JPH0677101B2 - Focus detection device - Google Patents

Description

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 projection lens, and detects a focus state.

Prior Art The first part and the second part of the projection lens sandwiching the optical axis of the projection lens
A focus detection device has already been proposed, which detects the correlation position of two images formed by the subject light fluxes that have respectively passed through the above-mentioned portions to detect the focus state. The principle configuration of the optical system is as shown in FIG. 1, in which a condenser lens (4) is arranged at a position equivalent to the planned focal plane of the projection lens (2) and is 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.

Now, the relative positional relationship can be obtained by comparing two image patterns. At that time, the average size of the image patterns (that is, the charge accumulation level of the line sensor) of the line sensor is set to be around a certain value. It is necessary to control the charge storage time, and for that purpose, a light receiving element for detecting the average luminance of the subject is provided in the vicinity of the line sensor, and the charge storage time is controlled according to the photometric value. Kaisho 57
-64711.

However, in the conventional device, only one light receiving element is provided in a position in the vicinity of and above the line sensor in parallel with the pixel array direction of the line sensor. However, the proper luminance could not be detected. That is, for example, in the case of a subject whose brightness changes in a direction perpendicular to the extending direction of the light receiving element, such as a person wearing a horizontal striped shirt,
A brightness difference occurs between the light receiving element and the line sensor, which causes the charge accumulation level of the line sensor to deviate from the desired level.

It is an object of the present invention to solve the above-mentioned inconvenience and provide a focus detection device in which a light receiving element is arranged so as to be able to deal with a subject having a change in brightness.

Means for Solving the Problems The present invention provides a light-receiving element having sensitivity in a direction parallel to the arrangement direction of each pixel of a line sensor and also in a direction perpendicular to the arrangement direction.
A second side different from the first side in the vicinity of the first side (for example, the upper side) with respect to one of the pair of line sensors and a second side different from the first side so as to sandwich the pair of line sensors. The light receiving element is arranged in the vicinity of the side (for example, the lower side).

Action By arranging the light receiving element as described above, the light receiving element has sufficient sensitivity not only in the direction parallel to the arrangement direction of each pixel of the line sensor but also in the vertical direction.

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 projection 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 projection lens (22) can drive the focus adjustment optical system by the lens driving device (30) including a motor. Is configured as follows. The reflector (24)
The central part is made semi-transparent, and the secondary mirror (32) is provided behind it, and a part of the subject light is placed at the bottom of the mirror box through this, and the light receiving part (34) of the focus detection device is provided. Be led to. 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 drive lens (30) drives the projection lens (22) to the in-focus position.

FIG. 3 is a diagram showing an optical system of the light receiving section (34).
8) shows the optical axis of the projection 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 separated from it by the focal length f 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. 60) is provided. The imaging plane of each imaging lens (54), (56)
CCD line sensors (62) and (64) are provided.
Here, the reason why the condenser lens (52) is arranged at a position deviated from the exposure equivalent surface (50) is as follows. The line sensors (62) and (64) are configured with an optical system so that the object image on the exposure equivalent surface (50) is re-imaged. A condenser lens (52) is attached to the exposure equivalent surface (50). When arranged, if the surface of this lens has a flaw or dust is attached, this appears as an image on the line sensor and becomes noise to the image of the original object. Therefore, if the condenser lens (52) is removed from the exposure equivalent surface, the above noise can be avoided. further,
When incorporated in a camera, it can be stored without making major changes to the optical system of the camera. Further, the masks (58) and (60) are configured to receive only the subject light passing through a specific aperture value, for example, an aperture area corresponding to F5.6, of the subject light passing through the projection lens, so that the condenser lens (5
2) In relation to. If you do this,
When various interchangeable lenses are used as the projection lens,
If the projection lens has an open aperture value smaller than F56,
This eliminates the case where the line sensors (62) and (64) receive an image in which a part of the light rays are distorted by the pupil mask portion of the projection lens itself, and a commonly used interchangeable lens of various sizes 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 projection 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 focus, focus, rear focus (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 of the amount of movement h of the image in the line sensor (62) with respect to the amount of deviation e of the image from the in-focus position will be described. Of the light rays of the image (68) that are formed on the optical axis (48) when focused, after passing through the condenser lens (52), the optical axis (4
Consider a ray traveling parallel to 8). In the case of the images (66) and (70) that are front-focused or rear-focused by the displacement amount e with respect to the image (68), the above-mentioned light ray is transmitted through the optical axis (4) at the position of the exposure equivalent surface (50).
Pass point (67) or (71), which is separated from point 8) by g. Here, three points (68) on the exposure equivalent surface (50),
(67) and (71) are used as light sources, and an image of the light source is formed on the line sensor (62) by the image forming system (55) including the condenser lens (52) and the image forming lens (54). Each image is (74), (72), (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, Since f ₁ / αH 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 varies depending on the positions of the images (66) and (70) which are light sources with respect to the imaging system (55). 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, the movement amount h and the shift amount e
A circuit for detecting is 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). In addition, a dummy pixel is provided in the blank portion between the pixels (L ₂₆ ) and (R ₁ ),
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
It is for monitoring the incident light intensity for determining the charge accumulation time of. The monitor photodiode may be shaped so as to fill the gap between the pixels (L ₁ ) 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 is compared with the image of the comparison unit (64). For example, when using the image of the first block, the following comparison operation is performed. First, the pixels (R ₁ ) to (R ₁
The image of the portion ₁₀ ) is made symmetrical and the comparison with the image of the first block is performed. 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.

