Refraction-type projection lens

Claim 2

A projection lens for projecting an image on a screen, comprising from the screen side a first lens means comprising at least a meniscus element with both surfaces convex relative to the screen, a second lens means comprising a cemented glass lens, a single glass lens separate from said cemented glass lens and a plastic aspherical lens, said single glass lens being disposed between said cemented glass lens and said plastic aspherical lens, said single glass lens and said plastic aspherical lens having confronting surfaces of which that of said single glass lens is of lesser radius than that of said plastic aspherical lens, and a third lens means of negative power with one concave surface toward the screen.

Claim 3

A projection lens as defined in claim 1, wherein said second lens means has the highest lens power of the three said lens means.

Claim 4

A projection lens as defined in claim 1, wherein said single glass lens has the highest lens power of the three lenses of said second lens means.

Claim 5

A projection lens as defined in claim 1, wherein said first lens means comprises a single plastic meniscus lens.

Claim 6

A projection lens as claimed in claim 1, wherein said first lens means comprises a meniscus lens with one aspherical surface.

Claim 7

A projection lens as claimed in claim 1, wherein said third lens means comprises a field-flattener lens with one aspherical surface.

Claim 8

A projection lens as defined in claim 5, wherein said meniscus lens is made of plastic.

Claim 9

A projection lens as defined in claim 6, wherein said field-flattener lens is made of plastic.

Claim 10

A projection lens as defined in claim 1, wherein said plasti caspherical lens has an aspherical surface defined by the following equation: Z=a.sub.1 y.sup.2 +a.sub.2 y.sup.4 +a.sub.3 y.sup.6 +a.sub.4 y.sup.8 +a.sub.5 y.sup.10 where Z: the surface sag at a semi-aperture distance y (mm) from the optical axis (Z axis) of the lens, the origin being the point of intersection of the lens surface and the optical axis, a 1 , a 2 , . . . , a 5 : aspherical coefficient.

Claim 11

A projection lens as defined in claim 1, wherein both exposed surfaces of said cemented glass lens are aspherical and both exposed surfaces of said single glass lens are spherical.

Claim 12

A projection lens as defined in claim 1, wherein one surface of said plastic aspherical lens is flat.

Claim 13

A projection lens for projecting an image on a screen, comprising from the screen side a first lens means comprising at least a meniscus aspherical lens with both surfaces convex relative to the screen, a second lens means comprising a cemented glass lens, a single glass lens and a plastic aspherical lens, and a third lens means of negative power which is an aspherical lens with one concave surface toward the screen, wherein said aspherical lenses have aspherical surfaces each of which is defined by the following equation: Z=a.sub.1 y.sup.2 +a.sub.2 y.sup.4 +a.sub.3 y.sup.6 +a.sub.4 y.sup.8 +a.sub.5 y.sup.10 where Z: the surface sag at a semi-aperture distance y (mm) from the optical axis (Z axis) of the lens, the origin being the point of intersection of the lens surface and the optical axis, a 1 , a 2 , . . . a 5 : aspherical coefficient, and said respective lenses have the following values: ______________________________________ r.sub.1 145.89 d.sub.1 3.50 n.sub.1 1.492 ν.sub.1 57.2 r.sub.2 177.10 d.sub.2 107.65 r.sub.3 71.54 d.sub.3 25.00 n.sub.2 1.623 ν.sub.2 60.3 r.sub.4 -143.81 d.sub.4 2.50 n.sub.3 1.678 ν.sub.3 32.2 r.sub.5 139.41 d.sub.5 0.80 r.sub.6 92.67 d.sub.6 16.50 n.sub.4 1.518 ν.sub.4 64.0 r.sub.7 -257.11 d.sub.7 2.00 r.sub.8 ∞ d.sub.8 2.50 n.sub.5 1.492 ν.sub.5 57.2 r.sub.9 -963.18 d.sub.9 54.65 r.sub.10 -50.31 d.sub.10 4.00 (mm) n.sub.6 1.492 ν.sub.6 57.2 r.sub.11 ∞ (mm) ______________________________________ Aspherical Coefficients: ______________________________________ r.sub.1 r.sub.9 r.sub.10 ______________________________________ a.sub.1 3.4273 × 10.sup.-3 -5.1911 × 10.sup.-4 -9.9394 × 10.sup.-3 a.sub.2 -8.6020 × 10.sup.-8 8.5020 × 10.sup.-7 -2.3211 × 10.sup.-6 a.sub.3 -1.6183 × 10.sup.-11 1.0470 × 10.sup.-11 4.9388 × 10.sup.-10 a.sub.4 -9.0629 × 10.sup.-16 7.0244 × 10.sup.-14 -3.4879 × 10.sup.-13 a.sub.5 -1.4306 × 10.sup.-19 -1.3909 × 10.sup.-17 -1.1994 × 10.sup.-16 ______________________________________ where r 1 -r 11 is the paraxial radius (mm) of curvature of the lens surface starting with the lens surface nearest the screen, d 1 -d 10 is the axial distance (mm) between the lens surfaces starting with the lens surface nearest the screen, n 1 -n 6 is the refractive index of the respective lenses starting from the lens nearest the screen, and ν 1 -ν 6 is the Abbe-number of the respective lenses starting with the lens nearest the screen.

