Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
1999-09-08
2001-05-29
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C359S622000, C396S121000, C396S104000, C396S090000
Reexamination Certificate
active
06239912
ABSTRACT:
This application claims the benefits of Japanese Application Nos. 10-258204, 10-258205 and 11-191855 which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focal point detection apparatus to be used in a single lens reflex camera or the like.
2. Related Background Art
As a focal point detection apparatus provided with a plurality of focal point detection areas, there is generally known an apparatus of a phase shift detection system as shown in
FIGS. 11 and 12
.
FIG. 11
is a perspective view for showing a schematic configuration of a conventional focal point detection apparatus, and
FIG. 12
is a view for schematically shown optical paths of the focal point detection apparatus
49
shown in
FIG. 11
, seen along the axis y in FIG.
11
. Light flux from an object comes into the vicinity of a view field mask
12
through an unrepresented photographing lens to form an image there. Lens units
43
b
,
43
c
of a condenser lens
43
are arranged such that the optical axes of the respective lens units are eccentric with respect to the view field apertures
12
Y
a
,
12
Y
b
, and the optical axes L
4
a
, L
4
b
of the lens units
43
b
,
43
c
are parallel with the optical axis L of the entire optical system of the photographing lens. Out of light fluxes from the object field, a light flux passing the view field aperture
12
X which takes a rectangular form elongated along the axis y is divided through the lens unit
43
a
, like chief rays r
4
a
, r
4
b
shown in
FIG. 12
, and through stop apertures
44
a
,
44
b
of an aperture mask
44
disposed at a position substantially conjugate with an exit pupil of the photographing lens and re-imaging lens units
45
a
,
45
b
of a re-imaging optical system
45
, thereby forming images respectively on light receiving element arrays
46
a
,
46
b
of a CCD chip
46
.
It is possible to detect a focal point control condition of the photographing lens by photo-electrically converting a pair of object images formed on the light receiving element arrays
46
a
,
46
b
. Specifically, when the focal point control condition of the photographing lens is in a so-called in-focus state in which a clear image is formed on a plane equivalent to a film, the paired object images on the light receiving element arrays
46
a
,
46
b
are imaged at positions with a predetermined distance between a front focus state and a rear focus state. Also, when the focal point control condition of the photographing lens is in the so-called front focus state in which the image is clearly formed in front of the plane equivalent to a film, the paired object images on the light receiving element arrays
46
a
,
46
b
are formed at positions having a first distance therebetween which is shorter than the predetermined distance. On the other hand, when the focal point control condition of the photographing lens is in the so-called rear focus state in which the clear image is formed in the rear of the plane equivalent to a film, the paired object images on the light receiving element arrays
46
a
,
46
b
are formed at positions having a second distance which is longer than the predetermined distance. Accordingly, these paired object images are photo-electrically converted into electric signals by the light receiving element arrays
46
a
,
46
b
, and a correlative arithmetic operation or the like is performed based on these electric signals, like in a shift amount detection apparatus disclosed in Japanese Patent application Laid-Open No. 60-37513, to obtain an amount of relative positional shift between the paired object images, whereby the focal point control condition of the photographing lens in a focal point detection area corresponding to the view field aperture
12
X is detected.
Also, out of light fluxes from the object field, a light flux passing the view field aperture
12
Y
a
which takes a rectangular form elongated along the axis y of the view field mask
12
is divided through the lens unit
43
b
, like chief rays r
4
c
, r
4
d
shown in
FIG. 12
, and through stop apertures
44
c
,
44
d
of the aperture mask
44
and re-imaging lens units
45
c
,
45
d
of the re-imaging optical system
45
, thereby forming images respectively on light receiving element arrays
46
c
,
46
d
of the CCD chip
46
. In the same manner, a light flux passing the view field aperture
12
Y
b
is divided through the lens unit
43
c
, like chief rays r
4
e
, r
4
f
shown in
FIG. 12
, and through stop apertures
44
e
,
44
f
of the aperture mask
44
and re-imaging lens units
45
e
,
45
f
of the re-imaging optical system
45
, thereby forming images respectively on light receiving element arrays
46
e
,
46
f
of the CCD chip
46
. Then, the focal point conditions of the photographing lens are detected in the focal point detection areas out of the optical axis corresponding to the view field aperture
12
Y
a
by use of the paired object images on the light receiving element arrays
46
c
,
46
d
and corresponding to the view field aperture
12
Y
b
by use of the paired object images on the light receiving element arrays
46
e
,
46
f.
In this manner, it is rendered possible to detect the focal point in a plurality of focal point detection areas.
Generally, for the focal point detection in a plurality of focal point detection areas, on a light receiving element array consisting of a CCD chip corresponding to a certain focal point detection area, a light (a so-called stray light) from another focal point detection area is incident, to give a great influence on the accuracy in the focal point detection. For this reason, the art of shielding this stray light by use of a light shielding member is disclosed in the Japanese Patent Application Laid-Open No. 63-289513.
FIG. 13
is a view for schematically showing the optical paths of the focal point detection apparatus
49
shown in
FIG. 11
seen along the axis y in this drawing, plus a light shielding member. Note that the identical members to those in
FIGS. 11 and 12
are given the same numerals and description thereof will be omitted. A light flux R
41
passing through the view field aperture
12
X is a focal point detection light flux for entering the light receiving element array
46
a
through the stop aperture
44
a
, while a light flux R
42
passing through the view field aperture
12
Y
b
is a focal point detection light flux for entering the light receiving element arrays
46
e
,
46
f
through the stop apertures
44
e
,
44
f
. In this case, a light flux R
43
which passes through the stop aperture
44
a
also transmits through the view field aperture
12
Y
b
. This light flux R
43
, however, enters the light receiving element array
46
a
which is an undesired light receiving element array. In other words, the light flux R
43
becomes a stray light. Therefore, in order to prevent such stray light, a light shielding member m
41
is provided. However, out of the light fluxes transmitting the field view aperture
12
Y
b
, a stray light such as the light flux R
44
which passes through the stop aperture
44
b
can not be completely shielded by the light shielding member m
41
. Also, the light shielding member m
41
is formed to have holes at positions for passing the focal point detection light fluxes, like the view field mask
12
, so that, in order to completely shield the light flux R
44
, a light shielding member having a more complicated form is required.
In addition, when a plurality of focal point detection areas are provided in a photographing frame, a pair of stop apertures and a pair of re-imaging lens units for forming images of a pair of objects on light receiving element arrays are required for each of the focal point detection areas. Then, there is disclosed in the Japanese Patent No. 2663657 a focal point detection apparatus having a focal point detection area at the center of the photographing frame, an aperture mask for using in common stop apertures for focal point detection areas on the both sides of the above-mentioned focal point dete
Epps Georgia
Nikon Corporation
Thompson Timothy
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