JPS597322A - Focus detector - Google Patents

Abstract

PURPOSE:To enable the detection of focusing with high accuracy by detecting the focusing state on the intended focal plane of an imaging optical system or the plane conjugate therewith in accordance with the information relating to the sharpness of the image projected on each photodetector array and the information relating to a movement of a transverse direction. CONSTITUTION:An example of the case in which a titled detector is adapted to a single lens reflex camera is illustrated. The 1st photodetector array 12A and the 2nd photodetector array 12B are provided so as to receive the respective luminous fluxes before and behind the intended focal plane of an imaging optical system, for example, a photographing lens 1 or the plane conjugate therewith. An optical system for splitting luminous fluxes, for example, a striped mask, which is so constituted that the luminous flux from the 1st region bordering at the plane including the optical axis of the photographing lens and the luminous flux from the 2nd region are made incident essentially and respectively separately to the adjacent photodetectors in the arrays 12A, 12B is provided in the optical path between the arrays 12A, 12B and the lens 1, that is, between a beam splitter 7 and the arrays 12A, 12B.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device for detecting the focus state of an optical device such as a camera or a microscope.

2. Description of the Related Art Conventionally, so-called blur image detection methods and lateral shift image detection methods are well known as methods for detecting the in-focus state of an object image formed by an imaging optical system. FIG. 1 is a diagram showing a configuration example when a focus detection device implementing the blurred image detection method is applied to a single-lens reflex camera. In the figure, a part of the light beam from a photographing lens 1 is split by a quick return mirror 8 formed into a half mirror 2, and the whole is divided into two parts, one of which is divided into two by a focusing screen 4,
The other side that passes through the no-f mirror 2 is a total reflection mirror 6 placed behind the quick return mirror 8.
The beam is guided downward to the beam splitter, where it is further divided into two parts, and the two parts are placed at a certain distance apart, sandwiching a plane conjugate to the intended focal plane 8 (film plane) of the photographic lens l. The image is formed on each of the light receiving element arrays 9a and 9b.

In the above configuration, assuming that the output of one light receiving element array is X, for example,
Considering a value such as UBMAX, this gives an evaluation value for image sharpness that varies according to the sharpness of the image.

Regarding the outputs of the two light receiving element arrays 9a and 9b,
From the above formula, the desired evaluation value S is S□.

S2, Sl and S change as shown in FIG. 2 with respect to defocus. Therefore, if you observe the difference between S□ and S, the 2 defocus direction and the focus position will be the same: S□〈S2 is the front focus, S>S is the rear focus, 51==SZ is the focus, and so on. This means that it can be detected.

The conventional example described above has the advantage of being able to detect the in-focus state with high accuracy by using a relatively simple optical system, but the image forming plane of the photographing lens 1 deviates sharply from the expected focus position. In the condition, as can be seen from Figure 2, the evaluation value S□ and 82
Since the difference disappears and it becomes difficult to compare both evaluation values S It has been extremely difficult to detect the in-focus state over the entire driving range of the optical system.

In addition, as a conventional example using the lateral shift image detection method, the 8th
There is a configuration shown in the figure. In this figure, the same functional parts as in FIG. 1 are designated by the same reference numerals 2. In this focus detection device, the light beam from the photographing lens 1- reflected by the total reflection mirror 6 is directed to a lenticular lens located on or near a surface conjugate to the prefocal plane of the photographic lens l, that is, the frame surface 8. Via a minute auxiliary optical system 1O such as a lens, the light is made incident on a light receiving element array 11 arranged on a plane optically substantially conjugate with the exit pupil plane of the photographing lens 1 for this auxiliary optical system 10. As shown in FIG. 4, the light-receiving element row 11 includes light-receiving element groups 11A and IIB, and each fluorescent element 11A-1 to 11A of these light-receiving element groups 11A and IIB.
-n and 11B-1 to 11B-n each have a corresponding one light receiving element pair 11A-1, 11B-1; 1
1A-n.

