JP2656046B2 - Metering system for electronic cameras - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention uses an imaging member such as an imaging tube or a CCD,
The present invention relates to a photometric system suitable for a single-lens reflex electronic camera that electrically performs still image processing.

(Prior art)

Conventionally, single-lens reflex cameras using a penta roof prism for 35 mm film have been greatly developed as being the most suitable for system development. FIG. 3 shows a configuration diagram of a finder optical system of a typical single-lens reflex camera.
In the figure, 101 is a rotatable total reflection mirror, 102 is a shutter unit, 103 is a film surface, 104 is a focusing screen, 105 is a penta roof prism, 106 is an eyepiece, and 107 is an observation pupil. The finder optical system shown in FIG. 3 has a ratio of the field of view of the image taken on the film surface to the object image observed by the finder optical system, that is, a field ratio of 90.
%, The field magnification γ when the standard lens is attached is 0.8
It has excellent optical performance more than twice. The finder optical system has a feature that the entire apparatus can be made relatively small.

However, when the above-mentioned pentada-hap-zoom is used for the viewfinder optical system of a two-panel or three-panel electronic camera using a plurality of imaging bodies such as a so-called CCD, the field of view and the same degree of view as the conventional single-lens reflex camera It is difficult to obtain a visual field magnification. Further, it becomes difficult to reduce the size of the entire apparatus. It is for the following reasons.

(A) For example, the effective screen of a 2 / 3-inch image sensor is about 1/4 smaller than the 35mm film in diagonal length ratio, so if a conventional penta roof prism is adopted, the optical path length is too long.
It becomes difficult to obtain a high field ratio and a high field magnification.

(B) More space is required for arranging the electric processing circuit behind the image pickup body, and the distance from the image plane of the photographing lens to the rear end of the camera becomes longer. Therefore, the pupil position of the finder optical system must be extended rearward on the camera side. As a result, it becomes difficult to obtain a high field rate and a high field magnification.

(C) A lot of space is required in front of the image pickup body for disposing a plurality of light beams such as a decomposing prism, a low-pass filter, an infrared cut filter, and a protective glass. The distance from the imaging surface must be large, and the entire device becomes large.

Next, for reference, FIG. 4 is a schematic view of an example of a finder optical system in a case where it is intended to achieve a field ratio of 90% or more using a conventional penta roof prism in an electronic camera. In the figure, 200 is a photographic lens, 201 is a division unit for dividing an optical path from a photographic optical path to a finder optical system, 202 is a low-pass filter, 203 is a shutter unit, 204 is an imaging surface of an imaging body, and 205 is an infrared cut. Imager package with an effective protective glass on the front, 20
6 is a viewfinder optical system unit including an upright image system, 2
07 is a focusing screen, 208 is an electric signal processing circuit unit for imaging signals, and 209 is a pupil for observation. Reference numeral 204 'denotes another imaging surface. Decomposition prisms 210 and 211 decompose the imaging light beam.

Generally, the larger the field magnification γ, the easier it is to observe the finder image. Assuming that the standard focal length of the taking lens is fe and the focal length of the eyepiece is fe, γ = f
It is represented by θ / fe. In order to increase the field magnification γ, it is necessary to reduce the focal length fe of the eyepiece since the focal length fθ of the standard lens is substantially constant. Since the eyepiece is arranged so that its front focal point is located near the finder image plane of the finder optical system, the field magnification γ
It is necessary to shorten the optical path length of the optical system for obtaining an erect image from the focusing screen to the eyepiece lens as much as possible.

However, in the case of an electronic camera, as described above, a unit such as an infrared cut filter or a low-pass filter, and further, an electric processing circuit for electrically processing image information, must be arranged around the imaging surface of the imaging system. It is necessary to shift the movable mirror (quick return mirror) that guides the light beam of the object to the finder optical system to the object side (forward), and also to shift the observation position to the rear.

Therefore, when the finder image on the focusing plate of the photographing lens is directly observed with the eyepiece, the focal length of the eyepiece must be increased, and the viewfinder magnification becomes small, making the viewfinder difficult to observe. For example, Japanese Patent Application Laid-Open No. Sho 60-43628 proposes to reduce the focal length of the eyepiece, but the finder magnification is still limited to about 0.5.

