JP2641853B2 - Camera auto focus device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device for a camera that detects a focus state of a photographic lens by receiving subject light that has passed through a photographic lens of the camera to perform focus detection.

2. Description of the Related Art A subject light beam that has passed through each of a first region and a second region of a taking lens that is symmetrical with respect to an optical axis is re-imaged to form two images, and the two images are mutually reciprocated. Focus detection that obtains the positional relationship and obtains the amount of deviation of the image formation position from the planned focus position and its direction (whether the image formation position is before or after the planned focus position, that is, whether front focus or rear focus). Devices have already been proposed. The optical system of such a focus detection device has a configuration as shown in FIG.
This optical system has a condenser lens (6) at or behind a predetermined focal plane (4) behind the taking lens (2), and further behind it a re-imaging lens (8), (10). ), And each re-imaging lens (8), (10)
Image sensors (12) and (14) each having, for example, a CCD as a light receiving element are arranged on the image forming surface. As shown in FIG. 7, the images on the respective image sensors (12) and (14) are so-called front pins in which the images (9) and (11) of the object to be focused are formed ahead of the predetermined focal plane. In the case of, the optical axis (1)
, And approach each other. Conversely, in the case of the rear focus, they are far from the optical axis (1). When focus is achieved, the distance between two corresponding points of the two images (9) and (11) is a specific distance defined by the configuration of the optical system of the focus detection device. Therefore, in principle, the focus state can be determined by detecting the interval between two corresponding points of two images. In an automatic focus adjustment device for a camera that incorporates this type of focus detection optical system, the integration of the amount of light by the CCD image sensor, the focus state detection calculation (defocus amount calculation) using the CCD image sensor output, and the defocus amount The sequence of the corresponding lens driving and stopping at the in-focus position (shutter release ... when the shutter button is pressed) is program-controlled by a control circuit composed of a microcomputer.

Then, even when the subject image comes near the focus, the automatic focus adjustment device continuously performs the sequential automatic focus adjustment control so that the in-focus position can be finally accurately set. Perform continuous auto focus (AF).

Problems to be Solved by the Invention When focus detection is performed, image sensors (12), (1)
4) The distance between the upper images must be detected. Therefore,
A correlation is obtained for two light distributions on the image sensors (12) and (14). By shifting the positions of the light receiving elements constituting both image sensors (12) and (14) relatively, a shift position (ie, an interval between two images) at which the best correlation is obtained is obtained.
The principle of this detection is described in detail, for example, in JP-A-60-4914.

By the way, since the correlation calculation is performed with the position relatively shifted in a wide range, a considerable time is required. For this reason, there is a problem that the responsiveness and the object tracking property of the automatic focusing device are deteriorated.

Now, in consideration of the followability of the subject, the above-described automatic focusing device detects the amount of defocus by one-open distance measurement when the subject approaches or moves away from the camera. When the photographing lens is moved to the in-focus position based on the defocus amount, the subject is moving during that time, so that the subject is not actually in focus.

FIG. 8 shows this state. The horizontal axis is the time axis, and the vertical axis is the defocus amount on the film surface. In FIG. 8, a curve 1 indicates the degree of increase in the defocus amount on the film surface when the subject approaches at a constant speed, and a straight line m tracks the position where the taking lens attempts to form an image. It is a thing. The product of the time axis is CC
D represents the integration time, and “act” represents the calculation time of the defocus amount. Since the subject approaches during the calculation time, even when the lens is driven based on the calculation result, the subject has already moved when the lens is stopped. As the subject approaches, the amount of defocus increases, and the subject immediately comes out of the depth of field and becomes out of focus.

Therefore, it is necessary to shorten the calculation time of the defocus amount as much as possible.

JP-A-59-126517 discloses that the detection zone of an image sensor is divided into three blocks, the entire area is shifted for each block, the best correlation position in each block is obtained, and the best correlation position in each block is calculated. A method that employs the value with the highest correlation among them has been proposed. However, in this method, after all, calculation is performed over the entire correlation range for each focus detection, and an effective time reduction cannot be obtained.

In Japanese Patent Application Laid-Open No. 56-75607, the maximum shift amount is adjusted using the first shift amount because the shift amount in the second and subsequent focus detections does not become larger than the shift amount in the first focus detection. Although a method has been proposed,
It does not show how to set the shift range once the focus adjustment operation is completed, and cannot cope with the case where the focus adjustment operation is repeated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic focus adjusting device for a camera, which can reduce the time required for correlation calculation in focus detection when the focus adjusting operation is repeated.

