JPS6115105A - Finder optical system - Google Patents

Abstract

PURPOSE:To constitute a small-sized finder optical system having a high visual field rate and a high visual field magnification with respect to an electronic camera, too, by combining and using three prisms having a specified shape. CONSTITUTION:Three prisms 10, 11 and 12 are combined and used for a finder optical system. The first prism 10 consists of an incident surface S1. a reflecting surface S2 and an emitting S3, the second prism 11 consists of an incident surface S4, a reflecting surface S5 and an emitting surface S6, and the third prism 12 is constituted of an incident surface S7, a reflecting surface 9, and a roof surface S'88 consisting of two reflecting surfaces S8, S'8. In this way, a small-sized finder optical system of >=90% visual field rate and 0.5 visual field magnification can be formed with respect to an electronic camera whose effective picture is comparatively small, too, by setting appropriately an optical path length and an optical arrangement of the finder optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder optical system, and particularly to a finder optical system suitable for an eye reflex camera, a TTL optical type so-called electronic camera using a solid-state image sensor such as an image pickup tube, or a COD. It is.

Conventionally, single-lens reflex cameras using a pentagonal roof prism for 35fIs1 film have been greatly developed as optimal for system development.

FIG. 1 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 10
3 is the film surface, 104 is the focusing screen,
105 is a penta roof prism, 106 is an eyepiece, 1
07 is a pupil for observation. The finder optical system shown in Figure 1 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%.
Above, the visual field magnification γ when wearing the standard lens is 0.8
It has optical performance that is more than twice as good. This finder optical system has a feature that the entire device can be configured to be relatively small.

However, recently, when the above-mentioned penta roof prism is used in the finder optical system of an electronic camera using an image pickup body such as 1 ccn, it is difficult to obtain a field of view ratio and field magnification comparable to that of a conventional single-lens reflex camera. Furthermore, it becomes difficult to downsize the entire device. This is due to the following reasons.

(1') For example, the effective screen of a 273-inch image pickup body is about 1/4 smaller in diagonal length ratio than that of a 35mm film, so if a conventional pentagonal roof prism was used, the optical path length would be too long, resulting in a high field of view. It becomes difficult to obtain high field of view magnification and 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.

←In order to make the photographic lens telecentric for color separation of the image pickup object, the effective light beam from the photographic lens is spread out greatly at the part where the finder optical path is divided, and the reflecting mirror becomes larger.

2) Since a large amount of space is required to place optical components such as a low-pass filter, infrared cut filter, and protective glass in front of the image pickup body, the distance between the dividing point of the finder optical path and the image pickup surface must be large. First, the entire device becomes larger.

Next, for reference, FIG. 2 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 N1 effective protective glass! 206 is a finder optical unit including an erecting image system; 207 is a focusing screen; 208 is an electrical processing circuit unit for imaging signals; 209
are eyes for observation.

Generally, the larger the field magnification γ, the easier it is to observe the finder image. The field magnification γ is γ-fθ, where the standard focal length of the photographing lens is fθ, and the focal length of the eyepiece is f6.
It is represented by /fe. In order to increase the field of view magnification γ,
Since the focal length [fθ] of the standard lens is approximately constant, it is necessary to reduce the focal length fe of the eyepiece. The eyepiece is arranged so that its front focal point is located near the viewfinder imaging plane of the finder optical system, so in order to increase the field magnification γ, it is necessary to obtain an erect image from the focusing screen to the eyepiece. It is necessary to make the optical path length of the optical system as short as possible. For now, focal length f
If θ is set to fθ-125 so that it corresponds to a standard lens for a 2/3-inch image pickup body, and field magnification γ is set to γ-0.5, the focal length fe becomes f6-2511111.

In addition, in order to obtain a high field of view, it is necessary to have a focusing screen that is about the same size as the effective m-shadow screen, and an erect image system that is large enough to establish an optical path that allows sufficient observation of the focusing screen. Requires.

Therefore, in Fig. 2, in order to obtain a field of view ratio of 90% or more and a field magnification of γ-0.5 or more, first, the optical path length from the focusing screen to the front principal point of the eyepiece is called the focal length of the eyepiece. It is necessary to make the lenses equally 25 and 25, and to configure the lens so that enough light from the focusing screen enters the eyepiece. Although a pentagonal roof prism that satisfies such requirements may exist,
As shown in the figure, a pentagonal roof prism 210 is arranged at the forefront of the finder unit 206, and the eyepiece lens 21
1 must be placed on the exit surface of the pentagonal roof prism 210 in a shielded manner. On the other hand, the observation pupil 209 needs to be located behind the rear end of the camera and far away from the eyepiece 211.

