Photography – Having variable focal length of camera objective – Having focus operation
Reexamination Certificate
1999-08-16
2001-01-30
Perkey, W. B. (Department: 2851)
Photography
Having variable focal length of camera objective
Having focus operation
C359S701000
Reexamination Certificate
active
06181876
ABSTRACT:
This application is based on application No. 10-235093 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens for use in cameras and the like, and specifically relates to a zoom lens for varying the magnification at a plurality of predetermined magnifications.
2. Description of the Prior Art
The zoom lens used in cameras has a plurality of lens units, and has a zoom mechanism for arranging each lens unit at desired positions for zooming and has a focusing mechanism for arranging each lens unit at desired positions for focusing. A zoom mechanism capable of zooming at a plurality of magnifications and using the same mechanism for the focusing both simplifies construction and reduces the number of parts, and it also has the advantage of making the zoom lens more compact and reducing cost.
The construction of a conventional zoom lens for cameras having such a zoom mechanism is described below with reference to the brief section view shown in FIG.
1
. As shown in the drawing, a helicoid
2
a
is formed on the interior surface of a stationary barrel
2
fixedly attached to the camera, and a helicoid
1
a
which meshes with the spiral of the helicoid
2
a
is formed on the exterior surface of a drive ring
1
which is rotatable within the stationary barrel
2
.
A helicoid
1
b
is formed on the interior surface of the drive ring
1
, and meshes with the spiral of a helicoid
3
a
provided on the exterior surface of a first moving frame
3
which supports a first lens unit L
1
, and the first moving frame
3
engages an advance guide groove
2
b
provided on the stationary barrel
2
via a connector
3
b
so as to be guided in advancement. A cam
1
c
is formed on the drive ring
1
and engages a guide pin
6
integratedly formed with a second moving frame
4
which supports a second lens unit L
2
, and the guide pin
6
advances in an advance guide groove
3
c
provided on the first moving frame
3
.
When the drive ring
1
rotates, the drive ring
1
moves in the optical axis direction, that is, lateral direction in the drawing, via the helicoids
1
a
and
2
a.
The first lens unit L
1
advances in extension via the helicoids
1
b
and
3
a,
and the second lens unit L
2
advances in extension in accordance with the shape of the cam
1
c.
The amount of the extension of the first and the second lens units L
1
and L
2
is the combined amount of both the movement of the drive ring
1
via the helicoids
1
a
and
2
a,
and the movement of the first and the second moving frames
3
and
4
via the helicoids
1
b
and
3
a
and the cam
1
c.
A brief development view of the drive ring
1
is shown in
FIG. 2
; the cam
1
c
comprises three identically shaped cams
20
a,
20
b,
20
c,
and three guide pins
6
are simultaneously connected. The helicoid
1
b
and the cam
1
c
are provided with retracting sections
10
s
and
20
s
to house the first and the second lens units L
1
and L
2
within the camera; when the camera operation is enabled, the first and the second lens units L
1
and L
2
are arranged near the end points e
1
of the retracting sections
10
s
and
20
s.
At the end points e
1
, the helicoid
1
b
and the cam
1
c
are formed so as to set the first and the second lens units L
1
and L
2
to focus at infinity at a first magnification on the most wide angle side.
The zoom section of the helicoid
1
b
(not illustrated) and the zoom sections
22
z,
23
z,
24
z,
25
z
of the cam
1
c
connect to the helicoid
3
a
and the guide pins
6
so as to move the first and the second lens units L
1
and L
2
and position the first and the second lens units L
1
and L
2
to focus at infinity at the second through fifth magnifications at the endpoints e
2
, e
3
, e
4
, e
5
of the respective zoom sections.
When a desired magnification is selected and the first and the second lens units L
1
and L
2
are positioned near the endpoint of one zoom section, the distance to a photographic object is measured by a distance measuring device (not illustrated), and the first and the second lens units L
1
and L
2
are set at positions corresponding to the measured distance within the focus section of the helicoid
1
b
with the endpoint set as the starting point, and the focus sections
21
f,
22
f,
23
f,
24
f,
25
f
of the cam
1
c
to attain focus at the desired magnification.
According to the zoom lens of the aforesaid construction, the amount of movement of the first lens unit L
1
relative to the rotational angle of the drive ring
1
is normally uniform in order that the movement of the first lens unit L
1
is accomplished by the helicoids
1
b
and
3
a.
As a result, when the pressure angle &thgr; of the helicoid
1
b
is reduced to reduce the torque and improve the resolution during focusing, an area of intersection (area D in the drawing) occurs between the helicoid
1
b
and the cam
20
b.
For this reason, the cam
20
b
is formed on the bottom part of the groove of the helicoid
1
b
to allow movement of the guide pin
6
, thus increasing the thickness of the drive ring
1
and enlarging the zoom lens.
The endpoints (not illustrated) of the zoom sections at adjoining magnifications of the helicoid
1
b
cannot approach due to the focus section therebetween. The zoom magnification is restricted to the magnification corresponding to positions separated to some degree from each extension position of the first lens unit L
1
. Since the magnification changes particularly markedly with small movement of the first lens unit L
1
at the wide angle side, camera operating characteristics are adversely affected inasmuch as the first through, e.g. fifth magnifications cannot be magnifications of uniform intervals.
When the amount of retraction of the lens barrel is increased to reduce the overall length of the zoom lens when housed, the retracting section
10
s
must be lengthened. Lengthening the retracting section
20
s
produces intersection of the cam
20
a,
20
b,
20
c,
and complicates the structure for normal connection of the guide pins
6
corresponding to the cams
20
a,
20
b,
20
c,
thereby enlarging the zoom lens.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a zoom lens which is compact in size.
Another object of the present invention is to provide a zoom lens in which the thickness of the drive ring is reduced and the amount of retraction is increased.
Still another object of the present invention is to provide a zoom lens which improves resolution during focusing, improves focus precision by reducing torque, and uses low power.
To attain the above object, one aspect of the present invention comprises, a first and a second lens unit; a drive ring rotatable around an optical axis; a first cam having a plurality of zoom sections for moving the first lens unit so as to set the magnification stepwise, and having a plurality of focus sections each adjacent to the respective zoom sections for moving the first lens unit so as to focus at the set magnification; and a second cam having a plurality of zoom sections for moving the second lens unit so as to set the magnification stepwise, and having a plurality of focus sections each adjacent to the respective zoom sections for moving the second lens unit so as to focus at the set magnification;
wherein the amount of movement of the first and the second lens units relative to the rotational angle of the drive ring is different between at least one zoom section in the respective first and second cams and the focus sections corresponding to the zoom sections.
According to this construction, when the drive ring rotates, the first and the second lens units move in accordance with the shape of the first and the second cams through a zoom section of a desired magnification and are moved to a focus position within the focus section of this magnification. The amount of movement of the first lens unit relative to the rotational angle of the drive ring is different between at least one zoom sec
Minolta Co. , Ltd.
Perkey W. B.
Sidley & Austin
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