Projection variable focusing lens and projection display device
View Patent ↗A projection variable focusing lens and a projection display device that has a reduction side which is telecentric, a high magnifying power, a small size, a light weight, and a low manufacturing cost and is capable of correcting all aberrations occurring when power varies with good balance. A projection variable focusing lens that moves only one lens group when power varies includes a first negative lens group G 1 , a second positive lens group G 2 , a third lens group G 3 , and a fourth positive lens group G 4 arranged in this order from a magnification side. When a focal length varies, only the second lens group G 2 is moved along an optical axis X. During focusing, the third lens group G 3 is moved along the optical axis X. A reduction side is substantially telecentric.
1. A projection variable focusing lens comprising:
a first lens group having a negative refractive power;
a second lens group having a positive refractive power;
a third lens group, wherein the third lens group includes a first negative lens, a second positive lens having a convex surface facing the reduction side, and a third positive lens having a convex surface facing the reduction side arranged in this order from the magnification side; and
a fourth lens group having a positive refractive power,
wherein the first to fourth lens groups are arranged in this order from a magnification side, and
when a focal length varies, the second lens group is moved in an optical axis direction,
during focusing, the third lens group is moved in the optical axis direction, and
a reduction side is substantially telecentric.
2. The projection variable focusing lens according to claim 1 ,
wherein the second lens group satisfies the following conditional expression:
1.0 <f 2 /f w <4.0
where f w indicates the focal length of the entire system at a wide angle end, and f 2 indicates the focal length of the second lens group.
3. The projection variable focusing lens according to claim 2 , wherein
the second lens group satisfies the following conditional expression:
1.3 <f 2 /f w <3.0.
4. The projection variable focusing lens according to claim 2 , wherein
the second lens group satisfies the following conditional expression:
1.5 <f 2 /f w <2.5.
5. The projection variable focusing lens according to claim 1 ,
wherein the second lens group satisfies the following conditional expression:
0.15 <D 2 /L< 0.55
where D 2 indicates the largest surface spacing between lenses in the second lens group and L indicates the total length of the lenses.
6. The projection variable focusing lens according to claim 1 ,
wherein the second lens group includes two positive lenses.
7. The projection variable focusing lens according to claim 1 ,
wherein the fourth lens group includes one positive lens having a convex surface facing the magnification side.
8. The projection variable focusing lens according to claim 1 ,
wherein the third lens group satisfies the following conditional expression:
f 3 /f w <−3.0
where f 3 indicates the focal length of the third lens group.
9. The projection variable focusing lens according to claim 1 ,
wherein the first lens group has two lenses including a negative lens that has a concave surface facing the reduction side.
10. The projection variable focusing lens according to claim 1 ,
wherein the first lens group includes one negative lens having a concave surface facing the reduction side.
11. The projection variable focusing lens according to claim 9 ,
wherein the first lens group includes at least one aspheric surface.
12. The projection variable focusing lens according to claim 10 ,
wherein the first lens group includes at least one aspheric surface.
13. The projection variable focusing lens according to claim 1 ,
wherein the first lens group has two lenses including a negative lens that has a concave surface facing the reduction side,
the second lens group includes two positive lenses,
the fourth lens group includes one positive lens having a convex surface facing the magnification side, and
the entire system includes eight lenses.
14. The projection variable focusing lens according to claim 1 ,
wherein the first lens group includes one negative lens having a concave surface facing the reduction side,
the second lens group includes two positive lenses,
the fourth lens group includes one positive lens having a convex surface facing the magnification side, and
the entire system includes seven lenses.
15. A projection display device comprising:
at least one light source;
at least one light valve;
at least one illumination optical unit that guides light emitted from the light source to the light valve; and
the projection variable focusing lens according to claim 1 ,
wherein the light valve modulates the light emitted from the light source, and
the modulated light is projected onto a screen by the projection variable focusing lens.