Photography – With exposure objective focusing means – focusing aid – or... – Lens characteristic compensating
Reexamination Certificate
2001-06-04
2004-11-02
Fuller, Rodney (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Lens characteristic compensating
C396S093000
Reexamination Certificate
active
06813442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a camera system having a focus detection device and, more particularly, to a lens-interchangeable digital single-lens reflex camera system having the focus detection device.
2. Related Background Art
FIG. 2
is a block diagram showing the main part of focus detection operation in a conventional lens-interchangeable silver halide film camera. Referring to
FIG. 2
, a lens body
1
includes an image taking optical system. The lens body
1
incorporates an image taking optical system
2
that is formed by one or a plurality of lens groups and can change the focal length by moving all or some of the lens groups, a lens state detection means
37
for detecting the focal length, i.e., the zoom state, of the image taking optical system
2
, a driving means
3
for adjusting the focus state of the image taking lens
1
by moving all or some of the lenses forming the image taking optical system
2
, a storage means
4
such as a ROM, and a lens control means
5
for controlling these components. In this case, the lens state detection means
37
detects the movement state of a lens or an amount that characterizes the movement state of the lens that moves to change the focal length (zoom state) of the image taking optical system
2
by a known method, e.g., using an electrode for an encoder which is provided for a lens barrel that rotates or moves to change the focal length of the image taking optical system
2
, an electrode for detection which is in contact with the electrode for the encoder, and the like.
A camera (camera body)
6
incorporates a main mirror
7
, a focusing screen
8
on which an object image is formed, a pentaprism
9
for image reversal, and an eyepiece lens
10
. These elements constitute a finder system. This camera also includes a sub-mirror
11
, a focus detection means
12
, a computation means
13
, a camera control means
14
, and a film
15
serving as an image taking medium. The lens
1
and camera body
6
have contacts
16
. While the lens
1
and camera body
6
are attached to each other, communication of various information and supply of power are performed through the contacts
16
.
FIG. 13
is a view showing the focus detection means
12
having a plurality of focus detection points.
Referring to
FIG. 13
, a field mask
116
has a crucial aperture portion
116
-
1
in the center and vertically elongated aperture portions
116
-
2
and
116
-
3
in peripheral portions on two sides of the aperture portion
116
-
1
. A field lens
117
is made up of three portions
117
-
1
,
117
-
2
, and
117
-
3
in correspondence with the three apertures
116
-
1
,
116
-
2
, and
116
-
3
of the field mask. A stop (aperture)
118
has an aperture portion
118
-
1
in the central portion. The aperture portion
118
-
1
has a total of four apertures
118
-
1
a
,
118
-
1
b
,
118
-
1
c
, and
118
-
1
d
located at upper, lower, left, and right positions each. In addition, two aperture portions
118
-
2
and
118
-
3
are respectively formed in the left and right peripheral portions of the stop
118
. The areas
117
-
1
,
117
-
2
, and
117
-
3
of the field lens
117
respectively have the effects of imaging these aperture portions
118
-
1
,
118
-
2
, and
118
-
3
on portions near the exit pupil of an image taking optical system (not shown). An optical member
119
is an integral secondary imaging system made up of four pairs of lenses
119
-
1
a
and
119
-
1
b
,
119
-
c
and
119
-
1
d
,
119
-
2
a
and
119
-
2
b
, and
119
-
3
a
and
119
-
3
b
, a total of eight lenses. These lenses are arranged behind the respective apertures of the stop
118
. A photoelectric conversion element
120
is constituted by four pairs of sensor arrays
120
-
1
a
and
120
-
1
b
,
120
-
1
c
and
120
-
1
d
,
120
-
2
a
and
120
-
2
b
, and
120
-
3
a
and
120
-
3
b
, a total of eight sensor arrays. These sensor arrays are arranged in correspondence with the respective lenses of the secondary imaging system to receive image light beams from the lenses.
FIG. 14
shows how an object image is formed on the photoelectric conversion element
120
. After light beams transmitted through the central aperture portion
116
-
1
of the field mask
116
and the central portion
117
-
1
of the field lens
117
are partially selected by the apertures
118
-
1
a
,
118
-
1
b
,
118
-
1
c
, and
118
-
1
d
of the stop, image areas
121
-
1
a
,
121
-
1
b
,
121
-
1
c
, and
121
-
1
d
are formed on the photoelectric conversion element
120
by the lenses
119
-
1
a
,
119
-
1
b
,
119
-
c
, and
119
-
d
of the secondary imaging system
119
located behind the apertures. After light beams transmitted through the peripheral aperture portion
116
-
3
of the field mask
116
and the peripheral portion
117
-
3
of the field lens
117
are partially selected by the apertures
118
-
3
a
and
118
-
3
b
of the stop
118
, image areas
121
-
2
a
and
121
-
2
b
are formed on the photoelectric conversion element
120
by the lenses
119
-
3
a
and
119
-
3
b
of the secondary imaging system
119
located behind the apertures. The focus detection principle of the focus detection means shown in
FIG. 13
is generally called a phase difference detection scheme. When the imaging point of the image taking optical system
2
is located in front of an expected focal plane, i.e., on the image taking optical system
2
side, light amount distributions associated with object images formed on a pair of sensor arrays come close to each other. In contrast to this, when the imaging point of the image taking optical system
2
is located behind the expected focal plane, i.e., on the opposite side to the image taking optical system
2
, light amount distributions associated with object images formed on the pair of sensor arrays separate from each other. The offset amount between the light amount distributions associated with object images formed on a pair of sensor arrays has a function relationship with the defocus amount of the image taking optical system
2
, i.e., the focus deviation amount. If, therefore, the offset amount is calculated by a proper computation means, the direction and amount of focus deviation of the image taking optical system
2
can be detected. Assume that these focus detection means are used for a camera capable of interchanging image taking lenses such as a single-lens reflex camera. In this case, however, if a lens is controlled on the basis of a focus state detection signal associated with a focus deviation amount which is directly obtained from the focus detection means, a proper focus state may not be obtained. The main reason for this is that an image taking optical system for forming an image to be observed or taken and a focus detection means generally receive different light beams. In addition, the focus detection means based on the phase difference detection scheme obtains a focal position or focus deviation amount to be determined on the basis of the amount of aberration in the vertical (optical axis) direction upon converting it into an image deviation associated with aberration in the horizontal direction. For this reason, when aberration occurs in the image taking optical system, the two values may differ from each other depending on the aberration correction state.
To solve this problem, a correction means is provided to correct a focus detection signal D representing a focus deviation amount by
D
C
=D−C
(1)
using a unique correction value C for each image taking lens, and the driving means
3
is used to drive the image taking optical system entirely or partly on the basis of an obtained correction focus detection signal D
C
, thereby controlling the lens to match the best imaging position with respect to the film surface. In this case, the best imaging position is the peak position of an MTF corresponding to an on-axis spatial frequency of 30 lines/mm.
FIG. 3
shows a conventional lens-interchangeable digital single-lens reflex camera. Most conventional len
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Rodney
Smith Arthur A
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