JPH0666007B2 - Camera focus detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for a camera that receives a subject light flux that has passed through an objective lens, for example, a photographing lens, and detects a focus state.

Prior Art The first part and the second part of the photographic lens sandwiching the optical axis of the photographic lens
There has already been proposed a pin and a detection device for detecting the correlation position of two images formed by the light flux of the subject that has respectively passed through the part of FIG. The principle configuration of the optical system is as shown in FIG. 1, and a condenser lens (4) is arranged at a position equivalent to the planned focal plane of the taking lens (2), and further connected behind the condenser lens (4). Image lenses (6) and (8) are arranged, and CCD line sensors (10) and (12) are arranged on their image forming planes. Image (14) on line sensor (10), (12)
In the case of the so-called front focus, in which the image of the object to be focused is formed in front of the planned focal plane, (16) approach each other toward the optical axis (18), and conversely in the case of the rear focus, the optical axis ( 18)
Stay away from. When in focus, two images (14),
The distance between two mutually corresponding points in (16) is a specific length determined by the configuration of the optical system. Therefore, the focus state can be known by converting the light distribution patterns of the images on the line sensors (10) and (12) into electric signals and determining the relative positional relationship between them. When comparing patterns of two images in such a device, for example, if the number of pixels of one line sensor is 30, half of that is 15
The image pattern of the individual pixels is compared with the image pattern of the other line sensor to detect in which region the best match occurs. The pixel is then incremented by one and the image pattern of 16 pixels is compared with the other pattern. Thereafter, the image patterns are compared by sequentially increasing the number of pixels. In such a comparison operation, the combination with the highest degree of coincidence is detected to detect the focus state. However, if the number of pixels giving an image pattern to be compared is changed, a large number of compared images may be detected depending on the subject condition. In many cases, it was difficult to detect the combination with the highest degree of coincidence from the results.

Aim The present invention has been made to solve the above problems, and an object of the present invention is to provide a focus detection device capable of performing accurate focus detection.

In summary, the present invention forms a first image and a second image on a first line sensor and a second line sensor by subject light fluxes that have respectively passed through different portions of an objective lens,
In a focus detection device that detects the relative position of two images using photoelectric conversion signals from these line sensors to detect the focus state, the image pattern signal from one line sensor is divided into multiple blocks. The main feature is that the two image pattern signals in each of the divided blocks are compared to obtain the relative distance between the two images for each of the divided blocks.

Second Embodiment FIG. 2 is a diagram showing a configuration example of an optical system and the like when the focus detection device according to the present invention is applied to a single-lens reflex camera. In FIG. 2, the taking lens (22) and the reflecting mirror (2
4), the focusing screen (26), the penta prism (28), etc. are well-known elements that constitute a single-lens reflex camera. However, when the camera is configured to automatically focus using the output of the focus detection device, the focusing lens optical system of the taking lens (22) can be driven by the lens driving device (30) including a motor. Is configured as follows. The reflector (24)
The central part is made semi-transparent, and a sub-mirror (32) is provided behind it, and a part of the subject light passes through it to the light receiving part (34) of the focus detection device arranged at the bottom of the mirror box. Be guided. The light receiving section (34) includes a condenser lens (36), a reflecting mirror (38), an imaging lens group (40), a line sensor (42), and the like. Line sensor (4
The output of 2) is processed by the signal processing circuit (44) as described later, and a defocus signal indicating the amount of focus deviation from the in-focus position and its direction is output. A focus state is displayed on the display device (46) based on the defocus signal, and the photographing lens (22) is driven to the in-focus position by the drive device (30).

