Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-10-03
2002-12-24
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S687000, C359S690000
Reexamination Certificate
active
06498687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens and an optical apparatus having the zoom lens, and more particularly to a zoom lens suited for a video camera, digital still camera, a silver-halide film camera, a broadcasting camera or the like, which has a relatively small number of constituent lens elements to make the entirety of a lens system thereof reduced in size while having a high variable magnification ratio, and an optical apparatus having such a zoom lens.
2. Description of Related Art
In recent years, with the advancement of high performance of an image pickup apparatus (camera), such as a video camera or a digital still camera, using a solid-state image sensor, such a CCD or an MOS, a zoom lens having a large aperture ratio including a wide angle of view is desired for the purpose of being used for an optical system of such an image pickup apparatus.
Since, in such an image pickup apparatus, a variety of optical members, including a low-pass filter, a color correction filter, etc., are disposed between the rearmost portion of the zoom lens and the image sensor, a lens system having a relatively long back focal distance is required for the optical system. In addition, in the case of a color camera using an image sensor for color images, a zoom lens excellent in telecentricity on the image side is desired for an optical system of the color camera so as to prevent color shading.
As one method for achieving the above-mentioned requirements, heretofore, there have been proposed a variety of two-unit zoom lenses of the so-called negative lead type each of which is composed of a first lens unit of negative refractive power and a second lens unit of positive refractive power, the separation between the first lens unit and the second lens unit being varied to effect the variation of magnification. In such a zoom optical system of the negative type, the variation of magnification is effected by moving the second lens unit of positive refractive power, and the compensation for the shift of an image plane due to the variation of magnification is effected by moving the first lens unit of negative refractive power. In such a lens construction composed of two lens units, to keep optical performance well, the upper limit of a variable magnification ratio is 2× or thereabout.
Further, in order to make the entirety of a lens system in a compact form while having a high variable magnification ratio greater than 2×, there have been proposed, for example, in Japanese Patent Publication No. Hei 7-3507 (corresponding to U.S. Pat. No. 4,810,072), Japanese Patent Publication No. Hei 6-40170 (corresponding to U.S. Pat. No. 4,647,160), etc., the so-called three-unit zoom lenses in each of which a third lens unit of negative or positive refractive power is disposed on the image side of the two-unit zoom lens so as to correct the various aberrations occurring due to the high variable magnification.
Further, in U.S. Pat. Nos. 4,828,372 and 5,262,897, there is disclosed a three-unit zoom lens composed of three lens units of negative, positive and positive refractive powers, respectively, in which the second lens unit is composed of six lens elements, as a whole, including two cemented lenses.
However, since the above-stated kind of three-unit zoom lens is designed mainly for 35-mm film photographic cameras, it is hard to say that the length of the back focal distance required for an optical system using a solid-state image sensor and the excellent telecentricity are made compatible with each other.
Three-unit zoom lenses of the negative lead type satisfying both the back focal distance and the telecentric characteristic have been proposed in, for example, Japanese Laid-Open Patent Application No. Sho 63-135913 (corresponding to U.S. Pat. No. 4,838,666), Japanese Laid-Open Patent Application No. Hei 7-261083, etc. In addition, in Japanese Laid-Open Patent Application No. Hei 3-288113 (corresponding to U.S. Pat. No. 5,270,863), there is disclosed a three-unit zoom lens in which a first lens unit of negative refractive power is fixed and a second lens unit of positive refractive power and a third lens unit of positive refractive power are moved to effect the variation of magnification.
However, in these zoom lenses, there are such tendencies that the number of constituent lens elements of each lens unit is relatively large, the total length of the lens system is great, and the production cost is high.
Further, in recent years, there has been widely used the so-called barrel-retractable zoom lens in which, in order to make the compactness of a camera and the high magnification of a lens system compatible with each other, the separation between the respective adjacent lens units at the time of nonuse of the camera is reduced up to the separation different from that at the time of use of the camera, thereby lessening the amount of protrusion of the zoom lens from the camera body. However, in a case where, as in the conventional zoom lenses, the number of constituent lens elements of each lens unit is large and, as a result, the length of each lens unit on the optical axis is great, or in a case where the amount of movement of each lens unit during zooming and during focusing is large and the total lens length is, therefore, great, it is sometimes impossible to attain the desired length of the zoom lens as retracted.
Further, in the zoom lens disclosed in Japanese Laid-Open Patent Application No. Hei 7-261083, a convex lens (positive lens) is disposed on the most object side of the first lens unit of negative refractive power, so that an increase of the outer diameter of the zoom lens when made to have a wide angle is inevitable.
In addition, in this zoom lens, since the focusing onto a close object is effected by moving the first lens unit of negative refractive power, there is such a tendency that the construction of a lens mounting mechanism is complicated in combination with the movement for zooming.
Further, in U.S. Pat. No. 4,999,007, there is disclosed a three-unit zoom lens in which each of the first lens unit and the second lens unit is composed of a single lens.
However, in this zoom lens, the total lens length at the wide-angle end is relatively great, and, because the distance between the first lens unit and the stop at the wide-angle end is large, the height of incidence of an off-axial ray of light is large to increase the diameter of a lens element of the first lens unit. Therefore, there is such a tendency that the entirety of a lens system becomes large.
Further, as a problem peculiar to a case where an angle of view at the wide-angle end is enlarged, there is the insufficiency for correcting distortion. In addition, in order to use a zoom lens in association with a high-pixel-density image sensor whose sensitivity is relatively low, the zoom lens is required to have a larger aperture ratio.
On the other hand, as one method of attaining a higher variable magnification ratio while making the length of the back focal distance and the excellent telecentricity compatible with each other, there has also been widely used a zoom lens of the so-called positive lead type in which a first lens unit of positive refractive power is disposed on the most object side.
Among the zoom lenses of the positive lead type, there are disclosed, in Japanese Laid-Open Patent Application No. Sho 62-206516, Japanese Laid-Open Patent Application No. Sho 62-215225 (corresponding to U.S. Pat. No. 4,859,042), Japanese Laid-Open Patent Application No. Sho 62-24213, Japanese Laid-Open Patent Application No. Hei 4-43311 (corresponding to U.S. Pat. No. 5,189,558), Japanese Laid-Open Patent Application No. Hei 5-72472 (corresponding to U.S. Pat. No. 5,572,364), Japanese Laid-Open Patent Application No. Hei 6-34882 (corresponding to U.S. Pat. No. 5,424,869), etc., zoom lenses of the so-called rear focus type, each of which comprises, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative
Hamano Hiroyuki
Sekita Makoto
Epps Georgia
Spector David N.
LandOfFree
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