Claim 14

A projection lens for projecting an image on a screen, comprising from the screen side a first lens means comprising at least a meniscus aspherical lens with both surfaces convex relative to the screen, a second lens means comprising a cemented glass lens, a single glass lens and a plastic aspherical lens, and a third lens means of negative power which is an aspherical lens with one concave surface toward the screen, wherein said aspherical lenses have aspherical surfaces each of which is defined by the following equation: Z=a.sub.1 y.sup.2 +a.sub.2 y.sup.4 +a.sub.3 y.sup.6 +a.sub.4 y.sup.8 +a.sub.5 y.sup.10 where Z: the surface sag at a semi-aperture distance y (mm) from the optical axis (Z axis) of the lens, the origin being the point of intersection of the lens surface and the optical axis, a 1 , a 2 , . . . a 5 : aspherical coefficient, and said respective lenses have the following values: ______________________________________ r.sub.1 145.89 d.sub.1 3.50 n.sub.1 1.492 ν.sub.1 57.2 r.sub.2 177.10 d.sub.2 107.65 r.sub.3 71.54 d.sub.3 25.00 n.sub.2 1.623 ν.sub.2 60.3 r.sub.4 -143.81 d.sub.4 2.50 n.sub.3 1.678 ν.sub.3 32.2 r.sub.5 139.41 d.sub.5 0.80 r.sub.6 92.67 d.sub.6 16.50 n.sub.4 1.518 ν.sub.4 64.0 r.sub.7 -257.11 d.sub.7 2.00 r.sub.8 ∞ d.sub.8 2.50 n.sub.5 1.492 ν.sub.5 57.2 r.sub.9 -963.18 d.sub.9 54.65 r.sub.10 -50.31 d.sub.10 4.00 (mm) n.sub.6 1.492 ν.sub.6 57.2 r.sub.11 ∞ (mm) ______________________________________ Aspherical Coefficients: ______________________________________ r.sub.1 r.sub.9 r.sub.10 ______________________________________ a.sub.1 3.4273 × 10.sup.-3 -5.1911 × 10.sup.-4 -9.9394 × 10.sup.-3 a.sub.2 -8.6020 × 10.sup.-8 8.5020 × 10.sup.-7 -2.3211 × 10.sup.-6 a.sub.3 -1.6183 × 10.sup.-11 1.0470 × 10.sup.-11 4.9388 × 10.sup.-10 a.sub.4 -9.0629 × 10.sup.-16 7.0244 × 10.sup.-14 -3.4879 × 10.sup.-13 a.sub.5 -1.4306 × 10.sup.-19 -1.3909 × 10.sup.-17 -1.1994 × 10.sup.-16 ______________________________________ where r 1 -r 11 is the paraxial radius (mm) of curvature of the lens surface starting with the lens surface nearest the screen, d 1 -d 10 is the axial distance (mm) between the lens surfaces starting with the lens surface nearest the screen, n 1 -n 6 is the refractive index of the respective lenses starting from the lens nearest the screen, and ν 1 -ν 6 is the Abbe-number of the respective lenses starting with the lens nearest the screen.