FIG. 3 is a diagram showing an optical system of the light receiving section (34).
8) shows the optical axis of the taking lens, and the dotted line (50) shows the surface equivalent to the exposed surface of the film. The condenser lens (52) is
It is arranged not at the position of the exposure equivalent surface (50) but at a position away from it by the focal length ₁ of the condenser lens (52). Imaging lenses (54) and (56) are arranged behind the condenser lens (52) with the optical axis (48) as a symmetry axis, and the field limiting masks (58) and (56) are provided in front of these imaging lenses. 6
0) is provided. CCD line sensors (62) and (64) are arranged on the imaging planes of the imaging lenses (54) and (56). Here, the reason why the condenser lens (52) is arranged at a position deviated from the exposure equivalent surface (50) is as follows. Exposure equivalent surface (50) for line sensors (62) and (64)
The optical system is configured so that the object image of
When a condenser lens (52) is placed on this exposure equivalent surface (50), if there are scratches or dust on the surface of this lens, this will appear as an image on the line sensor, and originally It becomes noise to the image of the object. Therefore, if the condenser lens (52) is removed from the exposure equivalent surface, the above noise can be avoided. Furthermore, when it is built into the camera, it can be stored without making a large change to the optical system of the camera. Further, the masks (58) and (60) are provided with a condenser lens (52) so as to receive only a specific aperture value of the subject light passing through the taking lens, for example, subject light passing through an aperture area corresponding to F5.6. Composed in the context of. By doing so, when various interchangeable lenses are used as the taking lens, if the taking aperture lens has an aperture value smaller than F5.6, some of the light rays are kicked by the pupil mask portion of the taking lens itself. The line sensor (62), (64) no longer receives the received image, and most commonly used interchangeable lenses can be applied.

Next, points (66), (68), and (70) on the optical axis represent images in a front-focused, in-focus, and rear-focused state with respect to one object point in front of the taking lens. The incident points on the line sensor (62) of the images (66), (68) and (70) are (72) and (7), respectively.
4) and (76), and (78), (80) and (82) on the line sensor (64).

Fig. 4 shows images of front pin, focus, and rear pin (84), (86)
Re-imaging in the line sensor area for (88) is shown. The re-imaging images (90) and (92) for the front pinned image (84) are located in front of the light receiving surface (94) of the line sensor, and the optical axis (4
8) Close to each other. The re-imaging (96) and (98) for the focused image (86) coincide with the light receiving surface (94) of the line sensor, and the re-imaging (100) and (102) for the rear focus image (88) are the line sensor. Is located behind the light-receiving surface (94) of the optical axis (4
8) away from. Therefore, the re-imaging (90), (92) for the front pinned image (84) is
4) Above, the image is slightly blurred and stretched. Also,
The re-imagings (100) and (102) for the rear focus image (88) are slightly blurred on the light receiving surface (94) and become a reduced image.

Next, with reference to FIG. 5, the relationship between the image shift amount h of the line sensor (62) and the image shift amount e from the in-focus position will be described. Image (68) formed on the optical axis (48) when focused
Consider the ray of light that travels parallel to the optical axis (48) after passing through the condenser lens (52). In the case of the images (66) and (70) in front of or behind the image (68) by the shift amount e, the above-mentioned rays are only g from the optical axis (48) at the position of the exposure equivalent surface (50). Passes the distant point (67) or (71). Here, three points (6
8), (67), (71) as the light source, condenser lens (5
By the imaging system (55) consisting of 2) and the imaging lens (54),
It is assumed that the images for the light source are formed on the line sensor (62) and the images are (74), (72), and (76). Further, the magnification of the imaging system (55) is α. From a geometrical view of FIG. 5, the following equation holds.

Eliminating g from these two equations, Therefore, since α ₁ / H in the equation (3) is a constant determined by the configuration of the imaging system, the shift amount e can be obtained if the movement amount h is detected. However, as shown in FIG. 4, only the in-focus image is normally formed on the exposure equivalent surface (50), and the other images are located in front of and behind it. α is not constant, and the imaging system (55)
The positions of the images (66) and (70), which are the light sources, differ with respect to each other. If the magnification upon focusing and alpha _0, in the case of front focus, as FIG. 13 larger than alpha _0, in the case of rear focus smaller than alpha _0. Further, the magnification varies depending on the position of the image on the sensor surface due to aberrations such as field curvature of the optical system. Therefore, in more accurate calculation of the shift amount, a magnification is prepared in advance according to the movement amount h and used as will be described later. Hereinafter, a circuit that detects the movement amount h and the shift amount e will be described.

