Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1998-08-31
2001-05-01
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C396S055000, C359S554000, C348S208400
Reexamination Certificate
active
06225614
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Application No. 09-234267 filed Aug. 29, 1997 and Japanese Patent Application No. 10-004423 filed Jan. 13, 1998, the contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel and motion compensation device to compensate for motion causing image blur in a camera, such as a silver salt camera, digital camera, or the like. More particularly, the present invention relates to a motion compensation device having a motion compensation optical system position detection device to detect a position of a motion compensation optical system relative to the lens barrel.
2. Description of the Related Art
A conventional motion compensation device in a camera compensates for blur of an image projected onto an image plane which occurs during photography as a result of vibration of the camera caused by, for example, hand shake of the photographer, or the like. The conventional motion compensation device includes a motion detection unit to detect vibration caused by hand shake or the like, and to output a motion detection signal; a motion compensation optical system, constituting at least a portion of the photographic optical system, which moves relative to the lens barrel in a direction at right angles to the photographic optical axis (referred to as “optical axis” hereinbelow), and causes the optical axis to change to compensate for the motion in the image plane causing image blur; a position detection unit to detect the relative position of the motion compensation optical system with respect to the lens barrel and to output a position detection signal; a calculating unit to calculate an amount of optical axis change necessary to compensate for the motion causing image blur; and a drive unit to drive the motion compensation optical system according to the correction amount.
FIG. 12
illustrates a conventional position detection unit of a motion compensation device. The conventional position detection unit includes a position sensing device (PSD) and a light emitting diode (LED) to detect the position of the motion compensation optical system. More particularly,
FIG. 12
is a schematic diagram showing the change of position of a light beam incident on the PSD
54
when the relative position of the LED
51
and the PSD
54
changes. The relationship between the detection position of a light beam incident on the position sensing device (PSD) and the relative position of the light emitting diode (LED) will now be described in detail below with reference to FIG.
12
.
As shown in
FIG. 12
, a distance D
1
L
(D
1
S
) is the length between the LED
51
positioned at point A (point B) and a light receiving surface
54
a
of the PSD
54
. The distance D
1
L
is longer than the distance D
1
S
. Moreover, a light beam L
L
(L
S
) emitted from the LED
51
positioned at point A (point B) passes through a slit
52
a
and is incident on the light receiving surface
54
a
. A point O is a center position of the detection direction of the PSD
54
. The slit position X is the distance the center position of the slit
52
a
has moved from the point O. The detection position P
L
(P
S
) is the distance from the point O to the centroid of the light beam L
L
(L
S
) on the light receiving surface
54
a
of the PSD
54
. A perpendicular N is an imaginary perpendicular to the light receiving surface
54
a
of the slit plate
52
, and is a straight line through the center of the slit
52
a
. The angle of incidence &agr;
L
(&agr;
S
) is an angle a light beam incident on the center of the slit
52
a
makes with the imaginary perpendicular N.
As shown in
FIG. 12
, the detection position P
L
and the detection position P
S
do not coincide with each other, and the slit position X does not coincide with the respective detection positions P
L
, P
S
. In particular, when the positional relationship of the LED
51
and the PSD
54
becomes closer, the angle of incidence &agr;
S
becomes greater than the angle of incidence &agr;
L
. The error of the detection position P
L
and the slit position X is marked. When the slit position X is to be found by a position detection device
54
as shown in
FIG. 12
, the actual slit position X and the detection positions P
L
, P
S
do not coincide. Accordingly, as the slit position X becomes larger, the error of the position X and the detection positions P
L
, P
S
becomes large in proportion to the amount of movement of the slit plate
52
. Moreover, the error between the actual slit position X and the detection positions P
L
, P
S
becomes larger as the distance between the LED
51
and the PSD
54
becomes shorter.
FIG. 13
is a graph showing the centroid position of the light incident on the PSD
54
from the LED
51
with respect to the slit position X. As shown in
FIG. 13
, the abscissa represents the slit position X and the ordinate represents the result when the centroid position of the light beam incident on the PSD
54
is calculated based on the output signal of the PSD
54
. The full line P
L
represents the result of calculation of the centroid position when the LED
51
is positioned at the point A shown in
FIG. 12
; the full line P
S
represents the result of calculation of the centroid position when the LED
51
is positioned at the point B shown in FIG.
12
. Furthermore, the origin O is the center position of the detection position of the PSD
54
; and, the broken line represents the center position of the slit
52
a
. As shown in
FIG. 13
, according to the output of the PSD
54
, the respective detection positions P
L
, P
S
and the slit position X do not coincide. Thus, the greater the slit position X with respect to the center of the PSD
54
, and the shorter the distance between the LED
51
and the PSD
54
, the greater the error of the respective detection points P
L
, P
S
and the slit position X.
Moreover, the error between the respective detection points P
L
, P
S
and the slit position X becomes large in proportion to the amount of movement of the slit
52
a
when the range of the slit position X becomes large, and the light incident from the LED
51
does not impinge on the light receiving surface
54
a
of the PSD
54
. Because of the error between the detection points P
L
, P
S
and the slit position X, when the slit position X exceeds the effective range of the slit position X, as shown in
FIG. 13
, the results of calculation of the centroid position based on the output of the PSD
54
with respect to the movement of the slit plate
52
become disproportionately distorted. More particularly, the range of the detection positions P
L
, P
S
detected by the PSD
54
, which is in a proportional relationship with respect to the movement of the slit plate
52
, becomes narrow. Further, the range in which position detection is possible becomes limited to the case in which the slit position X is small (i.e., a small amount of movement). The range in which position detection is possible tends to become narrower as the distance between the PSD
54
and the slit plate
52
becomes narrower. When position detection is performed in the above-described manner, a problem occurs in a position detection device which uses a slit plate
52
in that the effective stroke of the slit plate
52
in which position detection is possible changes according to the distance between the PSD
54
and the LED
51
.
Furthermore, when the LED
51
and PSD
54
are positioned close to each other, the conventional position detection device receives many effects of the profile of the light emitting device, causing a fall in the linearity of the position calculation results. As a result of the fall in linearity of the position calculation results, when the relative positional relationship of the LED
51
and the PSD
54
is close, the effective range of the slit plate
52
becomes short, and the error between the actual position of the motion compensation lens and the detection positions P
Le Que T.
Nikon Corporation
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