JPH0296727A - Finder optical system for single-lens reflex camera - Google Patents

Abstract

PURPOSE:To reduce a finder optical system in weight and height by leading an optical path going to almost the upper part from a focusing screen forward, backward and sideway, and obtaining a normal image by means of vertically and horizontally reversing an image with a relay lens system. CONSTITUTION:An image reflected by a movable reflecting mirror 2, formed on a focal platen 4 and horizontally reversed in an erecting position is led forward and almost parallel to a photographing lens optical axis (l) by a first reflecting mirror 5, led sideway by intersecting almost orthogonally, with the optical axis (l) by a second reflecting mirror 6 and led backward and almost parallel to the optical axis l by a third reflecting mirror 7 again. Then, in the course of the process, a midair image reversed vertically and horizontally is formed on a first image forming plane S1 by an image forming lens 8. The midair image is formed as a vertically and horizontally normal midair image on a second image forming plane S2 by a relay lens 9, and it is enlarged by an eyepiece 10. Therefore, the height and the weight of the finder optical system can be kept minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a finder optical system suitable for single-lens reflex cameras, particularly medium- and large-sized single-lens reflex cameras.

[Conventional technology]

Recently, among the 6X4.5 size, 6X6 size, 6x7 size, etc.

As large-format single-lens reflex cameras are also required to be mobile, eye-level finders have come to be used frequently instead of waist-level finders.

Conventionally, reflective optical systems used in eye-level finders of medium- and large-format single-lens reflex cameras are broadly divided into pentagonal roof prisms, which are similar to those used in 35 ns cameras, and compound prisms, which consist of two or three prisms including a roof prism. .

The former not only has a short optical path length from the eyepiece to the focus plate, but the optical path is inside glass with a high refractive index, so the optical path length is even shorter and the finder magnification can be increased, while the latter Since the height of the prism is lower than that of the former, the height of the camera can be lowered.

[The problem that the idea aims to solve]

However, the finder optical system of such conventional single-lens reflex cameras uses a large prism made of optical glass for the reflective optical system, which is already heavy, but the weight of large-format single-lens reflex cameras becomes even heavier. This has led to the problem that mobility and portability have been significantly impaired.

In order to solve these problems, it is also possible to use a pentamirror, which has a hollow interior with a reflective surface similar to a pentagonal roof prism, or a boro mirror, which has a reflective surface similar to a porro prism. However, there is a problem in that the height of the finder optical system increases and the finder magnification decreases.

It is an object of the present invention to solve these problems and provide a finder optical system for a single-lens reflex camera that can keep the height and weight to a minimum while ensuring finder magnification.

[Means to solve the problem]

In order to achieve the above object, the finder optical system for a single-lens reflex camera according to the present invention includes a first reflector that guides an optical path from the focusing plate of the single-lens reflex camera forward, which is generally upward;
A second reflecting mirror that guides the optical path guided by the first reflecting mirror to the side; a third reflecting mirror that guides the optical path guided by the second reflecting mirror backward; an imaging lens that forms an image on a first imaging surface, a relay lens that forms an image on the first imaging surface on a second imaging surface, and an eyepiece that magnifies the image on the second imaging surface. It consists of.

[For production]

By configuring as described above, the height and weight of the finder optical system can be kept to a minimum without reducing the finder magnification.

In addition, by moving the eyepiece to the side, it is possible to secure space that can be used effectively at the rear of the reticle, and there is considerable freedom in the position and angle of each reflector. , it becomes possible to arrange the finder optical system within the smallest space, avoiding the mechanical part of the single-lens reflex camera.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figures 1 to 4 show an embodiment in which the present invention is applied to a 6x4.5 size camera. Figure 1 is a perspective view, Figure 2 is a plan view, Figure 3 is a side view, and Figure 3 is a side view. 4 each shows a front view.

The finder optical system of a single-lens reflex camera includes a photographic lens 1, a movable mirror 2 that reflects upward the light beam that has passed through the photographic lens 1, and a position that is conjugate with the photosensitive material surface 3a of the film 3 with respect to the movable mirror 2. a focusing plate 4 having a focal plane 4a; a first reflecting mirror 5 that is obliquely disposed above the focusing plate 4 and guides a substantially upward optical path forward from the focusing plate 4;
A second reflecting mirror 6 guides the optical path guided forward by the first reflecting mirror 5 to the side, and a second reflecting mirror j! A third reflecting mirror 7 that guides the optical path guided laterally by the lens 6 and the second and third reflecting mirrors 6 and 7 is inserted between the second and third reflecting mirrors 6. An imaging lens 8 forms an image on the first imaging surface S1, and an image formed on the first imaging surface S1 by the imaging lens 8 is transferred to a second imaging surface S2.
a relay lens 9 that forms an image on the second image forming surface S2, and an eyepiece lens 1 that magnifies the image formed on the second image forming surface S2 by the relay lens 9.
It consists of 0.

