Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-07-31
2003-11-25
Spector, David N. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S696000, C359S697000, C359S701000
Reexamination Certificate
active
06654181
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical apparatus for driving a focusing optical element to the focus position according to the movement of a variable power optical element (that is, according to variations in focal distance).
The driving mechanism for a focusing optical element in the driving mechanism of a variable power optical system comprises, as in the focal length adjusting apparatus disclosed in the Japanese Patent No. 2,856,557, a first lens unit, a second lens unit, a motor for moving the second lens unit with respect to the first lens unit, moving means for moving the first and the second lens units and the motor in the direction of the optical axis as a single unit, detecting means for detecting the stop position of the first lens unit to be moved by the moving means, and determining means for determining the moved position of the second lens unit to be moved by the motor with respect to the first lens unit according to the result detected by the detecting means.
A general construction of the embodiment disclosed in the Japanese Patent No. 2,856,557 is shown in FIG.
8
and FIG.
9
.
Part A of
FIG. 8
shows the general construction of a camera according to an embodiment described above, and part B of
FIG. 8
shows the extended position of each optical element at a prescribed zoom position.
FIG. 9
shows a sequence of focusing operations in the camera of the embodiment described above.
In Part A in
FIG. 8
, the reference numeral L
301
designates a first lens unit, the reference numeral
303
designates a lens-barrel of a first group, the reference numeral L
302
designates a second lens unit, and the reference numeral
308
designates a lens-barrel of a second group. The reference numeral L
303
designates a third lens unit.
The reference numeral
304
designates a cam pin of the first group provided around the outer periphery of the lens-barrel
303
of the first group, the cam pin
304
of the first group engages a cam groove of the first group formed on a rotatable cam cylinder
305
of the first group on the outer peripheral side of the lens-barrel
303
of the first group. The lens-barrel
303
of the first group is linearly guided by a linear guide member. Therefore, when the rotatable cam cylinder
305
of the first group rotates, the lens-barrel
303
of the first group is linearly driven in the direction of the optical axis by engagement between the cam groove of the first group and the cam pin
304
of the first group.
The reference numeral
306
designates a cam barrel of the second group, which is disposed inside the lens-barrel
303
of the first group. A cam pin
309
of the second group provided on the outer peripheral surface of the lens-barrel
308
of the second group engages a cam groove of the second group formed on the cam barrel
306
of the second group. In the cam barrel
306
of the second group, a drive pin
307
is provided, which passes through an elongated hole formed so as to extend in the circumferential direction on the lens-barrel
303
of the first group and engages the linearly guiding elongated hole formed so as to extend in the direction of the optical axis on the rotatable cam barrel
305
of the first group.
Therefore, the cam barrel
306
of the second group rotates in the same phase with the cam barrel
305
of the first group, and moves in the direction of the optical axis together with the lens-barrel
303
of the first group. When the cam barrel
306
of the second group rotates, the lens-barrel
308
of the second group is driven in the direction of the optical axis by engagement between the cam groove of the second group and the cam pin
309
of the second group, and then is linearly driven in the direction of the optical axis by the amount added with the distance moved of the cam barrel
306
of the second group in the direction of the optical axis.
The reference numeral
310
designates a drive unit for focusing for driving the third lens unit L
303
in the direction of the optical axis, and is mounted on the bottom board of the second group fixed on the lens-barrel
308
of the second group.
The reference numeral
311
designates a power zoom driving unit comprising a motor and a decelerator for rotating the cam barrel
305
of the first group.
The reference numeral
312
designates a fixed cylinder, which also serves as a body of the apparatus for rotatably supporting the cam barrel
305
of the first group, and the reference numeral
313
designates a photosensitive member such as film, a solid-state imaging device or the like supported by the fixed lens barrel
312
.
The reference numeral
314
designates an amplifier for amplifying the detected signal from a photodetector
301
described later, and the reference numeral
315
designates a distance measuring circuit. The reference numeral
316
designates a microcomputer, and the reference numeral
317
designates a drive circuit for focusing, which controls the drive unit for focusing
310
. The reference numeral
318
designates an outer covering provided with the operating members such as a release switch, a zoom switch, or the like.
The photodetector
301
is fixed on the bottom board of the second group described above to be driven with the lens-barrel
308
of the second group as a single unit. The photodetector
301
comprises, as shown in
FIG. 10
, an infrared radiation floodlighting element
301
a
facing toward the entrance surface of a prism
302
held by the lens-barrel
303
of the first group, and a light receiving element portion
301
b
facing toward a slit plate
302
a
provided on the side of the projecting surface of the prism
302
.
The infrared radiation emitted from the floodlighting element
301
a
is reflected by a reflecting surface
302
d
of the prism
302
, and a portion of reflected light passed through the slit formed on the slit plate
302
a
is thrown on the light receiving element portion
301
b
as slit light. On the light receiving element portion
301
b
, two slit-shaped light receiving areas
301
c
,
301
d
are formed.
In the slit plate
302
a
, as shown in
FIG. 11
, slit rows S
1
and S
2
extend in parallel in the direction of the optical axis and are disposed so as to be orthogonal to the optical axis. Slit light passed through the slits in the row S
1
is received in the light receiving area
301
c
and slit light passed through the slits in the row S
2
is received in the light receiving area
301
d.
In the row S
1
, the slits are formed at a regular pitch P
1
in the direction of the optical axis, and a distance D between the slits of both ends of the row S
1
is the same as the maximum value of the relative distance moved between the first lens unit L
301
and the second lens unit L
302
.
On the other hand, each slit in the row S
2
is displaced by an amount Z
1
with respect to the corresponding slit in the row S
1
except for the slit located at the center. The amount of displacement Z
1
is the same for all the slits except for the slits on both ends of the row S
2
, and the direction of displacement is counterbraced. A displacement amount Z
2
of the slits located on both ends of the row S
2
is larger than Z
1
. The driving direction of the first lens unit L
1
can be detected by the direction of displacement of the slit.
The position of the second lens unit L
302
with respect to the first lens unit L
301
(zoom position) can be detected by reading the amount of displacement described above from the output difference between the light receiving areas
301
c
and
301
d.
More specifically, the photodetector
301
moves in the direction of the optical axis with respect to the prism
302
and the slit plate
302
a
together with the second lens unit L
302
, and wave shaped signals as shown in
FIG. 12
are fed from the photodetector
301
every time the photodetector
301
passes over pairs of slits of the rows S
1
and S
2
. The level of the signal of the photodetector
301
at the moment when the photodetector
301
is positioned at the center of the pairs of slits of the ro
Canon Kabushiki Kaisha
Robin Blecker & Daley
Spector David N.
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