Lens control device for moving range correction

Details Lens control device for moving range correction Lens control device for moving range correction

1998-01-13

2004-06-01

Vu, Ngoc-Yen (Department: 2612)

Television

Camera, system and detail

Optics

C348S240300, C348S351000, C348S360000

Reexamination Certificate

active

06744468

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a camera which is provided with a zoom lens and a lens capable of being mounted onto the zoom lens in a detachable manner to modify the focal length and magnifying power of the zoom lens.
2. Description of the Related Art
Conventionally available as one type of camera is the one provided with a zoom lens and a conversion lens which is mounted onto the zoom lens in a detachable manner to modify the focal length and power of the zoom lens.
Referring to drawings, the conventional arrangement of the zoom lens and the conversion lens which is mounted onto the zoom lens in a detachable manner to modify the focal length and magnification of the zoom lens is discussed below.
FIG. 1
is a diagrammatic view showing the arrangement of a conventional camera comprising a zoom lens and a conversion lens which is mounted onto the zoom lens to modify the focal length and power of the zoom lens.
A zoom lens unit
100
comprises a first (front) lens group
101
mounted onto a lens casing as shown in FIG.
1
. Disposed behind the first lens group
101
is a second lens group (hereinafter referred to as “a variator lens”)
102
for varying power. The variator lens
102
shares the same optical axis with the first lens group
101
. To vary its power, the variator lens
102
is moved in a direction in parallel with the optical axis of its own by driving means (not shown).
An iris
103
is disposed behind the variator lens
102
to adjust light quantity. Disposed further behind the iris
103
is a third lens group
104
that is attached onto the lens casing. The third lens group
104
also shares the same optical axis with the variator lens
102
.
Arranged behind the third lens group
104
is a fourth lens group (hereinafter referred to as “a focus-compensation lens”)
105
. The focus-compensation lens
105
has a focusing function, and a compensation function, namely compensating for the displacement of the focal plane arising from power variation. The focus-compensation lens
105
shares the same optical axis with the third lens group
104
. The focus-compensation lens
105
is moved in a direction in parallel with the optical axis of its own by the driving means so that the focusing and compensation are performed.
An image pickup device
106
such as a CCD is arranged behind the zoom lens unit
100
, namely the focus-compensation lens
105
. An imaging surface that bears an optical image of an object is provided on one side of the CCD
106
facing the focus-compensation lens
105
.
A wide-angle attachment lens
121
is mounted onto the zoom lens unit
100
in a detachable manner to modify the focal length and power of the lens unit
100
. When mounted onto the zoom lens unit
100
, the wide-angle attachment lens
121
is positioned in front of the first lens group
101
in a manner that allows the optical axes of both are aligned. The mounting of the wide-angle attachment lens
121
causes the focal length of the zoom lens unit
100
to shift toward the wide-angle side.
Discussed below referring to drawings are a relationship between the focal length (the position of the variator lens
102
) of the zoom lens unit
100
and the position of the focus-compensation lens
105
with no wide-angle attachment lens
121
mounted and a similar relationship but with the wide-angle attachment lens
121
mounted. FIGS.
2
(
a
) and
2
(
b
) illustrate, respectively, the relationship between the focal length (the position of the variator lens
102
) of the zoom lens unit
100
and the position of the focus-compensation lens
105
with no wide-angle attachment lens
121
mounted and the same relationship but with the wide-angle attachment lens
121
mounted in FIG.
1
.
FIG. 3
shows the relationship between the position of the variator lens and the position of the focus-compensation lens with no wide-angle attachment lens mounted in FIG.
1
.
FIG. 4
shows a similar relationship.
A discussion of the relationship between the focal length (the position of the variator lens
102
) of the zoom lens unit
100
and the position of the focus-compensation lens
105
with no wide-angle attachment lens mounted follows.
When the focal length of the zoom lens unit
100
is set to a predetermined value, the position of the focus-compensation lens
105
that results in an optical image on the imaging surface of the CCD
106
, namely, the focused position of the focus-compensation lens
105
varies with the distance to the object as shown in FIG.
2
(
a
). When the object distance remains constant, the focused position of the focus-compensation lens
105
varies with the focal length of the zoom lens unit
100
, namely, the position of the variator lens
102
. As a result, an optical image is obtained through the light which is focused by shifting the focus-compensation lens
105
according to the curve resulting from the focal length set and the object distance.
A discussion of how to follow the above-mentioned curve follows.
Referring to
FIG. 3
, the relationship between the focal length (the position of the variator lens
102
) of the zoom lens unit
100
and the position of the focus-compensation lens
105
with no wide-angle attachment lens
121
mounted is illustrated by a first curve f1 that is a plot of a series of positions of the variator lens
102
, z0, z1, z2, . . . , z6 versus a corresponding series of positions of the focus-compensation lens
105
, a0, a1, a2, . . . , a6. Data, z0, z1, z2, . . . , z6 and a0, a1, a2, . . . a6, are stored in a lens control microcomputer (not shown). Equally, a second curve f2 is a plot of a series of positions of the variator lens
102
, z0, z1, z2, . . . , z6 versus a corresponding series of positions of the focus-compensation lens
105
, b0, b1, b2, . . . , b6. These data are also stored in the lens control microcomputer.
A third curve f3, however, is calculated from the first curve f1 and the second curve f2. The third curve f3 is a plot of a series of positions of the variator lens
102
, z0, z1, z2, . . . , z6 versus a corresponding series of positions of the focus-compensation lens
105
, p0, p1, p2, . . . , p6. These data are also stored in the lens control microcomputer.
p0, p1, p2, . . . , p6 are calculated by the following equation.
p
(
n
+1)={|
p
(
n
)−
a
(
n
)|/|
b
(
n
)−
a
(
n
)|}*{|
b
(
n+
1)−
a
(
n+
1)|}+
a
(
n+
1)  (1)
Equation (1) determines the ratio of interior division of p0 on a line segment, b0-a0, when the focus-compensation lens
105
is positioned at p0. According to the ratio, p1 is plotted on a line segment, b1-a1. The speed of the focus-compensation lens
105
required to keep the zoom lens unit
100
focused is thus determined by the positional difference between p1 and p0 and the time the variator lens
102
requires to travel from z0 to z1.
Referring to
FIG. 4
, interpolation applied to the variator lens
102
in its one direction is discussed. In
FIG. 4
, the position of the variator lens
102
is arbitrarily set, and representative (cam) locus (the positions of the focus-compensation lens relative to the variator lens) is a plot of the positions of the variator lens
102
, z0, z1, z2, . . . , zn and a0, a1, a2, . . . , an, and b0, b1, b2, . . . , bn relative to the object distance.
When the variator lens
102
is positioned at zx, not on any of the zooming boundaries represented by z0, z1, z2, . . . , zn within the range of travel of the variator lens
102
(namely, somewhere between zk−1 and zk) and when the focus-compensation lens
105
is positioned at px, both ax and bx are given by the following equations.
ax=ak−
(
zk−zx
)*(
ak−ak−
1)/(
zk−zk−
1)  (2)
bx=bk
−(
zk−zk
)*(
bk−bk−
1)/(
zk−zk−
1)  (3)
As understood from the above equations, ax and bx are determined by interpolating, respectively, between two sets of stored

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