Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-04-12
2001-02-06
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
Reexamination Certificate
active
06185049
ABSTRACT:
RELATED CROSS-REFERENCED APPLICATIONS
This application is based on Application Nos. 10-100898, 10-158913, 11-31537, and 11-31538 filed in Japan, the contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a zoom lens system, and specifically relates to a compact wide-angle zoom lens system suitable, for example, as a photographic lens for a lens shutter camera.
DESCRIPTION OF THE RELATED ART
Various conventional zoom lens system for lens shutter cameras have been proposed comprising three lens units of positive-positive-negative lens units to achieve high variable magnification (Japanese Laid-Open Patent Application Nos. 4-303809, 4-338910, 8-152559, 8-179215). Recently, zoom lens systems have been proposed with the object of providing a high variable magnification and compact lens system constructed of fewer lens units (Japanese Laid-Open Patent Application Nos. 4-260016, 5-188296, 8-179215).
The zoom lens systems disclosed in Japanese Laid-Open Patent Application Nos. 4-303809, 4-338910, 8-152559, and 8-179215 have zoom ratios of 3× and higher, and are effective constructions from the perspective of high variable magnification. However, these lens constructions invariably use seven or more lens units, and cannot be said to provide adequate performance from the perspective of use of fewer lens units and compactness. The zoom lens systems disclosed in Japanese Laid-Open Patent Application Nos. 4-260016, 5-188296 and 8-179215 are constructed of fewer lens units, and provide adequate performance from the perspective of reducing the number of lens units and compactness. In these systems, however, the zoom ratio is approximately 1.5× to 2×, which cannot be said to be a high variable magnification.
From the perspective of cost reduction, a zoom lens system may be effectively realized using plastic lens units to construct the zoom lens. In a zoom lens systems used in lens shutter cameras, however, the effective use of plastic lens units is not known relative to a high variable magnification zoom lens system comprising three lens units of positive-positive-negative lens units with a zoom ratio of 3× and higher.
In the zoom lens systems of the aforesaid disclosures, attempting to reduce the overall length of the system and reduce the number of lens units to attain greater compactness increases the optical power of each lens surface and generates greater aberration by each lens surface. Although it is possible to correct spherical aberration and coma among the generated aberrations by providing an aspherical lens surface, chromatic aberration is not correctable by an aspherical lens surface and is difficult to correct directly. Accordingly, correction of chromatic aberration is extremely difficult in conventional zoom lens systems even when the number of lens units is reduced to achieve greater compactness.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved zoom lens system.
A further object of the present invention is to provide a compact high variable magnification zoom lens system using few lens units.
These objects are attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power, a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units and a third lens unit having a negative optical power and provided at the image side of the second lens unit with a second variable air space between the second and third lens units, wherein a zooming operation is performed by varying the first and second air spaces, and wherein the zooming fulfills the following condition:
1.7<&bgr;3
W<
2.0
where
&bgr;3W represents a lateral magnification of the third lens unit in a shortest focal length condition.
These objects are further attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power, a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units, and a third lens unit having a negative optical power and provided at the image side of the second lens unit with a second variable air space between the second and third lens units, wherein a zooming operation is performed by varying the first and second air spaces, and wherein the zooming fulfills the following conditions:
1.00
<TLW/Y′<
1.75
−0.8<
f
3/
fW<−
0.4
where
TLW represents a total length in the shortest focal length condition (the total length is defined as a distance between a summit of a most object surface of the zoom lens system and an image plane),
Y′ represents a maximum image height,
f3 represents a focal length of the third lens unit, and
fW represents a entire focal length in the shortest length condition.
These objects are further attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power and a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units, and a third lens unit having a negative optical power and provided at the image side of the second lens unit with a second variable air space between the second and third lens units, wherein a zooming operation is performed by varying the first and second air spaces, and wherein the zooming fulfills the following conditions:
1.00
<TLW/Y′<
1.75
1.8
<fT/fW<
5.0
where
TLW represents a total length in the shortest focal length condition (the total length is defined as a distance between a summit of a most object surface of the zoom lens system and an image plane),
Y′ represents a maximum image height,
fT represents a entire focal length in a longest focal length condition, and
fW represents a entire focal length in the shortest focal length condition.
These objects are further attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power and including a first resin lens unit; a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units, and a third lens unit having a negative optical power and provided at the image side of the second lens unit with a second variable air space between the second and third lens units, the third lens unit including a second resin lens unit, wherein a zooming operation is performed by varying the first and second air spaces.
These objects are further attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power and including a resin lens unit; a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units, and a third lens unit having a negative optical power and provided at the image side of the second lens unit with a second variable air space between the second and third lens units, wherein a zooming operation is performed by varying the first and second air spaces, and wherein the zoom lens system fulfills the following condition:
1.00
<TLW/Y′<
1.75
where
TLW represents a total length in the shortest focal length condition (the total length is defined as a distance between a summit of a most object side surface of the zoom lens system and an image plane), and
Y′ represents a maximum image height.
These objects are further attained by a zoom lens system comprising, from the object side, a first lens unit having a positive optical power; a second lens unit having a positive optical power and provided at the image side of the first lens unit with a first variable air space between the first and second lens units, and a third lens
Ishimaru Kazuhiko
Okada Takashi
Terada Mamoru
Yamamoto Yasushi
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Sugarman Scott J.
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