Optical: systems and elements – Image stabilization
Reexamination Certificate
2000-01-27
2001-09-04
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Image stabilization
C359S557000, C359S682000, C359S683000
Reexamination Certificate
active
06285501
ABSTRACT:
This application claims the benefit of Japanese Patent application No. 11-018086 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens with a vibration reduction function and, more particularly, to a vibration reduction technology for zoom lenses having a long back focal length so as to suitable for use with an electronic image equipment employing CCD imaging devices and the like.
2. Related Background Art
The demand for increased performance of zoom lenses in recent years has resulted in a variety of types of zoom lenses. In particular, zoom lenses for an electronic image equipment, such as video cameras and digital still cameras, have employed to date so-called Yamaji-type zoom lenses and four-group type zoom lenses having, in order from object side, positive-negative-positive-positive refractive power arrangement. However, disclosure of a vibration reduction method relating to these types of zoom lenses is rare and, so far, only one publication of Japanese Laid-Open Patent Application No. 7-199124, filed by the present applicant, is known. With the progress in lens barrel technology in recent years, zoom lens types having five or more lens groups have been proposed. However, it has been extremely difficult to simultaneously achieve superior imaging performance, superior vibration reduction function, an increased field of view, increased variable power (i.e. an increased zoom ratio), a compact size, and the like.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high-performance zoom lens having superior vibration reduction function with a long back focal length and that has superior imaging performance even in the intermediate focal length state. The zoom lens also has satisfactory imaging performance in an optical system for focusing an object at infinite distance (hereinafter referred as “infinite focus”) as well as an optical system for focusing an object at short distance(hereinafter referred as “short-distance focus”).
In order to achieve the above object, according to the present invention, a zoom lens having a long back focal length, which comprises, in order from an object side:
a first lens group G1 having a positive refractive power;
a second lens group G2 having a negative refractive power;
a third lens group G3 having a negative refractive power;
a fourth lens group G4 having a positive refractive power; and
a fifth lens group G5 having a positive refractive power;
wherein the zoom lens is designed such that when zooming is effected from the wide-angle end to the telephoto end, the interval between the first lens group G1 and the second lens group G2 increases, the interval between the second lens group G2 and the third lens group G3 changes linearly or non-linearly, and the interval between the fourth lens group G4 and the fifth lens group G5 changes linearly or non-linearly;
wherein vibration reduction is attained by shifting a vibration reduction lens group G4v consisting of the fourth lens group G4 or a partial lens group of the fourth lens group in a direction substantially perpendicular to an optical axis; and
wherein the following conditional formulae are satisfied:
&Dgr;4/|f4v|<0.1
where f4v is a focal length of the vibration reduction lens group G4v, &Dgr;4 is a maximum displacement amount of the vibration reduction lens group G4v in the direction substantially perpendicular to the optical axis upon vibration reduction.
According to a preferred aspect of the present invention, a zoom lens satisfies the following conditional formulae:
2.0<BFw/Y0<8.0
0.03<(D23t−D23w)/fw<1.5
where BFw is the back focal length at the wide-angle end, Y0 is a maximum image height, fw is the focal length of the entire zoom lens system at the wide-angle end, D23w is the interval along the optical axis between the second lens group G2 and the third lens group G3 at the wide-angle end, and D23t is the interval along the optical axis between the second lens group G2 and the third lens group G3 at the telephoto end.
According to a preferred aspect of the present invention, a zoom lens further satisfies the following conditional formulae:
0.1<f2/f3<2.0
2.0<|f3|/fw<10.0
wherein f2 is a focal length of the second lens group G2, f3 is a focal length of the third lens group G3, and fw is the focal Length of the zoom lens at the wide-angle end.
According to a preferred aspect of the present invention of a zoom lens, the first lens group G1 and the fourth lens group G4 is fixed during zooming from the wide-angle end to the telephoto end, and the following condition is satisfied:
0.001<&Dgr;4/&PHgr;4<0.2
where &PHgr;4 is a diameter of an effective aperture at the most object side of the fourth lens group G4 and &Dgr;4 is a maximum displacement amount of the vibration reduction lens group G4v in the direction substantially perpendicular to the optical axis while attaining vibration reduction.
According to a preferred aspect of the present invention of a zoom lens, the fifth lens group G5 includes a cemented lens having a divergent convex cemented surface facing to the image side.
According to a preferred aspect of the present invention of a zoom lens further satisfies the following conditional formula:
0.3<D23m/fw<3.0
wherein D23m is an interval along the optical axis between the second lens group G2 and the third lens group G3 in an intermediate focal length state, and fw is the focal length of the zoom lens at the wide-angle end.
According to a preferred aspect of the present invention, a zoom lens further satisfies the following conditional formulae:
0.5<|f23w|/fw<2.0
0.3<D23t/fw<1.5
wherein f23w is a composite focal length of the second lens group G2 and the third lens group G3 at the wide-angle end, fw is the focal length of the zoom lens at the wide-angle end, and D23t is an interval along an optical axis between the second lens group G2 and the third lens group G3 at the telephoto end.
According to a preferred aspect of the present invention of a zoom lens, the fourth lens group G4 includes a positive lens; L4p arranged at the most object side and negative lens L4n arranged at the most image side; the fifth lens group G5 include a cemented lens having a divergent convex cemented surface facing to the image side; and the following conditional formula is satisfied:
0.18<&Dgr;N
wherein &Dgr;N is a mean value of a difference of a refractive index for d-line between the positive lens L4p and the negative: lens L4n of the fourth lens group G4, and a difference of a refractive index for d-line between the object side lens and the image side lens that interpose the cemented surface in the fifth lens group G5.
According to a preferred aspect of the present invention, a zoom lens further satisfies the following conditional formula:
0.00001<PTZ·&Dgr;4/f4<0.0001
wherein PZT is Petzval sum of the vibration reduction lens group G4v, f4 is focal length of the fourth lens group G4, aind &Dgr;4 is a maximum displacement amount of the vibration reduction lens group G4v in the direction substantially perpendicular to the optical axis upon vibration reduction.
REFERENCES:
patent: 5585966 (1996-12-01), Suzuki
patent: 5898525 (1999-04-01), Suzuki
patent: 6141156 (2000-10-01), Aoki
Lucas Michael A.
Nikon Corporation
Sugarman Scott J.
Vorys Sater Seymour and Pease LLP
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