JPS58221814A - Focus detector - Google Patents

Abstract

PURPOSE:To improve the accuracy of focus detection by using prism arrays having a minute critical angle for the pupil splitting means of an imaging optical system and detecting the transverse deviation of the images on the intended imaging plane which arises with the deviation in the focus of the imaging optical system. CONSTITUTION:Two prism arrays 6A and 6B having a minute critical angle have the same construction but have the reflection surfaces of the critical angle which incline in opposite directions; therefore, the split pupil images of an imaging optical system are projected on the respective photodetector arrays 7A, 7B disposed on the intended imaging plane of said imaging optical system and the directions of the transverse deviation of said images are opposite in direction. Since the arrays 7A, 7B arranged on a substrate 11 permit the substantial reduction in the pitch between the photodetectors, the output distribution signals corresponding to the respective split pupil images of the imaging optical system obtained from the arrays 7A, 7B are obtained with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection device for an optical device such as a camera.

As shown in FIG. 1, when the exit pupil of the imaging optical system 1 is shielded from damage by the pupil shielding member 2, the image created by the light flux that has passed through the remaining half of the exit pupil is from the focal position f to y It is well known that an image is formed at a position that is laterally shifted by δ in a direction perpendicular to the optical axis at a position separated by δ in the optical axis direction.

Many attempts have been made to detect the focal shift of the imaging optical system 1 by utilizing this phenomenon, and a typical example is splitting the pupil using a fly-eye lens or a lenticular lens. There is a way.

- Figure 2 shows the main parts of the conventional pupil division means using the fly's eye lens.

That is, in order to project the image of the exit pupil of the imaging optical system 1 onto the light receiving element array 8 as shown in FIG. adjacent 2
For example, a pair of light-receiving elements indicated by A, , B□ or A, , B2 is assembled into a set G, and the individual microlens elements 5, 51 constituting the 7 Lie's eye lens 4 are arranged to face each other. It is placed in With this configuration, the light beams 11 r 12 from the respective different regions b of the imaging optical system (not shown) are transformed into A1 + 12---
In addition to the light-receiving element group of A group consisting of An,
B, -m-Bn are respectively incident on the light-receiving element groups of the B group, so that the light-receiving elements A of the A group,
, A.

---An row and B group of light receiving elements B, B.

---Bn outputs are extracted separately to obtain output distribution signals corresponding to each pupil-divided image.

In this conventional model, the photodetector is A, B, A2°BQ.
-"-AnBn, two divided pupils G should be arranged in correspondence with each other, so the spacing of 1,000 light-receiving elements A11-"-An and the interval of A11-"-An forming group B. Light-receiving element Bl + Bs--
- It is difficult to make the Bn interval sufficiently narrow, which not only deteriorates the accuracy of focus detection, but also makes it difficult to manufacture a microlens array such as a prior eye lens.
It is not always easy to do so, and it also has structural drawbacks that reduce productivity.

An object of the present invention is to eliminate the drawbacks of the conventional configurations as described above, to enable highly accurate pupil division of an imaging optical system with a relatively simple configuration, and thereby to be able to perform focus detection with high accuracy. The purpose of this invention is to provide a focus detection device with a high focus.

The focus detection device of the present invention detects the in-focus state of the imaging optical system from the lateral shift of an image due to each light beam obtained by dividing the exit pupil of the imaging optical system. Each of the means for separating an image by each light beam obtained by the division from an image by other light beams is connected to a first region or a first region of the imaging optical system whose boundary is a plane including the optical axis of the imaging optical system. A plurality of micro optical members each having a reflecting surface formed such that a part of the light flux passing through the region No. 2 is incident at an angle equal to or less than the critical angle, and an individual light receiving element are respectively attached to each reflecting surface of the micro optical member. The present invention is characterized in that it is constructed entirely of a light-receiving element array arranged so as to receive only a beam of light incident at an angle of incidence equal to or less than a critical angle.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 8 shows an array of micro optical members 5 in the present invention. That is, the individual micro optical members 5 are formed into micro critical angle prisms, and a large number of them constitute a micro critical angle prism array 6.

As is clear from the figure, all surfaces of the small critical angle prism array 6 are flat, so manufacturing is relatively easy and manufacturing accuracy is guaranteed.

FIG. 4 shows the main parts of the configuration of the device of the present invention. In the figure, 7a, 7b, 70--1 are individual light receiving elements that constitute the light receiving element array 7. The critical angle prism array 6 is arranged in the vicinity of the intended imaging plane of an imaging optical system (not shown) or a plane conjugate thereto. On the incident light side of the light receiving element array 7, the critical angle prism array 6 explained in FIG. It has a configuration in which it is arranged in a relationship facing m-.