On the other hand, an electronic camera using an image sensor such as a CCD has a narrower latitude than a camera using a silver halide film, and is about 1/2 to 1/3 of a silver halide film. Therefore, accurate photometry needs to be performed. However, unless the photometric element is placed on the photographing optical axis, accurate photometry cannot be performed due to the influence of perspective and the like.

[Object of the invention]

The object of the present invention is to improve the finder magnification,
It is an object of the present invention to provide a photometering system for an electronic camera in which the height of a finder optical system is reduced, the housing of the camera is compactly formed, and accurate photometry without a perspective is possible.

The invention of the present application is directed to a photometric system of an electronic camera for observing an image formed by the photographing lens by bending and reflecting a photographing light beam that has passed through a photographing lens by a movable mirror. A first reflecting surface for reflecting a light beam reflected by the movable mirror in a direction substantially orthogonal to a surface including the optical axis of the photographing lens, and a light beam reflected by the first reflecting surface being reflected by the movable mirror. The second reflecting surface, which is formed of a semi-transmissive mirror, is reflected in the same direction as the bent light beam traveling direction, and reflects the light beam reflected by the second reflecting surface in the same direction as the light beam traveling direction of the photographing lens. A third reflecting surface to be formed, and a secondary imaging lens positioned on an optical path reflected by the third reflecting surface to re-image an image formed by the photographing lens. A fourth reflecting surface that emits the secondary imaging lens and reflects a light beam reflected by the third reflecting surface in a direction opposite to a traveling direction of the light beam reflected by the first reflecting surface; A fifth reflecting surface that reflects the light beam reflected by the reflecting surface in the same direction as the light beam traveling direction of the photographing lens and guides the light to the eyepiece, on the extension of the light beam traveling direction reflected by the first reflecting surface. An imaging lens and a photometric element are arranged behind the second reflecting surface.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment in which the finder optical system of the present invention is applied to a two-panel electronic camera. 1 is a shooting lens,
Reference numeral 2 denotes a movable mirror that retracts out of the light beam during exposure and bends the optical axis upward by 90 °. 3 is a front prism of the two-beam splitting prism, and 4 is a rear prism of the two-beam splitting prism.
D is provided to decompose and guide the light beam on the half mirror surface 5a to the image pickup device units 5, 5 'composed of D. A light beam from an object that has passed through the photographic lens 1 is reflected by the movable mirror 2 in an upward direction substantially perpendicular to the optical axis of the photographic lens system, and the optical path length of a prism and a filter member (not shown) in the photographic optical path is determined. It is incident on a finder glass block 6 having substantially the same optical path length and a reflecting surface 6-a. The glass block 6 is a right-angle prism and has a reflecting surface 6-a.
The light beam from the movable mirror 2 is bent on the surface such that the optical axis of the reflected light beam is also orthogonal to the virtual plane including the optical axis of the imaging lens system 1 and the optical axis of the light beam reflected from the movable mirror 2. . Then, the photographing light beam forms an image on the viewfinder image forming surface of the focusing plate 7 at a position optically equal to the image pickup surface of the image pickup device unit 5.

The finder image formed on the focus plate 7 passes through the field lens 8 and is reflected by the semi-transmissive mirror 9 in the same direction as the direction in which the optical axis of the finder is bent by the movable mirror 2. The reflected luminous flux is incident on the prism 10 at the entrance surface 10-a, the reflection surface 10-b, and the exit surface.
The light is guided in parallel with the photographing optical axis O via 10-c.

On the other hand, an imaging lens 17 and a photometric element 18 are arranged on the optical axis transmitted through the semi-transmissive mirror 9.

Further, the light beam exiting the prism 10 passes through the secondary imaging lens 11, and the mirror of 12 causes the optical axis of the reflected light beam to be substantially parallel and opposite to the optical axis of the light beam reflected by the reflecting surface 6-a. It is reflected so that it faces. Next, the light is reflected by the mirror 14 so that the optical axis of the reflected light beam is substantially parallel to the optical axis of the one taking lens. Reference numeral 13 denotes a secondary image forming surface on which a primary image forming surface on the reticle 7 is enlarged and formed by the secondary image forming lens system 11, and is observed by 15 eyepieces. 16 indicates an eye point.

