JPH01134440A - Finder optical system - Google Patents

Abstract

PURPOSE:To obtain high visual field magnification by specifying an optical element and bending a finder optical path properly. CONSTITUTION:A prism 11 is a parallelogram shape having two reflecting surfaces and is so set as to have optical path length nearly equal to the total optical path length of the two-luminous-flux separating prism 100 and filter member 9 (10) of a photography equal distance from the image pickup surface of an image pickup element unit 7 (8). Luminous flux from a 1st finder image formed on the surface of the focus plate 12 passes through a field lens 13 and reflected by a reflecting surface 14 so that the optical axis of the reflected luminous flux is parallel to an optical axis of photography, thereby forming an enlarged image of the 1st finder image as a secondary finder image on a secondary image formation surface 16 through a secondary image formation system 15. Then the secondary finder image is observed at the position of an eye point 18 through an ocular 17. Consequently, the finder system has high visual field magnification by using the secondary image formation system.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a finder optical system, and in particular to a so-called electronic camera of TTL optical type that electrically obtains a still image using an image pickup tube or a solid-state image sensor such as a CCD. The present invention relates to a finder optical system suitable for.

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

FIG. 3 shows a schematic diagram of the configuration of a finder optical system of a typical single-lens reflex camera. In the same figure, +01 is a rotatable total reflection mirror, 102 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, 10
7 is a pupil for observation.

The finder optical system shown in Fig. 3 has a ratio of the screen photographed 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.

However, if the aforementioned penta roof prism is used in the finder optical system of recent two-panel or three-panel electronic cameras that use multiple imaging bodies such as so-called CCDs, it is possible to achieve field of view and field magnification comparable to that of conventional single-lens reflex cameras. difficult to obtain. 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 35 mm film.
If a conventional pentagonal roof prism is used, the optical path length is too long, making it difficult to obtain a high field of view and a high field of view magnification.

(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 in front of the imaging body to arrange optical components such as a resolving prism that separates the light beam into multiple beams, a low-pass filter, an infrared cut filter, and a protective glass, the dividing point of the finder optical path is required. This requires a large distance between the image pickup surface and the imaging surface, resulting in an increase in the size of the entire device.

Next, for reference, Figure 4 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 penta roof prism in a two-panel electronic camera.
As shown in the figure. 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 an imaging surface of an imaging object, and 205
206 is a finder optical system unit including an erecting image system; 207 is a focusing screen; 208 is an electrical processing circuit unit for image pickup signals;
9 is a pupil for observation.

Further, 204a is another imaging surface, and 210 and 211 are decomposition prisms that decompose the photographic light flux into images.

Generally, the larger the field magnification γ, the easier it is to observe the finder image. The field magnification γ is the standard focal length of the photographic lens, fe, and the focal length of the eyepiece lens is fe, then γ=fθ/
It is expressed as fe. In order to increase the field magnification γ, it is necessary to decrease the focal length fe of the eyepiece since the focal ratio @fθ of the standard lens is approximately constant.

The eyepiece lens is arranged so that its front focal point is located near the finder imaging plane of the finder optical system.
In order to increase the field magnification γ, it is necessary to make the optical path length of the optical system for obtaining an erect image from the focusing screen to the eyepiece as short as possible.

However, as mentioned above, in the case of electronic cameras, units such as infrared cut filters, low-pass filters, and electrical processing circuits that electrically process image information must be placed before and after 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 closer to the object side (forward), and also to shift the observation position further to the rear.

Therefore, if the viewfinder image on the focusing plate of the photographic lens is directly observed with the eyepiece, the focal length of the eyepiece must be made longer, and the field of view magnification becomes smaller, making it difficult to observe. . For example, Japanese Patent Laid-Open No. 60-4:1628 proposes an attempt to further shorten the focal length of the eyepiece, but even so,
The viewfinder magnification is limited to about 0.5x.

(Problems to be Solved by the Invention) The present invention is characterized in that it provides a finder optical system having a high field of view and a high field of view magnification suitable for electronic cameras having a relatively small photographic screen. In this case, a secondary imaging system is used in the finder system to obtain a high field of view magnification, and when this secondary imaging system is used, the height of the finder optical system can be lowered, making the camera housing more compact. A further object of the present invention is to provide a finder optical system capable of observing an erect image.

(Means for solving the problem) The light beam passing through the photographing lens causes a first image to be formed on the primary image plane.
forming a second finder image based on the first finder image on a second image forming plane by a second imaging system, and transmitting the second finder image through an eyepiece. When observing, the light beam passing through the photographing lens is guided to the eyepiece lens after passing through four reflecting mirrors including at least one reflecting mirror that reflects the incident light beam toward the object side. be.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment in which the finder optical system of the present invention is applied to a so-called two-panel electronic camera having two image pickup elements.

In the figure, 1 is a photographing lens, 2 is a movable mirror that retreats outside the photographic optical path during photographing and reflects the light beam 90 degrees upward, and 3 is a 2
The front prism 4 of the beam splitting prism 100 is 2
This is the rear prism of the beam splitting prism 100. 4a is a half mirror surface which separates the incident light beam into two light beams, and is provided on either the front prism 3 or the rear prism 4. 5.6 is the shutter unit,
9゜10 is a filter member such as a low-pass filter, 7
．． Reference numeral 8 represents an image sensor unit consisting of a CCD, and reference numeral 19 represents an electrical signal processing unit.

Next, the imaging state of the finder image of the finder optical system in this embodiment will be described.

A light flux from an object that passes through the photographic lens 1 and is reflected by the movable w1.2 is guided to a prism 11 that is part of a finder optical system disposed above the photographic system.

