JPH01227135A - finder optical system - Google Patents

Abstract

PURPOSE:To easily obtain high visual field rate and high visual field magnification and to perform miniaturization by constituting a secondary image-formation lens system of the two groups of a front group and a back group, specifying each optical element and appropriately bending a finder light path. CONSTITUTION:On a finder system observing the image from a finder on the image-focusing surface of the finder, a field lens 9, a 2nd image-focusing lens system consists of two lens groups 10a, 10b of front and behind groups, respectively, and a first reflecting mirror reflecting the light from the front group 10a to a body side, are provided. The finder images are formed again on a secondary image-formation surface 14 through the back group 10b, a 2nd reflecting mirror 12 reflecting light from the back group 10b in the direction of the light axis side of a photographing lens 1 and a 3rd reflecting mirror 13 reflecting light from the 2nd reflecting mirror 12 in the direction of an image surface side. The finder images on the secondary image-formation surface 14 are observed through an eye lens 15. Thus, the optical system of a secondary image-formation system can be obtained which has high visual field rate and high visual field magnification appropriate for an electronic camera, etc., having relatively small photographic image planes.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a finder optical system, and particularly to a finder optical system that uses a solid-state image sensor such as an eye reflex camera, an image pickup tube, or a CCD.
The present invention relates to a finder optical system suitable for TL optical type so-called electronic cameras and the like.

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

FIG. 2 shows a schematic diagram of the configuration 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, and 103
is the film surface, 104 is the focus sync screen, 1
05 is a penta roof prism, 106 is an eyepiece, 10
7 is an observation Q) pupil. The finder optical system shown in Fig. 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 0.0 when a standard lens is attached. It has superior optical performance of 8 times or more. This finder optical system has the characteristic that the entire device can be constructed relatively small.

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 CCD, 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 % inch image pickup body is about 100% smaller than that of a 35mm film in terms of diagonal length ratio, so if a conventional pentagonal roof prism was used, the optical path length would be too long, resulting in a high field of view and a high field of view. It becomes difficult to obtain the magnification.

(b) A large amount of space is required to arrange the electrical 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 1 (<. Therefore, the pupil position of the finder optical system is The structure 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 crow on the +'6f side of the image pickup body, the distance between the dividing point of the finder optical path and the image pickup surface is increased. This increases the size of the entire device.

Next, for reference, FIG. 3 shows a schematic diagram of an example of a finder optical system for achieving 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 k7
13 A dividing unit for dividing the optical path from the optical path to the finder optical system, 202 is a low bass filter, Ilter, 203
20 is a shutter unit, 204 is an imaging surface of an imaging object, and 20
5 is a package of an image pickup body in which a protective glass with an infrared cut effect is arranged on the 11η plane, 206 is a finder optical system unit including an erecting normal image system, 207 is a focusing screen, 208 is an electric processing circuit unit for image pickup signals, 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. 60-263101 and Japanese Patent Laid-Open No. 60-43628.

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 about 0.6.

Generally, the larger the field magnification γ, the easier it is to observe the finder image. Field of view magnification γ is given by γ=fθ/, where fe is the standard focal length of the photographic lens and fe is the focal length of the eyepiece lens.
It is expressed as fe. In order to increase the field magnification γ, since the focal length rafθ of the standard lens is approximately constant, it is possible to reduce the focal length fe of the eyepiece lens or configure the finder optical system with a secondary imaging system.

Field of view magnification γ of finder optical system using secondary imaging method
2 is γ2-(fθ/fe) x β2, where fe is the standard focal length of the photographing lens, fe is the focal length of the eyepiece lens, and β2 is the 48 ratio of the secondary imaging lens.

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

However, it is generally difficult to obtain a finder image with high optical performance in a secondary imaging type finder optical system because aberrations due to the eyepiece lens and aberrations from the secondary imaging lens are added. In particular, if the magnification of the secondary imaging lens is increased to increase the visual field magnification, many aberrations will 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.

(Problems to be Solved by the Invention) The present invention provides a finder optical system using a secondary imaging method that has a high field of view and a high field of view magnification, and is suitable for electronic cameras having a relatively small photographic screen. Let be [1 target.