FIG. 6 is a diagram showing an embodiment of the pixel configuration of the line sensors (62) and (64) in FIG. 3, and the line sensor (62) is called a standard part and the line sensor (64) is called a reference part. Pixel (L ₁ ) ~
(L ₂₆ ) and (R ₁ ) to (R ₃₀ ) are photodiodes, which form a charge coupled device (CCD). A blank pixel between the pixels (L ₂₆ ) and (R ₁ ) is provided with a dummy pixel,
CC of two line sensors (62), (64) in one line
May be configured as D. Further, as shown in FIG. 7, a charge transfer line (65) may be provided between the line sensors (62) and (64). Photodiodes (67) and (69) are CCD
Is for monitoring the incident light intensity to determine the integration time of. The monitor photodiode may be shaped so as to fill the gap between the pixels (Li) as shown in FIG. By doing so, it becomes possible to monitor the light having the intensity almost close to that of the pixel surface.

Next, in the embodiment, the image pattern in the reference portion (62) of the line sensor is divided into three blocks. The first block has pixels (L ₁ ) to (L ₁₀ ), and the second block has pixels (L ₁ )-(L ₁₀ ).
₉ ) to (L ₁₈ ), the third block is pixels (L ₁₇ ) to (L ₂₆ ).
In the image pattern. The image pattern of each block consists of 10 pixels. Here, each block has 10 pixels, but the numbers of pixels do not necessarily have to be the same. In focus detection,
The image of each block and the image of the comparison unit 64 are compared. For example, when using the image of the first block, the following comparison operation is performed. First, the pixels (L ₁ ) to (L ₁
The image of the portion ₁₀ ) is compared with the image of the first block. The content of the comparison in this case is expressed by the equation (4), and the sum of the absolute values of the pixel output differences in each group of the pixels L ₁ and R ₁ , L ₂ and R ₂ , ..., L ₁₀ and R ₁₀ is calculated. To be done.

Next, the image of the pixels (L ₂ ) to (L ₁₁ ) of the comparison unit (64) is compared by shifting by 1 pixel from the previous image. The processing content is shown by equation (5).

In the same manner, the comparison process shown in the following equation is performed, and a total of 21
Individual comparison results are obtained.

Now, for example, when the image of the first block matches the image of the portion of the pixels R _{2 to} R ₁₁ , H ₁ (l ₂ ) is the smallest among the 21 comparison results. A rough focus position can be detected by finding a pixel area corresponding to this minimum value.

An operation similar to the comparison operation using the image of the first block is
This is done using the images of the second and third blocks. The content of each comparison is generally expressed by the following equation.

Here, l = 1, 2, ..., 21.

By the above comparison operation, 21 comparison results are obtained for each block image, and 63 comparison results are obtained as a whole. Now, if in focus,
The image of the second block is the pixels (R ₁₁ ) to (R ₁₁ ) of the comparison unit (62).
₂₀ ) Configure the optical system so that it matches the image of the part. By doing this, in the case of focusing, the image of the first block is pixels (R ₃ ) to (R ₁₂ ) and the image of the third block is pixel (R ₁₉ ) to (R ₁₉ ).
Consistent with the image of each part of (R ₂₈ ). In this case, depending on the state of the image, the focus position can be detected using any block. However, in a block covered with an image having a low image contrast, the minimum value may not be specified from the comparison results. Therefore, a plurality of blocks having a contrast equal to or higher than a certain fixed value are selected, and the focus position is detected from the comparison result corresponding to those blocks.