The apparatus of the present invention divides the imaging optical system into pupil divisions using the above-mentioned optical system configuration, and the principle of pupil division will be explained with reference to the same figure.

The material index of the micro critical angle prism is B8, the external (air) index is no, the incident angle is θ, and the exit angle is θ. Then, according to Snell's law 1, n1 sin θ0-n B Q in θi critical angle θic is given by: That is, of the incident light, that which is incident at an angle larger than θic is totally reflected by the critical angle reflection surface 5-1 of the small critical angle prism 5, and reaches the plane shown by 5-2, which is formed in this plane. The light is absorbed by the light absorption layer 8. Therefore, the index n of the material of the small critical angle prism 5
, and by appropriately selecting the angle Φ formed by the critical angle reflecting surface 5-1 of the small critical angle prism 5 and the light receiving element array 7,
As shown in FIG. 4, among the convergent light from the imaging optical system (not shown), the light flux R from, for example, the right half region of the imaging optical system is totally reflected by the critical angle plane 5-1. The light is absorbed by the light absorption layer, and only the light flux from the left half region is transmitted to the individual light receiving elements 7a, 7 of the light receiving element array 7.
b, 7C-- can be made to lead to one.

The light-absorbing layer 8 can be easily formed by roughening the plane 5-2 on which the light-absorbing layer 8 is to be formed and applying a black paint such as black ink.

Next, using the small critical angle prism array 6, we will explain how lateral shift occurs in the image due to the defocus of the imaging optical system.
This will be explained using figures.

Among the light beams from the imaging optical system 1, the light beam R in the right half of the plane including the optical axis 0 has an incident angle equal to or greater than the critical angle for each small critical angle prism 5 constituting the small critical angle prism 6. Therefore, as shown by the dotted line, the light is totally reflected regardless of the focusing state, and is absorbed by the light absorption layer 8 of each small critical angle prism 5 as explained in FIG.

The left half of the light beam has an incident angle less than the critical angle with respect to the small critical angle prism 5, so it passes through the small critical angle prism 5d and reaches the light receiving element array arranged behind it. (see Figure 4).

In this case, the light beam passes through a small critical angle prism of 5b to 5d at the rear pin, and 5d to 5d at the front pin.
Transmit f. Focusing on the center light Ig of this transmitted light, we find that it is 60 for rear focus, 5d for focus, and 5e for front focus.
□ passing through each tiny critical angle prism. Therefore, it can be seen that the overall image becomes an image that is slightly blurred and shifted laterally from left to right as the focus shifts.

If we use a small critical angle brism array with prisms with opposite inclinations, the left half of the light beam will be totally reflected and absorbed, and the entire image of the right half of the light will be out of focus. There is no need to explain that it shifts in the opposite direction.

FIG. 6 shows another example of the structure of the micro optical member array, that is, the micro critical angle prism array according to the present invention.

The light rays incident on each critical angle reflecting surface 5-1 of the micro critical angle prism array 6 have various incident positions and angles of incidence, and the light rays incident on each critical angle reflecting surface 5-1 of the micro critical angle prism array 6 have various incident positions and angles. There are also rays that pass through the side planes 5-8 and exit the prism. In the small critical angle prism array shown in FIG. 8, the side plane portion indicated by 5-8 in FIG. 6 is empty, and the light receiving elements 7 a and 7 b
--- is arranged on the bottom surface of each prism, so the light beam that reaches the side plane cannot enter the light receiving element, resulting in a loss of light quantity. In the one in Figure 6, to prevent this loss of light quantity,
It has a structure in which total reflection mirrors are installed on each side plane 5-8 of the small critical angle prism b.

・With this structure, the optical beam, which used to be exposed outside the prism. is guided to the bottom surface of the prism by a total reflection mirror installed on the side plane 5-8, as shown by the solid line, and incident on the light receiving element placed at the bottom surface, thereby reducing the loss of light quantity. It is something.

FIG. 7 is a configuration diagram of an example of an optical system for forming left-right laterally shifted images according to the present invention. A light beam from an imaging optical system (not shown) is split into two by a half mirror 9-1 of the beam splitter 9, and one passes through the minute critical angle prism array 6A described above and reaches the light receiving element array 7A. The optical path of the other one is changed by the half mirror 9-1 and the reflecting mirror 9-2 of the beam splitter 9, and the optical path length is corrected by the optical path length correction plate 10 to be the same as that of the light beam incident on the micro critical angle prism array 6A. After that, it passes through a small critical angle prism 6B having the same configuration as the above-mentioned small critical angle prism array 6A, and in which only the slope of the critical angle reflecting surface is reflected, and reaches the light receiving element array 7B.