A further object of the present invention is that the secondary imaging lens system is composed of two lens groups, a front group and a rear group, and that the imaging system is used to create a space between the front group and the rear group of the secondary imaging lens system. By placing a reflector with a predetermined inclination angle between the rear group of the secondary imaging lens system and the eyepiece, a field of view of 90% or more and a field magnification of about 0.8 can be easily obtained, and the entire finder system The object of the present invention is to provide a finder optical system that can be easily miniaturized.

(Means for solving the problem) In the finder optical system that observes the finder image that passes through the photographic lens and is formed on the finder imaging plane,
The finder image on the finder image forming plane is transferred to a field lens, and the light from the field lens is transferred to two groups, the front group and the rear group.
After passing through the front group of a secondary imaging lens system consisting of two lens groups and a first reflecting mirror that reflects the light from the front group toward the object side, the light from the rear group and the rear group are photographed. The light is re-imaged on a secondary imaging plane through a second reflecting mirror that reflects the light toward the optical axis side of the lens and a third reflecting mirror that reflects the light from the second reflecting mirror toward the image plane side. The finder image on the secondary imaging plane is observed through an eyepiece.

(Actual Mi Example) 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, l 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, and each of these elements is This constitutes the shooting system. Reference numeral 10 denotes a secondary imaging lens system, which consists of two lens groups: a front group 10a and a rear group 10b.

Next, the imaging state of the finder image of the finder optical system 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 mirror 2 is guided to a finder optical system disposed above the photographic system, and an optical path correction plate 7 is used to make the aberration equal to the spherical aberration of the wL shadow system. After passing through, an image is formed on the finder imaging plane of the focusing plate 8, which is located at approximately the same optical position as the image pickup target.

The finder image formed on the focusing plate 8-L enters the front group 10a of the secondary imaging lens system 10 via the field lens or condenser lens 9. The light incident on the front group 10a of the secondary imaging lens system is incident on the first reflecting mirror 11 and then reflected toward the object side, and then passes through the rear group 10 of the secondary imaging lens system.
incident on b. Then, the rear group 10 of the secondary imaging lens system
The light from the photographing lens 1 is reflected by the second reflecting mirror 12 which reflects the light from the lens 1 in the direction of +1' [b f11, and the third reflecting mirror which reflects the light from the second reflecting mirror in the direction toward the image plane. The finder image is enlarged and re-imaged on the image plane 14.

A viewfinder image enlarged and re-formed on the secondary imaging plane 14 is observed through the eyepiece lens 15.

In this embodiment, the first reflecting mirror 11 may be configured as a prism-shaped reflecting mirror, or the second reflecting mirror 12 and the third reflecting mirror 13 may be integrated and configured as a prism-shaped reflecting mirror. .

In this embodiment, the finder image formed on the focusing plate 8 is imaged by the secondary imaging lens system 10 at a predetermined magnification on the secondary imaging surface 14-L, thereby ensuring a high field of view and a high field of view magnification. The structure is such that the image can be observed through an eyepiece. At this time, the light beam for viewfinder image observation is transferred to the movable mirror 2. 1st゜2nd. A total of four even-numbered reflections are performed by the third reflecting mirrors 11, 12, and 13, and a finder image of a positive η image is obtained as IH+. In addition, by adopting a two-result image method, the viewfinder image is reversed twice and returned to its original state, thereby obtaining a viewfinder image that is corrected in the left and right directions without using a roof, and as a result, the left and right and up and down directions are corrected as a whole. This makes it possible to observe an erect viewfinder image.

Further, the exit pupil of the photographing lens 1 is imaged near the entrance pupil of the secondary imaging lens system 10 by the condenser lens 9, so that when the finder image is observed with the eyepiece lens 15, the brightness is uniform throughout the finder field of view. That's what I do.

In this embodiment, the first. Second. Third reflector 11.12
．． 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 beam intersects with the field lens 9 and the surface group 10a of the secondary imaging lens system. The finder optical axis between the third reflecting mirror 13 and the eyepiece lens 15 is configured to intersect with each other, for example, to be substantially perpendicular to each other. In addition to making the adjustment easier, the height of the finder system is also reduced, making effective use of space and downsizing the entire finder system.