Further, in the case of the front focus state, referring to FIG. 4, the images in the reference portion (62) and the comparison portion (64) match at the portion closer to the optical axis (48) side, so the third block The image of is in agreement with the image of a part of the comparison part (64). On the other hand, in the case of the rear focus state, the two layers coincide with each other at a portion distant from the optical axis (48), so that the image of the first block coincides with a portion having the comparison portion (64). Therefore, in the case of out-of-focus, there is a possibility that the minimum value can be found in the comparison result regarding the image of the first block or the third block. However, if the image does not have sufficient contrast, it is considered that focus detection is impossible and the minimum value is not detected. The pixels L ₉ and L ₁₀ and the pixels L ₁₇ and L ₁₈ are shared in each of the first block and the second block and the second block and the third block. When pixels are shared in this way, for example, pixel L ₉ and
Focus detection is possible even in the case where image contrast exists in the portion L ₁₀ and contrast does not exist in other pixel regions. If the pixels are not shared, if the contrast of the image is located only at the boundary between the two blocks, the contrast does not exist in each block, and the focus detection becomes impossible.

Now, when the minimum value of the comparison result is found in any of the blocks and the matching area of the image is specified, the amount of deviation from the focus position or the in-focus position of the image is specified correspondingly. However, the accuracy of the displacement amount obtained in the above process is only the resolution corresponding to the pixel arrangement pitch.
Therefore, the accuracy of the deviation amount can be improved by performing an interpolation calculation process as described below and further correcting an error factor based on the optical system of the focus detection device.

FIGS. 9A and 9B are block circuit diagrams showing a circuit configuration for processing the image pattern signal from the line sensor outlined above. This signal processing circuit has a control logic (106) that outputs a control signal for the operation of the entire system including the CCD (104). Pixel signals sent in series from the CCD (104) are digitized by a digital circuit (108).
Is converted into, for example, an 8-bit digital signal, and each is stored in the random access memory (110) of each predesignated address. When the pixel signal storage is completed,
Contrast detection circuit (11
By 2), the contrasts C ₁ , C ₂ , and C ₃ of the first, second, and third blocks are detected, and it is determined whether or not the contrasts are above a predetermined level. The contrasts C ₁ , C ₂ , and C ₃ correspond to the sum total of the absolute values of the differences between the outputs of two adjacent pixels as shown by the following equation. It should be noted that the calculation of the contrast does not exceed the block area. Alternatively, the difference between the outputs of every other pixel or every other pixel may be used.

The obtained contrasts C ₁ , C ₂ and C ₃ are respectively stored in the memory (114) at the prespecified address, and the magnitude relationship is determined by the predetermined level C ₀ and the comparison circuit (116). If the level C ₀ is exceeded, for example, “1” is output. If the level C ₀ is not exceeded, “0” is output, and the contrast C ₁ , C ₂ ,
Each determination result d _1, d ₂ relative to C _3, d ₃ is the memory (12
Stored in 0).

Next, the image comparison circuit (122) compares the image of each block with the comparison image. In this case, it not performed comparison for an image block that contrast does not reach the predetermined level C _0, compared with the image of the comparison unit and the image of only the blocks exceeds a predetermined level C ₀ is executed. The contents of this comparison are as shown in the equations (8), (9) and (10). 21 comparison results are obtained for each block, which are sequentially stored in the memory (124) at a predetermined address.
Then, the minimum value among the calculated comparison results of each block
H ₁ (l ₁ ), H ₂ (l ₂ ), H ₃ (l ₃ ) and their comparison
l _1, l _2, l ₃ is retrieved by the search circuit (126), the result is stored in the memory (128).

Next, the standardization circuit (130) sets the above minimum value H for the block whose contrast exceeds a predetermined level.
The ratio of ₁ (l ₁ ), H ₂ (l ₂ ), H ₃ (l ₃ ) and the contrast C ₁ , C ₂ , C ₃ is obtained. Each is shown by the following formula.

