JPS5827110A - Focus detector - Google Patents

Abstract

PURPOSE:To provide decreased angles in spreading of luminous fluxes, improved aberrations of a reimaging optical system, higher accuracy of detection and reduction in size by providing a transparent medium of >=1 refractive index on the reflection surface of a reimaging concave mirror roughly in tight contact therewith. CONSTITUTION:The luminous flux past a photographic lens L0 is reflected by a main mirror 12, and formes an image on a focal plate 14. The image is visible through the finder. On the other hand, the light past the mirror 12 is reflected by an auxiliary mirror 13, and forms an image on a primal focal plane F1. Further the light from said image enters a high refractive index medium 10, is reflected by a concave mirror 9, again passes through the medium 10 and forms the images respectively on the two photodetectors 15 disposed on the secondary imaging plane. If the device is arranged in the above-mentioned way, the spreading of the luminous fluxes is decreased and aberrations are suppressed over wide angles, whereby the incident luminous fluxes of large spreading are utilized, the accuracy of detection is improved and the reimaging optical system is confined in a small space.

Description

[Detailed description of the invention] The present invention relates to a focus detection device.

As prior art, the optical system of a camera focus detection device disclosed in Japanese Patent Application Laid-Open No. 54-104859 is shown in Fig. 1, and the optical system disclosed in German Patent No. 2060194 is shown in Fig. 2.
As shown in the figure.

The one in Figure 1 is the photographing lens L. The primary imaging plane F by
, the above aerial images are re-formed onto the surfaces of the detection elements 1a and 1b by the imaging lenses La and Lb, respectively, and taken by the photographing lens L. It is an optical system that forms images of light beams that pass through different parts of the exit pupil of the lens, and determines focus based on the direction and amount of relative displacement when the images are out of focus. However, the volume of this reconcentration one-zoom optical system S is too large and it is difficult to accommodate it inside the camera body. This can be made a little easier by using a concave mirror instead of a re-imaging lens to fold the light beam. A concave mirror 2a is used in the re-imaging optical system.

An example using 2b is Germany M! ″f2060194, and its outline is shown in Figure 2.

In order to be able to detect objects that are as dark as possible, it is preferable to utilize as much of the light beam that has passed through both the photographic lenses Ln as possible. If a light beam having a brightness of F is used for detection with respect to the light beam transmitted through the photographing lens Lo, the brightness of the incident side of the re-imaging optical system is naturally required to be F as well. However, if such bright F concave mirrors 3a and 3b are used, large aberrations will occur in the second f-image regardless of whether it is a spherical mirror or a 2-spheroidal mirror. This method has the disadvantage of reducing detection accuracy due to

The present invention solves this drawback and provides a focus detection device having an optical configuration that effectively utilizes the light beam formed by the photographing lens over as wide an angle as possible, that is, the light beam relating to a wide pupil area, while reducing aberrations. .

The present invention is effective not only for focus detection using the pupil division method as shown in FIG. 3, but also for detecting blur using a single concave surface as a re-imaging optical system.

Below, in order to first explain the essential part of the present invention, the re-imaging optical system is composed of one concave mirror, and the main axes of the incident light and reflected light are aligned with the optical axis of the concave mirror. , will be explained based on an example as shown in FIG.

In Figs. 4 and 5, the primary image formed by the light flux of brightness F (light flux of spread F) transmitted through the photographing lens Lo is F.
1 Formed on top.

This aerial image is again brought to the same plane F by the re-imaging concave mirrors 4 and 5 which also have brightness F on the incident side.

A secondary image is formed thereon.

In the case of FIGS. 4 and 5, regarding the secondary image formation ■2 regarding the end portion of the imaging area F of the same size,
As shown in FIG. 4, it is obvious that the aberration becomes smaller as the position of the re-imaging concave mirror 4 is further away from the position of the surface F, but the volume occupied by the re-imaging optical system increases greatly. -It becomes impossible to accommodate it in the body of an eye reflex camera.