11B-n, and all of these light receiving elements are arranged in a straight line. ! [Auxiliary optical system] 0 is a light receiving element pair 11A-1, IIB-1i"'i
There are n pieces corresponding to IIA n and IIB-n, and two light receiving elements forming each light receiving element row 5z are connected to the photographing lens l.
is approximately the same as the exit pupil plane [-, the plane perpendicular to the arrangement direction of the light-receiving elements and containing the optical axis of the photographing lens 1 (but in Fig. 8, the optical IQI
The part of the fly 1gl on each side of the border of the plane perpendicular to the plane of the paper, i.e., the light 1
The west device is designed to receive light from the upper and lower portions of the exit pupil plane, which are the f4h IF boundaries.

In such a configuration, the photographing lens l and the auxiliary optical system 1
When a small common part of the subject's image is projected onto the light-receiving element array 11 after passing through 0, only the optical beam passes through the lower part of the photographing lens l and enters the light-receiving element group 11A. On the contrary, only the light beam that has passed through the first side is incident on the light-receiving element groups 11A and II.
The illuminance distribution of the image projected on B matches when in focus, and when out of focus, shifts laterally in the opposite direction depending on the direction of the shift. In the focus detection device shown in FIG. 8, the light receiving element group 11. The outputs of A and IIB are appropriately processed to detect the direction of lateral shift of the image, and based on this, the front focus, rear focus, and in-focus states are detected.

The advantage of the focus detection device using such a lateral shift image detection method is that the focus detection range is much wider than that of the focus detection device using the blurred image detection method explained with reference to FIG. On the other hand, the gain of the lateral shift signal that falls near the in-focus area is small, and the configuration is generally complicated. In particular, in the conventional focus detection device η not shown in FIG. It is difficult to manufacture the system 1O, and the entire device is expensive and bulky due to its rigidity.In addition, it is difficult to optically adjust each auxiliary optical system and its corresponding photodetector pair. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device having a simple structure, which has the respective advantages of the blurred image detection method and the lateral shift image detection method as described above, and eliminates the above-mentioned disadvantages.

The focus detection device of the present invention is arranged before and after a plane conjugate to the planned focal plane of the imaging optical system, and then the front optical system is arranged on the light incident side of the first and second light receiving element rows. The projection image of each light-receiving element row 1- by each light beam transmitted through the first region and the second region bounded by a plane including the optical axis of By arranging a beam splitting optical system with a light beam splitting optical system, an image having a clear image and a lateral deviation corresponding to the defocus state of the imaging optical system is projected onto each of the light receiving element arrays, and these Based on the information regarding the sharpness of the scratches projected on each light-receiving element array and the information regarding the lateral shift, determine the focal state of the imaging optical system at the predetermined focal plane or a plane conjugate thereto. PyA
The present invention is characterized in that it detects a defocus state as well as detects a defocus state.The present invention will be described in detail below with reference to the drawings.

FIG. 5 is a diagram showing an example of the configuration of an embodiment in which the device of the present invention is applied to a single-lens reflex camera.

In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and since these parts have been explained previously, their explanation will be omitted here.

As shown in the figure, the apparatus of the present invention, like the conventional blur image detection method, detects each light beam before and after the predetermined focal plane of the imaging lens 1 or a plane conjugate to the plane. The first light-receiving element row 12A and the second light-receiving element row 12B are depleted so as to receive light. Further, in the optical path between the light receiving element arrays 12A, 12B and the photographing lens 1, that is, the beam splinter 7 and each light receiving element array 12A, 1.
2B, light fluxes from a region [7, bounded by a plane including the optical axis of the photographic lens] and second inclination angles are applied to adjacent light receiving elements in each of the light receiving element rows 12A and 12B. A light beam splitting optical system configured to mainly input the light beams separately, for example, a stripe mask plate 18, the details of which will be described later, is an example of this.

