Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-09-26
2003-08-12
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
Reexamination Certificate
active
06606202
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens system and optical apparatus using the same, and more particularly those suitable for video cameras, digital cameras, and cameras using a film.
Along with the recent advance of high performance and miniaturization of cameras (or optical apparatuses), such as video, digital, and electronic still cameras using a charged-coupled device (CCD), and film cameras using a film, an optical system for use with them has been required to meet both high optical performance and miniaturization.
Among a lens system used for an optical apparatus, such as video and digital still cameras, a four-unit zoom lens includes four lens units of positive, negative, positive and positive refractive powers, more specifically, it includes, in order from the object side, a first lens unit of positive refractive power that is fixed during zooming and focusing, a second lens unit of negative refractive power that moves along the optical axis and exhibits a zooming operation, a third lens unit of positive refractive power that is fixed during zooming and focusing, and a fourth lens unit of positive refractive power that moves during zooming and focusing. This four-unit zoom lens exhibits the high optical performance by composing the first lens unit of a cemented lens of a concave lens (or negative lens) and a convex lens (or a positive lens), the second lens unit of two concave lenses and a convex lens, the third lens with one or two convex lenses and a concave lens.
For example, U.S. Pat. Nos. 5,963,378 and 6,166,864 each disclose a zoom lens including, in order from the object side, a fixed first lens unit of positive refractive power, a zooming second lens unit of negative refractive power, a fixed condenser third lens unit of positive refractive power, and a fourth lens unit of positive refractive power that moves along an optical axis to maintain a position of an image plane.
Japanese Laid-Open Patent Applications Nos. Sho 62-206516, Sho 62-24213, Sho 63-247316, and Sho 63-247316, U.S. Pat. No. 5,189,558 disclose another type of four-unit zoom lens including, in order from the object side, a first unit of positive refractive power, a second unit of negative refractive power, a third unit of positive refractive power, and a fourth unit of positive refractive power, wherein the second unit moves and zooms, and the fourth unit corrects fluctuations of the image plane along with the zooming and conducts focusing.
Characteristically, this rear focus type of four-unit zoom lens may easily obtain the predetermined zoom range and easily miniaturize the entire lens system.
On the other hand, various vibration resistant optical systems that serve to prevent blurs in a shot image have been conventionally proposed.
For example, Japanese Laid-Open Patent Application No. Hei 7-128619 discloses a four-unit zooming optical system including four lens units of positive, negative, positive and positive refractive powers, wherein the third lens unit comprises two lens units of positive and negative refractive powers, which lens unit of positive refractive power is made vibratory for vibration resistant purposes.
U.S. Pat. No. 5,585,966 discloses a four-unit zooming optical system including four lens units of positive, negative, positive and positive refractive powers, wherein third lens unit is vibrated for vibration resistant purposes.
Characteristically, these lens units do not require a specific optical member such as a prism, to prevent vibrations, and facilitates the vibration resistance.
Along with the recent advance of high pixel density of image-taking devices, such as digital and video cameras, and miniaturization of optical apparatuses, a smaller and higher performance lens system has been required as a shooting lens for use with them.
In addition, the video camera has been required to record static images with high image quality and to use a high performance and compact lens system.
In general, the enhanced refractive power in each lens unit in the zoom lens would result in a higher zoom range and a shorter lens span because each lens unit moves by a shorter distance to obtain the predetermined zoom range.
However, the simply enhanced refractive power in each lens unit would make stricter the manufacturing precision; for example, the shooting performance remarkably deteriorates due to a relative axial shift among lenses in the third lens unit in the above four-unit zoom lens of positive, negative, positive and positive refractive powers.
On the other hand, the rear focus type zoom lens has been required to have smaller aberrational fluctuations during focusing and during high-range zooming.
Moreover, smaller defocus aberrations are required, when vibrations are prevented, in the optical system that prevents vibrations by decentering part of lenses in a shooting system in a direction perpendicular to the optical axis in order to correct blurred images caused when the lens system vibrates.
SUMMARY OF THE INVENTION
Accordingly, it is a primary but exemplified object of the present invention to provide a zoom lens system and an optical apparatus using the same, that are suitable for a shooting system using a photoelectric conversion element such as CCD, compact, and superior in optical performance.
In order to achieve the above object, a zoom lens system of one aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power that doesn't move along an optical axis for zooming, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power that doesn't move along the optical axis for zooming, the third lens unit including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power that is stronger at the image side than at the object side, with a convex surface of a positive lens element of refractive power that is stronger at the object side than at the image side, and a fourth lens unit of positive refractive power. The zoom lens system prevents the deterioration of the optical performance, when vibrations are prevented and the third lens unit moves in the direction perpendicular to the optical axis. In addition, the cemented lens in the second lens subunit prevents the performance deterioration caused by the relative axial shift in the third lens unit. This configuration in the third lens unit may make the principal point relatively closer to the second lens unit, shorten a distance from the third lens unit to the image plane, and facilitate the miniaturization of the lens span. Moreover, the lens barrel structure may be made simple and strong to the static pressure by the first lens unit not moved for zooming.
A zoom lens system of another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power that is stronger at the image side than at the object side, with a convex surface of a positive lens element of refractive power that is stronger at the object side than at the image side, and a fourth lens unit of positive refractive power, wherein a condition 0.09<Dab/f3<0.35 is satisfied where Dab is a separation be
Canon Kabushiki Kaisha
Collins Darryl J.
Morgan & Finnegan L.L.P.
Sugarman Scott J.
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