Then, the image of the pixels (R ₂ ) to (R ₁₁ ) of the reference portion (64) is compared by shifting the pixel 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 low 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.

Also, in the case of the front focus state, referring to FIG. 4, since the images of the reference portion (62) and the reference portion (64) match at the portion closer to the optical axis (48) side, the third block Of the image of the reference part (64) coincides with the image of a certain part. On the other hand, in the case of the rear pinning, the two images coincide with each other at a position away from the optical axis (48), so that the image of the first block coincides with a part of the reference 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 there is not enough contrast in the image, focus detection is considered 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 the pixels are shared in this way, focus detection can be performed even in the case where image contrast exists in the pixels L ₉ and 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
According to 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 of the absolute values of the differences between the outputs of two adjacent pixels, as shown in 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). For example, if the level C ₀ is exceeded, “1” is output, and if the level C ₀ is not exceeded, “0” is output, and the contrast C ₁ ,
C _2, each of the determination results of _{C 3 d 1, d 2,} d 3 are stored in the memory (120).

Next, the image comparison circuit (122) compares the image of each block with the image of the reference portion. In this case, not performed comparison for an image block that contrast does not reach the predetermined level C _0, compared with the images of the reference portion of only the blocks exceeds a predetermined level C ₀ is executed. The contents of this comparison are as shown in 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
The search circuit (126) searches H ₁ (l ₁ ), H ₂ (l ₂ ), H ₃ (l ₃ ) and their respective comparison numbers l ₁ , l ₂ , l ₃ and the results are stored in the memory (128). Stored in.