Further, in this embodiment, the finder light beam reflected upward by the movable mirror 2 is transferred to the front group 10a of the secondary imaging lens system.
A reflecting mirror 11 disposed between the rear group 10b and the rear group 10b reflects the light toward the object side, thereby effectively correcting aberrations generated in the secondary imaging lens system, and also achieving a compact structure that keeps the height of the finder system low. ing.

Further, the optical axis of the reflected light beam is made approximately parallel to the optical axis of the photographing lens 1 by the third reflecting mirror 13 disposed between the rear group 10b of the secondary imaging lens system and the secondary imaging surface 14. This allows observation at any height from the horizontal direction, maintaining good operability during photographing and viewfinder image observation.

In this embodiment, a two-result image system is adopted for displaying information within the field of view of the finder, so that a display object can be placed near the secondary imaging plane 14, where a relatively large space can be taken up.

In this embodiment, the secondary image plane 14 is located in the finder optical axis between the field lens 9 and the front group 10a of the secondary imaging lens system, but the arrangement of the reflecting mirrors 12 and 13 is slightly different. By this change, the secondary imaging surface 14 is moved a little toward the object side, and the secondary imaging surface 14 is placed outside the finder optical axis between the field lens 9 and the front group 10a of the secondary imaging lens system. It is also possible to display information within the field of view of the finder by moving a display object and arranging a display object near the secondary imaging plane 14 at that time.

Next, numerical examples of each optical element after the focusing plate 8 of the finder optical system shown in FIG. 1 will be shown. In addition, Table 1 shows the focus plate 8.
The point on the optical axis of the finder above is taken as the origin of the X, Y coordinate system, and the numerical values on the coordinates of each element at this time are shown.

In the numerical example, Ri is the radius of curvature of the i-th optical element in the order of progression of the light beam from the focusing plate 8 side, Di is the i-th lens thickness and air gap, Ni and νi are the refractive index of the i-th optical element. This is Atsbe's number.

Number 111 example oo O, 5 (primary imaging plane) R1', +-C
o 015411.06
(Secondary imaging plane) 1+2 :l = (1) Secondary imaging magnification 1,39x Finder magnification O58x - viewing
Degrees -1 Dayopter Table 1 Note that the (X, Y) coordinates are defined as the upper direction, the positive X direction, or the positive Y direction.

(Effects of the Invention) As described above, according to the present invention, when a secondary imaging system is adopted as a finder optical system, the secondary imaging lens system is composed of two groups, a front group and a rear group, and As mentioned above, by specifying each optical element and appropriately bending the finder optical path, the viewfinder image can be observed from the horizontal direction, and the viewfinder display can be easily done because there is a large space, and it has a high field of view and a high Especially when the field of view magnification can be easily obtained.
A compact finder optical system suitable for an eye reflex electronic camera can be achieved.

[Brief explanation of the drawing]

Figure 1 shows the result when the present invention is 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 a finder optical system when a pentagonal roof prism is used in an electronic camera. 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 field lens, 10 is a secondary imaging lens system, 10a
is the front group of the secondary imaging lens system, 10b is the rear group of the secondary imaging lens system, 11 is the first reflecting mirror, 12 is the second reflecting mirror, 13 is the third reflecting mirror, and 14 is the secondary imaging lens system. The surface 15 is an eyepiece. Patent applicant Yukio Takanashi, representative of Canon Co., Ltd.
□Aoi 1 time

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 viewfinder image-forming surface, the finder image on the finder image-forming surface is used as a field lens, and the light from the field lens is combined with the front group. After passing through the front group of the secondary imaging lens system consisting of the two lens groups of the rear group and the first reflecting mirror that reflects the light from the front group toward the object side, the light from the rear group and the rear group The light is refocused onto a secondary imaging plane via a second reflecting mirror that reflects the light toward the optical axis of the photographic lens and a third reflecting mirror that reflects the light from the second reflecting mirror toward the image plane. A finder optical system characterized in that the finder image on the secondary imaging surface is observed through an eyepiece. (2) The finder optical axis between the field lens and the front group of the secondary imaging lens system and the finder optical axis between the third reflecting mirror and the eyepiece lens intersect with each other. The finder optical system according to claim 1.