JPH01101535A - Finder optical system having photometric means - Google Patents

Abstract

PURPOSE:To effectively arrange a photometric system for obtaining the distribution of photometric sensitivity on the field side, to obtain a high visual field ratio and high visual field magnification and to miniaturize a finder optical system by adopting a secondary image forming system, specifying respective optical elements and properly bending the optical path of a finder. CONSTITUTION:A finder image formed on a finder image forming face 8 through a photographing lens 1 is passed through a field lens 9 and reflected to the object side by the 1st reflector 10. The reflected finder image is reformed on a secondary image forming face 14 by a secondary image forming lens 11 through the 2nd reflector 12 for reflecting the beams from the lens 11 to the optical axis side direction of the lens 1 and the 3rd reflector 13 for reflecting the beams to the image face side direction. The finder image is observed through a eyepiece 15 and a part of the finder beams passed through one area of the reflecting face of the 1st reflector 10 is guided to a photometric means 17 by an optical guiding means 16. Consequently, the TTL type photometric means for obtaining optional photometric sensitivity distribution can be obtained, a high visual field ratio and a high visual field magnification can be obtained and the system can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a finder optical system having a photometric means,
In particular, the present invention relates to a finder optical system having a photometric means suitable for an eye reflex camera, a TTL optical type electronic camera using a solid-state image sensor such as an image pickup tube or a COD, and the like.

(Prior Art) Single-lens reflex cameras using pentagonal roof prisms for 35m film have developed greatly as an optimal system for system development.

Figure 2 shows a schematic diagram of the construction of the finder optical system of a typical single-lens reflex camera. In the figure, 101 is a rotatable total reflection mirror, +02 is a shutter unit, and 103
is the film surface, 104 is the focusing screen, 1
05 is a penta roof prism, 106 is an eyepiece, +0
7 is a pupil for observation.

The finder optical system shown in Figure 2 has a ratio of the image taken on the film surface to the object image observed by the finder optical system, that is, a field of view ratio of 90% or more, and a field magnification γ of 0 when a standard lens is attached. It has excellent optical performance of 8 times or more. This finder optical system has the characteristic that the entire device can be constructed relatively small.

Then, the so-called TT measures the light flux that passes through the photographic lens.
In many cases, the photometry means for performing L photometry is placed near the bottom surface of the pentagonal roof prism, or near the exit surface.

However, if the aforementioned penta roof prism is used in the finder optical system of a recent electronic camera using an imaging body such as a so-called COD, it becomes difficult to obtain a field of view ratio and field magnification comparable to those of a conventional single-lens reflex camera. Furthermore, it becomes difficult to downsize the entire device. This is due to the following reasons.

(b) For example, the effective screen of a 273-inch image pickup body is smaller in diagonal length ratio at about 174 compared to 3511101 film, so if a conventional penta roof prism was used, the optical path length would be too long, resulting in a high field of view ratio and high field of view magnification. It becomes difficult to obtain.

(b) A large amount of space is required to arrange the electric processing circuit at the rear of the image pickup body, and the distance from the image plane of the photographing lens to the rear end of the camera becomes long. For this reason, the pupil position of the finder optical system must be extended to the rear on the camera side, and as a result, it becomes difficult to obtain a high field of view and a high field of view magnification.

(c) Since a large amount of space is required to arrange optical components such as a low-pass filter, infrared cut filter, and protective glass in front of the WL image body, the distance between the dividing point of the finder optical path and the imaging plane must be large. As a result, the entire device becomes larger.

Next, for reference, FIG. 3 shows a schematic diagram of an example of a finder optical system when it is intended to achieve a field of view of 90% or more using a conventional pentagonal roof prism in an electronic camera. In the figure, 200 is a photographing lens, 201 is a dividing unit for dividing the optical path from the photographing optical path to the finder optical system, 202 is a low-pass filter, 203 is a shutter unit, 204 is the imaging surface of the imaging object, and 205 is an infrared cut effect. 206 is a finder optical system unit including an erecting image system; 207 is a focusing screen;
08 is an electrical processing circuit unit for image pickup signals, and 209 is an observation pupil.

The present applicant has previously proposed a relatively small finder optical system suitable for electronic cameras, for example, in Japanese Patent Laid-Open No. 60-233629 and Japanese Patent Laid-Open No. 60-263101.

In this publication, a finder optical system of the primary imaging method is achieved which can obtain a good finder image with a field coverage of 90% or more and a field magnification of approximately 0.6.

In addition, a finder optical system with photometric means was developed in Japanese Patent Application Laid-Open No. 1983
This method has been proposed in Japanese Patent Laid-Open No. 61-4032 and Japanese Patent Application Laid-Open No. 61-4032.

Generally, the larger the field of view magnification γ is, the larger the viewfinder image will be.
It will be easier to stay in a dormitory. Field of view magnification γ is J! If fe is the standard focal length of the IN shadow lens and fe is the focal length of the eyepiece lens, then γ=fθ/fe. In order to increase the visual field magnification Y, since the focal path 111fθ of the standard lens is approximately constant, the focal length fe of the eyepiece lens should be decreased, or
Alternatively, it is conceivable to configure the finder optical system using a secondary imaging method.