These ratios mean the following. As described above, for example, when the taking lens is at or near the focus position, focus detection may be possible using any of the three blocks. In such a case, there arises a problem of selecting a block, which block is optimum to be adopted. Further, in the case of out-of-focus, there arises a problem of determining which block should be adopted to detect the state of the front pin or the rear pin. When adopting a specific block, the minimum value H ₁ (l ₁ ), H of each block found
_It seems possible to specify the block with the smallest value among ₂ (l ₂ ) and H ₃ (l ₃ ), but this is not appropriate. In general, the contrast state of the image is not uniform. For example, an image with high contrast may be located in the area of the first block, and an image with low contrast may be located in other blocks. When detecting the coincidence of two image patterns, it is generally advantageous that the contrast is high. Therefore, contrast is also added as an element for selecting a specific block. By the way, for example, the comparison result H ₁ (l ₁ −1), H ₁ when the pixel is shifted back and forth by one pixel pitch with respect to the minimum value H ₁ (l ₁ ) for the first block
Consider (l ₁ +1). If this minimum value H ₁ (l ₁ ) is for a focused state, then H ₁ (l ₁ −1) or H ₁ (l ₁ +1) is the contrast C obtained by the contrast detection circuit (112). It almost matches ₁ . I mean,
This is because each of the contrast C ₁ comparison results H ₁ (l ₁ −1) and H ₁ (l ₁ +1) relates to the difference between the outputs of the adjacent pixels. The difference is that the contrast C ₁ is for the same image, whereas the comparison result is for different images. Since this is the case, the minimum value H
₁ (l ₁ ) divided by contrast C ₁ NH ₁ is the minimum value H
_This is approximately equivalent to the ratio between ₁ (l ₁ ) and the comparison result when the pixel pitch is shifted by one pitch. This can be expressed by the formula However, i = 1,2,3.

Now, when NHi is called a standardized index, the standardized index corresponding to a block having a high contrast, which corresponds to an in-focus state or a substantially in-focus state, is considered to be the smallest among the three values. Stipulated in the selection criteria of.

Actually, the light distribution pattern of the image of the comparison part and the reference part is
Due to the aberration of the optical system and the positional asymmetry of the first image and the second image with respect to the optical axis, they cannot completely match.
The minimum value H ₁ (l ₁ ) never takes 0. Further, in the non-focused state, the standardization index takes a relatively large value for a block in which no image match is seen. Therefore, a standard value NH ₀ is set in advance for the standard air index, and if it exceeds the standard value, focus detection is determined to be impossible. Thus, regarding the minimum value of the obtained at most three standardization indexes, when this is smaller than the reference value NH ₀ , the detection data Lk of the block corresponding to this minimum value is adopted as the information indicating the focus shift amount. To do.

That is, the minimum value detection circuit (132) finds a true minimum value over a plurality of blocks. At the same time, the corresponding block is detected, and the comparison number lk having the minimum value Hk (lk) is taken out from the memory (128) by the selection circuit (134). Thereafter, the standardized minimum value NHk of the block having the minimum value Hk (lk) is compared with a predetermined value NH ₀ in a subtraction circuit (132), and NHk is NH
_If it is less than ₀ , proceed to the next step. If not, the focus cannot be detected. Now, suppose that l ₁ is obtained for the image of the first block, for example, l ₁ = 18.
This is the image on pixels (L ₁ ) to (L ₁₀ ) and pixels (R ₁₈ ) to (R ₁₈ ).
₂₇ ) Means that the above image is the best match.
In this case, the distance D ₁ between the images on the two pixel areas is obtained, and this distance D ₁ is the distance between the pixels (L ₁ ) and (R ₁₈ ).
As shown in FIG. 6, the distance between the pixels (L ₁ ) and (R ₁ ) is 1.50.
mm, and the pixel pitch P is 30 μ, it can be calculated as D ₁ = 1.50 + 0.03 × 18 = 2.04 (mm) (18). Using the comparison number l ₁ for the first block, the image spacing D ₁ is given by:

D ₁ = 1.50 + 0.03l ₁ Similarly, when the image interval D ₂ for the _second block is obtained, it becomes 8 pixels shorter than that for the first block, so D ₂ = 1.50−0.03 × 8 + 0.03l ₂ ... (19) for the third block, since become even eight pixels shorter than those of the second block, and _{D 3 = 1.50-0.03 × 8 × 2} + 0.03l 3 ... (20). Dk = 1.50-0.03 {8 (k-1) + lk} (21), which is a generalization of the above three equations. The marginal accuracy of the interval represented by (Equation 21) corresponds to the pixel pitch P.

