Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-09-27
2003-04-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S676000, C359S684000, C359S739000, C359S740000, C359S649000
Reexamination Certificate
active
06545817
ABSTRACT:
RELATED APPLICATIONS
This application is based on Patent Application Nos. 2000-293342 and 2000-293343 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection zoom lens, for example, a projection zoom lens suitable for use as a projection optical system in a projection device (e.g., a liquid crystal projector for projecting an image on a liquid crystal panel onto a screen or the like).
2. Description of the Related Art
Various types of projection zoom lens have been proposed, the mainstream being a projection zoom lens for a liquid crystal projector having a half field angle of 20° front and back (Japanese Laid-Open Patent No. 11-202200).
If the field angle of the projection zoom lens is wider, a display image can be projected larger at a shorter projection distance. For this reason there is commercial demand for a projection zoom lens of the wide field angle type having a half field angle of 35° or greater. However, when the field angle is widened, it becomes difficult to correct aberration such as curvature of field.
SUMMARY
An object of the present invention is to provide an improved zoom lens.
Another object of the present invention is to provide a wide angle type projection zoom lens having excellent optical performance.
These objects are attained by a zoom lens system comprising, sequentially from the enlarging side to the reducing side, a first lens unit having negative optical power; a second lens unit having positive optical power, the second lens unit having a positive lens element positioned nearest the reducing side; a diaphragm; a third lens unit having positive optical power, the third lens unit comprising, sequentially from the enlarging side to the reducing side, a cemented lens unit having a positive lens element and a negative lens element with a concave surface facing the reducing side, and a positive lens element having a concave surface facing the reducing side; a fourth lens unit having negative optical power; and a fifth lens unit having positive optical power; wherein the second lens unit, the third lens unit, and the fourth lens unit move from the enlarging side to the reducing side when zooming from the telephoto end to the wide angle end, and wherein the zoom lens system satisfies the condition below:
−1.5<(
fw/r
2
A
)+(
fw/r
3
A
)<−0.05
where fw represents the focal length of the entire system at the wide angle end, r
2
A represents the radius of curvature of the surface on the enlarging side of the lens element positioned nearest the reducing side of the second lens unit, and r
3
A represents the radius of curvature of the surface nearest the enlarging side of the third lens unit.
These objects are further attained by a zoom lens system comprising, sequentially from the enlarging side to the reducing side, a first lens unit having negative optical power; a second lens unit having positive optical power, the second lens unit having a positive lens element positioned nearest the reducing side; a diaphragm; a third lens unit having positive optical power, the third lens unit comprising, sequentially from the enlarging side to the reducing side, a cemented lens unit having a positive lens element and a negative lens element with a concave surface facing the reducing side, and a positive lens unit having a concave surface facing the reducing side; a fourth lens unit having negative optical power; and a fifth lens unit having positive optical power; wherein the second lens unit and the third lens unit move from the enlarging side to the reducing side when zooming from the telephoto end to the wide angle end, and the fourth lens unit does not move during zooming, wherein the zoom lens system satisfies the condition below:
−1.5<(
fw/r
2
A
)+(
fw/r
3
A
)<−0.05
where fw represents the focal length of the entire system at the wide angle end, r
2
A represents the radius of curvature of the surface on the enlarging side of the lens element positioned nearest the reducing side of the second lens unit, and r
3
A represents the radius of curvature of the surface nearest the enlarging side of the third lens unit.
These objects are further attained by a zoom lens system comprising, sequentially from the enlarging side to reducing side, a first lens unit having negative optical power; a second lens unit having positive optical power, the second lens unit comprising, sequentially from the enlarging side to the reducing side, a positive lens element having a concave surface facing the enlarging side, and a negative meniscus lens element having a concave surface facing the enlarging side, a third lens unit having positive optical power; a fourth lens unit having negative optical power; and a fifth lens unit having positive optical power; wherein the second lens unit, third lens unit, and fourth lens unit move from the enlarging side to the reducing side when zooming from the telephoto end to the wide angle end, and wherein the zoom lens system satisfies the conditions below:
3.5
<f
2
/
fw
<7.0
0.05<(
r
2
F−r
2
R
)/(
r
2
F+r
2
R
)<0.45
where fw represents the focal length of the entire system at the wide angle end, f
2
represents the focal length of the second lens unit, r
2
F represents the radius of curvature of the surface on the enlarging side of the negative meniscus lens element of the second lens unit, and r
2
R represents the radius of curvature of the surface on the reducing side of the negative meniscus lens element of the second lens unit.
These objects are attained by a zoom lens system comprising, sequentially from the enlarging side to the reducing side, a first lens unit having negative optical power, a second lens unit having positive optical power, the second lens unit comprising, sequentially from the enlarging side to the reducing side, a positive lens element having a concave surface facing the enlarging side, and a negative meniscus lens element having a concave surface facing the enlarging side; a third lens unit having positive optical power; a fourth lens unit having negative optical power; and a fifth lens unit having positive optical power; wherein the second lens unit and third lens unit move from the enlarging side to the reducing side when zooming from the telephoto end to the wide angle end, and the fourth lens unit does not move during zooming, and wherein the zoom lens system satisfies the conditions below:
3.5
<f
2
/
fw
<7.0
0.05<(
r
2
F−r
2
R
)/(
r
2
F+r
2
R
)<0.45
where fw represents the focal length of the entire system at the wide angle end, f
2
represents the focal length of the second lens unit, r
2
F represents the radius of curvature of the surface on the enlarging side of the negative meniscus lens element of the second lens unit, and r
2
R represents the radius of curvature of the surface on the reducing side of the negative meniscus lens element of the second lens unit.
REFERENCES:
patent: 5668668 (1997-09-01), Shibayama et al.
patent: 6008952 (1999-12-01), Yamamoto
patent: 6222680 (2001-04-01), Yamamoto et al.
patent: 11-202200 (1999-07-01), None
Epps Georgia
Hasan M.
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
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