Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-01-31
2002-03-26
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S716000, C359S684000, C359S685000
Reexamination Certificate
active
06362925
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens system of three-group construction in which each lens group consists of a single lens alone, and more particularly to a zoom lens system which is suitable for use as an image pickup lens for still cameras, video cameras or the like, and which comprises three groups, each consisting of one lens.
So far, some proposals have been made of a zoom lens system of simple group construction, each group consisting of one single lens. For instance, JP-A 11-6960 discloses a zoom lens optical system of three-group construction, each group consisting of one lens using a gradient index medium rather than a homogeneous medium that is easily available and easy to process.
SUMMARY OF THE INVENTION
In view of such a problem with the prior art as mentioned above, it is an object of the present invention to provide a zoom lens system of three-group construction, each consisting of one single lens, which is less susceptible to aberration variations even upon zooming and can achieve entire-length reductions, large lens aperture and high zoom ratio.
According to one aspect of the invention, this object is achievable by the provision of a zoom lens system of three-group construction, which comprises, in order from an object side thereof, a first lens group consisting of one single lens formed of a homogeneous medium and having positive refracting power, a second lens group consisting of one single lens formed of a homogeneous medium and having negative refracting power, and a third lens group consisting of one single lens formed of a homogeneous medium and having positive refracting power, and wherein for zooming from a wide-angle end to a telephoto end of said zoom lens system, at least said second lens group moves from said object side toward an image side of said zoom lens system.
Preferably in this case, the first lens group should consist of one convex lens having a strong convex surface directed to an object plane side of the zoom lens system and the second lens group should consist of one concave lens having a strong concave surface directed toward an image plane side of the zoom lens system.
The zoom lens system of the invention should preferably satisfy the following relation:
f
W
<f
3
<f
T
(1)
where f
W
is a focal length at which the focal length of the zoom lens system is shortest, f
T
is a focal length at which the focal length of the zoom lens system is longest and f
3
is a focal length of the third lens group.
Preferably, a convex lens in the third lens group should have at least one surface defined by an aspherical surface.
Preferably, the convex lens in the third lens group should be a double-convex lens.
Preferably, the zoom lens system of the invention should satisfy the following ratio relation:
−3.5<f
1
/f
2
<−2.0 (2)
where f
1
is a focal length of the first lens group and f
2
is a focal length of the second lens group.
Preferably, the zoom lens system of the invention should satisfy the following ratio relation:
5.0<f
1
/f
3
<10.0 (3)
where f
1
is a focal length of the first lens group and f
3
is a focal length of the third lens group.
Preferably, the zoom lens system of the invention should satisfy the following ratio relation:
0.5<L/f
T
<1.5 (4)
where L is a distance from a rear surface in the second lens group to an image plane of the zoom lens system, at which the focal length of the zoom lens system is longest and f
T
is a focal length at which the focal length of the zoom lens system is longest.
Preferably, the first lens group should remain fixed during zooming from the wide-angle end to the telephoto end of the zoom lens system.
According to another aspect of the invention, there is provided a display device with a built-in three-group zoom lens system having phototaking function, which comprises:
a first lens group consisting of one positive lens, a second lens group consisting of one negative lens, a third lens group consisting of one positive lens, and an electronic image pickup element for receiving an object image formed by only refracting powers of said first lens group, said second lens group and said third lens group,
a processing circuit for electrically processing information on said object image received by said electronic image pickup element, and
an image display element for displaying the information on said object image fed through said processing circuit to an viewer.
Preferably in this case, the three-group zoom lens system should be constructed in such a way that separations between the first lens group, the second lens group and the third lens group are varied for zooming from a wide-angle end to a telephoto end of the system.
Alternatively, the three-group zoom lens may be constructed for zooming from the wide-angle end to the telephoto end of the system in such a way that the separation between the first lens group and the second lens group becomes wide and the separation between the second lens group and the third lens group becomes narrow.
Preferably, a stop should be located between the second lens group and the third lens group.
A filter may be located between the third lens group and the electronic image pickup element.
The filter may be in a plane-parallel plate form.
The first lens group may consist of one cemented lens comprising a plurality of cemented lens elements.
The first lens group may consist of one lens element.
The second lens group may consist of one cemented lens comprising a plurality of cemented lens elements.
The second lens group may consist of one lens element.
The third lens group may consist of one cemented lens comprising a plurality of cemented lens elements.
The third lens group may consist of one lens element.
The image display element may be built up of a liquid crystal display having a flat screen.
Preferably, the third lens group should have at least one aspherical surface configured to make correction for aberrations.
In the another aspect of the invention, too, the following ratio relation should preferably be satisfied:
f
W
<f
3
<f
T
(1)
where f
W
is a focal length at which the focal length of the zoom lens system is shortest, f
T
is a focal length at which the focal length of the zoom lens system is longest and f
3
is a focal length of the third lens group.
Preferably, the following ratio relation should be satisfied:
−3.5<f
1
/f
2
<−2.0 (2)
where f
1
is a focal length of the first lens group and f
2
is a focal length of the second lens group.
Preferably, the following ratio relation should be satisfied:
5.0<f
1
/f
3
<10.0 (3)
where f
1
is a focal length of the first lens group and f
3
is a focal length of the third lens group.
Preferably, the following ratio relation should be satisfied:
0.5<L/f
T
<1.5 (4)
where L is a distance from a rear surface in the second lens group to an image plane of the zoom lens system, at which the focal length of the zoom lens system is longest and f
T
is a focal length at which the focal length of the zoom lens system is longest.
The first lens group may remain fixed during zooming from the wide-angle end to the telephoto end.
Preferably, the zoom lens system should be compactly housed in the display device by allowing the first lens group and the second lens group to move in such a way that a distance from a surface located nearest to the object side in the first lens group to the electronic image pickup element is reduced to a length between 20 mm and 2 mm.
Preferably, the first lens group should remain fixed form zooming from the wide-angle end to the telephoto end of the zoom lens system.
Preferably, the separations between the first lens group, the second lens group and the third lens group should be variable in such a way as to satisfy the following zoom ratio condition:
1.2<f
T
/f
W
<25.0 (6)
where f
W
is a focal length at which the focal length of the zoom lens system is shortest and f
T
is a focal l
Nakamura Tohru
Tsuchida Hirofumi
Lester Evelyn A.
Mack Ricky
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
LandOfFree
Lens group zoom lens system, and display device having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lens group zoom lens system, and display device having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lens group zoom lens system, and display device having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2862614