FIG. 6A is a perspective view showing the structure of the light receiving element array 12A and the stripe mask plate 18. Each of the light receiving element arrays IBA and 12B (see FIG. 6) consists of a large number of light receiving elements formed on the same substrate 14 at equal intervals. Both of these light receiving element rows 12A.

Although a stripe mask plate 18 is arranged for each light receiving element row 12B, the relationship between each light receiving element row 12A or 12B and the stripe mask plate 18 is exactly the same, so for the sake of simplicity, only one light receiving element will be described below. Only the configurations of the rows 12A and the stripe mask plate 18 will be described.

In this embodiment, among the large number of light-receiving elements constituting the light-receiving array 12A, odd-numbered light-receiving elements 15A, -]~]5 A-n and even-numbered light-receiving elements], 5 in the arrangement direction. R-1=15B-n constitute light-receiving element groups l-5A and 15B, respectively, and adjacent l elements of both groups constitute light-receiving element pairs 15A-1, 15B-1;・115A-n, 1
Configure 5B-nv. 13 stripe mask plates, n stripe masks 17-1 to 17- corresponding to each light-receiving element pair are placed on a transparent substrate 16+ such as glass or polymer film.
n is formed by vapor deposition, printing, etc., and using these stripe masks, as shown in FIGS. The first and second regions bounded by the plane containing the optical axis of 11t41. With this configuration, the two light receiving elements constituting each light receiving element pair, for example, light receiving elements 15A-1 and 15B-1, are formed as shown in FIG. As shown, the light receiving elements 15A-1 of the light receiving element group 15A have directivities in mutually different directions.
-15A-n is incident with the light flux that has mainly passed through the upper side bordering the optical axis of the photographing optical system l in FIG.
The light beam that has passed through the lower side is mainly incident on n. ]7 Therefore, the illuminance distributions of the images formed on the light-receiving element groups 15A and 15B are the same when focused on the light-receiving element array 12A, but during the out-of-focus period (conI no pin or rear focus) Since the images shift in opposite directions depending on the direction of the shift, if the lateral shift direction of the image is detected, the advantages of the lateral shift image detection method can be utilized as they are, and the blurred image detection method explained in Figure 1 On the other hand, when the predetermined focus detection range becomes a range that can be detected with high precision using the blurred image detection method, each of the light receiving element rows 1
2A.

If the sharpness of the image on the light receiving element array 12B is compared and a position where the sharpness of the image on both sides is equal is detected, that position corresponds to the focusing plane of the photographing lens l6. The output of the light receiving element group A is An, and the light receiving element f
The output of f'F B is combined with Br+, and its light receiving element array 12A
As the evaluation relationship F0 representing the sharpness of the image projected above, F1=l(A,+Bn)-(An4.l+B,+l
) l, Ax... Using (1), the evaluation function that represents the total sharpness of the image projected onto the light-receiving element array 12B is similarly expressed as F.
, then F and F2 are evaluation functions representing the sharpness of the image, so when a projected image is formed on each light receiving element array 11kA, 12B, as shown in FIG.
The evaluation values each change to a peak value.

On the other hand, as the evaluation function F8 representing the lateral shift of the image of the light-receiving element array 12A, for example, F8=Σ(iAn+1-Bo, I-IAn-Bn, 1)
- (2) and similarly, if the evaluation function representing the lateral shift of the image on the light-receiving element array 12B is F, then F8. As shown in FIG. 8(b), F is the evaluation function F obtained by the brush image detection method. At the position of each peak value of F2, there is no lateral shift in the image, so the value is zero, and this value is (If it deviates from i Iff, a full lateral shift occurs, resulting in a curve whose positive and negative signs are reversed depending on the direction of defocus. Therefore, for the defocus direction of front focus and rear focus, the evaluation function F of the above equation (11) , F4 are calculated, and when F and F have the same sign, judgment is made based on the positive or negative sign of both signs, and when F8. By determining the focus direction and in-focus state, the in-focus state can be detected over an extremely wide driving range of the imaging optical system, compared to the focus detection device using the conventional blurred image detection method explained in Fig. 1. It is now possible to
The in-focus state can be detected with high detection accuracy, which is an advantage of the blurred image detection method.

