Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-07-26
2003-10-14
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S685000
Reexamination Certificate
active
06633437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens and a photographing apparatus using it and, more particularly, to those suitably applicable to a photographing apparatus, such as photographic cameras, video cameras, digital cameras, SV (still video) cameras, and so on, which has a plurality of lens units including a leading lens component of negative refractive power (optical power) and in which high optical performance is realized across the entire zooming range by properly setting the lens configuration, the zoom type, etc. of these lens units.
2. Related Background Art
Zoom lenses of various types have been used heretofore in the photographing apparatus such as the photographic cameras, video cameras, and so on.
Among them, the zoom lenses of a so-called negative lead type having a leading lens component of negative refractive power are commonly used as standard zoom lenses for many cameras because of their relative easiness of increase in the angle of view.
As the standard zoom lenses of this type, there are proposals of so-called two-unit zoom lenses wherein two lens units consist of a first unit of negative refractive power and a second unit of positive refractive power and wherein these two lens units are moved along the optical axis to change the spacing between the lens units so as to effect zooming, for example, as described in Japanese Patent Application Laid-Open No. 53-132360 (corresponding to U.S. Pat. No. 4,299,452), Japanese Patent Application Laid-Open No. 56-19022 (corresponding to U.S. Pat. No. 4,370,031), U.S. Pat. No.5,283,639, and so on.
Further, Japanese Patent Application Laid-Open No. 07-52256 suggests the zoom lens which has three lens units consisting of a first unit of negative refractive power, a second unit of positive refractive power, and a third unit of positive refractive power, arranged in the order named from the object side, and in which the spacing between the second unit and the third unit is increased to effect zooming from the wide-angle end to the telephoto end.
U.S. Pat. No. 5,434,710 discloses the zoom lens which has three lens units consisting of a first unit of negative refractive power, a second unit of positive refractive power, and a third unit of positive refractive power, arranged in the order named from the object side, and in which the spacing between the second unit and the third unit is decreased to effect zooming from the wide-angle end to the telephoto end.
Applicant filed Japanese Patent Application Laid-Open No. 06-27377 to propose the multi-unit zoom lenses consisting of three or more units.
Japanese Patent Applications Laid-Open No. 05-72472 (corresponding to U.S. Pat. No. 5,572,364) and Laid-Open No. 07-270684 (corresponding to U.S. Pat. No. 5,963,378) disclose the four-unit zoom lenses which have a first unit of positive refractive power fixed on the occasion of zooming and focusing, a second unit of negative refractive power moving for zooming, a third unit of positive refractive power fixed and having a converging action, and a fourth unit of positive refractive power moving on the optical axis in order to keep the image plane position from moving with zooming, which are arranged in the order named from the object side.
Recently, there are demands for zoom lenses having a predetermined zoom ratio, including a wide angle of view, and having a compact overall lens system as those used in the photographing apparatus such as single-lens reflex cameras, video cameras, and so on.
In general, the zoom lenses of the negative lead type in which the front component of negative refractive power and the rear component of positive refractive power are constructed of two lens units have such features that it is relatively easy to increase the angle of view and that predetermined back focus is assured readily.
In the two-unit zoom lenses consisting of only two lens units, however, the relative positions of the two units are uniquely determined on the optical axis from restrictions on zooming and on the image plane position and it is difficult to control the optical performance at zoom positions midway through zooming from the wide-angle end to the telephoto end. For this reason, in order to improve the optical performance at the positions midway through the zooming, it is necessary to keep variations in aberration as small at each of the units during the zooming operation as possible. For accomplishing this, the refractive power of each unit needs to be set to be gentle, or each unit needs to consist of the larger number of lenses. However, this method will result in increasing the entire length of the lens.
The four-unit zoom lenses consisting of a first unit of positive refractive power fixed during zooming, a second unit of negative refractive power acting as a zooming unit monotonically moving during zooming, a third unit of positive refractive power fixed during zooming, and a fourth unit of positive refractive power acting as an image-plane correcting unit moving during zooming, had problems including the problem that the power of the second unit became strong, because the zooming was effected substantially by only the second unit, thereby making it difficult to suppress the variations in aberration during zooming, because the image plane correction was implemented by only the fourth unit, and so on.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a zoom lens capable of demonstrating excellent optical performance at any zoom position in the zooming range and capable of readily achieving high optical performance throughout the entire zooming range and throughout the entire view-angle range, by properly setting the lens configuration of each lens unit in a zoom lens of the negative lead type having a leading lens component of negative refractive power, and a photographing apparatus using it.
In order to accomplish the above object, a zoom lens according to one embodiment of the present invention is a zoom lens comprising the following lens components in the order named from the object side:
a front lens component of a negative optical power, the front lens component having a first lens unit of a positive optical power and a second lens unit of a negative optical power in the order named from the object side; and
a rear lens component of a positive optical power, the rear lens component having a third lens unit of a positive optical power and a fourth lens unit of a positive optical power in the order named from the object side;
the zoom lens varying the spacing between principal points of the front lens component and the rear lens component by varying the spacing between the first lens unit and the second lens unit and the spacing between the third lens unit and the fourth lens unit, in order to effect zooming, and
wherein the first lens unit and the fourth lens unit change their moving direction midway through zooming from the wide-angle end to the telephoto end.
Another zoom lens according to another embodiment of the present invention is a zoom lens comprising the following lens components in the order named from the object side:
a front lens component of a negative optical power, the front lens component having a first lens unit of a positive optical power and a second lens unit of a negative optical power in the order named from the object side; and
a rear lens component of a positive optical power, the rear lens component having a third lens unit of a positive optical power and a fourth lens unit of a positive optical power in the order named from the object side;
the zoom lens varying the spacing between principal points of the front lens component and the rear lens component by varying the spacing between the first lens unit and the second lens unit and the spacing between the third lens unit and the fourth lens unit, in order to effect zooming,
wherein the fourth lens unit changes its moving direction midway through zooming from the wide-angle end to the telephoto end, and
wherein the first lens unit consists of a lens element of a positiv
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