Projection zoom lens and projection type display device
The projection zoom lens essentially consists of a positive first lens group fixed while changing magnification and the second lens group through the fourth lens group which move while changing magnification, and a fifth lens group fixed while changing magnification; and an aperture stop positioned between adjacent moving lens groups or within one moving lens group, wherein the numerical number of the zoom lens is set to be constant over the entire zoom range, the reduction side is configured to be telecentric, and the projection zoom lens satisfies conditional formulas (4) and (5): 2.0< Bf/Imφ (4) L/Im φ<12 (5), where, Bf: the back focus (air converted length) at the reduction side of the entire system at the wide angle end, Imφ: the maximum effective image circle diameter, and L: the distance between the most-magnification-side lens surface and the most-reduction-side lens surface along the optical axis when the projection distance is infinite.
1. A projection zoom lens consisting of:
a first lens group having a positive refractive power fixed while changing magnification, a second lens group having a negative refractive power that moves while changing magnifications, a third lens group having a negative refractive power that moves while changing magnification, a fourth lens group having a positive refractive power that moves while changing magnification, and a fifth lens group having a positive refractive power that is fixed while changing magnification in this order from the magnification side; and
an aperture stop positioned between adjacent moving lens groups or within one moving lens group, wherein
the numerical number of the zoom lens is set to be constant over the entire zoom range,
the reduction side is configured to be telecentric, and
the projection zoom lens satisfies conditional formulas (4) and (5):
2.0< Bf/Imφ (4)
L/Imφ< 12 (5),
where,
Bf: the back focus, which is an air converted length, at the reduction side of the entire system at the wide angle end,
Imφ: the maximum effective image circle diameter, and
L: the distance between the most-magnification-side lens surface and the most-reduction-side lens surface along the optical axis when the projection distance is infinite.
2. The projection zoom lens of claim 1 that satisfies conditional formula (1) below:
0.3< mr/fw (1),
where,
mr: the amount of movement between the wide angle end and the telephoto end of the fourth lens group, and
fw: the focal length of the entire system at the wide angle end.
3. The projection zoom lens of claim 2 that satisfies conditional formula (1′) below:
0.5< mr/fw (1′).
4. The projection zoom lens of claim 1 that satisfies conditional formula (2) below:
2.0< fe/fw< 7.0 (2),
where,
fe: the focal length of the fifth lens group, and
fw: the focal length of the entire system at the wide angle end.
5. The projection zoom lens of claim 2 that satisfies conditional formula (2) below:
2.0< fe/fw< 7.0 (2),
where,
fe: the focal length of the fifth lens group, and
fw: the focal length of the entire system at the wide angle end.
6. The projection zoom lens of claim 4 that satisfies conditional formula (2′) below:
3.0< fe/fw< 5.0 (2′).
7. The projection zoom lens of claim 5 that satisfies conditional formula (2′) below:
3.0< fe/fw< 5.0 (2′).
8. The projection zoom lens of claim 1 that satisfies conditional formula (3) below:
−1.0< mm/mr<− 0.2 (3),
where,
mm: the amount of movement between the wide angle end and the telephoto end of the second lens group, and
mr: the amount of movement between the wide angle end and the telephoto end of the fourth lens group.
9. The projection zoom lens of claim 2 that satisfies conditional formula (3) below:
−1.0< mm/mr<− 0.2 (3),
where,
mm: the amount of movement between the wide angle end and the telephoto end of the second lens group, and
mr: the amount of movement between the wide angle end and the telephoto end of the fourth lens group.
10. The projection zoom lens of claim 8 that satisfies conditional formula (3′) below:
−0.7< mm/mr<− 0.3 (3′).
11. The projection zoom lens of claim 9 that satisfies conditional formula (3′) below:
−0.7< mm/mr<− 0.3 (3′).
12. The projection zoom lens of claim 1 , wherein an aperture stop varies the aperture diameter thereof such that the numerical aperture is constant over the entire zoom range.
13. The projection zoom lens of claim 2 , wherein an aperture stop varies the aperture diameter thereof such that the numerical aperture is constant over the entire zoom range.
14. The projection zoom lens of claim 1 that satisfies conditional formula (4′) below:
2.5< Bf/Imφ (4′).
15. The projection zoom lens of claim 1 that satisfies conditional formula (5′) below:
7< L/Imφ< 11 (5′).
16. The projection zoom lens of claim 1 that satisfies conditional formula (6) below:
1.0< f 1/ fw< 5.0 (6),
where,
f 1 : the focal length of the first lens group, and
fw: the focal length of the entire system at the wide angle end.
17. The projection zoom lens of claim 16 that satisfies conditional formula (6′) below:
2.0< f 1/ fw< 4.0 (6′).
18. The projection zoom lens of claim 1 that satisfies conditional formula (7) below:
1.4< Zr (7),
where,
Zr: the zoom ratio of the telephoto end with respect to the wide angle end.
19. The projection zoom lens of claim 18 that satisfies conditional formula (7′) below:
1.6< Zr (7′).
20. A projection type display device comprising:
a light source;
a light valve into which light from the light source enters; and
the projection zoom lens of claim 1 that projects an optical image formed by the light modulated by the light valve onto a screen.