Camera

Details Camera Camera

1999-04-22

2001-01-02

Perkey, W. B. (Department: 2851)

Photography

With exposure objective focusing means, focusing aid, or...

Optical detail with photoelement system

C396S272000, C396S358000, C396S447000

Utility Patent

active

06169856

ABSTRACT:

This application is based on Application No. HEI 10-114769 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a camera, and more specifically relates to a camera provided with a detecting or measuring unit for receiving light through an opening or an aperture provided on a wall.
2. Description of the Related Art
A center vertical cross section view of a conventional single lens reflex camera is shown in FIGS.
1
(
a
) and
1
(
b
). FIG.
1
(
a
) shows the focus detection condition, in which light flux a
1
transmitted through the half mirror portion of a main mirror
1
is reflected by a sub-mirror
2
, passes through an aperture
3
a
provided on the bottom wall
3
of a mirror box, and is directed to a focus detection unit (autofocus (AF) module)
8
. On the other hand, viewing light flux a
2
is reflected by the main mirror
1
, and is directed to a viewfinder system including a pentagonal roof prism
4
and an eyepiece lens
5
. During the exposure time shown in FIG.
1
(
b
), both the main mirror
1
and the sub-mirror
2
are retracted from the photographic optical path, and a shutter
6
is controlled to expose a photosensitive member, that is, a film
7
.
As shown in FIG.
1
(
a
), the aperture
3
a
is provided in the bottom wall of the mirror box
3
to direct the light to the focus detection unit
8
, and in recent years the photoreceptive surface of the focus detection unit have tended to become larger as the focus detection area in the object field (AF area) has become wider. Accordingly, The aperture provided on the bottom wall of the mirror box has also naturally become larger. This situation is shown in FIGS.
2
(
a
) and
2
(
b
).
Since the focus detection unit
18
in the camera shown in FIGS.
2
(
a
) and
2
(
b
) is overall larger in size compared to the focus detection unit shown in FIGS.
1
(
a
) and
1
(
b
), the bottom side of the camera is increased in size when the distance in the former from the photoreceptive surface
18
a
to the bottom wall surface
13
b
of the mirror box is the same distance as in the latter from the photoreceptive surface
8
a
to the bottom wall surface
3
b
of the mirror box of FIGS.
1
(
a
) and
1
(
b
). That is, the height dimension of the camera is increased simply by the amount of enlargement of the focus detection unit. In FIGS.
1
(
a
) and
1
(
b
) and FIGS.
2
(
a
) and
2
(
b
), a comparison of the distances h
1
and h
2
in the respective drawings from the bottom edge of the focus detection unit to the photographic optical axis shows the distance h
2
is greater.
In order to prevent such and enlargement of the camera, i.e., increase in height, the position of the focus detection unit is modified as shown in the examples of FIGS.
3
(
a
) and
3
(
b
). In this example, an increase in the camera height dimension is prevented by reducing the distance from the photoreceptive surface
28
a
of the focus detection unit
28
to the bottom wall surface
23
b
of the mirror box so as to be shorter than the distances in FIGS.
1
(
a
) through
2
(
b
). In FIGS.
3
(
a
) and
3
(
b
), the distance h
3
from the bottom edge of the focus detection unit to the photographic optical axis is shorter than the distance h
2
in FIGS.
2
(
a
) and
2
(
b
). In this construction, however, the aperture
23
a
formed in the bottom wall
23
of the mirror box is larger. Although the aperture
13
a
of FIGS.
2
(
a
) and
2
(
b
) is larger than the aperture
3
a
of FIGS.
1
(
a
) and
1
(
b
), the aperture
23
a
of FIGS.
3
(
a
) and
3
(
b
) is the largest aperture of the three.
Although an increase in the height dimension of the camera while achieving a wider AF area is prevented in the construction shown in FIGS.
3
(
a
) and
3
(
b
), new disadvantages arise as described below. As can be understood from FIG.
3
(
a
), in addition to the aperture
23
a
on the bottom wall of the mirror box being larger, the photoreceptive surface
28
a
of the focus detection unit is positioned very close to the bottom wall surface
23
b
of the mirror box. As a result, the incident light is reflected by the photoreceptive surface
28
a
of the focus detection unit, and impinges a film
27
and generates a flare, as indicated by the arrow A in FIG.
3
(
b
). The photoreceptive surface
28
a
of the focus detection unit readily reflects light since it is usually made of a filter or a lens, but naturally cannot be a diffusion surface due to the nature of the photoreceptive surface. In the construction shown in FIGS.
1
(
a
) and
1
(
b
), this problem does not occur because the AF area is narrow and, as a result, the aperture
3
a
formed on bottom wall of the mirror box is small, and the photoreceptive surface
8
a
of the focus detection unit is largely indented relative to the bottom wall surface
3
b
of the mirror box.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a camera which does not generate flare even in a construction in which the focus detection unit is positioned adjacent to a large aperture formed in the wall of a mirror box.
One aspect of the present invention is the provision of a cover to effectively close the aperture during exposure in a camera provided with a focus detection unit disposed so as to a photoreceptive surface adjacent to an aperture provided in the wall of a mirror box.
That is, a main mirror is provided which rotates within the mirror box between a viewing position to reflect toward a viewfinder a part of the light from an object positioned within the photographic optical path and an exposure position retracted from the photographic optical path during exposure, and a sub-mirror is provided which reflects toward the photoreceptive surface of the focus detection unit the light transmitted through the half mirror portion of the main mirror when the main mirror is set at the viewing position and itself retracts from the photographic optical path when the main mirror is retracted to the exposure position. An aperture is formed on the wall of the mirror box to direct the light reflected by the sub-mirror toward the photoreceptive surface of the focus detection unit. A cover is provided to permit the light reflected from the sub-mirror to pass through the aperture when the main mirror is at the viewing position, and to effectively close the aperture in conjunction with the retraction of the main mirror to the exposure position. In this instance, “effective closure of the aperture” includes the meaning that the aperture is closed to the degree that there is no reflection generated to cause flaring at the photoreceptive surface of the focus detection unit positioned within the aperture, even though the aperture is not completely sealed.
Since, in this construction, the aperture which directs light to the focus detection unit is effectively closed in conjunction with the operation to retract the mirror during exposure, the light from an object is not reflected by the photoreceptive surface of the focus detection unit during exposure and does not cause flaring. Accordingly, the enlargement of the photoreceptive surface of the focus detection unit in conjunction with the widening of the AF area does not produce flaring even when the entire focus detection unit is enlarged, and the overall height of the camera is not increased.
It is desirable that the cover is positioned to block the optical path to prevent the incident light entering through the finder system and the half mirror when the main mirror is at the viewing position from directly entering into the focus detection unit. When such a construction is used, light shielding is improved when waiting between photographs and when the camera is not in use.
The surface of the cover on the side exposed to the interior of the mirror box is desirably a light diffusing surface, so as to increase the anti-flaring effectiveness.
These and other objects, advantages and features of the invention will become apparent from the following des

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