 105.148 d.sub.1 = 24.00 n.sub.1 = 1.49294 ν.sub.1 = 57.0 first unit r.sub.2 = -295.628 d.sub.2 = 23.00 r.sub.3 = -303.011 d.sub.3 = 20.00 n.sub.2 = 1.81264 ν.sub.2 = 25.3 second unit r.sub.4 = 955.215 d.sub.4 = 46.00 r.sub.5 = 129.893 d.sub.5 = 23.50 n.sub.3 = 1.72341 ν.sub.3 = 50.1 third unit r.sub.6 = -184.952 d.sub.6 = 44.00 r.sub.7 = -62.901 d.sub.7 = 4.00 n.sub.4 = 1.49294 ν.sub.4 = 57.0 fourth unit r.sub.8 = 247.546 d.sub.8 = 11.30 r.sub.9 = ∞ d.sub.9 = 11.30 F r.sub.10 = -2350.000 __________________________________________________________________________ Coefficient of aspheric surface K AD AE AF AG __________________________________________________________________________ first surface: -3.44481 × 10.sup.-1 -1.51906 × 10.sup.-7 1.77335 × 10.sup.-11 -9.44829 × 10.sup.-15 -1.31041 × 10.sup.-19 second surface: 0.0 -3.65923 × 10.sup.-8 6.05177 × 10.sup.-12 1.96865 × 10.sup.-15 -9.35704 × 10.sup.-19 seventh surface: -8.27440 × 10.sup.-1 -2.34074 × 10.sup.-6 8.17269 × 10.sup.-10 -1.45157 × 10.sup.-13 1.50963 × 10.sup.-17 eighth surface: 0.0 -1.35724 × 10.sup.-6 4.21621 × 10.sup.-10 -6.44595 × 10.sup.-14 3.93434 × 10.sup.-18 __________________________________________________________________________ where: r 1 , r 2 , r 3 . . . are curvature radii of surfaces sequentially from the screen end; d 1 , d 2 , d 3 . . . , thicknesses of and distances between said units from the screen end; n 1 , n 2 , n 3 . . . , refractive indexes with respect to wavelength of 546 nm of said units from the screen end;

Claim 8

ν 1 . ν 2 , ν 3 . . . , Abbe numbers with respect to wavelength of 546 nm of said units from the screen end; F, a face plate of said CRT: the shape of each aspheric surface indicated by asterisk (*) being a rotationally symmetrical aspheric surface expressed as follows, supposing r to be a curvature at the apex of said spheric surface, K to be a conical constant, and AD, AE, AF, AG to be higher order constants in an orthogonal system of coordinates with X-axis in the direction of optical axis: ##EQU3##

Claim 9

ν 1 . ν 2 , ν 3 . . . , Abbe numbers with respect to wavelength of 546 nm of said units from the screen end; F, a face plate of said CRT: the shape of each aspheric surface indicated by asterisk (*) being a rotationally symmetrical aspheric surface expressed as follows, supposing r to be a curvature at the apex of said spheric surface, K to be a conical constant, and AD, AE, AF, AG to be higher order constants in an orthogonal system of coordinates with X-axis in the direction of optical axis: ##EQU3##