Photography – Having variable focal length of camera objective – Power zoom
Reexamination Certificate
2000-07-11
2003-04-22
Gray, David M. (Department: 2851)
Photography
Having variable focal length of camera objective
Power zoom
C396S144000, C359S676000, C359S696000, C359S699000
Reexamination Certificate
active
06553185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical apparatus, such as a lens barrel, adapted for an image pickup apparatus, such as a video camera or the like.
2. Description of Related Art
Known zoom lenses for video cameras include such a zoom lens that is composed of four lens units including, for example, a fixed convex lens unit (having a positive refractive power), a movable concave lens unit (having a negative refractive power), a fixed convex lens unit (having a positive refractive power) and a movable convex lens unit (having a positive refractive power) arranged in this order from the side of an object of shooting.
FIGS.
6
(
a
) and
6
(
b
) show a popular lens barrel arrangement of a zoom lens of the above-stated four-lens-unit structure. FIG.
6
(
a
) is a sectional view taken on a line A—A in FIG.
6
(
a
).
Referring to FIGS.
6
(
a
) and
6
(
b
), the zoom lens is composed of four lens units, i.e., a front lens unit
201
a
arranged to be stationary, a variator lens unit
201
b
arranged to perform a magnification varying action by moving in the direction of an optical axis
205
, an afocal lens unit
201
c
arranged to be stationary, and a focusing lens unit
201
d
arranged to keep a focal plane unvaried by the variation of magnification as well as to adjust focus by moving in the direction of the optical axis
205
.
Guide bars
203
,
204
a
and
204
b
are arranged in parallel with the optical axis
205
to guide and restrain the moving lens units from turning. A DC motor
206
is a drive source arranged to drive and move the variator lens unit
201
b.
The front lens unit
201
a
is held by a front lens tube
202
. The variator lens unit
201
b
is held by a V moving ring
211
. The afocal lens unit
201
c
is held by an intermediate frame
215
, and the focusing lens unit
201
d
is held by an RR moving ring
214
.
The front lens tube
202
is positioned on and secured to a rear tube
216
. By using these two tubes
202
and
216
, the guide bar
203
is positioned and held by them while a guide screw shaft
208
is rotatably supported by these tubes
202
and
216
. The guide screw shaft
208
is arranged to be driven to rotate with the rotation of the output shaft
206
a
of the DC motor
206
transmitted through a gear train
207
.
The V moving ring
211
which holds the variator lens unit
201
b
is provided with a ball
210
, which engages a pressing spring
209
and is caused by the force of the pressing spring
209
to engage a screw groove
208
a formed in the guide screw shaft
208
. The V moving ring
211
is thus arranged to move back and forth in the direction of the optical axis
205
while being guided and restricted from turning by the guide bar
203
when the guide screw shaft
208
is driven to rotate by the DC motor
206
.
The guide bars
204
a
and
204
b
are fitted into and supported by the rear tube
216
and the intermediate frame
215
which is positioned on the rear tube
216
. The RR moving ring
214
is arranged to be movable back and forth in the direction of the optical axis
250
while being guided and restrained from turning by the guide bars
204
a
and
204
b.
The RR moving ring
214
, which holds the focusing lens unit
201
d
, has sleeve parts into which the guide bars
204
a
and
204
b
are slidably fitted. A rack
213
is mounted on the RR moving ring
214
and is arranged to be integral with the RR moving ring
214
in the direction of the optical axis
250
.
A stepping motor
212
is arranged to drive and rotate a lead screw
212
a
formed integrally with the output shaft thereof. The lead screw
212
a
engages the rack
213
which is mounted on the RR moving ring
214
. When the lead screw
212
a
rotates, the RR moving ring
214
moves in the direction of the optical axis
250
while being guided by the guide bars
204
a
and
204
b.
As for a drive source to be used for the variator lens unit
201
b
, a stepping motor may be used similarly to the drive source for the focusing lens unit
201
d.
A lens barrel body in which the lens units, etc., are housed in an approximately sealed state is formed by the front lens tube
202
, the intermediate frame
215
and the rear tube
216
.
In a case where the lens unit holding frames are arranged to be moved by means of stepping motors, the absolute position of each holding frame is detected by counting driving pulses applied to the stepping motor after the holding frame is detected to be at a reference position in the direction of the optical axis by means of a photo-interrupter or the like.
FIG. 7
shows the electrical arrangement of a camera body in a conventional image pickup apparatus. In
FIG. 7
, the components of the lens barrel described above with reference to FIGS.
6
(
a
) and
6
(
a
) are indicated by the same reference numerals as those used in FIGS.
6
(
a
) and
6
(
a
).
Referring to
FIG. 7
, a solid-state image sensor
221
is composed of a CCD or the like. A zoom driving mechanism
222
is arranged to drive the variator lens unit
201
b
and includes the motor (or a stepping motor)
206
, the gear train
207
and the guide screw shaft
208
, etc.
A focusing driving mechanism
223
is arranged to drive the focusing lens unit
201
d
and includes the stepping motor
212
, the lead screw
212
a
, the rack
213
, etc.
An iris driving mechanism
224
is arranged to drive an iris device
235
which is disposed between the variator lens unit
201
b
and the afocal lens unit
201
c.
A zoom encoder
225
and a focus encoder
227
are arranged to detect the absolute positions of the variator lens unit
201
b
and the focusing lens unit
201
d
, respectively, in the direction of the optical axis. In a case where a DC motor is employed as a variator drive source as in the case of FIGS.
6
(
a
) and
6
(
a
), a potentiometer or a magnetic encoder is employed as the absolute position encoder. If a stepping motor is employed as the drive source, it is generally practiced to set the holding frame at a reference position and, after that, to continuously count the number of operation pulses applied to the stepping motor as mentioned above.
An iris encoder
226
is arranged to detect a relation between the rotating position of a rotor and that of a stator with a Hall element disposed within the iris driving mechanism
224
which includes a motor, etc.
A CPU
232
presides over control of the camera, i.e., the image pickup apparatus. A camera signal processing circuit
228
performs various signal processing actions such as amplifying and gamma correcting actions on a video signal, etc., outputted from the solid-state image sensor
221
. A contrast signal (Y) included in the video signal thus processed is allowed to pass through an AE gate
229
and an AF gate
230
. These gates
229
and
230
are arranged to set optimum signal take-out ranges within a whole image plane for deciding an exposure and focusing. In some cases, the take-out ranges are variable in size or are provided at a plurality portions of the image plane.
An AF signal processing circuit
231
is arranged to process an AF signal for AF (automatic focusing or focus adjustment). The AF signal processing circuit
231
forms one or a plurality of outputs relative to a high-frequency component of the video signal. The camera is provided with a zoom switch
233
and a zoom tracking memory
234
. The zoom tracking memory
234
is arranged to store positions of the focusing lens unit
201
d
to be set according to object distances and positions of the variator lens unit
201
b
in performing a magnification varying action. A memory disposed within the CPU
232
may be used as the zoom tracking memory
234
.
When the zoom switch
233
is operated by a user of the camera, the CPU
232
performs control in such a way as to keep the position of the variator lens unit
201
b
and that of the focusing lens unit
201
d
in a predetermined relation computed on the basis of information obtained from the zoom tracking memory
234
. For this purpose, the zoom driving mechanism
Inaba Hiroyoshi
Miyakawa Masae
Okada Tadanori
Canon Kabushiki Kaisha
Robin Blecker & Daley
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