Field of view magnification γ of finder optical system using secondary imaging method
2 is the standard focal length of the photographic lens, fe is the focal length of the eyepiece, and β2 is the magnification of the secondary imaging lens, then γ2=(fθ/fe)Xβ2.

Therefore, in order to increase the visual field magnification γ2, it is sufficient to increase the magnification β2 of the secondary imaging lens.

However, in the finder optical system of the secondary imaging method, since aberrations caused by the eyepiece lens and aberrations of the secondary imaging lens are added, it is generally difficult to obtain a finder image with high optical performance. In particular, when attempting to increase the field magnification by increasing the magnification of the secondary imaging lens, many aberrations occur from the secondary imaging lens. For this reason, it has been very difficult to achieve a finder optical system that can obtain a good finder image with a large field of view magnification while reducing the overall optical length.

In addition, if a photometric means is provided in a part of the finder optical system of the secondary imaging method, and an arbitrary photometric sensitivity distribution is attempted to be obtained on the object side, the entire finder optical system becomes larger, and as a result, the overall size of the camera becomes smaller. It was very difficult to figure out.

(Problems to be Solved by the Invention) The present invention has a TTL type photometry means that can easily obtain an arbitrary photometry sensitivity distribution suitable for electronic cameras having a relatively small photographic screen, and has a high field of view and The object of the present invention is to provide a finder optical system having a photometry means using a secondary imaging method and having a high field of view magnification.

A further object of the present invention is to arrange a reflector having a predetermined inclination angle between the finder imaging surface of the photographing system and the 21st-order imaging lens, and between the secondary imaging lens and the eyepiece lens. Another object of the present invention is to provide a finder optical system having a photometry means that can easily obtain a field of view ratio of 90% or more and a field magnification of about 0.8, and can easily downsize the entire finder system.

(Means for solving the problem) In a finder optical system that observes a finder image that passes through a photographic lens and is formed on a finder image-forming surface, the finder image on the finder image-forming surface is connected to a field lens and the field. After passing through a first reflecting mirror that reflects the light from the lens toward the object side, a second reflecting mirror that reflects the light from the secondary imaging lens toward the optical axis side of the photographing lens by a secondary imaging lens. The light from the second reflecting mirror is re-imaged on a secondary imaging plane via a third reflecting mirror that reflects the light from the second reflecting mirror in the direction toward the image plane, and the finder image on the secondary imaging plane is transferred to the eyepiece. A light guiding means is provided for guiding a part of the finder light beam passing through a region of the reflecting surface of the first reflecting mirror to the photometric means.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment in which the finder optical system of the present invention is applied to an electronic camera.

In the figure, 1 is a photographing lens, 2 is a movable mirror that is retracted out of the photographing optical path during photographing, 3 is a shutter unit, 4 is a low-pass filter, 5 is an image sensor unit, and 6 is an electrical signal processing unit, each of these elements. This constitutes the shooting system.

Next, the imaging state of the finder image of the finder optical system having the photometry means and the photometry method in this embodiment will be described.

The light flux from the object that passes through the photographic lens 1 and is reflected by the movable member 112 is guided to a finder optical system placed above the photographic system, and an optical path correction plate 7 is installed to make the aberration equal to the spherical aberration of the photographic system. After passing, the image is formed on the finder imaging surface of the focusing plate 8, which is optically located at approximately the same position as the imaging surface.

The finder image formed on the focusing plate 8 is formed into a prism shape via a field lens or condenser lens 9, and is formed by a reflecting surface 10 at 45 degrees with respect to the photographing optical axis 1a.
After being incident on the first reflecting mirror 10 having an angle a, the light is reflected toward the object side and is incident on the secondary imaging lens 11 . The secondary imaging lens 11 includes a second reflection w112 that reflects the light from the secondary imaging lens 11 toward the optical axis of the photographing lens 1, and a second reflection w112 that reflects the light from the second reflecting mirror toward the image plane. The finder image is enlarged and re-imaged on the secondary imaging plane 14 via three reflecting mirrors. Then, the finder image, which has been enlarged and re-imaged on the secondary imaging plane 14, is observed through the eyepiece lens 15.

Incidentally, the first reflecting mirror 10 may be constructed of a simple reflecting mirror having a reflecting surface instead of having a prism shape. Also, conversely, the second
The reflecting mirror 12 and the third reflecting mirror 13 may be integrated into a prism shape.

The reflective surface 10a of the first reflective mirror 10 has a negative region that is a semi-transparent surface that allows a portion of the finder light beam to pass through.

Then, a part of the finder light beam that has passed through the semi-transparent surface 10a is guided onto the surface of the photometry means 17 via the light guide means 16 having a condensing function to perform TTL photometry. Note that the light guiding means 16 may have a deflecting effect, for example, by a reflective surface, or the light converging effect of the light guiding means 16 may be performed using a Fresnel lens in addition to a spherical lens.