Next, the standardization circuit (130) sets the above minimum value H for the block whose contrast exceeds a predetermined level.
₁ (l ₁ ), H ₂ (l ₂ ), H ₃ (l ₃ ) and contrast C ₁ , C ₂ , C
The ratio with ₃ is required. 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 values H ₁ (l ₁ ) and 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, comparison results H ₁ (l ₁ −1) and H ₁ (l ₁ +) when the pitch is shifted back and forth with respect to the minimum value H ₁ (l ₁ ) for the first block.
Think about 1). If this minimum value H ₁ (l ₁ ) is for the focused state, then H ₁ (l ₁ -1) or
H ₁ (l ₁ +1) substantially matches the contrast C ₁ obtained by the contrast detection circuit (112). This is because the contrast C ₁ and the comparison results H ₁ (l ₁ −1) and H ₁ (l ₁ +1) each relate to the difference between the outputs of 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 value NH ₁ obtained by dividing the minimum value H ₁ (l ₁ ) by the contrast C ₁ is approximately equivalent to the ratio between the minimum value H ₁ (l ₁ ) and the comparison result when the pixel 1 bit is shifted. .
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 standard 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 _i (l _i ) 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 reference value NH ₀ is set in advance for the standardized index, and if it exceeds this value, focus detection is determined to be impossible. Thus, regarding the minimum value of at most three standardized indexes obtained, when this is smaller than the reference value NH ₀ , the detection data L _k of the block corresponding to this minimum value is used as information indicating the focus shift amount. adopt. That is, the minimum value detection circuit (13
In step 2), find the true minimum value over multiple blocks. At the same time, the block corresponding to it is detected, and the minimum value H
_The comparison number l _k that takes _k (l _k ) is retrieved from the memory (128) by the selection circuit (134). Thereafter, the standardized minimum value NH _{k of the} block having the minimum value H _k (l _k ) is compared with a predetermined value NH ₀ in a subtraction circuit (136), and when NH _k is smaller than NH ₀ , the next step is performed, Otherwise, 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 pixel (L ₁ ) ~
It means that the image on (L ₁₀ ) and the image on pixels (R ₁₈ ) to (R ₂₇ ) are in best agreement. In this case, the distance D ₁ between the images on the two pixel areas is obtained. This distance D ₁ is the distance between the pixels (L ₁ ) and (R ₁₈ ). As shown in FIG. 6, if the distance between the pixels (L ₁ ) and (R ₁ ) is 1.50 mm and the pixel pitch P is 30 μ, then D ₁ = 1.50 + 0.03 × 18 = 2.04 (mm) ...... (18) can be obtained. 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, if the image interval D ₂ for the _second block is obtained, it will be 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 it becomes even eight pixels shorter than those of the second block, and _{D 3 = 1.50-0.03 × 2 + 0.03l} 3 ...... (20). D _k = 1.50-0.03 {8 (k-1) + l _k } (21), which is a generalization of the above three equations. The marginal accuracy of the interval represented by the 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 with a gradient opposite to this extended line and passing through H ₂ (l ₂ +1) is drawn, the intersection of the two is Consider it a true match. By doing so, H _k (l _k −1) ≧ H _k (l _k +) as shown in FIG.
In the case of 1), the length β between l _k and the true coincidence point q is expressed by the following equation from the Uno geometric configuration.

When H _k (l _k −1) <H _k (l _k +1) as shown in FIG. 12, Becomes

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

D ′ _k = D _k ± 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 D' _k between the two images in the standard part (62) and the reference part (64) from the interpolation calculation circuit (138).
Is calculated.

Next, the shift amount calculation circuit (140) obtains the shift amount e of the image of the projection lens from the in-focus position by using the interval D' _k .
If the distance between the two images at the time of focusing is D ₀ , the image movement amount h in FIG. 5 is given by the following equation.

Here, h <0 indicates a front pin and h> 0 indicates a rear pin. Fifth
In the case of the imaging system shown in the figure, D ₀ = 2H, but it actually varies slightly due to an assembly error or the like, so it is preferable to set an appropriate value as D ₀ during 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 as 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 becomes the charge accumulation start time. CCD (104) terminal (q ₂ )
Outputs a ramp voltage having a temporally different drop rate 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 which the charge accumulated charge of each pixel of the CCD (104) is transferred to the transfer line. For CCD (104), between at terminal shift pulse from given the clear pulse to (q ₇₎ to the terminal (q ₆₎ is given a charge accumulation time. In addition to the pixels shown in FIG. 6, the CCD (104) includes a plurality of pixels used as a dummy and a plurality of pixels for obtaining a dark output. The CCD (104) first outputs a dummy signal and a dark signal from an output terminal (q ₁ ) to which a shift pulse is given, and then outputs a required pixel signal. still,
When the power supply voltage Vcc changes, this change is superimposed on the CCD output, so a circuit for canceling and eliminating this change (15
It is input to 0). 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 pixel signals R _i and L after that are held.
_i is a sample hold circuit (15
It is reduced by the dark signal of 8). Thus the pixel signal is
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) at an amplification factor according to the brightness level. 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 given to the input (170) of the voltage comparison circuit (168) which comprises a digitization circuit via a multiplexer (166). The digitizing circuit is programmed to provide a voltage comparison circuit (168), a digital-analog conversion circuit (172), an 8-bit binary number to the DA conversion circuit (172), and store the comparison result. Microcomputer (configured as a successive approximation type A / D conversion circuit from a 146 computer. Digitized pixel signals are stored in a memory of a predetermined address corresponding to pixel addresses R _i and L _i ) After that,
By the above-mentioned data processing, the deviation amount of the projection lens,
The direction is detected and used for automatic focusing control of the projection lens and display of the focus state.

