JPH04342Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder device for a single-lens reflex camera, and particularly to a finder device suitable for a small-sized single-lens reflex camera used for endoscopic photography and the like.

In single-lens reflex cameras, generally, the photographing light beam that passes through the photographic lens is reflected and refracted by a reflector in the photographic optical path and guided to the finder device, where the optical system in the finder device converts it into an erect image, which is then observed through the eyepiece. . In conventional devices, the conversion to an erect image is simultaneously performed using a pentaprism that makes the optical axes of the finder optical system and the photographing optical system parallel, or a composite prism that has an equivalent function. It is configured to be observed through an eyepiece. However, the optical path length occupied by pentaprisms and other compound prisms is relatively long, and for this reason, the focal length of the photographing lens is long, as in small single-lens reflex cameras such as those used for endoscopic photography. When the distance up to the lens is made relatively short, or when the position of the reflecting mirror in the photographing optical path is specially set, the image formed by the photographing lens may be formed inside the pentaprism or compound prism. In other words, a surface conjugate with the photographic film surface is generated within the prism. In this case, it becomes difficult to set the field diaphragm, and even if it is possible to form an image near the incident surface or reflective surface of the prism, the portion of the photographing lens or eyepiece corresponding to the back focus will not reach the prism. Therefore, the focal length of the eyepiece is limited, and it may be difficult to obtain the desired viewfinder magnification.

The present invention was developed to solve this problem.In place of the pentaprism in the conventional finder device, a reflector consisting of a triangular prism or a reflector with a shorter optical path length is used. The light beam reflected by the reflector is reflected and refracted almost parallel to the photographing light beam, and a condenser lens is provided on at least one of the front and rear sides of the reflector, and the condenser lens is provided behind the image plane formed by the reflector and the condenser lens. The present invention is characterized in that the image is inverted into an erect image by an image inverting prism, and the position of the exit pupil can be adjusted by the condenser lens, so that a desired finder magnification can be obtained.

The invention will now be described with reference to the illustrated embodiments. The figure shows the arrangement of the optical system of the finder device 10 of the present invention and the relationship between the photographing lens 1 and the film surface 2. The photographing optical path reflection mirror 3 is positioned in the photographing optical path between the photographing lens 1 and the film surface 2. are doing. This reflecting mirror 3 in the photographing optical path normally forms an angle of 45° with respect to the photographing optical axis A-A, and reflects and refracts the light beam transmitted through the photographing lens 1 to the present finder device 10.
When taking a photograph, it is withdrawn from the photographing optical path and a photographing light beam is applied to the film surface 2. The shutter is not shown.

The finder device 10 has a triangular prism 4 that receives the reflected light from the photographing optical path reflector 3 and reflects and refracts it parallel to the photographing optical axis A-A. Condenser lenses 5, 5 are attached. a-a is the axis of the light beam reflected and refracted by the triangular prism 4, that is, the axis of the finder optical system, and behind the triangular prism 4 on this optical axis a-a are a field stop 6, an image reversing prism 7, and An eyepiece lens 8 is provided. The image reversing prism 7 includes two prisms 7a, 7
The prism 7b is a combination of prisms 7b and 7b, which reflect and bend the incident light beam shown by the thick chain line as shown in the figure.
The image is inverted on the roof surface 9 to form an erect image. The eyepiece lens 8 is for observing this erect image.
It is located substantially in the same plane as the film surface 2.

In the finder device 10 having the above configuration, since the optical path length of the triangular prism 4 is shorter than that of the pentaprism used in the conventional device, the conjugate surface with the film surface 2 can be easily set to the rear of the triangular prism 4. Therefore, it is possible to obtain a compact single-lens reflex camera designed to reduce the flange back of the camera body and to reduce the distance between the reflecting mirror 3 in the photographing optical path and the film surface 2. Furthermore, it becomes easy to position the film surface 2 and the eyepiece lens 8 within the same plane.

The condenser lens 5 obtains a desired finder magnification together with the eyepiece lens 8 by giving it an appropriate refractive power. In the example shown, it is attached to the entrance surface and the exit surface of the triangular prism 4, but if either one But that's fine. Further, the triangular prism 4 may be constructed from a simple reflecting mirror.

As described above, the finder device of the present invention replaces the pentaprism in the conventional device with a triangular prism or a reflector, so unless the distance between the reflector in the photographing optical path and the film surface is set very small, A conjugate plane of the film surface is not formed, and therefore the distance from the reflecting mirror in the photographing optical path to the film surface can be made relatively short even for photographic lenses with long focal lengths, making it possible to use a small camera body. Obtainable. Since the image is inverted by the image inverting prism, an erect image can be observed through the eyepiece, and the magnification of the finder optical system can be appropriately set by adjusting the focal lengths of the condenser lens and the eyepiece. Furthermore, since the condenser lens suppresses the spread of the light flux, it becomes possible to use a small image reversing prism.

[Brief explanation of the drawing]

The figure is an optical system diagram showing an embodiment of the finder device of the present invention. 1...Photographing lens, 2...Film surface, 3...
Photographing optical path reflector, 4...Triangular prism, 5...
Condenser lens, 7... Image reversing prism, 8...
...Eyepiece, 10...Finder device.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) The photographic light beam that has passed through the photographic lens is reflected and refracted by a reflector in the photographic optical path and guided to a finder device, and the erected image is displayed by the optical system in the finder device. A finder device for a single-lens reflex camera configured to allow observation through a lens, comprising: a reflector that catadioptrically refracts the light beam reflected by the reflecting mirror in the photographing optical path in a direction substantially parallel to the photographing light beam; and at least one of the front and rear sides of the reflector. A finder device for a single-lens reflex camera, comprising: a condenser lens disposed in the triangular prism or an image reversing prism disposed behind the image forming plane formed by the triangular prism or the reflecting mirror and the condenser lens. (2) Claim 1 of the Utility Model Registration Claim: The viewfinder device for a single-lens reflex camera, wherein the eyepiece is positioned substantially flush with a film surface. (3) Utility Model Registration Claim 1, wherein the reflector is a triangular prism or a reflector, is a single-lens reflex camera's viewfinder device.