The light guiding means 16 is composed of a prism body, and the first reflecting mirror 10
The reflective surface 10a is fixed to a part of the reflecting surface 10a, or is placed with a slight space between the reflective surfaces 10a and 10a.

In this embodiment, the photometering means 17 can be placed close to the focusing plate 8, directly facing the surface of the focusing plate 8, so that even a bright beam of light can be guided to the photometering means. Photometric values can be obtained.

Further, by specifying the shape, arrangement, etc. of the light guiding means 16 and the photometric means 17, it is possible to obtain an arbitrary photometric sensitivity distribution on the object side, such as center-weighted average side light.

Note that the reflecting surface 10a of the first reflecting mirror 10 may be divided in terms of area into a specular reflecting surface and a transmitting surface or a semi-transmitting surface to obtain a light beam for viewfinder image observation and a light beam for photometry.

In this embodiment, the finder image formed on the focusing plate 8 is re-imaged on the secondary imaging surface 14 by the secondary imaging lens 11 at a predetermined magnification, thereby ensuring a high field of view and a high field of view magnification. It is configured to be observed using an eyepiece.

At this time, the light beam for viewfinder image observation is transferred to the movable mirror 2, the first . Second. A total of 4 even-numbered reflections are performed by the third reflecting mirror 10°12.13 to obtain an erect finder image, and a secondary imaging method is used to invert the finder image twice to obtain the original image. By restoring the lens to a roof surface, a viewfinder image corrected in the left and right directions is obtained, making it possible to observe an erect viewfinder image corrected in the left, right, up and down directions as a whole.

Further, the exit pupil of the photographing range 1 is imaged near the entrance pupil of the secondary imaging lens 11 by the condenser lens 9, so that when the finder image is observed with the eyepiece lens 15, the entire viewfinder field of view has uniform brightness. I have to.

In this embodiment, the first. Second. Third reflector 10.12
．． 13 are arranged at an angle of 45 degrees with respect to the photographing optical axis, as shown in the figure, so that the finder light beams intersect with each other, that is, between the field lens 9 and the secondary imaging lens 11, the finder optical axis and 2 Image plane 14 and eyepiece 1
The viewfinder optical axes between the viewfinder and the viewfinder are configured so that they intersect with each other, and this allows the optical path to be reflected in a folded manner to facilitate adjustment of the optical path length and to reduce the height of the finder system. The overall size of the finder system has been made smaller by making effective use of space.

Further, a third lens is provided between the secondary imaging lens 11 and the secondary imaging surface 14.
The reflector 13 allows the optical axis of the reflected light beam to be approximately parallel to the optical axis of the photographing lens 1 so that it can be observed at any height from the horizontal direction, improving operability during photographing and viewfinder image observation. is well maintained.

In this embodiment, information is displayed within the field of view of the finder by arranging the display object near the secondary imaging plane 14, where a relatively large space can be taken up by adopting the secondary imaging method.

(Effects of the Invention) As described above, according to the present invention, the secondary imaging method is adopted as the finder optical system, each optical element is specified as described above, and the finder optical path is appropriately folded. The photometric sensitivity distribution on the subject side can be controlled arbitrarily, and the photometric system can be placed effectively in an empty space.
Moreover, high field of view and high field of view magnification can be easily obtained.
In particular, it is possible to achieve a finder optical system having a compact photometric means suitable for an eye reflex electronic camera.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment of the present invention applied to an electronic camera, Fig. 2 is a schematic diagram of a finder optical system of a conventional single-lens reflex camera, and Fig. 3 is a schematic diagram of an electronic camera using a pentagonal roof prism. FIG. 3 is a schematic diagram of the finder optical system when In the figure, 1 is a photographing lens, 2 is a movable mirror, 3 is a shutter unit, 4 is a low-pass filter, 5 is an image sensor, 6 is an electrical processing unit, 7 is an optical path correction plate, 8 is a focusing plate, 9
is a condenser lens, 10 is a first reflecting mirror, 11 is a secondary imaging lens, 12 is a second reflecting mirror, 13 is a third reflecting mirror, 1
4 is a secondary image forming surface, 15 is an eyepiece lens, 16 is a light guide means,
17 is a photometric means. Patent applicant Satoshi Canon Co., Ltd. 1 Figure

Claims (2)

[Claims] (1) In a finder optical system that observes the finder image that passes through the photographic lens and is formed on the finder image-forming surface, the finder image on the finder image-forming surface is directed to the field lens and the light from the field lens is directed to the object side. a second reflecting mirror that reflects the light from the secondary imaging lens in a direction toward the optical axis of the photographic lens after passing through the first reflecting mirror; The light is re-imaged on a secondary imaging surface through a third reflecting mirror that reflects the light from the lens in the direction toward the image surface, and the finder image on the secondary imaging surface is observed through an eyepiece. 1. A finder optical system having a photometric means, characterized in that a light guiding means is provided for guiding a part of the finder light beam passing through one region of a reflecting surface of a reflecting mirror to a photometric means. (2) The finder optical axis between the field lens and the secondary imaging lens and the finder optical axis between the secondary imaging surface and the eyepiece intersect with each other. A finder optical system comprising a photometric means according to claim 1.