On the other hand, when the lens is made compact as shown in FIG. 5, aberrations become too large to be practical.

The principle of the present invention is as shown in FIG.
The space from the focal plane F of By providing almost in close contact with the reflecting surface, the angle of spread of the light beam reaching the re-imaging concave mirror 6 is reduced to 1 when the spread of the imaging light beam of the photographing lens is F, and the re-imaging concave mirror 6 By setting the required brightness on the incident side to nXF, the aberration of the re-imaging optical system is improved and the system is made more compact.

That is, in FIGS. 4 and 6, the radius of curvature of the mirror surface 4.6 is the same, the distance at the image plane is also the same, and the taking lens L6
The size of the luminous flux used for both is the same, but in the case of Fig. 6, only a narrow area close to the width of the mirror surface 6 is used, so it is much more advantageous in terms of aberrations than in Fig. 4. The occupied volume is also decreasing.

It is easily explained by Figure 7 that even if the primary imaging plane is separated into regions with different refractive indexes as a boundary, the presence of such an interface does not worsen aberrations. . That is, the refractive index of the transparent medium for two different wavelengths A and H is nA and nB, respectively.

When a ray enters the optical axis center (5) C of the primary imaging plane F at an incident angle ψ, the refraction angle θ after entering the medium is
θ8 is given by sin ψ= ”A sin 01 81n 9+ =nB l1InθB, and since it is θ Nθ6, it causes chromatic aberration, but in the case of this figure, the incident point C is at the 70 curvature of the concave mirror. When C is at the center of This has great effects on aberration improvement and compactness.

Furthermore, a case where the boundary between air and a high refractive index medium is more general will be explained with reference to FIG.

It is assumed that the region up to the front length L of the concave surface 8 is filled with a high refractive index medium (refractive index n).

The figure shows different wavelengths A and H incident on the medium surface at height h.
This figure shows a state in which a ray of light enters the medium on a line that passes exactly through the center of curvature 0 of the concave mirror 8 (radius of curvature R), and is reflected along the same line and returns (6). At this time, the point where the incident light beam and the reflected light beam cross the optical axis in the air is generally different because there is dispersion in the medium, and that point is A.

Represented by B. At this time, the length from the medium surface to point A is 1.
Let the difference (chromatic aberration) between point A and point B be dl. Also, θ and ψ
When is defined as shown in the figure, ψ=h/1. θ=
h/(R-L).

nθ=ψ holds, and dl=(RL)Xdn/n2 is obtained. Here, n is the refractive index at the wavelengths A and B (which are approximately equal), and dn is the difference in the refractive index at both wavelengths. In reality, since the starting points of both rays are considered to be the same, the chromatic aberration in the axial direction at the image plane in that case is approximately 2 dl.

Therefore, as long as the chromatic aberration 2dl = 2(RL) A space is provided between the first point surface F and the surface 10a provided on the front surface of the concave mirror 9 that becomes the high refractive index medium 10, as shown in the figure, so that the light beam reaching the film surface 11 will not be lost. It is also possible.

This example will now be explained.

When the main mirror 12 and the auxiliary mirror 13 are in the positions shown, one of the light beams passing through the photographic lens Lo is reflected by the main mirror 12 and forms an image on the focus plate 14, which can be seen through the finder. , the other one passes through the main mirror 12 and is reflected by the auxiliary mirror 13 to a primary focus of 100F.

Further, light from this image enters a high refractive index medium 10, is reflected by a concave mirror 9, passes through the high refractive index medium 10 again, and reaches a light receiving element 15 such as a one-dimensional photo array. This concave mirror 9 is formed by applying a reflective coating to a high refractive index medium.

