Photography – With viewfinder – With prism
Reexamination Certificate
1999-10-15
2001-08-28
Gray, David M. (Department: 2851)
Photography
With viewfinder
With prism
C359S834000
Reexamination Certificate
active
06282381
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a finder of an optical device, such as a camera, and more particularly, to a real-image finder.
2 . Description of the Related Art
In recent years, size reduction of optical devices, such as cameras, has further advanced, and a principal object in this development is to reduce the space in the optical device occupied by the finder.
On the other hand, an increasing number of optical devices require switching of visual field masks of different sizes, and zooming of objective lens systems. In order to satisfy these requirements in a compact system, a real-image finder is most preferable.
The real-image finder requires an image-inverting optical system to allow viewing of an erect image. For the purpose of size reduction, an increasing number of image-inverting optical systems have a roof reflecting surface.
FIG. 7
is a schematic structural view of a finder using a roof prism proposed in Japanese Patent Application Laid-Open No. 9-105863.
Referring to
FIG. 7
, the finder includes an objective lens
10
for forming an object image on a predetermined plane, an image-inverting optical system P composed of a triangular prism P
1
and a roof prism P
2
, and an eyepiece Le having positive retracting power.
A light beam from the objective lens
10
enters an incident surface P
1
a
of the triangular prism P
1
, is reflected by a surface P
1
b
toward a surface P
1
c
that is flush with the incident surface P
1
a
, and is totally reflected by the surface P
1
c
to emerge from an emergent surface P
1
d
. The light beam from the emergent surface P
1
d
enters an incident surface P
2
a
of the roof prism P
2
via an indication member
5
having a visual field frame and the like, is totally reflected by a surface P
2
b
to enter a roof surface P
2
c
, is reflected back in the direction perpendicular to the observation field, is totally reflected by a surface P
2
d
that is flush with the incident surface P
2
a
to emerge from an emergent surface P
2
e
that is flush with the surface P
2
b
, and is guided to an eyepoint E via the eyepiece Le.
In this way, an inverted object image formed by the objective lens
10
is inverted vertically and horizontally by the image-inverting optical system P, and is observed as an erect image from the eyepoint E via the eyepiece Le.
SUMMARY OF THE INVENTION
In view of such conventional art, an object of the present invention is to provide a more compact and higher-performance real-image finder.
In order to achieve the above object, according to an aspect of the present invention, there is provided a real-image finder including: an objective optical system for forming a real image; a reflecting member having a reflecting surface for reflecting light from the objective optical system; a transmissive prism for transmitting light from the reflecting member, the transmissive prism having an incident surface on which a light beam on the optical axis of the objective optical system deflected by the reflecting member is incident nearly perpendicularly, and an emergent surface placed at an angle to the incident surface; a reflecting prism on which light from the transmissive prism is incident, the reflecting prism having an incident surface placed close to the emergent surface of the transmissive prism, and a reflecting surface for reflecting light from the incident surface so that the light from the reflecting surface is totally reflected by the incident surface of the reflecting prism; and an eyepiece optical system for guiding light from the reflecting prism to an observer.
According to another aspect of the present invention, there is provided an optical device having the above-described real-image finder.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.
REFERENCES:
patent: 4171888 (1979-10-01), Shono et al.
patent: 4592636 (1986-06-01), Kato et al.
patent: 4609272 (1986-09-01), Yokota et al.
patent: 4949107 (1990-08-01), Kitagishi et al.
patent: 5253005 (1993-10-01), Koyama et al.
patent: 5392082 (1995-02-01), Ikemori et al.
patent: 5640632 (1997-06-01), Koyama et al
patent: 5751409 (1998-05-01), Koyama
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Gray David M.
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