That is, two small critical angle prism arrays 6A and 6
B has the same structure, but the inclination of the critical angle reflection surface is in the opposite direction, so that the pupil division image of the imaging optical system is the same as that of each light receiving element array 71 arranged on the intended imaging plane of the imaging optical system. .7B, and the horizontal shift direction of the image is in the opposite direction. However, the pitch between the light receiving element rows 7A and 7B arranged on the substrate 11 can be made sufficiently narrower than that of the conventional one explained in FIG.
7B, a highly accurate output distribution signal corresponding to each pupil division image of the imaging optical system can be obtained. Therefore, by comparing the output distributions of the respective light-receiving element arrays 7A and 7B using a known method, it is possible to easily detect the in-focus state of the imaging optical system on the intended imaging plane.

In other words, when the imaging optical system focuses on the planned imaging plane,
Since no lateral shift occurs in each image due to pupil division, the output distributions of the light-receiving element array 71.7B almost match. On the other hand, in the front focus state, a lateral shift occurs in the images on the light receiving element rows 7A and 7B, so the output distribution of the light receiving element rows 7A and 7B is
They are shifted as shown by A and B in the figure. Further, in the rear pin state, the output distribution will be shifted in the opposite direction from that in the case of FIG.

Therefore, if the number of light-receiving elements in the light-receiving element rows 7A and 7B is N, and the outputs of the first elements in the light-receiving element rows 7A and '7B are xAi and XBi, respectively, then the equations are as shown in FIG. gives the sum of the differences in the outputs of each light receiving element array 71°7B when the output B of the light receiving element array 7B is shifted by one element to the right. Also, gives the sum of the differences in the outputs of the light receiving element arrays 7A and 7B when the output of the light receiving element array 7B is shifted to the left by one element. Therefore, when considering s-s□-811', in the front pin state as shown in Fig. 8, S-work
Since it becomes SII, S becomes negative. In addition, the light receiving element array 7A,
If the output of 7B is opposite to that shown in FIG. 8, S will be positive, and if the outputs of light receiving element arrays 7A and 7B match, S will be zero. Using this S as an evaluation function, the relationship between the focusing state of the imaging optical system and its S is shown by a curve.
It will look like the figure.

FIG. 10 is a block diagram schematically showing a configuration example of a signal processing circuit for calculating the evaluation function S and displaying the in-focus state. In the figure, light receiving element arrays 7A and 7B are driven by a control circuit 12. When the output of the light receiving element array reaches a certain predetermined level, the photoelectric conversion output is held in the sample hold circuit 18, sequentially A/D converted by the A/D conversion circuit 14, and input to the arithmetic circuit 15. .

In the arithmetic circuit 15, S is fully calculated from the above-mentioned SL 181' and their values, and the result is sent to the control circuit 12.
send to The control circuit 12 determines the in-focus, front focus, and rear focus states based on the calculation results from the calculation circuit 15, and causes the display device 16 to display the results. Therefore, focus control may be performed manually or automatically based on the information displayed on the display device 16.

As described in detail above, according to the apparatus of the present invention, a minute critical angle prism array is used as the pupil division means of the imaging optical system, so that the image on the planned imaging plane due to the focal shift of the imaging optical system is It is designed to detect the lateral shift of the light-receiving element, and the individual light-receiving elements of the light-receiving element row are arranged in correspondence with the individual micro-critical angle prisms constituting the micro-critical angle prism array, so that the light-receiving elements Since the pitch interval of the rows can be made sufficiently small, a more accurate image output distribution signal can be obtained than in the conventional method using the outputs of every other light receiving element. Therefore, there is an effect that the focus detection accuracy is further improved compared to the conventional one.

Further, the configuration of the micro critical angle prism array is extremely easy to manufacture since each surface is a flat configuration.

