1. Field of the Invention
The present invention relates to a lens barrel. More particularly, this invention is concerned with a collapsible lens barrel or zooming lens barrel having a plurality of movable frames, which hold groups of photographic lenses or the like, designed to independently move in directions along an optical axis.
2. Description of the Related Art
Photography apparatuses (hereinafter, generically, cameras) including an ordinary compact camera and an electronic still camera (hereinafter, an electronic camera) are usually carried for use. The compact camera uses, for example, a silver film to perform photography, while the electronic camera electrically records an image signal or image information output from an imaging means such as a charge-coupled device (CCD). How to improve the compactness of the cameras and duly improve the portability thereof is a significant task that must be tackled in designing the cameras.
Among the component members of the cameras, a lens barrel composed of a plurality of lens frames for holding a photographic optical system so that the photographic optical system can move in directions along an optical axis occupies a large part in terms of both the volume and weight. Designing the lens barrel itself compactly therefore contributes largely to improvement in the compactness and portability of the cameras.
In recent years, a so-called variable power photographic optical system (hereinafter, a zoom lens) capable of continuously varying a focal length has been adopted as a photographic optical system employed in many cameras. Moreover, there is an increasing demand for a higher image magnification realized with a higher power (zooming ratio).
For constructing a lens barrel for a zoom lens capable of offering a high power, numerous photographic lenses and numerous lens frames for holding the lenses are needed. This leads to an increase in the number of component members. The increase in the number of component members discourages the effort to design the zoom lens barrel compactly. Besides, when an attempt is made to realize a zoom lens offering a high power, the lens barrel holding the zoom lens must be designed large in size.
Various proposals have been made of a means for improving the portability of cameras while adopting the zoom lens. Various means including, for example, a collapsible lens barrel have been proposed for photographic lenses and put to practical use. In cameras having this kind of collapsible lens barrel for photographic lenses, a plurality of lens frames is movable to enter two states, that is, a photographic state in which photography can be performed and a non-photographic state (collapsed state) in which a camera is being carried.
In the cameras, part of the lens barrel projects forward from a camera body (photographic state) during photography. In contrast, for placing a camera in the non-photographic state so as to carry it, the plurality of lens frames constituting the lens barrel is moved mutually independently in order to narrow the space between adjoining lens frames. Besides, the lens barrel itself is stowed in the camera body (collapsed).
In a conventional collapsible lens barrel for photographic lenses, a plurality of elongated guide shafts is usually used as movement restraint members. The movement restraint members support movable frames such as lens frames movable within the lens barrel, guide the movements of the frames in directions along an optical axis, and restrain the movements of the frames in directions of rotation.
However, when the guide shafts are used as the movement restraint members for restraining the movements of the movable frames, the guide shafts themselves must have predetermined lengths. Bearing members for bearing the guide shafts must be arranged in the optical-axis directions. Consequently, the adoption of the guide shafts becomes a factor in crippling the effort to making the lens barrel compact and short.
Moreover, the elongated guide shafts are placed in a stationary frame for supporting the movable frames stowed in the lens barrel. This poses a problem in that the layout of the movable frames and a movable range thereof are limited.
In efforts to shorten the lens barrel, a lens barrel disclosed in, for example, Japanese Unexamined Patent Publication No. 7-174956 has the bearings of the guide shafts placed in another lens frame interposed between two lens frames holding two groups of photographic lenses. This means proposed in the patent publication is intended to thus shorten the guide shafts.
According to the means disclosed in the Japanese Unexamined Patent Publication No. 7-174956, a plurality of guide shafts is used to stabilize the movements of the lens barrel in the optical-axis directions. This also contributes to reduction in the length in the optical-axis directions of the lens barrel.
When guide shafts are used to support a plurality of lens frames, the lens frames must have predetermined lengths for ensuring engagement in predetermined states.
However, according to the means disclosed in the Japanese Unexamined Patent Publication No. 7-174956, the engagement length of each lens frame is reduced or any other means is adopted. This poses a problem in that a limit is set on the stableness of movements to be attained.
An object of the present invention is to provide a lens barrel for moving a plurality of lens frames in directions along an optical axis. More particularly, the lens barrel has the overall length thereof reduced without the necessity of making the structure thereof complex. Besides, the lens barrel can move the lens frames on a stable basis.
Briefly, according to the first aspect of the present invention, a lens barrel has a stationary frame, a cam frame, a first lens frame, and a second lens frame. The cam frame has an external cam formed on the external surface thereof and an internal cam formed on the internal surface thereof. The first lens frame is freely movable in directions along an optical axis relative to the stationary frame when driven by the external cam of the cam frame. The second lens frame can freely slide in the optical-axis directions with its rotation restrained by the internal surface of the first lens frame when driven by the internal cam of the cam frame.
Moreover, according to the second aspect of the present invention, a lens frame has first and second lens frames, a cam frame, and a driving means. The first and second lens frames are engaged with each other so that they can freely move in the optical-axis directions alone. The cam frame has an external cam formed on the external surface thereof for driving the first lens frame, and an internal cam formed on the internal surface thereof for driving the second lens frame. The driving means gives drive to rotate the cam frame.
According to the third aspect of the present invention, a lens barrel has a first lens frame and a second lens frame. The first lens frame is freely movable in the optical-axis directions relative to a stationary frame when driven by an external cam formed on the external surface of a cam frame. The second lens frame is freely movable in the optical-axis directions relative to the stationary frame when driven by an internal cam formed on the internal surface of the cam frame. The lens barrel also has a rectilinear movement restraint member realized with part of the first lens frame and part of the second lens frame. The rectilinear movement restraint member is characterized in that: when the first lens frame and second lens frame both move in an optical-axis direction, the rectilinear movement restraint member restrains the second lens frame from rotating relative to the first lens frame and permits the second lens frame to rectilinearly move over the internal surface of the first lens frame.
These objects and other objects of the present invention and the advantages thereof will be apparent from the description made below.
According to the present invention, there is provided a lens barrel for moving a plurality of lens frames in directions along an optical axis. More particularly, although the structure of the lens barrel is simple, the lens barrel will not interfere with stable movements of the lens frames but the lens barrel has the overall length thereof reduced.