JPH04320224A - Finder construction for camera - Google Patents

Abstract

PURPOSE:To make an interval between a reticle and an eyepiece part small, to make a camera small in size and light in weight by disposing a trapezoid- shaped prism in which an image on the reticle is made to be an erect image between the reticle and the eyepiece part. CONSTITUTION:The reticle 32, an image inversion means 36 and the eyepiece part 38 are provided on a finder optical system, the image formed at the reticle 32 is inverted to be the erect image in an appropriate direction by the image inversion means 36, and the erect image is enlarged by the eyepiece part 38. And the image inversion means 36 is constituted of the trapezoid-shaped prism executing the image inversion in an up-and-down direction at least. This trapezoid-shaped prism whose cross section is nearly a trapezoid obtained by losing the angle of an obtuse isosceles triangle is disposed in such a way that a base 36a as a reflecting surface is nearly horizontal. Consequently, an object image is formed on the reticle 32, and this formed image is made incident on the trapezoid-shaped prism constituting the image inversion means 36. The image is inverted in the appropriate direction in the trapezoid-shaped prism, is to be the erect image, and is projected. This erect image is enlarged by the eyepiece part 38, and the object is confirmed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder structure suitable for a camera that requires a photographic lens with a long back focus, such as an electronic still camera equipped with an RGB three-color separation optical system.

0002

[Background Art] When a subject is photographed by a camera, in order to improve the image quality of the color imaging screen, the images separated into three colors of red, green, and blue are formed on separate imaging surfaces. A three-color separation optical system is sometimes used to do this.

For example, as shown in FIG. 3, in the case of an electronic still camera that uses a CCD as a solid-state image sensor, when the shutter 3 is open, the image emitted from the photographing lens 2 is captured by the resolving prism group 4. The image is separated into three color images and focused on a separate CCD 6.

When a single-lens reflex finder is used in a camera having a three-color separation optical system, a finder mirror 1 is disposed in front of the separation prism group 4. Since the image reflected by the finder mirror 1 must be formed on the focus plate of the finder optical system, the focus plate is disposed at a position having an optical path length equal to the optical path length from the finder mirror 1 to the CCD 6. There is a need.

However, from the finder mirror 1 to C
The optical path length up to CD 6 is large due to the presence of the resolving prism group 4, and if a focusing plate is disposed directly above the finder mirror 1, as in the structure of a camera with a short back focus, the focal point The board becomes out of focus. For this reason, a first focusing plate 10 is disposed behind the right-angle prism 8 disposed above the finder mirror 1 as a glass for changing the direction of the optical path and for correcting the optical path.

The image formed on the first focusing plate 10 is an inverted image whose top, bottom, left and right sides are reversed because the inverted image from the photographic lens 2 is reflected twice by the finder mirror 1 and the right angle prism 8. There is. In order to obtain a finder with a normal image in both the upper, lower, right and left directions, conventionally, the inverted image is reversed up and down, left and right by the re-imaging lens unit 14, and the second focus plate 1
6 as an erect image. This erect image is magnified by the eyepiece unit 18 to confirm the subject. Further, reference numeral 12 in FIG. 3 is a field lens.

[0007] In order to obtain a finder with a normal image in both the upper, lower, left and right directions, if an attempt is made to obtain a normal image from the image reflected by the finder mirror 1 using a prism optical path such as a penta-roof prism, a sufficient length of space is required within the penta-roha prism. Since the lens requires a large optical path, the focal point is within the pentagonal roof prism, making it impossible to provide a focus plate.

[0008]

However, as in the conventional optical system, the inverted image formed on the first focusing plate 10 is re-imaged as an erect image on the second focusing plate 16 through the re-imaging lens section 14. According to the system structure, the length of the re-imaging lens section 14, ie, the distance between the first focusing plate 10 and the second focusing plate 16, is required to be sufficient. For this reason, the length of the finder increases, which may make the camera larger or look worse.

Furthermore, in order to prevent vignetting of the visual field, the re-imaging lens section 14 needs to have an appropriate diameter, and the re-imaging lens section 14 requires a complicated structure to correct aberrations. Therefore, there is a risk that the finder structure will become expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a finder structure with a simple structure and a short optical path length.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the finder structure of a camera according to the present invention includes a focus plate, an image reversing means, and an eyepiece portion in the finder optical system, and the focus plate In a camera finder structure in which the image formed at the camera is inverted in an appropriate direction by the image reversing means to form an erect image, and the erect image is magnified by the eyepiece, the image reversing means performs image reversal at least in the vertical direction. It is characterized by being composed of trapezoidal prisms.

0012

[Operation] The image of the object is formed on the focusing plate, and this image is incident on the trapezoidal prism constituting the image reversing means. The image is inverted in an appropriate direction within the trapezoidal prism, becomes an erect image, and is emitted. This erect image is then magnified by the eyepiece to confirm the subject.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a camera finder according to the present invention will be explained below based on the illustrated embodiments.

FIG. 1 shows a partially omitted schematic diagram of the optical system of an electronic still camera having a resolving prism, cut along a perpendicular plane including the optical path. On the optical path, from the front F, a photographic lens section (partially not shown), a photographic lens 19, and a finder mirror 2
0, shutter 22, resolving prism group 24, first CCD 2
6, a second CCD 27 and a third CCD 28 are provided.