In a finder of the primary imaging system in which the focus plate is directly observed with an eyepiece, it is necessary to form a roof surface and convert the left-right direction into an erect image.
In the secondary imaging method in which the upper primary imaging surface is re-imaged on the secondary imaging surface with a secondary imaging lens system and then observed with an eyepiece, the left-right direction is used for two times imaging. Since the optical system returns to the original state by inversion, it is not necessary to use an expensive optical system such as a roof surface or a pentaprism, and the optical system can be simplified.

In the present invention, the movable mirror 2 and the 10-b
There is no image reversal because there are two reflections with the surface and two reflection surfaces 6-a and 9 between them. And 12 and
The fourteen mirrors are provided so that the optical path can be gained and an appropriate position can be observed, and the reflected light flux is observed in the same vertical and horizontal directions. Therefore, the erect image can be observed in the left, right, up, and down directions by the eyepiece.

According to the configuration of the present invention described above, the finder of the single-lens reflex electronic camera is formed as a secondary imaging system, and the optical path is appropriately bent by six reflections, so that the high-magnification finder can be compactly assembled. In particular, it contributes to miniaturization without taking too much camera height.

The optical axis of the eyepiece lens system is almost parallel to the optical axis of the photographing lens system and almost directly above the optical axis of the photographing lens system. It is at the same distance as the camera, improving operability.

In the case of primary image formation, display in the viewfinder requires a display member to be arranged near the primary image formation plane, and the display range is limited. A display member can be arranged near the next imaging plane. It is also possible to adjust the secondary image plane 13 to an appropriate position by moving the mirrors 12 and 14 in parallel.

The photometric element according to the present invention is arranged on the optical axis extension bent by the reflecting surface 6-a for improving the finder magnification and compactly, so that accurate photometry without parallax can be performed. Will be

The photometric system of the present invention performs evaluation photometry using an imaging lens 17 and a photometric element 18 including a plurality of divided light receiving units. Further, since the photometric lens 17 can be placed relatively close to the focus plate 7 and the condenser lens 8, the lens diameter is small and the F value is small, that is, a bright photometric lens can be designed.

In the present embodiment, the center-weighted average photometry is performed with the semi-transmissive mirror 9 having a uniform transmittance over the entire surface. With this arrangement, a desired photometric sensitivity distribution can be easily obtained.

〔effect〕

As described above, according to the present invention, the photometric element is arranged on the optical axis extension when the finder optical system having the finder magnification improved by using the secondary image forming optical system. Accurate photometry becomes possible without generation of light.

[Brief description of the drawings]

FIG. 1 is a perspective view of a photometric system according to the present invention. FIG. 2 is a diagram illustrating the vertical and horizontal relationship of an image in a finder optical system. FIG. 3 is a sectional view of a viewfinder optical system of a conventional single-lens reflex camera. FIG. 4 is a schematic view of a finder optical system when a pentaprism is used in a two-plate electronic camera. DESCRIPTION OF SYMBOLS 1 ... Photography lens 2 ... Movable mirror 6 ... Right angle prism 7 ... Focusing plate 10 ... Right angle prism 11 ... Secondary imaging lens system 12 ... Total reflection plate 13 ... Secondary imaging surface 14 ... ... total reflection plate 15 ... eyepiece

Claims (1)

(57) [Claims] 1. A photometric system of an electronic camera for observing an image formed by a photographing lens by bending and reflecting a photographing light beam that has passed through a photographing lens by a movable mirror, the light beam center folded by the movable mirror and the center of the light beam. A first reflecting a light beam reflected by the movable mirror in a direction substantially orthogonal to a plane including an optical axis of the photographing lens;
And a second reflecting mirror which reflects a light beam reflected by the first reflecting surface in the same direction as the light beam traveling direction bent by the movable mirror.
A third reflecting surface for reflecting the light beam reflected by the second reflecting surface in the same direction as the light beam traveling direction of the photographing lens; and a third reflecting surface located on the optical path reflected by the third reflecting surface. A secondary imaging lens for re-imaging an image formed by the photographing lens;
A fourth reflecting surface for reflecting the light beam reflected by the reflecting surface in the direction opposite to the direction of travel of the light beam reflected by the first reflecting surface; and transmitting the light beam reflected by the fourth reflecting surface to the photographing lens. A fifth reflecting surface that reflects light in the same direction as the light beam traveling direction and guides the light to the eyepiece; and an imaging lens behind the second reflecting surface on an extension of the light beam traveling direction reflected by the first reflecting surface. A photometric system for an electronic camera, comprising: a photometric element.