However, since the position of the pupil is approximately the focal length from the rear principal point of the eyepiece, as shown in FIG. It becomes necessary to take a long principal point interval. This is extremely difficult.

As described above, in a finder optical system of an electronic camera or the like with a relatively small effective screen, it becomes extremely difficult to achieve a high field of view and high field of view magnification when a pentagonal roof prism is used in terms of optical performance.

An object of the present invention is to provide a finder optical system having a high field of view and a high field of view magnification suitable for electronic cameras and the like having a relatively small photographic screen.

A further object of the present invention is to have a visual field ratio of 90% or more and a visual field magnification of 0.
．． The objective is to provide a finder optical system as small as 5.

The main feature of the finder optical system for achieving the object of the present invention is that the light beam from the object that has passed through the photographing system is reflected by a reflecting mirror and formed into an image on the focusing screen surface, and then the light beam from the focusing screen surface is reflected. The light flux from the incident surface S4 is passed through a first prism having an incident surface S1 for making the light incident thereon, a reflecting surface S2, and an exit surface SS for making the light beam incident thereon, and an incident surface S4 for making the light beam from the above-mentioned emission surface sS incident thereon. A second prism having a reflection surface SS for reflecting away from the optical axis of the imaging system and an exit surface S6, and an entrance surface S7 and the entrance surface for allowing the light beam from the exit surface S6 to enter. Reflective surface $9 on the same plane as S7
and two reflective surfaces s8. for reflecting the light flux from the incident surface S7 toward the reflective surface S9. Observe the finder image on the focusing screen surface through the eyepiece after passing through a third prism having a roof surface 888' consisting of s8' and an exit surface S10 for emitting the light beam from the reflecting surface S9. That's what I did.

In this way, in the present invention, 6
By combining two prisms, a compact finder optical system with high field of view and high field of view magnification is achieved.

In particular, the above objective is achieved by arranging a focusing screen near the entrance surface S1 of the first prism and appropriately setting the optical path length and optical arrangement of the finder optical system.

Next, one embodiment of the finder optical system of the present invention will be described with reference to each drawing.

FIG. 3 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 photographic lens, 2 is a movable mirror that is retracted from the photographic optical path during photographing, 6 is a low-pass filter, 4 is a shutter unit, 5 is a protective glass for the photographic object, 6 is an imaging surface, and 7 is the package for the photographic object. It is. The light beam from the object that passes through the photographic lens 1 and is reflected by the movable mirror 2 passes through an optical path correction plate 8 to make the aberration equal to the spherical aberration of the photographing system, and is brought to a position optically approximately equal to the imaging surface 6. An image is formed on a certain focusing screen 9. The finder image formed on the focusing screen 9 enters the entrance surface S1 of the first prism 10, is reflected by the reflection surface S2 substantially parallel to the optical axis of the photographing system, and then exits from the exit surface SS.

Then, the light enters through the entrance surface S4 of the second prism 11, is reflected by the reflection surface SS in a direction away from the optical axis of the imaging system, and exits from the exit surface S6. Then, it enters the entrance surface S7 of the third prism 12, and the two reflection surfaces s8. The light is reflected by a roof surface 888' formed by s8', reflected by a reflecting surface S9 which is substantially on the same plane as the incident surface S7 in a direction substantially parallel to the optical axis of the photographing system, and then exits from an exit surface S10. The light then enters the eyepiece lens 13 and is observed at 1i114.

Figure 4 shows the first part of Figure 3. Second. A perspective view of a third prism is shown.

In this embodiment, an inverted viewfinder image is formed on the focusing screen 9, and the reflecting surface SS of the second prism 11 and the roof surface 8 of the third prism 12 are formed on the focusing screen 9.
88' and the reflective surface S9 to invert the viewfinder image vertically and horizontally, thereby obtaining an upright, authentic viewfinder image as a whole.

In this embodiment, the reflective surface S2. S.S. S9 may utilize total reflection, or may utilize specular reflection by depositing a reflective film.

In this embodiment, the light beam is reflected by the first prism 100 reflecting surface S2 substantially parallel to the optical axis of the photographic lens 1, and the third prism
Similarly, the reflective surface S9 of the prism 12 reflects the light beam substantially parallel to the optical axis of the photographic lens, thereby reducing the size of the finder optical system. Here, "substantially parallel" means that the light beam passes through the optical axis of the photographic lens 1 within ±10°.

In this embodiment, in order to further downsize the entire finder optical system, the entrance surface S1 of the first prism 10 is made approximately parallel to the optical axis of the photographing lens 1, and the exit surface of the third prism 12 is It is preferable to configure the SiO so as to be substantially perpendicular to the optical axis of the photographic lens 1.