FIG. 9 is a block diagram showing a schematic configuration of an example of a signal processing circuit that obtains focus information representing in-focus, front focus, and back focus based on the output of each light receiving element array 12A, 12B.

In this example, the outputs of a large number of light receiving elements in each light receiving element row 1'2A, 12B are simultaneously held in the sample hold circuit 20, and this hold value is applied to each light receiving element row 1'2A, 12B for each output. They are sequentially read out in accordance with the arrangement order, sequentially converted from analog to digital by the A/D conversion circuit 21, and taken into the first and second arithmetic circuits 22 and 28. Part number.

The first circuit 22 calculates the evaluation functions F□ and F representing the sharpness of the image on each light receiving element array 12A, 12B based on equation (1), and the second circuit 28 calculates , each light-receiving element array 12 based on equation (2) above.
Evaluation functions F8 and F representing the lateral shift direction of the images on A and 12B are calculated, and the results of each calculation are led to the determination circuit 24.

These evaluation functions F□ F, F8, and F are in the range in which F8 and F have different signs when the front focus is on the predetermined focal plane or a plane conjugate thereto, as explained in FIG. In other ranges, F, > F2, and in other ranges, F, < O, F
, <O. In the rear bin state, Fl<F2 holds within the range where F8 and F have opposite signs, and F8>0. F,>+1.

Also, when the imaging optical system focuses on the predetermined focal plane or a plane conjugate to it, the relationship between F3 and F4 is "1" FB.
becomes.

In other words, for the range in the front pin direction and rear pin direction where F□ and F2 cannot be compared, the signs of F8 and F are positive,
It can be easily determined by the negative value, and in the range where 1F and FB4 have opposite signs, the in-focus state can be determined with high accuracy by comparing F□ and F.

In the determination circuit 24, F□ F2. F8 and F4
The above relationship is determined with respect to
Displayed by Note that the light receiving element arrays 12A, 12B, -
T? -7 pull hold circuit 20, A/D conversion circuit 21,
Each operation of the first and second arithmetic circuits 22 and 28, the determination circuit 24, and the display circuit 25 is controlled by a control circuit 26.

In the embodiment described above, a stripe mask is used as a beam splitting optical system that separates the exit pupil split beam of the imaging optical system and makes it incident on the adjacent light receiving elements in the first and second light receiving element rows. Although the structure using a plate has been described, the present invention is not limited to this. For example, a lenticular lens or a fly's eye lens shown as a conventional example in Figure #8 may be used. Of course. Furthermore, in the embodiment described above, the focus state is detected using lateral shift information when the focus is out of focus, and using blur image information when the focus is near the focus, but the focus state is Detection can be performed using both types of information, or detection can be performed using lateral shift information even in the vicinity of focus. As explained in detail above, the focus detection device of the present invention can detect First and second light-receiving element arrays arranged before and after the focal plane or a plane conjugate to that plane? , detection of the intensity distribution of the blurred image accompanying the driving of the imaging optical system, and lateral shift of the image due to the light beams from the first and second regions bounded by the plane containing the optical axis of the imaging optical system. The configuration is shared for detection. For the driving range of the imaging optical system where it is difficult to compare the blurred images, the out-of-focus direction is detected by the lateral shift image detection method, and for the driving range of the imaging optical system where it is easy to compare the blurred images, Therefore, according to the device of the present invention, the entire driving range of the imaging optical system, which is an advantage of the lateral shift image detection method, can be achieved with a relatively simple configuration. It is possible to provide a focus detection device that combines the effect of detecting out-of-focus directions over a wide range and the effect of detecting a focused state with high accuracy, which is an advantage of the blurred image detection method.

