Vari-focal lens

Details Vari-focal lens Vari-focal lens

2000-07-06

2001-12-25

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S701000, C359S695000

Reexamination Certificate

active

06333825

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vari-focal lens or vari-focal zoom lens, which requires slight focus adjustment as it varies the focal length, unless focused on infinity.
2. Description of the Related Art
Vari-focal lens or vari-focal zoom lens is defined as a lens whose focal plane slightly moves as the focal length varies. Therefore, the position of the focusing lens group (the amount of movement of the focusing lens group from a reference position) that is necessary for bringing an object at the same object distance into focus varies as the user varies the focal length. In AF (autofocusing) cameras, the amount of movement of the focusing lens group from a reference position at each focal length has only to be determined by taking into account the focal shift as the focal length varies, namely, the amount of movement of the focusing lens group at each focal length has only to compensate for a slight deviation of the focal plane from an in-focus position thereof as the focal length varies. Even in conventional MF (manual focusing) SLR cameras, even if the focal plane slightly deviates from an in-focus position thereof after the user varies the focal length, he or she has only to rotate the distance-scale bearing ring (focusing ring) provided on the lens, so that sharp object images can be viewed through the viewfinder. Therefore, there is practically no problem in focusing of the vari-focal lens.
However, in SLR cameras, since the distance-scale bearing ring needs to be provided thereon with a distance scale so that it can be seen by the user, the camera has to be sharply focused on an object at a distance indicated by the distance scale at each focal length. In other words, when the camera is to be focused on an object at the same distance, the camera has to be sharply focused on the object at different focal lengths by moving the focusing lens group by respective different amounts of movement by rotating the distance-scale bearing ring rotating by the same amount (angle) of rotation as the focusing lens group from, e.g., the infinity photographic position thereof. Accordingly, in this case where the SLR camera is used with a vari-focal lens, the user is required to manipulate the vari-focal lens as if it were a zoom lens with which the focal plane is substantially still even if the focal length varies. In this respect there is no practical difference between vari-focal lenses and zoom lenses. In the present specification and claims, the terms “zoom” and “zooming” will be herein after used so as to mean “vary” and “variation” of the focal length of the vari-focal lens.
Although various types of vari-focal lenses have been proposed and developed, not only are the structures thereof generally complicated, but also it is difficult to remove mutual interference (influence) between focus cams (e.g., cam grooves or slots) for varying the amount of movement of the focusing lens group per unit angle of rotation of the distance-scale bearing ring in accordance with a variation of the focal length, and zoom cams (e.g., cam grooves or slots) for driving a power varying lens or lenses in order to carry out a zooming operation.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a vari-focal lens which can zoom without the occurrence of mutual interference between the focus cams and the zoom cams.
To achieve the object mentioned above, according to an aspect of the present invention, a vari-focal lens is provided, including a plurality of power varying lens groups including a focusing lens group, which are guided so as to be movable in a direction of an optical axis of the plurality of power varying lens groups to vary a focal length thereof, the focusing lens group being moved in the optical axis direction by different amounts of movement at different focal lengths, respectively, to bring an object at the same object distance into focus; a zooming ring manually rotated about the optical axis; a focusing ring manually rotated independently of the zooming ring about the optical axis; a focusing lens frame which supports the focusing lens group; an intermediate moving frame which supports the focusing lens frame and is guided so as to be movable in the optical axis direction; a zoom cam ring which moves the intermediate moving frame and each of the plurality of power varying lens groups in the optical axis direction according to a predetermined zoom path when the zooming ring is rotated; a focus cam ring which rotates together with the zoom cam ring about the optical axis and is movable in the optical axis direction relative to the zoom cam ring, the focus cam ring including focus cams for compensating for a deviation of a focal plane from an in-focus position thereof at a focal length determined by a rotational position of the zooming ring; and first cam followers formed on the focusing lens frame and corresponding second cam followers formed on the intermediate moving member, the first cam followers and second cam followers being engaged with the focus cams of the focus cam ring. The focus cam ring moves in the optical axis direction relative to the focusing lens frame and the intermediate moving frame, and at the same time, rotates about the optical axis while being guided by the focus cams to thereby change a position of engagement of the first cam followers and the second cam followers relative to the focus cams.
According to the above construction, zooming can be carried out without the occurrence of mutual interference between the focus cams and the zoom cams.
The intermediate moving frame and the focusing lens frame can move together along the optical axis direction without varying a distance therebetween via the focus cams when the zooming ring is rotated in order to carry out a zooming operation.
In an embodiment, each of the focus cams includes a cam slot formed on the focus cam ring.
In another embodiment, each of the focus cams includes an elongated protrusion formed on the focus cam ring.
In an embodiment, each of the first cam followers and respective corresponding one of the second cam followers are engaged with the corresponding common focus cam from opposite directions in a radial direction of the focus cam ring.
Preferably, the focus cam ring is held between the focusing lens frame and the intermediate moving frame.
In an embodiment, the zoom cam ring includes a plurality of first zoom cams, and the intermediate moving frame includes a corresponding plurality of first zoom followers, each of the first zoom followers being engaged with each respective first zoom cams, so that the intermediate moving frame moves in the optical axis direction when the zoom cam ring is rotated.
In an embodiment, another lens frame is further provided, which supports a corresponding one of the plurality of power varying lens groups. The zoom cam ring includes a plurality of second zoom cams, and the another lens frame includes a corresponding plurality of second zoom followers, each of the second zoom followers being engaged with each respective the second zoom cams, so that the another lens frame moves in the optical axis direction when the zoom cam ring is rotated.
In an embodiment, yet another lens frame is further provided, which supports a corresponding one of the plurality of power varying lens groups. The zoom cam ring includes a plurality of third zoom cams, and the yet another lens frame includes a corresponding plurality of third zoom followers engaged with each respective the third zoom cams, so that the yet another lens frame moves in the optical axis direction when the zoom cam ring is rotated.
According to another aspect of the present invention, a vari-focal lens is provided which requires slight focus adjustment as the vari-focal lens varies the focal length, unless focused on infinity, the vari-focal lens including a plurality of lens groups including a focusing lens group, which are guided in a direction of an optical axis to vary a focal length thereof, the focusing lens group being mov

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