Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-12-21
2003-12-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S680000, C359S681000, C359S682000, C359S676000, C359S683000, C359S684000
Reexamination Certificate
active
06671103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens suitable for use in a digital still camera, a video camera, a silver halide camera or the like and, in particular, to a zoom lens in which an increase in photographing angle of view and a reduction in total lens length are achieved and which is superior in portability.
2. Related Background Art
Nowadays, as a result of the functional advancement of cameras (optical apparatuses) using a solid-state image sensor, such as a video camera, a digital camera, and an electronic still camera, there is a demand for compatibility between high optical performance of the optical system used therein and a reduction in its size.
Further, in a camera of this type, it is necessary to arrange between the lens rearmost portion and the image sensor various optical members, such as a low-pass filter and a color correction filter, so that the optical system used therein is required to have a lens system with a relatively long back focus. Further, in the case of a camera using a color image sensor, the optical system used therein is required to have satisfactory image-side telecentric characteristics in order to prevent color shading.
There has been proposed in Japanese Patent Application Laid-open No. 63-135913 (corresponding to U.S. Pat. No. 4,838,666), Japanese Patent Application Laid-open No. 7-261083, etc. a zoom lens system consisting of three lens units in a negative-positive-positive optical power arrangement satisfying both back focus and telecentric characteristics.
Japanese Patent Application Laid-open No. 7-52256 discloses a zoom lens consisting of three lens units in a negative-positive-positive optical power arrangement as from the object side, the distance between the second and third lens units increasing in zooming from wide-angle end to telephoto end.
The specification of U.S. Pat. No. 5,434,710 discloses a zoom lens consisting of three lens units in a negative-positive-positive optical power arrangement as from the object side, the distance between the second and third lens units decreasing in zooming from wide-angle end to telephoto end.
Japanese Patent Application Laid-open No. 3-288113 (corresponding to U.S. Pat. No. 5,270,863) discloses an optical system consisting of a zoom lens comprising three lens units in a negative-positive-positive optical power arrangement, in which the first lens unit of negative optical power is stationary, and the second and third lens units of positive optical power are moved to effect power variation.
Japanese Patent Application Laid-open No. 2000-147381 (corresponding to U.S. Pat. No. 6,243,213B), Japanese Patent Application Laid-open No. 2000-137164, and U.S. Pat. No. 4,465,343 disclose a zoom lens comprising three lens units in a negative-positive-positive optical power arrangement, focusing being effected with the second unit.
Japanese Patent Application Laid-open No. 2000-111798 (corresponding to U.S. Pat. No. 6,308,011B) discloses a zoom lens consisting of three lens units in a negative-positive-positive optical power arrangement as from the object side. In this zoom lens, a lens back of the requisite length for insertion of a filter or the like ensured on the image plane side, and the requisite telecentric characteristics for a solid-state image sensor are provided at the same time, in which the total length is reduced as much as possible while maintaining a variable power ratio of 2 or more to provide a compact zoom lens.
Japanese Patent Application Laid-open No. 60-31110 (corresponding to U.S. Pat. No. 4,687,302) discloses a zoom lens consisting of four lens units in a negative-positive-positive-positive optical power arrangement as from the object side, in which the distance between the second and third lens units decreases in zooming from wide-angle to telephoto end, with the fourth lens unit being stationary during zooming.
Japanese Patent Publication No. 4-14764 (corresponding to U.S. Pat. No. 4,687,302) discloses a zoom lens consisting of four lens units in a negative-positive-positive-positive optical power arrangement, in which focusing is effected with the third lens unit.
Nowadays, a solid-state image sensor has a large number of pixels, and there is a tendency for the pixel size in a particular image size to be rather small. As a result, there is a demand for a photographic lens having a higher optical performance as compared with the conventional ones of the same image size.
Further, there is a demand for a zoom lens in which the requisite lens back for insertion of a filter or the like is secured behind the lens system and, at the same time, the requisite telecentric characteristics for reducing shading for a solid-state image sensor are achieved, reducing the total lens length to provide a compact zoom lens of high variable power ratio.
For example, in the three-lens-unit zoom lens disclosed in Japanese Patent Application Laid-open No. 2000-147381, Japanese Patent Application Laid-open No. 2000-137164, and U.S. Pat. No. 4,465,343, there is no positive lens unit arranged in the entire zoom range in the vicinity of the image plane, so that it is difficult to secure a sufficiently long exit pupil to provide telecentric characteristics. To secure a sufficiently long exit pupil, it is necessary to relax the power of the first unit, with the result that the total lens length at the wide-angle end is rather large.
In the zoom lens disclosed in Japanese Patent Application Laid-open No. 60-31110, the number of lenses is large, so that the lens system as a whole tends to be rather large.
In the zoom lens disclosed in Japanese Patent Application Laid-open No. 4-14764, the air distance between the second and third lens units at the wide-angle end is small, so that it is difficult to secure a sufficiently long exit pupil in the wide-angle range.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel compact zoom lens that consists of few lenses and has an excellent optical performance with taking into account the above-mentioned conventional art.
In order to attain the above-mentioned object, a zoom lens according to a first aspect of the present invention is characterized by comprising:
a first lens unit of a negative optical power;
a second lens unit of a positive optical power, the second lens unit consisting of a first lens sub unit of a positive optical power arranged on an object side and a second lens sub unit of a positive optical power arranged on an image side with respect to a maximum gap in the unit; and
a third lens unit of a positive optical power, the first through third lens units being arranged in that order from the object side to the image side,
in which zooming is effected by moving the lens units such that the distance between the first lens unit and the second lens unit is smaller at a telephoto end than at a wide-angle end and that the distance between the second lens unit and the third lens unit is larger at the telephoto end than at the wide-angle end,
focusing is effected by moving the second lens sub unit or the third lens unit, and
when focusing is effected on an object at infinity at the wide-angle end, assuming that the distance between the first lens sub unit and the second lens sub unit is d
2
abw
and that the focal length of the entire system at the wide-angle end is fw, the following condition is satisfied:
0.2
<d
2
abw/fw
<1.0.
Also, a zoom lens according to another aspect of the present invention is characterized by comprising:
a first lens unit of a negative optical power;
a second lens unit of a positive optical power, the second lens unit consisting of a first lens sub unit of a positive optical power arranged on an object side and a second lens sub unit of a positive optical power arranged on an image side with respect to a maximum gap in the unit; and
a third lens unit of a positive optical power, the first through third lens units being arranged in that order from the object side to the image side,
in which zooming is effected by moving the lens units such that the
Canon Kabushiki Kaisha
Epps Georgia
Hasan M.
Morgan & Finnegan , LLP
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