Television – Camera – system and detail – Optics
Reexamination Certificate
1997-12-01
2003-06-10
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Optics
C348S345000, C348S240990
Reexamination Certificate
active
06577343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup apparatus such as a video camera and, more particularly, to an arrangement which is suitable for use in an apparatus using an inner focus type of lens system.
2. Description of Related Art
FIG. 2
is a view showing a simple arrangement of an inner focus type of lens system which has conventionally been used. The arrangement shown in
FIG. 2
includes a fixed first lens group
101
, a second lens group (variator lens)
102
for performing a magnification varying operation, an iris
103
, a fixed third lens group
104
, a fourth lens group (focusing lens)
105
having both a focus adjusting function and a so-called compensation function which compensates for a movement of a focal plane due to a magnification varying operation, and an image pickup element
106
.
As is already known, in the lens system which is arranged as shown in
FIG. 2
, since the focusing lens
105
has both the compensation function and the focus adjusting function, the position of the focusing lens
105
for forming an in-focus image on an image pickup surface of the image pickup element
106
differs for different subject distances even in the case of the same focal length. If a variation in the position of the focusing lens
105
for forming an in-focus image on the image pickup surface of the image pickup element
106
is continuously plotted against different subject distances for different focal lengths, the resultant loci are as shown in FIG.
3
. During a magnification varying operation, zooming free of defocusing is enabled by selecting a locus from the loci shown in
FIG. 3
according to the subject distance and moving the focusing lens
105
along the selected locus.
A front-lens focus type of lens system is provided with a compensator lens which is independent of a variator lens, and the variator lens and the compensator lens are connected to each other by a mechanical cam ring. Accordingly, if a knob for manual zooming is provided on the cam ring so that the focal length can be manually varied, no matter how fast the knob may be moved, the cam ring rotates in accordance with the movement of the knob, and the variator lens and the compensator lens move along a cam groove in the cam ring. Therefore, as long as the focusing lens is in focus, the above operation does not cause defocusing.
In the control of the above-described inner focus type of lens system, it is general practice to previously store a plurality of pieces of locus information such as those shown in
FIG. 3
in a lens control microcomputer in a particular form, select a locus according to the relative position between the focusing lens and the variator lens, and perform zooming while tracing the selected locus. In such control, it is necessary to read the position of each of the focusing lens and the variator lens with a certain degree of accuracy, because the position of the focusing lens relative to the position of the variator lens is read from a storage element and applied to lens control.
As can be seen from
FIG. 3
as well, if the variator lens moves at or near a uniform speed, the inclination of the locus of the focusing lens successively varies with a variation in the focal length. This indicates that the moving speed and direction of the focusing lens vary successively. In other words, an actuator for the focusing lens, if it is a stepping motor, needs to make a highly accurate speed response of 1 Hz up to several hundred Hz.
It is becoming general practice to use a stepping motor for the focusing lens group of the inner focus type of lens system as an actuator which satisfies the above requirement. The stepping motor is capable of rotating in complete synchronism with a step pulse outputted from a lens control microcomputer or the like and showing a constant stepping angle per pulse, so that the stepping motor can realize high speed response, high stopping accuracy and high positional accuracy. Furthermore, the stepping motor provides the advantage that since its rotating angle per step pulse is constant, the step pulse can be used for an increment type of encoder and a special position encoder is not needed.
As described above, if a magnification varying operation is to be carried out while keeping an in-focus state by using such a stepping motor, it is necessary to previously store the locus information shown in
FIG. 3
in the lens control microcomputer or the like in a particular form (the loci themselves may be stored or a function which uses lens positions as variables may be stored), and read locus information according to the position or the moving speed of the variator lens and move the focusing lens on the basis of the read locus information.
FIG. 4
is a view aiding in explaining a locus tracing method which has previously been proposed. In
FIG. 4
, Z
0
, Z
1
, Z
2
, . . . , Z
6
indicate the position of the variator lens, a
0
, a
1
, a
2
, . . . , a
6
and b
0
, b
1
, b
2
, . . . , b
6
respectively indicate representative loci stored in the lens control microcomputer, and p
0
, p
1
, p
2
, . . . , p
6
indicate a locus calculated on the basis of the two loci. An equation for calculating this locus is shown below:
p
(
n+
1)=(|
p
(
n
)−
a
(
n
)|/|
b
(
n
)−
a
(
n
)|)×|
b
(
n+
1)−
a
(
n+
1)|+
a
(
n+
1). (1)
According to Equation (1), for example, if the focusing lens is located at the point p
0
in
FIG. 4
, the ratio in which the point p
0
internally divides a line segment b
0
-a
0
is obtained, and a point which internally divides a line segment b
1
-a
1
in accordance with that ratio is determined as p
1
. The standard moving speed of the focusing lens required to keep an in-focus state can be found from the p
1
−p
0
positional difference and the time required for the variator lens to move from Z
0
to Z
1
.
A case in which the stop position of the variator lens is not limited only to boundaries having stored representative locus data will be described below with reference to FIG.
5
.
FIG. 5
is a view aiding in explaining a method of interpolating the position of the variator lens.
FIG. 5
is an extracted portion of
FIG. 4
(a dashed-line portion in
FIG. 4
) and shows a case in which the variator lens can be stopped at an arbitrary stop position. In
FIG. 5
, the vertical and horizontal axes respectively represent the position of the focusing lens and the position of the variator lens. Letting Z
0
, Z
1
, . . . , Zk−1, Zk, . . . Zn represent the position of the variator lens, the corresponding positions of the focusing lens for different subject distances, i.e., the representative locus positions (the position of the focusing lens relative to the position of the variator lens) stored in a lens control microcomputer are as follows:
a
0
, a
1
, . . . , ak−1, ak, . . . an,
b
0
, b
1
, . . . , bk−1, bk, . . . bn.
If it is now assumed that the position of the variator lens is Zx which is not a zoom boundary position and that the position of the focusing lens is px, positions ax and bx are obtained as follows:
ax=ak
−(
Zk−Zx
)×((
ak−ak
−1)/(
Zk−Zk
−1)), (2)
bx=bk
−(
Zk−Zx
)×((
bk−bk
−1)/(
Zk−Zk
−1)). (3)
Specifically, in accordance with an internal ratio which is obtained from the current position of the variator lens and two adjacent opposite zoom boundary positions (for example, Zk and Zk−1 in FIG.
5
), locus data corresponding to the same subject distance are selected from among four stored representative locus data (ak, ak−1, bk, bk−1 in
FIG. 5
) and are internally divided by the internal ratio shown by the above equation (1), whereby ax and bx can be obtained.
Then, in accordance with an internal ratio which is obtained from ax, px and bx, the locus data corresponding to the same focal length, which are selected from among the four st
Garber Wendy R.
Nguyen Luong
Robin Blecker & Daley
LandOfFree
Image pickup apparatus with lens control apparatus and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image pickup apparatus with lens control apparatus and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image pickup apparatus with lens control apparatus and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3106240