In Figs. 2 to 4, 11 is an auxiliary reflector mounted on the back surface of the movable reflector 2 so that it can be raised and lowered, 12 is an AF module for distance measurement, and 15 and 14 are a supply spool and a take-up spool for the film 3. , 15 is a supply drum for the focal brain shutter, 16 and 17 are its winding drums, and 18 is a motor for winding the film and the shutter.

In an embodiment having such a configuration, the photographing lens 1
The erect, horizontally inverted image formed on the focal plane 4a by being reflected by the movable reflector 2 is guided forward by the first reflection 115 almost parallel to the optical axis of the photographic lens, and is guided to the side by the reflector 6 of No. 2, almost perpendicular to the optical axis a;
The third reflecting mirror 7 guides the light toward the rear again substantially parallel to the optical axis a.

On the way, the imaging lens 8 forms a vertically and horizontally inverted aerial image on the first imaging surface S1, and this aerial image is transferred to the second imaging surface S2 by the relay lens 9 as a vertically and horizontally normal image. The image is formed as an aerial image and magnified by the eyepiece lens 10.

In this way, by sequentially guiding the finder optical path from the focus plate 4 upward, forward, sideways, and backward, the optical path length can be made as long as possible within a limited space, and the imaging lens 8 and relay It becomes possible to keep the lens 9 within a range that can be easily manufactured.

If this optical path length were to be shorter than this, the diameter and radius of curvature of each lens 8 and 9 constituting the finder optical system would be extremely small, and it would be impossible to maintain the distance between each member, making actual manufacturing almost impossible. It becomes possible.

For example, if the finder optical path is guided directly to the rear eyepiece with one reflection, in order to increase the optical path length, the height of the camera must be increased, and the first reflection will lead the viewfinder optical path to the side. If the next reflection is to guide the light backwards, the optical axis of the eyepiece lens 10 must be moved away from the photographic lens optical axis 2, resulting in the inconvenience that the width of the camera becomes too large.

This finder optical system does not require a large prism, and the imaging lens 8 and relay lens 9 can also be small, so the weight of the finder optical system can be significantly reduced, and compared to a prism, each reflection There is a lot of freedom in the position and angle of the mirror.

By choosing these appropriately, the size of the single-lens reflex camera, especially its height, can be kept to a minimum.

Furthermore, as can be seen from FIG. 2, since the finder optical system is placed at the front and side parts of the upper part of the single-lens reflex camera body, space is left above and behind the focusing plate 4, that is, behind the first reflecting mirror 5. This space can be effectively used, for example, as a film spool room or a battery room.

Furthermore, since a grip or the like can be provided in the shaded area in FIG. 4, that is, the lower part of the relay lens 9 and eyepiece lens 10, there is no wasted space inside the roughly cubic camera body. A 6x4.5 format camera can be packed into an extremely compact size.

In the above embodiments, the case where the present invention is applied to a 6x4.5 format camera has been described, but the present invention is not limited to this, and is applicable to 6x6 format, 6x7 format, and 6x8 format cameras.
It can also be applied to large-format cameras such as 6x9 and 6x9-format cameras without any problems.

〔Effect of the invention〕

As described above, according to the present invention, the optical path that goes almost upward from the focusing plate of a single-lens reflex camera is guided forward, sideways, and backward, and the relay lens system is used to reverse the vertical and horizontal directions to obtain a normal image. This eliminates the need for a large and heavy prism, making it possible to significantly reduce the weight and height of the finder optical system without reducing the finder magnification.

In addition, by placing the optical axis of the eyepiece on the side,
A space is created above and behind the focusing plate, and this space can be used effectively for the film spool room, battery compartment, etc., and since there is flexibility in the placement of each reflector, the size of the single-lens reflex camera can be reduced. can be minimized.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the invention, and FIG. 2 is a plan view thereof. Figure 3 is its side view, and Figure 4 is its front view. 1...Photographing lens 3...Film 5...First reflecting mirror 7...Third reflecting mirror 9...Relay lens 2...Movable reflecting mirror 4...Focal plate 6... ...Second reflecting mirror 8...Imaging lens 10...Eyepiece lens

Claims (1)

[Claims] 1. A first reflecting mirror that guides forward an optical path that goes approximately upward from the focus plate of a single-lens reflex camera; a second reflecting mirror that guides the optical path guided by the first reflecting mirror sideways; a third reflecting mirror that guides the optical path guided by the reflecting mirror backward; an imaging lens that forms the image on the focus plate onto a first imaging plane; and an image on the first imaging plane. 1. A finder optical system comprising: a relay lens that forms an image on a second imaging surface; and an eyepiece lens that magnifies the image on the second imaging surface.