In this embodiment, the focusing screen 9 is arranged near the entrance surface S1 of the first prism 10, and the focusing screen 9 is arranged in the vicinity of the entrance surface S1 of the first prism 10, Third
By setting the shapes of the prisms 10, 11, and 12 as described above, the optical path length from the focusing screen 9 to the eyepiece 16 can be shortened, making it possible to use an eyepiece with a short focal length and achieving a high field of view magnification. The viewfinder image is obtained.

For example, in this embodiment, the effective screen of the imaging surface 6 is set to 2.
/3 inches, the 1st. Second. Third prism 10
, 11.12 can be made less than 25 by setting the refractive index of the prism to 1.834, so by using a photographing lens with a focal length of 12.5 m, the visual magnification γ can be reduced to γ〉 05.

In this embodiment, a first prism 10, a second prism 11. The second prism 11 and the third prism 12 may be attached to each other, or they may be separated from each other since the optical performance will not deteriorate as long as the air spacing is about D, 05 to Q, 2 mm. Also, the first, second... The filter prism may be integrally formed by plastic molding.

In this embodiment, the first. Second. Third prism 10°11.
By filling the finder optical path with as much glass as possible using the 12, it is possible to shorten the optical path length of the finder optical system and downsize the entire finder optical system, and to obtain a finder image with a high field of view, for example, 09 or higher. There is.

In this embodiment, instead of the focusing screen 9, the entrance surface S1 of the first prism 10 may be used as a focusing screen by, for example, being sanded.

Second. The shapes of the third prisms 11 and 12 are configured so that a space is created in the middle when they are combined as shown in FIG.
Utilizing these spaces, for example, a rotary shutter unit or the like is installed to reduce the size of the entire camera. Further, the reflected light from the reflective surface S2 of the first prism 10 is not reflected by the reflective surface SS of the second prism 11 and is prevented from directly entering the eyepiece 16, thereby preventing the generation of ghost images.

In this embodiment, the exit surface S1 of the third prism 12
It is preferable to cut off lines other than the zero effective line because the prism can be made smaller.

As described above, according to the present invention, it is possible to construct a compact finder optical system having a high field of view and a high field of view magnification. In particular, the present invention has a high field of view and high field of view magnification in electronic cameras with relatively small effective screens, and moreover, the space behind the camera can be used efficiently, so the overall size of the camera can be reduced. can be easily achieved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a part of the optical system of a conventional single-lens reflex camera, Fig. 2 is a schematic diagram of a part of the optical system when a pentagonal roof prism is used in a multiple lens camera, and Fig. 3 is a schematic diagram of a part of the optical system of a conventional single-lens reflex camera. An explanatory diagram of the optical system, FIG. 4 is a perspective view of a part of FIG. 3. In the figure, 1 is a photographing lens, 2 is a movable mirror, 6 is a low-pass filter, 4 is a shutter unit, 5 is a protective glass, 6
is the imaging surface, 7 is the bagage of the object to be photographed, 10, 11.12
are the first. Second. A third prism, 9 a focusing screen, 13 an eyepiece, and 14 a pupil position.

Claims (4)

[Claims] (1) After the light beam from the object that has passed through the photographing system is reflected by a reflecting mirror and formed into an image on the focusing screen surface, an incident surface S_1 and a reflection surface S_2 are used to make the light beam from the focusing screen surface enter. an entrance surface S_4 for allowing the light beam from the exit surface S_3 to pass through a first prism having a surface S_3, and the entrance surface S_
an entrance surface for allowing the light flux from the exit surface S_6 to pass through a second prism having a reflection surface S_S_ for reflecting the light flux from 4 in a direction away from the optical axis of the imaging system and an exit surface S_6; S_7, a reflecting surface S_9 on the same plane as the incident surface S_7, and a roof surface S_8_8' consisting of two reflecting surfaces S_8 and S_8' for reflecting the light beam from the incident surface S_7 toward the reflecting surface S_9; Exit surface S_1 for emitting the luminous flux from the reflective surface S_9
A finder optical system, characterized in that the finder image on the focusing screen surface is observed through a rear eyepiece after passing through a third prism having a diameter of _0. (2) The finder optical system according to claim 1, wherein the reflecting surface S_2 is set at an angle that reflects the light beam from the incident surface S_1 substantially parallel to the optical axis of the photographing system. system. (3) The finder according to claim 2, wherein the reflecting surface S_9 is set at an angle to reflect the light beam from the roof surface S_8_8' substantially parallel to the optical axis of the photographing system. Optical system. (4) The incident surface S_1 is configured to be approximately parallel to the optical axis of the imaging system, and the exit surface S_1_0 is configured to be approximately perpendicular to the optical axis of the imaging system. Finder optical system.