Projection zoom lens and projection type display device
AssigneeFujinon Corporartion
InventorsAkiko Nagahara, Hiroshi Yamada
Life of this patent
Estimating the term…
Abstract
A projection zoom lens is provided and includes: in order from the magnification side, a negative first lens group performing focusing with being fixed during power-varying; a positive second lens group, a positive third lens group, a positive fourth lens group, a positive fifth lens group, which are moved with correlation; and a positive sixth lens group fixed during the power-varying. An aperture diaphragm is moved between the fourth lens group and the fifth lens group during the power-varying to keep Fno constant in the whole power-varying region. In addition, the expression of 1.7<Bf/f<3.0 is satisfied, where f is a focal length of the whole system, and Bf is a back focal length (air conversion distance) of the whole system.
Claims18
A zoom lens for projection comprising, in order from a magnification side of the zoom lens:
- a first lens group having a negative refractive power and adapted to perform focusing with being fixed during power-varying of the zoom lens;
- a second lens group having a positive refractive power and adapted to move during the power-varying;
- a third lens group having a positive refractive power and adapted to move during the power-varying;
- a fourth lens group having a positive refractive power and adapted to move during the power-varying;
- a stop adapted to independently move during the power-varying;
- a fifth lens group having a positive refractive power and adapted to move during the power-varying;
- and
- a sixth lens group having a positive refractive power and adapted to be fixed during the power-varying,
- wherein a reduction side of the zoom lens is configured to be telecentric,
- Fno is constant in a whole region of the power-varying, and
- the zoom lens satisfy conditional expression (1):
- 1.7<Bf/f<3.0 (1)
- wherein f is a focal length of the zoom lens at a wide angle end, and Bf is a back focal length of the zoom lens in air converted distance.
Dependencies are inferred from the claim text.