FIG. 10 shows an example of the comparison result for the image of block 2. The comparison number l ₂ that takes the minimum value H ₂ (l ₂ ) is 8. As shown in Fig. 10, the comparison results H ₂ (l ₂ -1) and H ₂ (l ₂ +
When 1) is not equal, the true coincidence point is not the point of the comparison number l ₂ = 8, but the comparison number l ₂ + 1 = which takes the second smallest comparison result of l ₂ = 8 and the minimum value H ₂ (l ₂ ). It exists between 9 and. When the position of such an intermediate point is obtained, the focus detection accuracy is improved more than the pixel pitch. Therefore, a method for obtaining the position of this intermediate point will be described. Now in FIG. 10, H ₂ (l ₂
-1) and the line connecting H ₂ (l ₂ ) are extended, and on the other hand, when a line passing through H ₂ (l ₂ +1) with an opposite gradient is drawn, the intersection of the two images To be a true match of. By doing so, Hk (lk-1) ≧ Hk (lk
In the case of +1), the length β between lk and the true coincidence point q is expressed by the following equation from the geometrical configuration of the figure.

When Hk (lk-1) <Hk (lk + 1) as shown in FIG. 12, Becomes

In the circuit shown in FIG. 9, the interpolation calculation circuit (138) calculates the equation (22) or (23). Further, the correction is added to the equation (21) by the interpolation value β as shown in the following equation.

Dk ′ = Dk + β (24) Here, the positive sign of the second term β on the right side corresponds to the case where the expression (22) is used, and the negative sign corresponds to the case where the expression (23) is used. As described above, the distance Dk 'between the two images in the standard part (62) and the reference part (64) is calculated from the interpolation calculation circuit (138). Next, in the shift amount calculation circuit (140), the interval Dk ′
The shift amount e of the image of the taking lens from the in-focus position is obtained by using. If the distance between the two images at the in-focus point is D ₀ , the image movement amount h in FIG. 5 is expressed by the following equation.

Here, h <0 indicates a front pin and h> 0 indicates a rear pin. Fifth
In the case of the image forming system shown in the figure, D ₀ = 2H, but it actually differs slightly due to an assembly error or the like. Therefore, it is preferable to set an appropriate value as D ₀ at the time of assembly adjustment.

Now, when the movement amount h is obtained, the shift amount e is calculated based on the equation (3).
However, the magnification α is set in advance according to h, for example, the first
Numerical values shown in the table are experimentally determined and prepared in the ROM (142), and the shift amount e is calculated using this.

As described above, the direction and amount of shift of the taking lens with respect to the subject are obtained.