At this time, the concave mirror 9 is divided into two parts, and the reflecting surfaces of each part are tilted slightly to each other, and two parts are placed on the secondary imaging plane.
The images are focused on two light receiving elements 15, respectively. This embodiment employs a pupil division method, and is provided with two concave mirrors and two light-receiving elements with different reflection directions. Next, the main mirror 12 and the auxiliary mirror 13 are the photographing lens L. When the light beam reaches the film surface 11 from the first point surface F l +the film surface 11 and the focus plate 14 are removed from the lens L. Since this is an optically conjugate surface, this light beam forms an image on the film surface 11. Returning to the explanation of how to set up the high refractive index medium, as shown in FIG.
It is also possible to provide a diaphragm or the like here immediately before.

However, the gap 1 that is not filled with this high refractive index medium
When 8 starts from the surface of reflective surface 19 as in FIG. 11, it does not produce any of the effects of the invention described previously. In this case, the aberrations are almost the same as in Fig. 12 (i.e., Fig. 5),
The presence of the high refractive index block 20 merely extends the optical path a little. In addition, even when the lens 21 is used in a reconcentration one-quadrant optical system as shown in FIG. 13, filling the optical path midway with blocks 22m and 22b of high refractive index medium simply lengthens the optical path and particularly reduces aberrations. There is no improvement effect. That is, in order for the effects of the present invention to be recognized, the refocusing one-quadrant optical system is constituted by a reflecting mirror, and the area from the surface of the reflecting mirror to the vicinity of the primary imaging plane is filled with a high refractive index medium. need something.

Now, before touching on a further specific example of the present invention that employs a pupil division type re-imaging optical system, a brief explanation will be given of the reflective optical system. First, in order to prevent the primary image plane and the two secondary image planes from overlapping, it is necessary to tilt the optical axes of the reflective optical system little by little with respect to each other as shown in FIG. In this case, when the primary image plane F and the two secondary image planes F2a+F2b are close, the reflecting surface can be a spherical surface, but the reflecting surface is the surface F1 and one surface Fta (or the surface F, and the other surface Fta). Face F
It is more effective to make tb) a spheroidal surface having two foci. In the case of Fig. 14, the spheroidal mirrors 23a and 23b, which have two focal points at surfaces F and F and a (or Ftb), are divided into two halves and arranged with their optical axes tilted to each other. be.

Re-imaging optical system using concave mirror for pupil division (Figure 14)
A specific example of a configuration to which the conditions of the present invention are applied is shown in FIG. 15 and subsequent figures.

FIGS. 15(a), 15(b), and 15(c) are a side view, a front view, and a plan view, respectively.

An entrance slit 24 is provided on the primary imaging surface F to remove unnecessary light except for the necessary portion, and an angular imaging optical system filled with a high refractive index medium is configured around this slit 24. do. The light beam has its spread narrowed to nF, travels through a high refractive index medium, is divided into pupils by reflecting mirrors 25a and 25b whose axes are tilted to each other, and is reflected and converged. F.

re-image.

FIG. 16 is a plan view of a modified example of FIG. Surface 27 a
+27 b is provided. Figure 17 shows the reflecting mirror 28.
This is the case when the two reimaging directions by a and 28b are arranged symmetrically with respect to the incident light, and the reflecting mirror 28a.

The light reflected by 28b is reflected by a reflection surface 29a of a high refractive index medium,
It is further reflected by 29b and reimaged through lenses 30a and 30b. FIG. 18 is a modification of FIG. 17, and 1
The light from the next image formation 11 is reflected by the reflection surface 31, reflection fi 32a, 3
2b and reflecting surfaces 33a and 33b to form secondary condensation I.
Make 2.

FIG. 19 shows a case where the main axes of the incident light and the reflected light on the concave surfaces @34a and 34b are made as close to parallel as possible, and the separation of the two is performed by a half mirror 35.

The above is an example of a case where the pupil is divided into two, but it is also possible to use a configuration as shown in Figure 20 to divide the pupil into four, thereby making it possible to detect pattern changes in the vertical direction as well. It is. The vertically elongated detection zone on the first fixed point plane F is imaged by the reflective surface 36a on the secondary imaging plane F2a, and similarly by the reflective surface 36b on the secondary imaging plane Ftb, and the first
The horizontally elongated detection zone above the point plane F is imaged by the reflective surface 36a on the secondary imaging plane F2o, and by the reflective surface 36d on the secondary imaging plane F2d. Focus detection is performed whenever the relative displacement of the images on the secondary imaging planes Fza and F2b or the relative displacement of the image on the secondary imaging plane FtcF2d is detected.

