Zoom lens for projection and projection-type display apparatus
A zoom lens for projection includes a negative magnification-side lens group fixed while magnification is changed, a plurality of lens groups that move while magnification is changed, and a positive reduction-side lens group fixed while magnification is changed which are arranged in this order from the magnification side. The magnification-side lens group is composed of a negative front-group and a positive rear-group, arranged in this order from the magnification side. The rear-group is composed of a positive lens, a negative lens and a positive lens, arranged in this order from the magnification side, and focusing is performed by moving the rear-group. Further, the following formulas (1) and (2) are satisfied: 1.73< N dRpAVE (1); and 60<ν dRn (2), where N dRpAVE is an average value of refractive indices of the positive lenses in the rear-group, and ν dRn is the Abbe number of the negative lens in the rear-group.
1. A zoom lens for projection comprising:
a magnification-side lens group having negative refractive power, and which is fixed while magnification is changed;
a plurality of lens groups that move along an optical axis while magnification is changed; and
a reduction-side lens group having positive refractive power, and which is fixed while magnification is changed, the magnification-side lens group, the plurality of lens groups, and the reduction-side lens group being arranged in this order from the magnification side of the zoom lens,
wherein the magnification-side lens group is composed of a front group having negative refractive power and a rear group having positive refractive power, which are arranged in this order from the magnification side, and
wherein the rear group is composed of a positive lens, a negative lens and a positive lens, which are arranged in this order from the magnification side, and
wherein focusing is performed by moving the rear group along the optical axis, and
wherein the reduction side of the zoom lens is telecentric, and
wherein the following formulas (1) and (2) are satisfied:
1.73 <N dRpAVE (1);
and
60<ν dRn (2),
where
N dRpAVE is an average value of refractive indices of the positive lenses in the rear group with respect to d-line, and
ν dRn is the Abbe number of the negative lens in the rear group with respect to d-line.
2. A zoom lens for projection, as defined in claim 1 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when the magnification-side lens group is a first lens group, the following formula (3) is satisfied:
−2.5 <f 1 /f<− 1.5 (3),
where
f 1 is a focal length of the first lens group when projection distance is at infinity, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
3. A zoom lens for projection, as defined in claim 1 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a most-magnification-side lens group of the plurality of lens groups is a second lens group, the following formula (4) is satisfied:
4.0 <f 2 /f< 7.0 (4),
where
f 2 is a focal length of the second lens group, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
4. A zoom lens for projection, as defined in claim 1 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a lens group located at a second position from the magnification side of the plurality of lens groups is a third lens group, the following formula (5) is satisfied:
5.0 <f 3 /f< 8.0 (5),
where
f 3 is a focal length of the third lens group, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
5. A zoom lens for projection, as defined in claim 1 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a lens group located at a third position from the magnification side of the plurality of lens groups is a fourth lens group and a lens group located at a fourth position from the magnification side of the plurality of lens groups is a fifth lens group, the following formula (6) is satisfied:
6.0 <f 4-5 /f< 9.0 (6),
where
f 4-5 is a combined focal length of the fourth lens group and the fifth lens group at wide angle end, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
6. A projection-type display apparatus comprising:
a light source;
a light valve; and
a zoom lens for projection, as defined in claim 1 ,
wherein the zoom lens for projection projects an optical image of light modulated by the light valve onto a screen.
7. A zoom lens for projection, as defined in claim 1 , wherein the plurality of lens groups are composed of four groups of a positive lens group, a positive lens group, one of a positive lens group and a negative lens group, and a positive lens group, which are arranged in this order from the magnification side, and
wherein a stop is arranged between a lens group located at a second position from the magnification side of the plurality of lens groups and a lens group located at a third position from the magnification side of the plurality of lens groups.
8. A zoom lens for projection, as defined in claim 7 , wherein when a lens group located at a third position from the magnification side of the plurality of lens groups is a fourth lens group, the fourth lens group is composed of a positive lens and a negative lens.
9. A zoom lens for projection, as defined in claim 7 , wherein when a lens group located at a fourth position from the magnification side of the plurality of lens groups is a fifth lens group, the fifth lens group is composed of a positive lens, a negative lens, a positive lens, and a positive lens, which are arranged in this order from the magnification side.
10. A projection-type display apparatus comprising:
a light source;
a light valve; and
a zoom lens for projection, as defined in claim 9 ,
wherein the zoom lens for projection projects an optical image of light modulated by the light valve onto a screen.
11. A zoom lens for projection, as defined in claim 1 , wherein the negative lens in the rear group is a double-concave lens, and
wherein the absolute value of the radius of curvature of a magnification-side surface of the negative lens in the rear group is smaller than the absolute value of the radius of curvature of a reduction-side surface of the negative lens in the rear group.
12. A zoom lens for projection, as defined in claim 11 , wherein the plurality of lens groups are composed of four groups of a positive lens group, a positive lens group, one of a positive lens group and a negative lens group, and a positive lens group, which are arranged in this order from the magnification side, and
wherein a stop is arranged between a lens group located at a second position from the magnification side of the plurality of lens groups and a lens group located at a third position from the magnification side of the plurality of lens groups.
13. A zoom lens for projection, as defined in claim 12 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when the magnification-side lens group is a first lens group, the following formula (3) is satisfied:
−2.5 <f 1 /f<− 1.5 (3),
where
f 1 is a focal length of the first lens group when projection distance is at infinity, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
14. A zoom lens for projection, as defined in claim 13 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a most-magnification-side lens group of the plurality of lens groups is a second lens group, the following formula (4) is satisfied:
4.0 <f 2 /f< 7.0 (4),
where
f 2 is a focal length of the second lens group, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
15. A zoom lens for projection, as defined in claim 14 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a lens group located at a second position from the magnification side of the plurality of lens groups is a third lens group, the following formula (5) is satisfied:
5.0 <f 3 /f< 8.0 (5),
where
f 3 is a focal length of the third lens group, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
16. A zoom lens for projection, as defined in claim 15 , wherein the zoom lens for projection as a whole is composed of six groups when the magnification-side lens group is regarded as one lens group, and
wherein when a lens group located at a third position from the magnification side of the plurality of lens groups is a fourth lens group and a lens group located at a fourth position from the magnification side of the plurality of lens groups is a fifth lens group, the following formula (6) is satisfied:
6.0 <f 4-5 /f< 9.0 (6),
where
f 4-5 is a combined focal length of the fourth lens group and the fifth lens group at wide angle end, and
f is a focal length of the entire system of the zoom lens for projection at wide angle end when projection distance is at infinity.
17. A zoom lens for projection, as defined in claim 16 , wherein the fourth lens group is composed of a positive lens and a negative lens.
18. A zoom lens for projection, as defined in claim 17 , wherein the fifth lens group is composed of a positive lens, a negative lens, a positive lens, and a positive lens, which are arranged in this order from the magnification side.
19. A projection-type display apparatus comprising:
a light source;
a light valve; and
a zoom lens for projection, as defined in claim 18 ,
wherein the zoom lens for projection projects an optical image of light modulated by the light valve onto a screen.