FIG. 14 is a circuit diagram showing an embodiment in which a microcomputer is used for the signal processing circuit of the focus detection device of the present invention. The CCD (104) receives the three-phase pulses φ ₁ , φ ₂ , φ ₃ from the transfer pulse generation circuit (144), and the internal transfer line is always in the data transfer state. The charge of each pixel of the CCD (104) is cleared by the clear pulse output from the terminal (P ₁₇ ) of the microcomputer (146). Therefore, the time when the charge is cleared is the time when the integration starts. With the start of this integration, a ramp voltage having a temporally different drop rate is output from the terminal (q ₂ ) of the CCD (104) according to the subject brightness. This voltage is compared with a predetermined constant voltage Vs by the comparison circuit (148), and when it drops to this voltage, the comparison circuit (148) outputs a "high" voltage. The "high" shift pulses from the terminal in response (P ₁₆₎ on voltage is output, in response to this integrated charge of each pixel of the CCD (104) is transferred to the transfer line. For CCD (104), during the period from the clear pulse supplied to the terminal (q ₇₎ until a shift pulse is supplied to the terminal (q ₆₎ is the integration time. In addition to the pixels shown in FIG. 6, the CCD (104) includes a plurality of pixels used as dummy and a plurality of pixels for obtaining a dark output. When the shift pulse is given, the CCD (104) first outputs a dummy signal and a dark signal from the output terminal (q ₁ ) and then outputs a required pixel signal. Incidentally, the output of the CCD is input to the circuit (150) for canceling and removing the change because the change is superimposed when the power supply voltage Vcc changes.
This voltage fluctuation eliminating circuit (150) is supplied with a voltage obtained by dividing the power supply voltage Vcc by resistors (154) and (156) at an input (152) and outputs a voltage according to the difference between the two inputs. When the pixel signal is output, one of the initial dark signals of the integrated data output of the CCD (104) is sampled and held by the sample and hold circuit (158), and the subsequent pixel signals Ri and Li are subtracted by the subtraction circuit (160).
Is reduced by the dark signal of the sample and hold circuit (158). In this way, the pixel signal becomes a signal in which the voltage fluctuation component and the dark output component are removed. The pixel signal from the subtraction circuit (160) is amplified by the amplification circuit (162) with an amplification factor according to the brightness level.
Is amplified by. The amplification factor is controlled to be higher as the brightness level is lower. The brightness level uses the ramp voltage from the terminal (q ₂ ), and is detected by the brightness level detection circuit (164) as a change amount of the tilt voltage per constant time, and this change amount is used as a signal indicating the brightness level. The amplified pixel signal is input via a multiplexer (166) to an input (17) of a voltage comparison circuit (168) which constitutes a digitization circuit.
Given to 0). The digitizing circuit is a voltage comparison circuit (1
68), a digital-analog converter circuit (172) and a microcomputer (146) programmed to give an 8-bit binary number to the DA converter circuit (172) and store the comparison result. It is configured as a comparison type AD conversion circuit. The digitized pixel signal is stored in the memory of a predetermined address according to the pixel addresses Ri and Li. After that, the above-described data processing is performed, the shift amount of the photographing lens and its direction are detected, and this is used for automatic focus adjustment control of the photographing lens and display of the focus state.

Focus detection command switch (174) for focus detection
When is closed, in response, the microcomputer (146) shifts to the initialization program of the CCD. Before the focus detection is started, charges are accumulated in the transfer line and pixels of the CCD (104) above the normal pixel signal level. However, before extracting the pixel signal, this unnecessary charge is transferred to the transfer line. And cleared from the pixel. This clear operation is the initialization of the CCD. In this initialization, a clock pulse with a shorter cycle (for example, 1/16 of normal) than when transferring a normal pixel signal is given to the CCD to make the transfer operation faster than normal repeated a plurality of times (for example, 10 times). Leave the line empty. In parallel with this, pixel clearing is also performed. In this case, the pixel signal acquisition operation is not performed. The transfer pulse generation circuit (144)
Transfer pulses φ ₁ , φ ₂ , φ _R using a clock pulse of a constant cycle from the terminal (P ₁₅ ) of the microcomputer (146)
To generate. When the flip-flop (176) is in the reset state and its output is at the “high” voltage, the transfer pulse having a shorter cycle than the normal time is generated in accordance with the “high” voltage. ), The division ratio of the clock pulse is changed by a predetermined value. The flip-flop (176) is reset by the pixel charge clear pulse from the microcomputer (146) and set by the shift pulse. Further, the shift pulse causes the transfer pulse generation circuit (144) to be in a state of generating a transfer pulse in a normal time. The DDD (104)
Is defined as the charge integration time from the generation of the charge clear pulse to the generation of the shift pulse. During this period, the transfer pulse generation circuit (144) outputs a transfer pulse having a shorter cycle than the normal period. However, during the integration period CCD (10
Since the signal output from 4) via the transfer line is treated as an unnecessary signal, there is no problem even if the transfer pulse becomes faster.

