Photography – Having variable focal length of camera objective
Reexamination Certificate
2001-02-01
2002-07-23
Adams, Russell (Department: 2851)
Photography
Having variable focal length of camera objective
C396S074000, C359S699000
Reexamination Certificate
active
06424807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, that can be used in digital cameras, and more specifically, to a zoom lens assembling mechanism which makes it easy for the zoom lens to be assembled and disassembled.
2. Description of the Related Art
A zoom lens, or a zoom lens barrel, having a movable barrel (e.g., a cam barrel) that is supported to be movable in the direction of the optical axis of the zoom lens while rotating about the optical axis relative to a stationary barrel of the zoom lens is known in the art. Such a zoom lens having a mechanism with which the movable barrel can be dismounted from the stationary barrel by rotating the movable barrel up to a position (disassembling position) toward the front of the operating range of the movable barrel, which includes the zooming range of the movable barrel, is also known in the art. The opposite ends of the zooming range of the movable barrel correspond to the wide-angle position and the telephoto position of the movable barrel, respectively. In a zoom lens having such a mechanism, the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction (i.e., the length of supporting part of the stationary barrel for the movable barrel) becomes smaller as the movable barrel moves toward the front of the operating range thereof. Therefore, when the movable barrel is moved to the maximum extended position in the operating range thereof, the strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel is low, so that there is a possibility of the movable barrel being eccentric and/or tilting with respect to the optical axis, and/or deviating in the optical axis direction. For instance, in the case where the movable barrel and the stationary barrel are engaged with each other via male and female helicoids (helicoidal threads) respectively formed on the movable barrel and the stationary barrel, a sufficient amount of engagement between the male and female helicoids cannot be ensured when the movable barrel is moved to the maximum extended position in the operating range thereof, which reduces the strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel. If the movable barrel is eccentric and/or tilts with respect to the optical axis, and/or deviates in the optical axis direction, the lens group or groups which are supported inside the movable barrel cannot stay at their right positions, which deteriorates the optical performance of the zoom lens.
Upon assembly, every lens element of a digital camera must be optically centered, correctly spaced, and held firmly with a relatively high precision, e.g., tens times greater than that required in conventional cameras using light-sensitive film since object images are formed on the sensitive surface of a small CCD (CCD image sensor) which is much smaller than the picture plane of conventional cameras using light sensitive film. For instance, if the angle of view is constant, the focal length of a photographing lens becomes shorter as the size of the picture plane reduces, which in turn reduces the sizes of all the elements of the photographing lens such as lens elements, lens frames and other elements. Therefore, the influence that a tolerance (e.g., 10 &mgr;m) has on a photographing lens system of a digital camera is much larger than the influence that the same tolerance would have on a photographing lens system of a conventional camera using light-sensitive film. Accordingly, manufacturing error which falls within tolerance of optical performance in the photographing optical system of a conventional camera using light-sensitive film can be outside the tolerance of optical performance in the photographing optical system of a digital camera.
To prevent such a deterioration of the optical performance from occurring, it is possible to increase the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction (increasing the amount of engagement of male and female helicoids if the movable barrel and the stationary barrel are engaged with each other via male and female helicoids) when the movable barrel is in the maximum extended position in the operating range thereof to ensure a sufficient strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel. However, in this structure, the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, which may impair the ease of assembly and disassembly of the zoom lens. In general, the movable barrel is coupled to a linear guide barrel to be rotatable about the optical axis relative to the linear guide barrel and to be movable in the optical axis direction together with the linear barrel, while the linear guide barrel is guided in the optical axis direction without rotating about the optical axis via linear guide grooves formed on the stationary barrel. Frictional resistance is generated between the linear guide barrel and the movable barrel when a driving force given to the movable barrel to rotate the same is converted into another driving force for moving the linear guide barrel linearly. Due to this fact, if the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, the frictional resistance continues to be generated between the linear guide barrel and the movable barrel while the movable barrel is being moved all the way to the disassembling position when the movable barrel is dismounted from the stationary barrel. This reduces efficiency of assembly and disassembly of the zoom lens. Furthermore, if the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, the movable barrel has to be rotated relative to the linear guide barrel to some degree in a range outside of the zooming range, which unnecessarily moves the lens group or groups supported within the linear guide barrel and the movable barrel. This is not preferable from the viewpoint of maintenance of the optical performance of the zoom lens and simplification of the lens group guiding structure of the zoom lens.
If the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction is small, in some cases a light shield structure has to be provided between the movable barrel and the stationary barrel, since unwanted light can possibly enter into the zoom lens from a gap between the movable barrel and the stationary barrel. Moreover, in the case where linear guide slots for guiding the linear guide barrel in the optical axis direction without rotating the linear guide barrel about the optical axis are formed on the stationary barrel to extend along the length thereof, unwanted light can easily enter into the zoom lens from the linear guide slots.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above-described problems, wherein an object of the present invention is to provide a zoom lens assembling mechanism with which the optical performance of the zoom lens can be maintained, which prevents unwanted light from entering into the zoom lens from a gap between two barrels of the zoom lens, and which makes it easy for the zoom lens to be assembled and disassembled.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens assembling mechanism is provided, including a stationary barrel having a female helicoid formed on an inner peripheral surface of the stationary barrel; a linear guide groove formed on the inner peripheral surface of the stationary barrel to cut across the female helicoid to extend parallel to an optical axis of the zoom lens; an inner inclined groove formed on the inner periphera
Aoki Nobuaki
Nakamura Satoru
Nomura Hiroshi
Yamazaki Yoshihiro
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Smith Arthur A
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