The finder mirror 20 has approximately 4 points in the optical path.
It is arranged with a mirror surface facing upward at a 5 degree incline, and swings upward in conjunction with the release of the shutter 22 with the upper side as an axis.

The resolving prism group 24 includes, in order from the front F, a first resolving prism 24a, a second resolving prism 24b, each having an approximately triangular cross section, and a third resolving prism 2, approximately having a trapezoidal cross section.
4c. And the first decomposition prism 2
4a, second decomposition prism 24b, third decomposition prism 24
A first CCD 26, a second CCD 27, and a third CCD 28 are arranged at positions to receive images separated by c. Note that the optical path lengths from the finder mirror 20 to the first CCD 26, second CCD 27, and third CCD 28 are all equal.

On the other hand, above the finder mirror 20,
Roof-shaped roof surface 30a with adjacent surfaces forming a right angle to each other
A rectangular prism 30 having a roof surface 30a is arranged such that the roof surface 30a is inclined at 45 degrees with respect to the optical path from the finder mirror 20 so that the optical path is directed backward. A focusing plate 32 and a field lens 34 are arranged close to the rear of the right-angle prism 30. The optical path length from the finder mirror 20 to the focus plate 32 is as follows:
The length of each optical path up to the CCD 28 is equal.

Behind the field lens 34, there is disposed an trapezoidal prism 36 whose cross section is an obtuse isosceles triangle with no corners, and whose bottom surface 36a as a reflective surface is substantially horizontal. (Illustrated in Figure 2).

At the rear of the trapezoidal prism 36, an eyepiece section 38 is provided which is constituted by a suitable group of lenses.

The operation of this embodiment constructed as above will be explained below.

The image of the object (not shown) captured by the photographic lens group is captured by the following steps:
This is an inverted image with the top, bottom, left and right sides reversed. Then, with the finder mirror 20 raised, the shutter 22
is open, the above-mentioned image passes below the finder mirror 20 and the shutter 22, and passes through the first resolving prism 2.
4a, only the blue component is reflected by one surface of the first resolving prism 24a. The blue component is further reflected within the first resolving prism 24a and transmitted to the first CCD 26.
image is formed. Imaging of components other than the blue component is performed using the second resolving prism 2.
4b, the red component is reflected by one surface of the second resolving prism 24b. The red component is further reflected within the second resolving prism 24b and forms an image on the second CCD 27. The image obtained by extracting the blue component and the red component is only the green component, and this green component passes through the third resolving prism 24c and forms an image on the third CCD 28.

On the other hand, when the finder mirror 20 is in a lowered state, the inverted image taken from the photographic lens 19 is reflected by the finder mirror 20 and becomes a horizontally inverted image with only the left and right sides being reversed, and the image is almost vertically upward. Head to. The horizontally inverted image enters the right angle prism 30 and is reflected by the roof surface 30a, thereby becoming a vertically inverted image in which only the top and bottom are reversed. Form an image. This image passes through the field lens 34, enters one of the slopes of the trapezoidal prism 36, is reflected by the bottom surface 36a inside the trapezoidal prism 36, and is turned upside down to become an erect image (as shown in FIG. 2). . This erect image is emitted from the opposite side of the slope of the trapezoidal prism 36 on an optical path that is substantially in line with the incident optical path, and is magnified by the eyepiece portion 38. The subject is then confirmed using this enlarged image.

In this embodiment, the roof surface 30a is formed on the reflective surface of the rectangular prism 30; however, it is sufficient that the roof surface 30a is formed on the optical path of the finder. However, a structure in which the reflecting surface of the right-angle prism is made flat may also be used. In this case, the image is captured as an inverted image with the top, bottom, left and right sides reversed on the focus plate.
This inverted image is flipped vertically and horizontally on the roof surface of the trapezoidal prism to become an upright image.

[0024]

As described above, according to the camera finder structure according to the present invention, the trapezoidal prism is disposed between the focusing plate and the eyepiece to make the image on the focusing plate an erect image. , the distance between the reticle and the eyepiece can be reduced. Therefore, the finder section becomes smaller, the appearance is improved, and the camera can be made smaller and lighter. Further, since there is no need to use a complicated image reversing means, the structure and assembly become simple and the cost becomes low.

Furthermore, by using a trapezoidal prism as the image reversing means, there is no need for complicated adjustments, and moreover, a high-performance image reversing means can be obtained at low cost.

[Brief explanation of drawings]

FIG. 1 is a partially omitted schematic diagram of an optical system cut vertically along an optical path.

FIG. 2 is a perspective view of a trapezoidal prism.

FIG. 3 is a schematic diagram of a conventionally used reimaging optical system, and corresponds to FIG. 1.

[Explanation of symbols]

32 Focus plate 36 Ladder prism 38 Eyepiece part

Claims (1)

[Claims] 1. A finder optical system includes a focusing plate, an image reversing means, and an eyepiece, an image formed on the focusing plate is reversed in an appropriate direction by the image reversing means to form an erect image, and the erect image is A finder structure for a camera that is magnified by an eyepiece, wherein the image reversing means is constituted by a trapezoidal prism that performs at least vertical image reversal.