Projection zoom lens with a long back focal length and exit...

Details Projection zoom lens with a long back focal length and exit... Projection zoom lens with a long back focal length and exit...

2000-11-08

2002-09-10

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S649000

Reexamination Certificate

active

06449101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens. More specifically, the present invention discloses a zoom lens with a long back focal length.
2. Description of the Prior Art
For projection devices, such as liquid crystal display (LCD) panel projectors or liquid crystal on silicon (LCOS) panel projectors, a projection lens with a long back focal length is needed due to the resolution requirements of the LCOS. Furthermore, a long back focal length is needed to accommodate the space required for additional optics, such as polarized beam splitters and a telecentric means with a long exit pupil position for parallel beams that pass through the polarized beam splitters. Hence, in the art of projection devices, a lens with a long back focal length and exit pupil position must be developed. This lens must have superior aberration, astigmatism and distortion characteristics to present a crisp image with micro-sized pixels. Furthermore, it should have a small f-number so that the projected image can be as bright as possible.
SUMMARY OF THE INVENTION
It is therefore a primary objective of this invention to provide a projection lens with superior optical qualities having a long back focal length and long exit pupil position and a small f-number.
Briefly summarized, the present invention discloses a projection lens with five optical groups, which may be labeled O
I
to O
V
, having effective focal lengths f
I
, to f
V
, respectively. The optical groups move on an optical axis to perform zooming and focusing functions. The projection lens has a total of at least thirteen lenses, which may be labeled L
1
to L
13
, having focal lengths f
1
to f
13
, respectively, Abbe numbers V
1
to V
13
, respectively, and indices of refraction N
1
to N
13
, respectively. Optical group O
I
has the first three lenses, L
1
to L
3
. Optical group O
II
has the next two lenses, L
4
and L
5
. Optical group O
III
has the next three lenses, L
6
to L
8
. Optical group L
IV
has lens L
9
. Finally, optical group O
V
has the remaining lenses, L
10
to L
13
, of which L
10
to L
12
combine to form a triplet. The lens groups satisfy the following conditions:
−0.45<(
f
11
/f
V
)<−0.25
V
10
+V
12
−2
V
11
>44
2
N
11
−N
10
−N
12
>0.5
0.5<(
f
N
+f
P
)/(
f
P
))<0.9
Where f
N
is the effective focal length (EFL) of O
I
and O
II
, and f
P
is the EFL of O
III
, O
IV
and O
V
.


REFERENCES:
patent: 4934795 (1990-06-01), Estelle

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