Photography – Having variable focal length of camera objective
Reexamination Certificate
2000-05-15
2001-08-21
Adams, Russell (Department: 2851)
Photography
Having variable focal length of camera objective
C396S075000, C396S076000, C396S079000, C396S085000, C396S348000, C396S349000, C359S704000, C359S701000
Reexamination Certificate
active
06278843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical instrument equipped with a zoom lens such as a photographic camera, an electronic still camera, a video camera, an overhead projector, a regular projector and the like.
2. Description of Related Art
Typically, various optical instruments such as cameras are equipped with zoom lenses. Such a zoom lens has two principle functions, namely a zooming function of varying a focal length to change the magnification of an image and a focusing function of focusing the zoom lens on an aimed object to form a sharp image. These two functions are achieved by causing relative movement of a plurality of lens elements of the zoom lens partly or wholly along the optical axis of the zoom lens.
There have been known various zoom lens drive systems (a)-(d) for achieving the two functions.
(a) Two motor system in which two electric motors are used to drive a focusing mechanism and a zooming mechanism, separately;
(b) One motor system in which a single electric motor is used to drive selectively a focusing mechanism and a zooming mechanism;
(c) A step zoom system adapted to cause zooming at a plurality of fixed zoom ratios in which a single electric motor is used to alternately drive a focusing mechanism and a zooming mechanism while the motor rotates in one direction such as known from, for example, Japanese Patent Publication No. 6(1994)-100707, and
(d) System that has been developed and installed in cameras on the market in the name of, “Epion 210 Zoom” and “Epion 270 Zoom” by the applicant of this application. In this unique system, there is provided rotational play between lens barrels of the zoom lens in which a plurality of lens groups are installed, respectively. For example, one of the lens barrels rotates following another lens barrel which is driven in one direction by an electric motor during zooming-up operation, and remains stationary until the other lens barrel is driven in the other direction through a rotational angle equivalent to the rotational play and rotates following the other lens barrel after the rotation of the other lens barrel through the rotational angle equivalent to the rotational play during zooming-down operation after the zooming-up operation. The zoom lens is adjusted in focus by means of relative rotation between the two lens barrels.
The first two zoom lens drive systems (a) and (b) need a number of constructional parts, which is always disadvantageous in terms of size and cost reduction. The third zoom lens drive system has to have lens barrels having large angles of rotation for an increased number of fixed zoom positions, which results in providing a complex driving mechanism and increasing the overall size of the zoom lens and making the camera bulky. The zoom lens drive system (d) is simple in mechanism and needs only a small number of constructional parts. However, there is a disadvantage that stops positions of the one lens barrel are inaccurate in the extent of the rotational play due to no members for restraining the one lens barrel in the fixed zoom positions and, in consequence, the one lens barrel is possibly displaced in position due to and impact, which leads to an image out of focus.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical instrument equipped with a zoom lens which provides a simplified and reliable mechanism for zooming and focusing.
According to one aspect of the present invention, the foregoing object is accomplished by an optical instrument equipped with a zoom lens which comprises a plurality of lens groups including at least a first lens group and a second lens group axially movable relatively to each other for focusing the zoom lens and installed in a lens barrel provided with zooming guide path means, such as a zooming cam groove, for guiding axially the first lens group when moving axially the second lens group in one of axial directions for zooming and focusing guide path means, such as focusing cam grooves, intersecting the zooming guide path means for guiding axially the first lens group when moving axially the second lens group in another axial direction for focusing the zoom lens on an aimed object. The lens barrel provided with the zooming guide path means and the focusing guide path means which intersect the zooming guide path means causes axial movement of the first lens group along the zooming guide path means or the focusing guide path means according to directions of axial movement of the second lens group. The lens barrel thus configured realizes a simplified mechanism for both zooming and focusing.
According to another aspect of the present invention, the foregoing object is accomplished by an optical instrument equipped with a zoom lens of a step zoom type having a plurality of fixed zoom positions which comprises a plurality of lens groups including at least a first lens group and a second lens group axially movable relatively to each other, the first lens group being axially movable relatively to the second lens group for focusing in each the fixed zoom position, and installed in a lens barrel provided with a zooming-up guide path, such as a zooming-up cam groove, having the fixed zoom positions along which the first lens group is guided to move in a zooming-up direction and positioning the first lens group in one of the fixed zoom positions for zooming-up, a zooming-down guide path, such as a zooming-down cam groove, arranged parallel to the zooming-up guide path and having the fixed zoom positions along which the first lens group is guided to move in a zooming-down direction and positioning the first lens group in one of the fixed zoom position for zooming-down, and a plurality of focusing guide paths provided arranged parallel to one another and connecting the zooming-up guide path and the zooming-down guide path at the fixed zoom positions, respectively, each focusing guide path axially guiding and moving the first lens group relatively to the second lens group for focusing. The lens barrel provided with the zooming-up guide path, the zooming-down guide path and the focusing guide paths which intersect the zooming-up and the zooming-down guide path at the fixed zoom positions realizes a simplified mechanism for both zooming and focusing.
In this instance, the zooming-up guide path, the zooming-down guide path and the focusing guide paths comprise cam grooves, respectively, all of which are connected to one another. A cam follower is urged by, for example, a spring against the cam grooves. The cam groove for the zooming-up guide path is provided with angled stops in the fixed zoom positions on the zooming-up guide path that prevent the come follower from moving beyond the fixed zoom position on the zooming-up guide path and force the cam follower to enter the cam groove for the focusing guide path when zooming down the zoom lens and when focusing the zoom lens after zooming up the zoom lens, and the cam groove for the zooming-down guide path is provided with angled stops in the fixed zoom positions on the zooming-down guide path that prevent the cam follower from moving beyond the fixed zoom position on the zooming-down guide path and force the cam follower to enter the cam groove for the focusing guide path when zooming up the zoom lens and when focusing the zoom lens after zooming down the zoom lens. Employing the cam grooves with the angled stops in the fixed zoom positions and the spring urged cam follower provides reliable ingress of the cam follower into one of the focusing cam groove from the zooming-up cam groove or the zooming-down cam groove.
The cam follower may be configured so as to move in the cam grooves for the zooming-up guide path and the zooming-down guide path keeping in contact with a wall of each of the cam grooves for the zooming-up guide path and the zooming-down guide path that is remote from the cam grooves for the focusing guide paths and shifting toward a wall of each of the cam grooves for the zooming-up guide path and the zooming-down gu
Iwasaki Hiroyuki
Takeshits Yukitaka
Adams Russell
Blackman Rochelle
Fuji Photo Film Co. , Ltd.
Young & Thompson
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