Further, as in the configuration shown in the above embodiment, the light flux from the exit pupil of the imaging optical system is directed to each of the first and second regions bounded by the plane containing the optical axis of the imaging optical system. As a beam splitting optical system for dividing the luminous flux of A device using a mask not only has a simple structure, but also has the advantage of being easy to manufacture, being economical, and being able to be made compact.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the configuration of a focus detection device using a conventional blurred image detection method, and Figure 2 is a diagram showing the change in the focus value, which represents the sharpness of an image, with respect to the focus direction in Figure 1. FIG. 8 is a scale diagram showing a configuration example of a conventional focus detection device using the lateral shift image detection method. FIG. 4 is a plan view showing the arrangement relationship between the auxiliary optical system and the light receiving element array in FIG. Figure 5 is a miniature diagram showing an example of the configuration of an embodiment of the present invention; Figures 6A, B, and C are diagrams showing the configuration of the strip mask and light-receiving element array shown in Figure 4, and their arrangement relationship. 7 is an example of the directivity characteristics of adjacent light receiving elements in the same row of light receiving elements; FIG. 8 is a diagram showing the form of a detection signal representing the focus state; FIG. L is a block diagram showing a schematic configuration of an example of a signal processing circuit of the focus detection device of the present invention. l...Taking lens, 2... Half mirror 18...
Quick return mirror, 6... Total reflection mirror, 7.
... Beam splitter, 8... Film surface, 12A,
12B... Light receiving element row, 1B... Strive mask plate, 14... Substrate, 15A, 15B... Light receiving element group, 15A-1 to 15A-n, 15B-1 to 15B
-n --- Light receiving element, 16... Transparent substrate, 17-i
~17-n... Strive mask, 18... Opening,
2o... Sample bold circuit, 21... A/D conversion circuit, 22... First arithmetic circuit, z8... Second arithmetic circuit, 24... Judgment circuit, 25... Display circuit , 2
6...Control circuit. Fig. 2 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Procedure sleeve correction book Showa 58 I [July] 811] Indication of the case 1988 Special revision request No. 114! l,1! 'i
No. 2, Name of the invention Focus detection device 3, Relationship with correction device P1 Special mention 1 Applicant 137) Olympus Optical Industry Co., Ltd. Correct 1 to read ``It consists of multiple tiny lenses.'' 2, page 5, line 6 of the same page, ``1. It says, “Receive the image.”
[-image, n1JffselfR small lens 10-1 to 10-n
(Receives light separately through each of the 7J solenoids.) Revised IE 03, page 6, line 13.
04, page 8, lines 10-11, the phrase ``1 beam splitter 7'' is changed to ``beam splitter 7''. 5. In the same page, page 11, line 14, "evaluation relation F□" is corrected to "evaluation function F□." 6 The 1 used in the 9th line of the 15th Tei of the same book is replaced with ``11''.
4.” Rev. 11:. 7. In the 17th line of the same page, the phrase ``1 focus direction'' was corrected to ``defocus direction,'' and in the 20th line of the same page, the phrase ``Figure 4'' was changed to ``Figure 5.'' correct. In Figure 5 of Figure 8 In1, as written in red in the attached revised Figure iE, the code ``14.

Claims (1)

[Claims] 1. On the light incident side of the first and second light receiving element arrays arranged before and after the predetermined focal plane of the imaging optical system or a surface conjugate thereto, the plane containing the optical axis of the imaging optical system is the boundary. By disposing a beam splitting optical system configured such that the projected image of each light receiving element F by each beam transmitted through the first region and the second region is shifted in the column direction according to the defocus state. 5. An image having a sharpness and a lateral shift corresponding to a defocus state of the imaging optical system is projected onto each of the light receiving element rows;5. Based on the information regarding the sharpness of the image projected onto each light receiving element array and the information regarding the lateral shift, the in-focus state of the imaging optical system at the predetermined focal plane or a plane conjugate thereto is detected, and the defocus state is detected. A focus detection device characterized by detecting a focus.