Photography – Camera detail – Diaphragm shutter unit
Reexamination Certificate
2000-06-09
2002-01-22
Gray, David M. (Department: 2851)
Photography
Camera detail
Diaphragm shutter unit
C396S463000, C396S507000, C396S485000
Reexamination Certificate
active
06340252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for controlling the quantity of light to be used in an apparatus, such as a video camera, a still video camera, or a copying machine.
2. Description of the Related Art
Hitherto, multimedia tools for handling not only voice and alphabetic information but also image information data have been widely used. Among these multimedia tools, video cameras and digital cameras are generally used for recording the image information. Recently, by using a portable terminal, such as a mobile phone or a handheld computer, having a small integrated camera as an image-capture device, image data can be transmitted through a telephone line immediately after image capture.
Camera units of these image-capture devices are generally configured with a single focal lens unit or a zoom lens unit including lenses in a common axial system of a size suitable for each image-capture element.
FIG. 19
shows a typical known digital camera. The known digital camera includes a camera body
101
, an optical part
102
, an electronic flash unit
103
, a release button
104
, and a liquid crystal display (LCD)
105
for confirming data. The camera body
101
includes a viewfinder, an LCD for confirming recording, and the like, at the back thereof.
The optical part
102
includes a lens barrel, lenses, an image-capture element, and a diaphragm unit (light-quantity controlling unit). Incident rays from an object are led to the image-capture element through the lenses and the diaphragm unit. By an electrical circuit which is not shown, a proper diaphragm stop number and a shutter speed are determined, whereby the most appropriate exposure is performed.
In order to perform the most suitable exposure, the diaphragm stop number must be controlled in accordance with the brightness of the object. For this purpose, most video cameras generally have iris galvanometers as diaphragm units. The basic configuration of the iris galvanometer is described with reference to
FIGS. 20A
,
20
B, and
20
C.
FIGS. 20A
to
20
C are schematic sectional views of a known iris galvanometer.
FIG. 20A
is a front view,
FIG. 20B
is a side view, and
FIG. 20C
is a rear view of the known iris galvanometer.
The iris galvanometer shown in
FIGS. 20A
to
20
C includes a casing
201
, a yoke
202
formed substantially in a U-shape and made of a magnetic material, and windings
203
having conductive wires around the yoke
202
, the windings
203
being connected to an electrical circuit (not shown). The iris galvanometer also includes a rotor
204
having a permanent magnet
205
and is disposed rotatably between the ends of the yoke
202
. The rotor
204
is provided with two protrusions
206
and
207
at the ends of arms thereof.
The iris galvanometer includes movable blades
208
and
209
having holes
210
and
211
, respectively, the blades
208
and
209
mating with the protrusions
206
and
207
at the holes
210
and
211
, respectively. The blades
208
and
209
slidingly move along directions parallel to each other in the casing
201
.
With reference to
FIGS. 21A
to
21
G, the operation of the iris galvanometer, in which the size of an aperture varies, is described below.
When electric current is applied to the windings
203
, the rotor
204
is rotated by a magnetic circuit in response to the current value, whereby the relative position of the movable blades
208
and
209
varies. By the movement of the blades
208
and
209
, the size of an aperture
212
(the shaded portion) defined by edges of the movable blades
208
and
209
is determined, the size of the aperture
212
corresponding to each diaphragm stop number.
FIG. 21A
shows the aperture
212
having a full aperture value of F2.5;
FIG. 21B
shows the aperture
212
having a size corresponding to F4.0;
FIG. 21C
shows the aperture
212
having a size corresponding to F5.6;
FIG. 21D
shows the aperture
212
having a size corresponding to F8.0;
FIG. 21E
shows the aperture
212
having a size corresponding to F11.0;
FIG. 21F
shows the aperture
212
having a size corresponding to F16.0; and
FIG. 21G
shows the aperture
212
completely closed.
As shown in these drawings, the diaphragm stop number is determined according to the rotational orientation of the rotor
204
. Each edge of the movable blades
208
and
209
defining the aperture
212
is formed so that the diaphragm stop number varies continuously.
Due to the recent technological advances, components and elements used in information terminal devices have been remarkably reduced in size. In particular, charge coupled devices (CCD) as image-capture elements have been significantly miniaturized. Therefore, it is particularly important to miniaturize lenses, diaphragm units associated therewith, and the like. Because the focal distance of a lens is reduced in accordance with the reduction in the size of image-capture elements, the full aperture of the lens must be reduced when designing a lens having the same specifications. Accordingly, the aperture of a diaphragm must be further reduced, thereby causing a problem in the configuration of a known iris galvanometer.
The problem of the known iris galvanometer is that a slight play exists in the mating parts of the holes
210
and
211
provided in the movable blades
208
and
209
with the associated protrusions
206
and
207
of the rotor
204
because it is difficult to completely eliminate gaps therefrom. A play of approximately 0.1 mm is generally produced in a normal production of the known iris galvanometers in which the movable blades
208
and
209
must move smoothly. The movable blades
208
and
209
do not follow the rotational movement of the rotor
204
in the range of the play of approximately 0.1 mm.
In the past, the lens was large and had a full aperture ranging from 6 to 8 mm in diameter because image-capture elements were large. Therefore, the play of 0.1 mm was a relatively small value.
Recently, image-capture elements have become small, thereby reducing the full aperture. Known iris galvanometers generally have a full aperture of not less than 4.0 mm in diameter.
FIG. 22
is a table showing the relationship between the F-number of a lens having a full aperture of 5.24 mm in diameter and an aperture area S of 21.56 mm
2
, and the variation in the aperture area S when the play is 0.1 mm. The amount of variation (%) in the aperture area S is considered by dividing the play of 0.1 mm into two values with respect to the center value thereof, that is ±0.05 mm, the amount of variation becoming greater as the diameter of the aperture becomes smaller. The variation in exposure value (EV-value) in relation to the amount of variation (%) is also shown in the table.
The shape of the aperture is determined according to the shape of the edges of the movable blades defining the aperture. Therefore, the aperture is not always formed as a circle between the full-aperture state and the completely-closed state. However, the amount of variation in the aperture area due to the play is computed by dividing the play into two values by conveniently considering the shape of the aperture as always being a circle.
As shown in
FIG. 22
, when the full aperture is large, the play of 0.1 mm does not significantly affect the diaphragm stop number. The variation in the EV-value is a maximum of 0.25 when the F-number is 11, and a maximum of 0.37 when the F-number is 16, which is not a problem in practical use.
As the aperture is closed, the image quality of a lens is reduced due to the effect of diffraction. Therefore, in a general lens unit, the mechanical minimum diaphragm stop number is set in a range of F8 to F11. Below this, the minimum diaphragm stop number is obtained optically by reducing the quantity of light by using a neutral density (ND) filter or the like. In this case, the aperture size can be reduced slightly more because the mechanical accuracy in the minimum diaphragm stop number must be ensured only down to the range of F8 to F11. However, such a
Blackman Rochelle
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Gray David M.
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