Projection lens
A projection lens, for enlarging and projecting a picture formed on a flat fluorescent plate of a CRT projection tube, includes: a first lens unit of a plus lens, having aspheric surfaces on both surfaces, being convex to the screen side at a central portion including an optical axis, a second lens unit of a minus lens, having aspheric surfaces on both surfaces, being concave to the screen side at a central portion including an optical axis; a third lens unit of a plus lens, having spherical surfaces on both surfaces, being convex on both sides; a fourth lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being curved in concave-like to the screen side, on a peripheral portion far from the optical axis into a radial direction; and a fifth lens unit of a minus lens, being made up with a transparent liquid, commonly serving a faceplate of the CRT projection tube and a cooling, and a meniscus lens, having a thickness being nearly equal to and at least an aspheric surface directing a concave surface thereof to the screen side.
1. A projection lens, for enlarging and projecting a picture formed on a flat fluorescent plate of a CRT projection tube, comprising:
a first lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being convex to the screen side at a central portion including an optical axis thereof;
a second lens unit of a minus lens, having aspheric surfaces on both surfaces thereof, being concave to the screen side at a central portion including an optical axis thereof;
a third lens unit of a plus lens, having spherical surfaces on both surfaces thereof, being convex on both sides;
a fourth lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being curved in concave-like to the screen side, on a peripheral portion far from the optical axis into a radial direction thereof; and
a fifth lens unit of a minus lens, being made up with a transparent liquid, commonly serving a faceplate of said CRT projection tube and a cooling, and a meniscus lens, having a thickness being nearly equal to and at least an aspheric surface directing a concave surface thereof to the screen side, being disposed successively from a screen side to said CRT projection tube, wherein the following conditions (1) to (5) are satisfied:
(1) 0.1<f 0 /f 1 <0.3;
(2) −0.15<f 0 /f 2 <−0.01;
(3) 0.7<f 0 /f 3 <0.9;
(4) 0.15<f 0 /f 4 <0.35;
(5) −1.3<f 0 /f 5 <−0.9;
where, f 0 is a focal distance of a total system;
f 1 is a focal distance of said first lens unit;
f 2 is a focal distance of said second lens unit;
f 3 is a focal distance of said third lens unit;
f 4 is a focal distance of said fourth lens unit; and
f 5 is a focal distance of said fifth lens unit.
2. The projection lens, as described in claim 1 , wherein magnification change is conducted through change on a surface of said fourth lens unit and/or change on distance between said fourth lens unit and said fifth lens unit.
3. A projection lens, for enlarging and projecting a picture formed on a flat fluorescent plate of a CRT projection tube, comprising:
a first lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being convex to the screen side at a central portion including an optical axis thereof;
a second lens unit of a minus lens, having aspheric surfaces on both surfaces thereof, being concave to the screen side at a central portion including an optical axis thereof;
a third lens unit of a plus lens, having spherical surfaces on both surfaces thereof, being convex on both sides;
a fourth lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being curved in concave-like to the screen side, on a peripheral portion far from the optical axis into a radial direction thereof; and
a fifth lens unit of a minus lens, being made up with a transparent liquid, commonly serving a faceplate of said CRT projection tube and a cooling, and a meniscus lens, having a thickness being nearly equal to and at least an aspheric surface directing a concave surface thereof to the screen side, being disposed successively from a screen side to said CRT projection tube, and further comprising:
a stop, being disposed between said first lens unit and said second lens unit, wherein the following conditions (1) to (5) are satisfied:
(1) 0.1<f 0 /f 1 <0.3;
(2) −0.15<f 0 /f 2 <−0.01;
(3) 0.7<f 0 /f 3 <0.9;
(4) 0.15<f 0 /f 4 <0.35;
(5) −1.3<f 0 /f 5 <−0.9;
where, f 0 is a focal distance of a total system;
f 1 is a focal distance of said first lens unit;
f 2 is a focal distance of said second lens unit;
f 3 is a focal distance of said third lens unit;
f 4 is a focal distance of said fourth lens unit; and
f 5 is a focal distance of said fifth lens unit.
4. The projection lens, as described in claim 3 , wherein the faceplate of said CRT projection tube, which builds up said fifth lens unit, is made from a material of a refractive index from 1.65 to 1.85, and has a thickness from 3 mm to 5 mm.
5. The projection lens, as described in claim 4 , wherein magnification change is made through change on a surface of said fourth lens unit and/or change on distance between said fourth lens unit and said fifth lens unit.
6. A projection lens, for enlarging and projecting a picture formed on a flat fluorescent plate of a CRT projection tube, comprising:
a first lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being convex to the screen side at a central portion including an optical axis thereof;
a second lens unit of a minus lens, having aspheric surfaces on both surfaces thereof, being concave to the screen side at a central portion including an optical axis thereof;
a third lens unit of a plus lens, having spherical surfaces on both surfaces thereof, being convex on both sides;
a fourth lens unit of a plus lens, having aspheric surfaces on both surfaces thereof, being curved in concave-like to the screen side, on a peripheral portion far from the optical axis into a radial direction thereof; and
a fifth lens unit of a minus lens, being made up with a transparent liquid, commonly serving a faceplate of said CRT projection tube and a cooling, and a meniscus lens, having a thickness being nearly equal to and at least an aspheric surface directing a concave surface thereof to the screen side, being disposed successively from a screen side to said CRT projection tube, wherein the faceplate of said CRT projection tube, which builds up said fifth lens unit, is made from a material of a refractive index from 1.65 to 1.85, and has a thickness from 3 mm to 5 mm, and the following conditions (1) to (5) are satisfied:
(1) 0.1<f 0 /f 1 <0.3;
(2) −0.15<f 0 /f 2 <−0.01;
(3) 0.7<f 0 /f 3 <0.9;
(4) 0.15<f 0 /f 4 <0.35;
(5) −1.3<f 0 /f 5 <−0.9;
where, f 0 is a focal distance of a total system;
f 1 is a focal distance of said first lens unit;
f 2 is a focal distance of said second lens unit;
f 3 is a focal distance of said third lens unit;
f 4 is a focal distance of said fourth lens unit; and
f 5 is a focal distance of said fifth lens unit.
7. The projection lens, as described in claim 6 , wherein magnification change is made through change on a surface of said fourth lens unit and/or change on distance between said fourth lens unit and said fifth lens unit.