Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-01-31
2002-03-19
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S680000, C359S682000, C359S745000, C359S748000
Reexamination Certificate
active
06359738
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens system of two-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 two groups, each consisting of one lens, and has an F-number of 4 or less at its wide-angle end.
So far, some proposals have been made of a zoom lens system of two-group construction, each group consisting of one single lens. Referring to an optical system disclosed in JP-A 7-333500 for instance, the power of the second lens group is too strong to reduce aberration variations upon zooming, making it very difficult to increase lens aperture and zoom ratio. JP-A's 10-3037 and 11-6960 put forward a zoom lens system of two-group construction using a gradient index medium. In consideration of material availability, etc., however, it is preferable to use a homogeneous medium.
SUMMARY OF THE INVENTION
In view of such problems with the prior art as mentioned above, it is an object of the present invention to provide a zoom lens system of two-group construction, each consisting of one single lens, which is less susceptible to aberration variations even upon zooming and can achieve 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 two-group construction, which comprises, in order from an object side thereof, a first lens group having negative refracting power and a second lens group having positive refracting power and in which a focal length thereof is varied by moving both said lenses while an optical axis separation therebetween is varied, wherein:
said first lens group consists of one concave lens having a strong concave surface directed toward an image plane side of said zoom lens system and formed of a homogeneous medium,
said second lens group consists of one convex lens formed of a homogeneous medium,
a stop is located between said first lens group and said second lens group, and
said first lens group moves from said object side toward an image side of said zoom lens system while said second lens group moves from said image side toward said object side during zooming from a wide-angle end to a telephoto end of said zoom lens system.
Preferably in this case, the convex lens in the second lens group should have at least one surface defined by an aspherical surface.
Preferably, the zoom lens system of the invention should satisfy the following ratio relation:
1.0<
f
2
/f
w
<4.0 (1)
where f
w
is a focal length at which said zoom lens system has the shortest focal length and f
2
is a focal length of the second lens group.
Preferably, the stop should move together with the second lens group while the following relation is satisfied:
0.5<{(
n
2
−1)/
R
2F
}/(1/
f
2
)<1.5 (4)
where n
2
is the refractive index of the convex lens in the second lens group, R
2F
is the radius of curvature of a surface of the convex lens located on the object side, and f
2
is the focal length of the second lens group.
According to another aspect of the invention, there is also provided a display device with a built-in two-group zoom lens system having phototaking function, which comprises:
a first lens group consisting of one negative lens and a second lens group consisting of one positive lens,
an electronic image pickup element for receiving an object image formed by only refracting powers of said first lens group and said second lens group, and 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 two-group zoom lens system should be constructed in such a way that a separation between the first lens group and the second lens group is varied for zomming from a wide-angle end to a telephoto end of the system.
Alternatively, the separation between the first lens group and the second lens group may be narrowed for zooming from the wide-angle end to the telephoto end of the system.
Preferably, a stop should be located between the first lens group and the second lens group.
A filter may be located between the second lens group and the electronic image pickup element.
A cover member may be located in front of the first lens group.
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 image display element may be built up of a liquid crystal display having a flat screen.
Preferably, the first lens group should have at least one aspherical surface configured to make correction for aberrations.
Preferably, the second 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:
1.0<
f
2
/f
w
<4.0 (1)
where f
w
is a focal length at which said zoom lens system has the shortest focal length and f
2
is a focal length of the second lens group.
Preferably, the stop should move together with the second lens group while the following relation is satisfied:
0.5<(
n
2
−1)
f
2
/R
2F
<1.5 (4)
where n
2
is the refractive index of the convex lens in the second lens group, R
2F
is the radius of curvature of a surface of the convex lens located on the object side, and f
2
is the focal length of the second lens group.
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, a separation between the first lens group and the second 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 said zoom lens system has the shortest focal length and f
t
is a focal length at which said zoom lens system has the longest focal length.
According to yet another aspect of the invention, there is provided a telephone handset comprising a display device with a built-in two-group zoom lens system having phototaking function, a microphone for entering an operator's voice therein, a speaker for producing a voice of a person at the other end and a dial button for entering at least a telephone number therein.
The telephone handset may be constructed in the form of a portable telephone set having an antenna for transmitting and/or receiving radio waves.
Why the aforesaid arrangements are used and how they word will now be described.
In the zoom lens system of two-group construction, one lens for each group or two lenses in all, according to the present invention, the first lens group consists of one concave lens having a strong concave surface directed toward the image plane side and formed of a homogeneous medium and the second lens group consists of one convex lens formed of a homogeneous medium with a stop located between them. For zooming from the wide-angle end to the telephoto end of the lens system, the first lens group is allowed to move largely from the object side to the image side of the lens system while the second lens group is allowed to move from the image side to the object side of the lens system. Thus, the convex lens in the second lens group takes a chief part in the image-forming action of the lens system. This arrangement is favorable in view of aberration c
Nakamura Tohru
Tsuchida Hirofumi
Epps Georgia
Lucas Michael A.
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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