When a predetermined number of transfer cycles are completed as the initialization operation, the microcomputer (146) shifts to the above-mentioned program for focus detection. First, when the clear pulse is output, the CCD (104) starts integration.
At the same time, a terminal (q ₂ ) of the CCD (104) outputs a ramp voltage that drops from a predetermined voltage at a rate according to the subject brightness, and when this voltage drops to a predetermined level Vs, a voltage comparison circuit (148 ) Output level is inverted from "low" to "high" voltage. The "high" voltage is used as an interrupt signal, the microcomputer (146) outputs a shift pulse from the terminal (P ₁₆₎ receives an interrupt. The charge accumulated in each pixel of the CCD (104) by the shift pulse is transferred in parallel to the transfer line, then transferred in series, and sequentially output as a voltage signal from the output terminal (q ₁ ).
This voltage signal is digitized as described above and taken into a predetermined memory. When the pixel signal acquisition is completed, the terminal (P ₁₁ ) temporarily outputs, for example, a “high” voltage signal, and in response thereto, the multiplexer (166) selects the constant voltage from the low voltage circuit (178). The constant voltage is digitized by a digitizing circuit (108) and taken into a predetermined memory. As described above, this data is the data for correcting this error because the distance between the two images formed on the standard portion and the reference portion at the time of focusing is not the designed value due to the assembly error of the optical system. Used as. Constant voltage circuit (178) is constant current circuit (180)
And a semi-fixed resistor (182), the semi-fixed resistor (182) is adjusted in the adjustment process of the focus detection device to set accurate image interval data.

FIG. 15 is a flowchart showing a flow of operations of the focus detection apparatus described above.

Effect As described in detail above, the present invention divides the signal indicating the light distribution pattern of the first line sensor into a plurality of blocks, and outputs the first and second line sensors in each of the divided blocks. The relative distance between the two images is obtained for each block by comparing the signals. As a result, it becomes possible to detect the focus more accurately as compared with the conventional focus detection device.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional example of an optical system of a focus detection device, FIG. 2 is a diagram showing an arrangement example of a focus detection device of the present invention in a camera, and FIG. 3 is a diagram showing a focus detection device of the present invention. FIG. 4 is a diagram showing the configuration of an optical system, FIG. 4 is a diagram showing an image formation state by the optical system of the focus detection apparatus of the present invention, and FIG. 5 is a focus shift amount in the optical system of the focus detection apparatus of the present invention. The figure which shows the relationship with the movement amount of the image on the line sensor, FIG.
7 and 8 are diagrams showing a pixel configuration example of the line sensor of the focus detection device according to the present invention, and FIG. 9 (A).
(B) is a block circuit diagram showing the configuration of the signal processing circuit of the focus detection apparatus according to the present invention, FIGS. 10, 11 and 12 are graphs for explaining the operation of the signal processing circuit, and FIG. 13 is FIG. 14 is a graph showing the magnification of the optical system of the focus detection apparatus according to the present invention, FIG. 14 is a block circuit diagram when a microcomputer is used for the signal processing circuit of the focus detection apparatus according to the present invention, and FIG. 15 is a signal processing circuit. 3 is a flowchart showing a flow of the operation of FIG. 2,22 …… Shooting lens, 12,14,62,64,104 …… Line sensor (CCD), 4,36,52 …… Condenser lens, 6,40,54,56
…… Imaging lens, 67,69 …… Subject brightness monitor photodiode

Claims (3)

[Claims] 1. A focus detection device for detecting a focus state of an objective lens by detecting an image interval between a first image and a second image formed by subject light fluxes that have passed through different parts of the objective lens. A first line sensor that receives the first image and outputs a first image signal according to the light distribution pattern of this image; and a second image sensor that receives the second image and outputs a second image signal according to the light distribution pattern of this image Each of the divided block by dividing the first image signal into a plurality of blocks and comparing the first image signal and the second image signal in each of the divided blocks. A correlating unit for calculating a relative distance between the two images for each block; and a calculating unit for calculating a focus shift amount of the objective lens based on the image distance for each block calculated by the correlating unit. To focus detecting device. 2. The correlation means according to claim 1, wherein the correlation means obtains the relative distance between the first image signal and the second image signal based on the correlation value that has obtained the best correlation. Focus detection device. 3. The range of the focus shift amount obtained by the correlation in each block has a fixed width for each block, and the division of the detection range of the focus shift amount is different for each block. The focus detection device according to item.