Therefore, not only can an improvement in accuracy be expected from a structural standpoint, but the structure is also simpler than conventional ones.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the lateral shift phenomenon of an image due to pupil division of the imaging optical system. Fig. 2 is an explanatory diagram of the main part of a conventional pupil division means using a fly-eye lens. A perspective view showing the structure of a micro critical angle prism array using micro critical angle prisms as micro optical members, FIG. An explanatory diagram of how a lateral shift occurs in an image due to the defocus of the imaging optical system using a prism array. Figure 6 is a perspective view showing another structure of the small critical angle prism array. FIG. 8 is an explanatory diagram of the output distribution of the light-receiving element array; FIG.
A curve diagram showing an example of the relationship between the focusing state of the imaging optical system and the evaluation function S. FIG. 10 is a block diagram showing an example of the configuration of a signal processing circuit for implementing the present invention. 1... Imaging optical system 5.5a to 5f... Small critical angle prism-like micro optical member l5-1... Critical angle reflecting surface 5-2... Flat surface 5-8
...Side plane (total reflection surface) 6.6A, 6B...Minute critical angle Brism array 7, 7
A, 7 B... Light receiving element array 7a-70... Light receiving element 8... Light absorption layer 9... Beam splitter 9
-1...Half mirror -9-2...Reflection mirror 1
0... Optical path length correction plate 11... Substrate 12
... Control circuit 18 ... Sample field, - field circuit 14 ... A/D conversion circuit 15 ... Arithmetic circuit 16.
...Display device. Fig. 1 Fig. 2 r”I Fig. 3 Fig. 4 ta'/b'i (Fig. 5
1T:! i Figure 6 Figure 7 Figure 8 Figure 9 Figure 1O Continued from page 1 0 Inventor Asao Hayashi 2-43-2 Hatagaya, Shibuya-ku, Tokyo Lymphus Optical Industry Co., Ltd. 0 Inventor Kenji Fukuoka 2-43-2 Hatagaya, Shibuya-ku, Tokyo, 1' Inside Lymphus Optical Industry Co., Ltd. Procedural Amendment July 26, 1981 1. Indication of the case 1988 Patent Application No. 103084 2. Name of the invention Focus detection Device 3, relationship with the case of the person making the correction Patent applicant (087) Olympus Optical Industry Co., Ltd. 1, 1 microlens element 5, 5'J in line 9, page 8 of the specification
Microlens element 4-1.4-24, corrected "column" in line 16 of the same page as "output", and F A11B1 r AB rB in lines 19-20 of the same page.
B-1-AnBn J as “A□ and B, , A, and Bg
, ---1An and Bn". 2. "@Regarding the individual micro critical angle prisms 6 constituting the small critical angle prism 6" in lines 2 to 8 on page 8 of the same page is changed to "
Individual minute critical angle prisms 5 (5a to 5f in FIG. 6 for convenience of explanation) constituting the minute critical angle prism array 6
It is shown with the symbol . )", and corrected "minor critical angle prism 5dJ" in lines 9 to IO of the same page to "
"Micro critical angle prism array 6" is corrected. In addition, in lines 18 to 14 of the same page, ``When focusing on the front, 5d to 5f is transmitted.'' , the image is formed on a light-receiving element array 7 (not shown). '', and in line 17 of the same page, ``The overall image is'' was changed to ``The overall image due to the light beam incident on the light receiving element array shown at 7 in Figure 4 is''.
I am corrected. 8. Correct the "solid line" in line 8 of page 10 to "dotted line" and insert the following between "this is a configuration diagram" and "illustration omitted" in line 8 of the same page. do. "In the figure, 6A and 6B are the small critical angle prism arrays 6 shown in FIGS. 8 and 6, and 7A and 7B correspond to the light receiving element array 7 shown in FIG. 4. Also, in lines 18-19 of the same page, [microcritical angle 1] 6
BJ is corrected as "micro critical angle prism array 6Bj. 4. Equation 5 on page 12, line 11, and symbols "5" and "5'" in Figure 2 of the drawing are written in red on the attached correction diagram. The code has been corrected to ``4-tJ'' and ``4-2J,'' and the code ``7'' has been corrected to ``4-tJ'' and ``4-2J.''
” is added along with the leader line. Figure 2 Figure 4

Claims (1)

[Scope of Claims] L In a focus detection device that detects the in-focus state of the imaging optical system from the lateral shift of an image due to each light beam obtained by dividing the exit pupil of the imaging optical system, the exit pupil is divided. Each of the means for separating the image obtained by each light beam from the image obtained by other light beams is included in the image forming optical system. A plurality of reflecting surfaces formed such that a part of the light flux that has passed through the first region or the second region of the imaging optical system bounded by the plane containing the optical axis of is incident at an angle equal to or less than the critical angle. and a light-receiving element array in which individual light-receiving elements are arranged so as to receive at least a part of the luminous flux incident on the reflective surface of the micro-optical member at an incident angle equal to or less than the critical angle. A focus detection device characterized by comprising: a. Out of the light flux that has passed through the reflective surface of the micro-optical member, each micro-optical member is fully configured to reflect the light flux that reaches outside the range of the light-receiving element that the micro-optical member faces toward the light-receiving element. The focus detection device according to claim 1, comprising a reflective surface.