Now, when power supply to the microcomputer (146) is started, in response to this, the microcomputer (146)
Moves to the CCD initialization program. 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. Cleared from lines and pixels. 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, the pixels are also cleared. In this case, the pixel signal acquisition operation is not performed. Transfer pulse generation circuit (144)
Is a transfer pulse φ ₁ , φ using a clock pulse of a constant period from the terminal (P ₁₅ ) of the microcomputer (146).
₂ and φ ₃ are generated. When the flip-flop (176) is in the reset state and the output thereof is at the “high” voltage, the transfer pulse having a shorter cycle than the normal time is generated in accordance with the “high” voltage. 144), the frequency 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 CCD (104) defines the charge accumulation time from the time the charge clear pulse is generated until the shift pulse is generated. During this period, the transfer pulse generation circuit (144) outputs a transfer pulse with a shorter cycle than normal. To be done. However, since the signal output from the CCD (104) via the transfer line during the charge accumulation period 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 charge accumulation. At the same time, from the terminal (q ₂ ) of the CCD (104), a ramp voltage that drops from the predetermined voltage at a rate according to the subject brightness is output, and when this voltage drops to the predetermined level Vs,
The output level of the voltage comparison circuit (148) is from "low" to "high"
Invert to voltage. The "high" voltage is used as an interrupt signal, the microcomputer (146) outputs a shift pulse when receiving an interrupt from the terminal (P _16). 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, for example, a “high” voltage signal is temporarily output from the terminal (P ₁₁ ), and in response thereto, the multiplexer (166) selects the constant voltage from the constant 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 corrected 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 data. 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 above, according to the present invention, the light receiving element is placed near the upper side of one of the pair of line sensors so as to sandwich the line sensor in the arrangement direction of each pixel. , The other is placed near the lower side. For example, if you want to detect focus on a subject whose brightness changes in the horizontal or vertical direction of the projection screen, you can set the desired level for any subject. The electric charges of can be taken out from the line sensor, and proper focus detection can be performed.

[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 an optical diagram of the focus detection device of the present invention. FIG. 4 is a diagram showing the configuration of the 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 and line in the optical system of the focus detection apparatus of the present invention. 6 and 7 are diagrams showing the pixel configuration of the line sensor of the focus detection device according to the present invention, and FIG. 8 is a diagram showing the relationship with the amount of movement of the image on the sensor. Reference diagram showing a pixel configuration example, FIGS. 9A and 9B
Is a block circuit diagram showing the configuration of the signal processing circuit of the focus detection device 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 according to the present invention. FIG. 14 is a graph showing the magnification of the optical system of the focus detection device, FIG. 14 is a block circuit diagram when a microcomputer is used for the signal processing circuit of the focus detection device according to the present invention, and FIG. 15 shows the operation of the signal processing circuit. It is a flowchart which shows a flow. 2,22 …… Projection lens, 12,14,62,64,104 …… Line sensor (CCD), 4,36,52… Condenser lens, 6,40,54,56…
Imaging lens, 67,69 ... Photodiode for monitoring subject brightness

Claims (1)

[Claims] 1. A pair of charge storage type line sensors that receive a subject light flux that has passed through an objective lens and output a charge signal according to the amount of light, and detect the focus state of the objective lens based on the output of the line sensors. In the focus detection device, the line sensor is sandwiched in the arrangement direction of each pixel of the line sensor with respect to one of the pair of line sensors near the first side and the other of the pair of line sensors. A light receiving element disposed near a second side different from the first side, and a control means for controlling the charge storage time of the line sensor based on the received light output. Focus detection device.