Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-11-13
2003-09-02
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S680000
Reexamination Certificate
active
06614599
ABSTRACT:
This application claims benefit of Japanese Application(s) No. Hei 11-322452 filed in Japan on Nov. 12, 1999, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens system and an image pickup system using the same, and more particularly to a zoom lens system suitable for video cameras or electronic still cameras using electronic image pickup devices such as CCDs or CMOSs and an image pickup system using the same.
Among zoom lens systems so far known to be suitable for use ON cameras using electronic image pickup devices, there is an optical system which comprises, in order from an object side thereof, a first lens group having negative power, a second lens group having positive power and a third lens group having positive power together with filters having a low-pass filter function, etc., and image pickup devices, and in which zooming is carried out by moving the first and second lens groups on the optical axis while varying the spacing between adjacent lens groups.
With an increase in the number of pixels in recently developed electronic image pickup devices such as CCDs or CMOSS, on the other hand, there are growing demands for a zoom lens system having ever-higher image-formation capability, a zoom lens system having an ever-higher zoom ratio and a zoom lens system having an ever-wider field angle on the wide-angle side in particular.
Size reductions of image pickup devices and a more increased number of pixels cause a decrease in the light sensing areas of individual pixels, resulting in strong demands for a lens system having a smaller F-number than ever before.
For a zoom lens system having a field angle (2&ohgr;) of the order of 60° to 67° on the wide-angle side, a zoom ratio of the order of 3 and an F-number of the order of 2, some proposals have already been made, as disclosed in JP-A's 11-23967 and 11-52246. However, this is still less than satisfactory in terms of the magnitude of field angle and distortion at the wide-angle end. A zoom lens system having a field angle (2&ohgr;) exceeding 70° on the wide-angle side, too, is put forward, as disclosed in JP-A's 11-174322 and 10-39214. However, this leaves much to be desired in terms of F-number. Zoom lens systems disclosed in JP-A's 10-39214 and 9-21950 are still unsatisfactory in terms of distortion, etc.
Generally, correction of off-axis aberrations and especially distortion and chromatic aberrations of magnification becomes difficult with an increasing field angle, and correction of spherical aberrations and coma becomes difficult with a decreasing F-number.
SUMMARY OF THE INVENTION
In view of such states of the prior art as explained above, one object of the present invention is to provide a zoom lens system having a zoom ratio of about 3, a wide field angle on its wide-angle side and a small F-number as well as a lens layout enabling satisfactory image-formation capability to be obtained. Another object of the invention is to provide a lens layout with emphasis placed on fabrication capability.
According to the first aspect of the present invention, these objects are achievable by the provision of a zoom lens system comprising, in order from an object side of said zoom lens system, a first lens group having negative power, an aperture stop, a second lens group having positive power and a third lens group having positive power, wherein:
for zooming, said first lens group and said second lens group move on an optical axis with a varying spacing between adjacent lens groups while said third lens group remains fixed,
during said zooming, said stop moves in unison with said second lens group,
said first lens group comprises, in order from an object side thereof, a negative lens component, a negative lens component and a positive lens component,
said third lens group consists of one lens element,
said first lens group further comprises a lens element having an aspherical surface that satisfies the following condition (1), and
said third lens group further comprises lens element having an aspherical surface that satisfies the following condition (2):
0<(1
/r
a1
−1
/r
m1
)
h
1
/(
n
a1
−n
a1
′)<1 (1)
−1<(1
/r
a3
−1
/r
m3
)
h
3
/(
n
a3
−n
a3
′)<0 (2)
where r
a1
is the paraxial radius of curvature of an aspherical surface I located in said first lens group, r
m1
is a distance from a point of intersection of an optical axis with said aspherical surface I located in said first lens group to a point on the optical axis where a normal to an arbitrary point (1) between the maximum diameter of an axial light beam on said aspherical surface I and an effective diameter including an off-axis light beam on said aspherical surface I is closest to the optical axis, n
a1
is the refractive index of said aspherical surface I on an object side thereof, n
a1
′ is the refractive index of said aspherical surface I on an image side thereof, h
1
is the height of said point (1) from the optical axis, r
a3
is the paraxial radius of curvature of an aspherical surface III located in said third lens group, r
m3
is a distance from a point of intersection of the optical axis with said aspherical surface III located in said third lens group to a point on the optical axis where a normal to an arbitrary point (3) between the maximum diameter of an axial light beam on said aspherical surface III and an effective diameter including an off-axis light beam on said aspherical surface III is closest to the optical axis, n
a3
is the refractive index of said aspherical surface III on an object side thereof, n
a3
′ is the refractive index of said aspherical surface III on an image side thereof, and h
3
is the height of said point (3) from the optical axis.
The action and effect of the first zoom lens system according to the present invention are now explained.
By moving the first lens group having negative power and the second lens group having positive power for zooming, it is possible to impart, with simple construction, a wide field angle to the zoom lens system at the wide-angle end in particular, and make the zoom lens system compact while satisfactory performance is kept. With the third lens group having positive power and designed to be fixed during zooming and the aperture stop designed to move in unison with the second lens group for zooming, it is possible to set up an exit pupil position suitable for an electronic image pickup device. In other words, it is possible to locate the exit pupil at a position farther off an image-formation plane with shadings, etc. mind. By the “shadings” are here intended color tone changes (color shading) and rim light quantity changes (shading). For instance, these shadings occur upon oblique incidence of light rays on an image pickup device such as a CCD. This oblique incidence of light occurs depending on the structure of the device, for instance, when color filters and light sensors are positioned in the back of the device, e.g., at a light-shielding portion for a charge transfer path or microlenses are located on the object side of the light-shielding portion for the charge transfer path. To avert this shading problem, it is preferable to locate the exit pupil at a farther position.
To reduce the overall length of the zoom lens system, it is preferable to construct the third lens group of one lens, because the axial length of the third lens group can be reduced.
The third lens group has a little influence on deterioration of aberrations with respect to axial beams. At the third lens group, however, off-axis light beams and especially astigmatism are likely to occur. By increasing the number of lenses to form the third lens group, image-formation capability may be enhanced depending on the performance, etc. of the image pickup device. In the present invention, however, the third lens group is composed of one positive lens by the introduction of the aspherical surface that satisfies condition (2). By satisfying conditi
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Schwartz Jordan M.
LandOfFree
Zoom lens system, and image pickup system using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zoom lens system, and image pickup system using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zoom lens system, and image pickup system using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017983