Zoom lens barrel

Details Zoom lens barrel Zoom lens barrel

2000-04-05

2001-07-31

Mack, Ricky (Department: 2873)

Optical: systems and elements

Lens

With support

C359S704000

Reexamination Certificate

active

06268970

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel, and in particular, to the construction for miniaturizing a zoom lens barrel having a lens barrel capable of advancing and retreating.
2. Related Art Statement
In a zoom lens barrel in which a plurality of lens groups including a focus lens group is made to move in the direction of an optical axis and to perform zoom operation, cam grooves for driving different lens groups that separately advance and retreat respectively are separately formed according to respective movements.
In addition, in such a lens barrel, advance of the focus lens group is performed using the infinite position as a datum, and in case of focusing in the vicinity, focusing is performed by advancing the focus lens group from the infinite position to a closeup position.
FIGS. 12A
,
12
B, and
12
C show a zoom lens whose phototaking lens is composed of three groups of lenses, and show an example of a tube-retraction type of zoom lens barrel in which the second lens group is a focus lens.
FIG. 12A
is an explanatory diagram showing positions of respective lens groups in a tube retracting state.
FIG. 12B
is an explanatory diagram showing positions of respective lens groups in a wide-angle state.
FIG. 12C
is an explanatory diagram showing positions of respective lens groups in a telescopic state.
As shown in
FIGS. 12B and 12C
, when the zoom lens barrel is in the wide-angle state and telescopic state, the second lens group (focus lens group)
202
is usually positioned at the infinite position shown by solid lines in the figure against the first and third lens group
201
and
203
. In addition, focusing to the vicinity is performed by advancing the second lens group
202
from the infinite position to the closeup position in the first lens group side that is shown by alternate long and two short dashes lines. After photo-taking, the second lens group
202
is moved to the infinite position by being reset.
Furthermore, a method for containing this zoom lens barrel at a tube retracting position after photo-taking is as follows. As shown in
FIG. 12A
, the second lens group
202
is not moved from the infinite position, that is, the second lens group
202
keeps the state being reset at the infinite position. On the other hand, with keeping the distance between the first lens group
201
and second lens group
202
and moving them as one piece, the entire length of the lens barrel is shortened and the lens barrel is contained by shortening a zoom distance between the first lens group
201
and third lens group
203
. Therefore, when the tube retraction is completed space remains for closeup feeding length of the focus lens group.
In conventional cam grooves for movement of lens groups, it is difficult to sufficiently secure movable ranges of respective lens groups because a plurality of cam grooves are provided on the same circumferential surface of the same cam tube.
Thus, if a plurality of different cam grooves are formed adjacent to each other, rotation angles of the cam grooves become small, and thus increase the pressure on each cam groove when the cam tube rotates. If the diameter of the cam tube is made to be large so as to reduce this pressure, the lens barrel becomes correspondingly large. In addition, if cam grooves are formed shifted to the thrust direction lest respective cam grooves should overlap without the cam grooves being adjacent to each other, the entire length of the cam tube becomes large. Hence, the lens barrel also becomes large in this case.
In this manner, using respective cam grooves separately causes a malfunction that the entire size of the lens barrel becomes large in radial directions or in the thrust direction.
Furthermore, as described above, when the zoom lens barrel is retracted, a surplus space for closeup feeding length of the focus lens group is kept in the front of the focus lens group. As a consequence, the entire length of the lens barrel at the tube retraction becomes large.
Moreover, in a lens barrel shown in
FIGS. 12A
to
12
C, if a cam for tube retraction is provided by extending a zoom cam moving the first lens group
201
for zooming so as to shorten the distance between the first lens group
201
and second lens group
202
for the sake of reducing the entire length of the lens barrel, this causes additional difficulty of cam layout in the cam tube and enlargement of the cam tube.
In addition, since the first lens group
201
that is a zoom lens is moved so as to shorten the distance between the first lens group
201
and second lens group
202
, the load for electrically driving the cam tube becomes large.
OBJECTS AND SUMMARY OF THE INVENTION
A first object of the present invention is to provide a zoom lens barrel with which movable ranges of respective lens groups can be sufficiently secured without enlarging a cam tube even if it is necessary to form a plurality of cam grooves on the same circumferential surface of the same cam tube.
In addition, a second object of the present invention is to provide a zoom lens barrel wherein a focus lens group is fed forward before tube retracting operation, and the tube retracting operation is performed thereafter, thereby shortening the entire length of the zoom lens barrel in the tube retraction.
In brief, a zoom lens barrel of the present invention that performs zooming by moving a plurality of lens groups in a photo-taking optical system with interlocking them with each other includes:
a frame supporting a first lens group;
a frame supporting a second lens group;
a cam tube supporting the frame supporting the first lens group and the frame supporting the second lens group so that the frames supporting the lens groups can move in the direction of the optical axis; and
a drive cam means that is provided in the cam tube and has a cam that has the first cam region for moving the frame supporting the first lens group in the direction of the optical axis and the second cam region for moving the frame supporting the second lens group in the direction of the optical axis and is formed so that the frame supporting the first lens group and the frame supporting, the second lens group may commonly use partial regions of the first cam region and the second cam region at the time of performing the zooming.
These objects and advantages of the present invention will become further apparent from the following detailed explanation.


REFERENCES:
patent: 5376983 (1994-12-01), Yamazaki et al.
patent: 5450242 (1995-09-01), Kohmoto et al.
patent: 6147814 (2000-11-01), Kitazawa et al.
patent: 10-148746-A (1998-06-01), None

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