Optical: systems and elements – Image stabilization – By movable refractive structure
Reexamination Certificate
2001-03-29
2003-05-06
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Image stabilization
By movable refractive structure
C359S554000, C359S676000, C359S688000
Reexamination Certificate
active
06560016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-stabilizing zoom lens, and, more particularly, to an image-stabilizing zoom lens which is suited for a television camera, a photographic camera, a video camera or the like, and which has high optical performance over the entire range of variable magnification even during an image stabilizing operation, with the refractive power arrangement of the whole zoom lens, the arrangement of the moving lens units for the variation of magnification, and the construction of the fourth lens unit appropriately set.
2. Description of Related Art
Heretofore, for use with a television camera, a photographic camera, a video camera or the like, there has been a demand for a zoom lens having high optical performance while having a large relative aperture and a high variable magnification ratio. In addition to such a demand, in the case of a color television camera for broadcasting, in particular, importance is attached to operability and mobility. In response to such a requirement, the usage of a CCD (charge-coupled device) of ⅔ inch or ½ inch has become the mainstream for an image pickup device in the color television camera. Since the CCD has an almost uniform resolution over the entire image pickup range, a zoom lens to be associated with the CCD is also required to have an almost uniform resolution from the center of an image plane to the periphery thereof. For example, the zoom lens is required to have the various aberrations, such as coma, astigmatism and distortion, corrected well and to have high optical performance over the entire image plane. In addition, the zoom lens is required to have a large relative aperture, a wide angle of view and a high variable magnification ratio while being small in size and light in weight, and moreover to have a long back focal distance for enabling a color separation optical system and a variety of filters to be disposed in front of an image pickup means.
In addition, it has become a large problem to suppress an image shake caused by the vibration of a photographing system which has a long focal length or by the vibration of hands holding the photographing system. Accordingly, a demand for an image stabilizing function of preventing an image shake has risen. Under the circumstances, there have been proposed a variety of types of image stabilizing methods.
For example, in Japanese Laid-Open Patent Application No. Sho 61-223819 (corresponding to U.S. Pat. No. 4,927,250), there has been proposed a photographing system in which a refraction-type variable angle prism is disposed on the most object side (the side nearest to the object) of the photographing system so as to stabilize an image by varying an apex angle of the refraction-type variable angle prism according to the vibration of the photographing system.
Further, in Japanese Laid-Open Patent Application No. Hei 1-116619 (corresponding to U.S. Pat. No. 5,270,857 and Japanese Laid-Open Patent Application No. Hei 2-124521 (corresponding to U.S. Pat. No. 5,039,211), there has been proposed a method of obtaining a stationary image by detecting the vibration of a photographing system by means of an acceleration sensor or the like and causing a lens unit that is a part of the photographing system to shift in a direction perpendicular to the optical axis according to a signal obtained by the acceleration sensor or the like.
Further, in Japanese Laid-Open Patent Application No. Hei 8-29738 (corresponding to U.S. Pat. No. 5,721,641), there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, in which the fourth lens unit is composed of a front lens subunit of positive refractive power and a rear lens subunit of positive refractive power, and the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the front lens subunit in a direction perpendicular to the optical axis.
Further, in Japanese Laid-Open Patent Application No. Hei 10-90601 (corresponding to U.S. Pat. No. 6,025,962), there has been proposed a zoom lens comprising five lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of negative refractive power and a fifth lens unit of positive refractive power, in which the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the fourth lens unit in a direction perpendicular to the optical axis.
Further, in Japanese Laid-Open Patent Application No. Hei 7-27978 (corresponding to U.S. Pat. No. 5,760,957), there has been proposed a zoom lens comprising four lens units, i.e., in order from the object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, in which the fourth lens unit is composed of a front lens subunit of positive refractive power and a rear lens subunit of positive refractive power, and the shaking of a photographed image caused by the vibration of the zoom lens is corrected by moving the third lens unit or the front lens subunit in a direction perpendicular to the optical axis.
In general, the method of obtaining a stationary image by disposing an image-stabilizing optical system in front of a photographing system and driving and controlling a movable lens unit that is a part of the image-stabilizing optical system to prevent the shaking of a photographed image would cause the whole apparatus to become large in size and a moving mechanism for moving the movable lens unit to become complicated.
In an optical system in which the image stabilization is performed by means of a variable angle prism, the amount of occurrence of decentering lateral chromatic aberration would become large, in particular, on the telephoto side during the image stabilization.
On the other hand, in an optical system in which the image stabilization is performed by causing a lens unit that is a part of a photographing system to decenter in a direction perpendicular to the optical axis, although there is such an advantage that it is unnecessary to provide a specific optical system used for the image stabilization, a space would be required for the lens unit to be moved and the amount of occurrence of decentering aberration during the image stabilization would become large.
In particular, in the four-unit zoom lens composed of four lens units of positive, negative, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the front lens subunit of positive refractive power of the fourth lens unit in a direction perpendicular to the optical axis, as proposed in the above-mentioned Japanese Laid-Open Patent Application No. Hei 8-29738, the front lens subunit, serving as an image-stabilizing lens unit, is a positive lens unit having a relatively small image-stabilizing effect (the amount of movement of the optical axis relative to the amount of decentering being small), and, as a result, there is a possibility that the amount of movement of the image-stabilizing lens unit becomes large to cause an increase of the size of a driving mechanism for the image-stabilizing lens unit.
Further, in particular, in the five-unit zoom lens composed of five lens units of positive, negative, positive, negative and positive refractive powers, respectively, in which the image stabilization is performed by moving the fourth lens unit in a direction perpendicular to the optical axis, as proposed in the above-mentioned Japanese Laid-Open Patent Application No. Hei 10-90601, since the fourth lens unit is a lens unit arranged to move in the optical axis direction during
Fukami Kiyoshi
Nurishi Ryuji
Usui Fumiaki
Canon Kabushiki Kaisha
Morgan & Finnegan , LLP
Nguyen Thong
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