Zoom lens for projection and projection-type display apparatus

A zoom lens for projection comprising:

• a first lens group having negative refractive power, and which is composed of two lenses;
• a second lens group composed of a positive lens;
• an aperture stop;
• a third lens group composed of a positive lens;
• a fourth lens group composed of three lenses of a fourth-group-first lens, which is a negative lens, a fourth-group-second lens arranged in such a manner that a negative air lens is formed between the fourth-group-first lens and the fourth-group-second lens, and a fourth-group-third lens, which is a positive lens, and the fourth-group-first lens, the fourth-group-second lens and the fourth-group-third lens being arranged in this order from the magnification side of the zoom lens;
• and
• a fifth lens group composed of a positive lens having a convex surface facing the magnification side, and the first lens group, the second lens group, the aperture stop, the third lens group, the fourth lens group, and the fifth lens group being arranged from the magnification side in the order mentioned above,
• wherein the following formulas (2) and (3) are satisfied:
• −0.85<(R72+R71)/(R72−R71)<0.85 (2);
• and
• −6.0<f4/f5 (3), where
• R71 is a radius of curvature of a magnification-side surface of the fourth-group-third lens,
• R72 is a radius of curvature of a reduction-side surface of the fourth-group-third lens,
• f4 is a focal length of the fourth lens group, and
• f5 is a focal length of the fifth lens group.

A zoom lens for projection comprising:

• a first lens group having negative refractive power, and which is composed of two lenses;
• a second lens group composed of a positive lens;
• an aperture stop;
• a third lens group composed of a positive lens;
• a fourth lens group composed of three lenses of a fourth-group-first lens, which is a negative lens, a fourth-group-second lens arranged in such a manner that a negative air lens is formed between the fourth-group-first lens and the fourth-group-second lens, and a fourth-group-third lens, which is a positive lens, and the fourth-group-first lens, the fourth-group-second lens and the fourth-group-third lens being arranged in this order from the magnification side of the zoom lens;
• and
• a fifth lens group composed of a positive lens having a convex surface facing the magnification side, and the first lens group, the second lens group, the aperture stop, the third lens group, the fourth lens group, and the fifth lens group being arranged from the magnification side in the order mentioned above,
• wherein the following formulas (4) and (5) are satisfied:
• −6.0<fn/fw<−2.0 (4);
• and
• −11.0<f4/f2 (5), where
• fn is a focal length of the negative air lens,
• fw is a focal length of the entire system of the zoom lens at a wide angle end,
• f2 is a focal length of the second lens group, and
• f4 is a focal length of the fourth lens group.

zoom lens for projection comprising:

• a first lens group having negative refractive power, and which is composed of two lenses;
• a second lens group composed of a positive lens;
• an aperture stop;
• a third lens group composed of a positive lens;
• a fourth lens group composed of three lenses of a fourth-group-first lens, which is a negative lens, a fourth-group-second lens arranged in such a manner that a negative air lens is formed between the fourth-group-first lens and the fourth-group-second lens, and a fourth-group-third lens, which is a positive lens, and the fourth-group-first lens, the fourth-group-second lens and the fourth-group-third lens being arranged in this order from the magnification side of the zoom lens;
• and
• a fifth lens group composed of a positive lens having a convex surface facing the magnification side, and the first lens group, the second lens group, the aperture stop, the third lens group, the fourth lens group, and the fifth lens group being arranged from the magnification side in the order mentioned above,
• wherein the following formula (6) is satisfied:
• −24.0<f4/fw<−6.0 (6), where
• fw is a focal length of the entire system of the zoom lens at a wide angle end, and
• f4 is a focal length of the fourth lens group.