Projection lens system with magnification-varying capability and projector
A projection lens system includes a first lens group including a 1a-th lens group having a negative refractive power, a 1b-th lens group having a positive or negative refractive power, and a 1c-th lens group having a positive or negative refractive power. During a zoom, the first lens group remains stationary on an optical axis. During a focus from a remote distance side to a close distance side, the 1a-th lens group remains stationary on the optical axis while the 1b-th and 1c-th lens groups move toward the enlargement conjugate side along different loci respectively. Conditional formula −4.7<fl/fw<−2.5 is fulfilled at both the remote and close distance sides, where fl represents a focal length of the first lens group, and fw represents a focal length of the entire system at a wide-angle end.
1. A projection lens system that performs a zoom by varying distances between a plurality of lens groups, the projection lens system comprising:
a first lens group comprising:
a 1a-th lens group having a negative refractive power,
a 1b-th lens group having a positive or negative refractive power, and
a 1c-th lens group having a positive or negative refractive power,
wherein, during a zoom, the first lens group remains stationary on an optical axis,
wherein, during a focus from a remote distance side to a close distance side, the 1a-th lens group remains stationary on the optical axis while the 1b-th and 1c-th lens groups move toward the enlargement conjugate side along different loci respectively, and
wherein conditional formula (1) below is fulfilled at both the remote and close distance sides:
−4.7< fl/fw<− 2.5 (1)
where
fl represents a focal length of the first lens group; and
fw represents a focal length of the entire system at a wide-angle end.
2. The projection lens system of claim 1 , wherein only the 1b-th or 1c-th lens group has a positive refractive power and comprises one positive lens element and one negative lens element.
3. The projection lens system of claim 2 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (2) below:
0<|Σ(1/( fn×vdn ))×1000|<2.7 (2)
where
fn represents a focal length of a single lens element included in the 1b-th and 1c-th lens groups; and
vdn represents an Abbe number of the single lens element included in the 1b-th and 1c-th lens groups.
4. The projection lens system of claim 3 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (3) below:
0<|Σ(1/( fn×ndn ))×1000|<6.1 (3)
where
fn represents the focal length of the single lens element included in the 1b-th and 1c-th lens groups; and
ndn represents a refractive index of the single lens element included in the 1b-th and 1c-th lens groups.
5. The projection lens system of claim 4 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
6. The projection lens system of claim 3 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
7. The projection lens system of claim 2 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (3) below:
0<|Σ(1/( fn×ndn ))×1000|<6.1 (3)
where
fn represents a focal length of a single lens element included in the 1b-th and 1c-th lens groups; and
ndn represents a refractive index of the single lens element included in the 1b-th and 1c-th lens groups.
8. The projection lens system of claim 7 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
9. The projection lens system of claim 2 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
10. A projector comprising an image forming device that forms image light and the projection lens system of claim 2 that projects the image light on a magnified scale.
11. The projection lens system of claim 1 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (2) below:
0<|Σ(1/( fn×vdn ))×1000|<2.7 (2)
where
fn represents a focal length of a single lens element included in the 1b-th and 1c-th lens groups; and
vdn represents an Abbe number of the single lens element included in the 1b-th and 1c-th lens groups.
12. The projection lens system of claim 11 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (3) below:
0<|Σ(1/( fn×ndn ))×1000|<6.1 (3)
where
fn represents the focal length of the single lens element included in the 1b-th and 1c-th lens groups; and
ndn represents a refractive index of the single lens element included in the 1b-th and 1c-th lens groups.
13. The projection lens system of claim 12 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
14. The projection lens system of claim 11 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
15. A projector comprising an image forming device that forms image light and the projection lens system of claim 11 that projects the image light on a magnified scale.
16. The projection lens system of claim 1 , wherein the 1b-th and 1c-th lens groups fulfill conditional formula (3) below:
0<|Σ(1/( fn×ndn ))×1000|<6.1 (3)
where
fn represents a focal length of a single lens element included in the 1b-th and 1c-th lens groups; and
ndn represents a refractive index of the single lens element included in the 1b-th and 1c-th lens groups.
17. The projection lens system of claim 16 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
18. A projector comprising an image forming device that forms image light and the projection lens system of claim 16 that projects the image light on a magnified scale.
19. The projection lens system of claim 1 , wherein conditional formula (4) below is fulfilled:
2.5<|( f 1 b/f 1 c )× dx|< 4.2 (4)
where
f1b represents a focal length of the 1b-th lens group;
f1c represents a focal length of the 1c-th lens group; and
dx represents a ratio of an amount of movement of the 1c-th lens group to an amount of movement of the 1b-th lens group for focusing.
20. A projector comprising an image forming device that forms image light and the projection lens system of claim 1 that projects the image light on a magnified scale.