Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
2001-05-30
2003-09-23
Adams, Russell (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C396S122000
Reexamination Certificate
active
06625397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focus detecting device employing a so-called passive auto-focus (“AF”) system (system for detecting a focus by light from a subject) such as a phase detection system, a contrast detecting system, and the like mounted on a photographing apparatus such as a camera, video camera, and the like and on various observing apparatuses, and more particularly, to a focus detecting device permitting auxiliary light to be projected effectively in the passive AF system.
2. Description of the Related Art
FIG. 15
shows an example of a camera to which a conventional focus detecting device is assembled. In
FIG. 15
, reference numeral
100
denotes an auxiliary light emitting device, reference numeral
101
denotes an objective lens for taking a picture, reference numeral
102
denotes a semi-transparent main mirror, reference numeral
103
denotes a focusing plate, reference numeral
104
denotes a pentaprism, reference numeral
105
denotes an eyepiece, reference numeral
106
denotes a sub-mirror, reference numeral
107
denotes a film, and reference numeral
108
denotes a focus detecting device, respectively. In
FIG. 15
, light beams coming from a subject (not shown) are reflected by the main mirror
102
upward after they pass through the objective lens
101
and form an image on the focusing plate
103
. The image formed on the focusing plate
103
is visually confirmed by a photographer or an observer through the eyepiece
105
after it is reflected by the pentaprism
104
a plurality of times.
In contrast, some light beams having reached the main mirror
102
from the objective lens
101
partly pass through the main mirror
102
and are reflected downward by the sub-mirror
106
and introduced to the focus detecting device
108
.
FIG. 16
is a view in which only the objective lens
101
and the focus detecting device
108
of
FIG. 15
are illustrated to explain a principle of focus detection.
In the interior of the focus detecting device
108
of
FIG. 16
, reference numeral
109
denotes field of view masks disposed at positions near to a scheduled focusing surface of the objective lens
101
, that is, near to a surface conjugate with a film surface, reference numeral
110
denotes a field lens similarly disposed in the vicinity of the scheduled focusing surface, reference numeral
111
denotes a secondary imaging system composed of two lenses
111
-
1
and
111
-
2
, reference numeral
112
denotes a photoelectric conversion element including two sensor rows
112
-
1
and
112
-
1
and disposed in correspondence to the two lenses
111
-
1
and
111
-
2
there behind, reference numeral
113
denotes a diaphragm including two openings
113
-
1
and
113
-
2
disposed in correspondence to the two lenses
111
-
1
and
111
-
2
, and reference numeral
114
denotes a projecting pupil of the objective lens
101
including two divided regions
114
-
1
and
114
-
2
, respectively. Note that the field lens
110
has an action for imaging the openings
113
-
1
and
113
-
2
of the diaphragm
113
in the vicinity of the regions
114
-
1
and
114
-
2
of the projecting pupil
114
of the objective lens
101
, so that light beams
115
-
1
and
115
-
2
having passed through the respective regions
114
-
1
and
114
-
2
form distributed quantities of light in the two sensor rows
112
-
1
and
112
-
2
, respectively.
The focus detecting device
108
employs a so-called phase difference detecting system arranged such that when an imaging point of the objective lens
101
is located forward of the scheduled focusing surface, that is, on the objective lens
101
side, the distributed quantities of light formed on the two sensor rows
112
-
1
and
112
-
2
, respectively, are separated from each other. Moreover, an amount of deviation of the distributed quantities of light formed on the two sensor rows
112
-
1
and
112
-
2
has a certain functional relationship with an amount of defocus of the objective lens
101
, that is, with an amount out of focus. Thus, when the amount of deviation is calculated by an appropriate calculation unit, an out of focus direction and amount of the objective lens
101
can be detected.
Further, to cope with conditions under which a focus cannot be detected accurately or cannot be detected at all because a subject is dark or has a low contrast, a camera having an auxiliary light emitting device mounted thereon or built therein is proposed to illuminate the subject or to project a pattern having a contrast onto the subject.
FIG. 17
is a view showing an arrangement of an ordinary auxiliary light emitting device, wherein light from a light emission unit
116
illuminates a pattern
117
and a light projection lens
118
for projecting the pattern
117
onto a subject is protected by a protection plate
119
.
FIG. 18
shows a pattern image
120
formed on the subject by the pattern
117
.
A camera having a focus detecting device assembled thereto cannot detect a focus when a subject has a low degree of luminance. Thus, detection of a focus is made possible in a subject having a low degree of luminance by increasing a contrast of the subject by illuminating the subject or projecting a pattern thereto by an auxiliary light emitting device. However, a focus detecting capability in a low degree of luminance greatly depends upon determination conditions for determining whether or not auxiliary light is to be emitted because auxiliary light (i) may be wastefully projected without any sufficient effect, or (ii) may not be emitted regardless of whether an increase in a focus detecting accuracy could be expected, depending upon a reflectance of a subject, a state of a background, and a focus detecting capability of a focus detecting device.
Recently, the number of focus detecting points has been increased and a focus detecting region has been enlarged. Accordingly, when a determination criterion for determining whether or not auxiliary light is to be projected is uniformly set in a focus detecting device having a plurality of focus detecting points, a problem arises in that wasteful projection of auxiliary light is more and more increased and that no auxiliary light is projected regardless of whether an increase of a focus detecting accuracy could be expected thereby because respective focus detecting points are located at different positions on a subject and focus detecting capabilities are different at the respective focus detecting points.
SUMMARY OF THE INVENTION
The present invention, in one aspect, is directed to an auxiliary light emitting device for a focus detecting device for emitting an auxiliary light, the focus detecting device having, a screen divided into a plurality of regions and a plurality of focus detecting areas respectively disposed on the plurality of regions, the focus detecting device respectively detecting a focus of a subject in the plurality of focus detecting areas. The auxiliary light emitting device comprises a determination circuit for determining whether the auxiliary light is to be emitted based on a determination reference value, and setting means for setting the determination reference value to a predetermined value according to a position of at least one of the plurality of focus detecting areas.
In another aspect, the present invention is directed to an auxiliary light emitting device for a focus detecting device for emitting an auxiliary light, the focus detecting device having a screen divided into a plurality of regions and a plurality of focus detecting areas respectively disposed on the plurality of regions, the focus detecting device respectively detecting a focus of a subject in the plurality of focus detecting areas. The auxiliary light emitting device comprises a selection circuit for selecting at least one of the plurality of focus detecting areas, and a setting circuit for setting an auxiliary light emission determination value to a predetermined value in accordance with the at least one focus detecting area selected by the selection ci
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