The light beam incident on the entrance surface 11a of the prism 11 is reflected on the reflection surface 1.
1b toward the object side approximately parallel to the photographing optical axis, and the reflection surface 11
After being reflected approximately perpendicularly to the photographing optical axis by c, the exit surface li
The light is emitted from point d in a direction substantially perpendicular to the photographing optical axis. A first finder image is formed on the focusing plate 12, which is the primary imaging surface.

In this embodiment, the prism 11 has a parallelogram shape with two reflecting surfaces, and the two-beam splitting prism 10 of the photographing system
0 and the filter member 9 (10).

Further, the focusing plate 12 is arranged at an optically equal distance from the imaging surface of the imaging element unit 7 (8).

The light beam from the first finder image formed on the surface of the focusing plate 12 passes through the field lens 13, and is reflected by the reflecting surface 14 so that the optical axis is approximately parallel to the photographing optical axis. A secondary imaging system 15 forms an enlarged image of the first finder image on a secondary imaging plane 16 as a secondary finder image. The second viewfinder image is observed from the eyepoint 18 through the eyepiece 17.

Generally, in a finder system of the primary imaging method, in which the finder image is observed directly on the focusing plate, which is the primary imaging plane, using an eyepiece, a prism with a roof surface is used to reverse the horizontal direction and create an erect image. need to be formed.

However, as in this embodiment, the first
When the secondary imaging plane is re-imaged onto the secondary imaging plane by the secondary imaging system, after an even number of reflections are performed a total of 4 times including the movable mirror, the secondary imaging plane is observed through the eyepiece lens. In the imaging method, the left-right direction returns to its original state by reversing when imaging is performed twice.

Therefore, this embodiment has the advantage that it is not necessary to use complicated and expensive optical members such as a roof surface or a pentaprism, and the finder optical system can be easily simplified.

In this embodiment, the light beam incident on the prism 11 is reflected by the reflective surface 11b toward the object side so as to be substantially parallel to the photographing optical axis, making it easy to adjust the optical path length, and also to reduce the height of the finder system. The aim is to reduce the size of the entire finder system by lowering the angle of view.

FIG. 2 is a schematic diagram showing a specific configuration of one embodiment of each optical element after the focusing plate 12 shown in FIG. 1, developed along the finder optical axis. Elements on the right side of the figure that are the same as those shown in FIG. 1 are given the same reference numerals.

Next, Table 1 shows numerical examples of each optical element after the focusing plate 12 shown in FIG. 2.

In the numerical example, Ri is the radius of curvature of the first optical element in the order of progression of the light beam from the focusing plate 12 side, Di is the thickness and air gap of the i-th lens, and Ni.

νi are the refractive index and Abbe number of the i-th optical element.

Table-1 R13-Secondary imaging plane 013-26.44 old 4-
76.07 014-3.40 N7-1.
69680 v 7-55.5R15--36,4
7015-0,15RI6-2:1.46
D16=3.20 N8-1.60311v
8-60.7817-163.09 017
0.15R18 self 13.36 DlB-5,
70N9-1.60311 v 9-60. July 9
= -49,85019-1,00Nl0=1.728
25 v lo-28, 5R20-9, 36020 1
8.00 R21-Eye point field lens f=38.72 Secondary imaging system f=20 Eyepiece f=20.52 Secondary imaging magnification 1.25 times (effects of the invention) As described above, the present invention According to , when adopting a secondary imaging method as a finder optical system, by specifying each optical element as described above and appropriately bending the finder optical path, a high field of view rate and high field magnification can be easily obtained. - A compact finder optical system suitable for eye reflex electronic cameras can be achieved.

In addition, by appropriately bending the optical path as a whole through four reflections, there is the effect of making a high-magnification finder compact, and in particular, it is possible to downsize the camera without taking up much height.

In addition, the optical axis of the eyepiece lens system is approximately parallel to the optical axis of the photographic lens system, and is located almost directly above the optical axis of the photographic lens system, and the distance from the optical axis of the photographic lens system is also the same as that of the 35 mm version. It is located at the same distance as an eye reflex camera, making it easier to operate.

In addition, in the case of primary image formation, the display in the finder requires the display member to be placed near the primary image formation surface, which limits the display range. It has the advantage that a display member can be placed near the next imaging plane.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment in which the present invention is applied to an electronic camera, and FIG. 2 is a schematic diagram of an embodiment in which the specific configuration of a portion of FIG. 1 is developed along the viewfinder optical axis. 3 is a schematic diagram of a finder optical system of a conventional single-lens reflex camera, and FIG. 4 is a schematic diagram of a finder optical system when a pentagonal roof prism is used in a two-panel electronic camera. In the figure, 1 is a photographic lens, 2 is a movable mirror, 100 is a two-beam splitting prism, 3 is a front prism, 4 is a rear prism, and 5
．． 6 is a shutter unit, 9°lO is a filter member, 7.8 is an image sensor unit, 19 is an electrical processing unit, 11 is a prism, 12 is a focusing plate, 13 is a field lens, 14 is a reflecting mirror, 15 is a second The secondary imaging system includes a secondary imaging surface 16 and an eyepiece lens 17. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] The light beam passing through the photographic lens forms a first image on the primary image plane.
forming a second finder image based on the first finder image on a second image forming plane by a second imaging system, and transmitting the second finder image through an eyepiece. When observing, the light beam passing through the photographing lens is guided to the eyepiece lens after passing through four reflecting mirrors including at least one reflecting mirror that reflects the incident light beam toward the object side. Features a finder optical system.