In addition, in the embodiment shown in FIG. 21, the primary imaging plane F,
In the vicinity of , there is a reimaging concave mirror surface 37a.

37b and the pupil plane of the photographic lens) is provided with a field lens 38 having a curvature such as Y-f to compensate for the symmetry of the illuminance distribution of the image due to pupil division, and further to the light-receiving element surface 39a.

A concave lens (or concave cylindrical lens) 40 a + 40 b is provided in front of the second image forming surface where the concave mirror 39b is located to correct field distortion that cannot be corrected by the concave mirrors 3γa and 37b alone. However, in a part of the high refractive index medium 41, the first
Next imaging plane F.

An embedded mirror 42 is provided to reflect one beam of light incident thereon toward the concave mirrors 37a and 37b.

By the way, in the above, one end of the high refractive index medium (glass material) may be formed into a spherical shape with a predetermined curvature, and aluminum or the like may be deposited thereon to form an integrated concave mirror, but it is also possible to make the concave mirror and the high refractive index medium separate. They can also be joined together. At this time, it is not necessary to make the curvature of one end of the high refractive index medium and the curvature of the concave mirror joined to it exactly match, but to make them almost equal so that there is a slight difference between the reflective surface of the concave mirror and the high refractive index medium. Even if a gap occurs, the effects of the present invention can be sufficiently achieved.

As described above, according to the present invention, by suppressing aberrations over a wide angle when re-imaging the incident light beam from the photographing lens, it is possible to effectively utilize the wide-spread incident light beam. Not only does it have the advantage of improving accuracy and enabling focus detection even on dark objects, but it also suppresses the spread of the light beam to 1 and folds the light beam multiple times, making it possible to integrate the re-imaging optical system in a small space. This allows it to be mounted on the camera body.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams for explaining the prior art and its drawbacks, Figures 4 to 8 are diagrams for explaining the present invention in detail, and Figure 9 is a diagram for explaining the principle of the present invention as well as the present invention. 10 to 14 are diagrams illustrating an example in which the method is applied to focus detection of a camera.
The figure is a diagram for explaining the present invention in detail, and FIG. 15 is a front and side view of one embodiment according to the present invention. 16 is a plan view of a modification of the embodiment shown in FIG. 15, FIG. 17 is a front view and a top view of the embodiment, and FIG. 18 is a modification of the embodiment shown in FIG. 17. FIG. 19 is a diagram showing a front view and a plane view of an embodiment. FIG. 20 is a diagram showing an example in which the pupil is divided into four parts. FIG. 21 is a diagram showing a front view of an example embodiment. It is a figure showing a plane. [Explanation of symbols of main parts] Concave mirror 9, 25a, 25b, 28m, 28b. 32a, 32b, 34m, 34b. 36a to 36d, 37a, 37b (15) Photo-receiving element 15.39a, asb Transparent medium...10.41 Applicant: Nippon Kogaku Kogyo Co., Ltd. Agent
: Masa Okabe, Yuyasu I, Yuki Kuribayashi, Mitsui Kami, Yuzan 1) Takashi - Hiroshi Kuramochi (16) Ward Ward Figure 47 Ward Ward Ward

Claims (1)

[Claims] An optical system capable of forming an image of an object whose focus is to be detected on a first image forming plane; and a concave mirror that refocuses the image of the first image forming plane on a second image forming plane. ; a light-receiving element disposed on the second imaging plane;
A focus detection device for detecting a focus according to an output signal of the light receiving element, characterized in that a transparent medium having a refractive index of 1 or more is provided in substantially close contact with the reflective surface of the concave mirror.