Means for Solving the Problems For this reason, the present invention re-images the subject light fluxes that have passed through the first and second regions of the projection lens that are symmetrical to each other with respect to the optical axis. An imaging lens is formed by forming two images on a first and a second photoelectric conversion element array and obtaining a relative positional relationship between the two images from signals indicating the illuminance distribution from the first and second photoelectric conversion element arrays. In the automatic focusing device for a camera which detects the focus adjustment state of the first and second photoelectric conversion element arrays, the positions of both photoelectric conversion element arrays are relatively shifted from the signal representing the illuminance distribution outputted from the first and second photoelectric conversion element arrays. Calculating means for obtaining a shift position at which the best correlation is obtained, detecting means for detecting a focus adjustment state based on the shift position, and focusing the photographing lens on the basis of the detected focus adjustment state. A driving means for driving the photographing lens by the driving means at least once, and a control means for repeating a focus detection operation by the calculating means and the detecting means and a focus adjusting operation by the driving means. All the signals output from the photoelectric conversion element array and corresponding to the focus detection sensitivity range are used without changing the focus detection sensitivity range for And a shift amount limiting means for limiting the shift amount to a position near the shift position corresponding to the above.

In general, in the focus detection of the automatic focusing device, once the best correlation position is found in a wide range, the lens is driven to the in-focus position according to the signal of this position.
Next, by scanning only a range that can be predicted without scanning a wide range as in the present case, the best correlation position can be obtained for most subjects, and the time is reduced. In addition, even if it is once determined that the subject is in focus, in the next calculation, it is sufficient to perform the calculation by shifting not the whole area but the position before and after the focus position. Therefore, in the present invention, the in-focus state in the previous focus adjustment is stored in the memory means, and the shift area in the next correlation calculation is limited by the shift area limiting means according to the output, thereby shortening the calculation time.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a circuit configuration of an automatic focusing apparatus for a camera according to the present invention.

FIG. 1 is a circuit diagram of a focus detection device in the case where a line sensor (15) made of a CCD as shown in FIG. 2 is used as a light receiving element and an automatic focus adjustment device using the same.

(20) is a photoelectric conversion circuit including the above-described line sensor (15) and a monitoring light-receiving element, to which a shift pulse (SH), a transfer clock (φ ₁ ), (φ ₂ ), and a clear pulse (ICG) are input, A time-series pixel signal (OS), monitor output (AGCOS), and reference voltage output (DOS) are output. Here, the clear pulse (ICG) is a pulse for setting each pixel in the line sensor (15) to an initial state. With this, each pixel in the line sensor (15) discharges the accumulated charge and newly performs light integration, That is, charge accumulation is started. or,
With this pulse, integration of the output of the monitor light receiving element is started in the photoelectric conversion circuit (20), and the monitor output (AGCO
S) changes over time with respect to the reference voltage output (DOS) at a speed corresponding to the brightness of the object. Shift pulse (S
H) is a pulse for shifting the accumulated charge from the pixel unit of the line sensor (15) to the shift register unit. When this pulse is input, the light integration in the pixel unit ends. The transfer clocks (φ ₁ ) and (φ ₂ ) are pulses 180 ° out of phase with each other for sequentially outputting the accumulated charges shifted in the shift register unit from the shift register unit in time series.
The stored charges thus output are converted into negative voltage signals in the photoelectric conversion circuit (20), and output as pixel signals (OS).

(22) is reference voltage output (DOS) from each pixel signal (OS)
Is subtracted and a pixel signal (DOS ') is output as a positive voltage signal. (24) is a pixel signal (DOS') output from the subtraction circuit (22) and is a light-shielded several pixel (for example, A peak hold circuit for peak-holding pixel signals corresponding to (pixels further left than (l ₁ ) in FIG. 2) and outputting a voltage (VP) corresponding to the maximum value of the pixel signals; (26) Is the pixel signal (DO) from the subtraction circuit (22)
S ') to the output voltage (VP) of the peak hold circuit (24)
Is a variable gain amplifier that amplifies the pixel signal by subtracting the dark current component. The dark current component included in each pixel signal (DOS ′) is removed by the subtraction in the amplifier circuit (26). An A / D converter circuit (28) converts the amplified pixel output (DOS ") from the amplifier circuit (26) into a digital value of a predetermined bit. The output of the A / D converter circuit is a microcomputer (30) (hereinafter referred to as a microcomputer). In (32), the gain control circuit detects the amount of change of the monitor output (AGCOS) with respect to the reference output (DOS), and the amount of change becomes a predetermined threshold value within a predetermined time from the start of the change of the monitor output. When it reaches (when it is bright), it outputs a signal (TINT) to that effect to the microcomputer (30), and outputs a gain signal for setting the gain of the amplifier (26) to "1". When a predetermined time elapses from the start of output of the monitor output (AGCOS), a forced shift signal (SHM) output from the microcomputer (30) is output to the gain control circuit (32). In this case, the gain control circuit (32) Is the monitor output (AGCOS) at the time of signal (SHM) input The gain of the amplifier (26) is set to “1” according to the amount of change with respect to the reference voltage output (DOS),
A gain signal set to "2 times", "4 times" or "8 times" is output. In this case, the smaller the amount of change, the larger the gain that is set. (AN) and (OR) are an AND circuit and an OR circuit, respectively. The AND circuit (AN) has the signal (TINT) from the gain control circuit (32) and the microcomputer (30)
(SHEN) is input to the OR circuit (OR), and the output signal of the AND circuit (AN) and the above-mentioned signal (SHM) from the microcomputer (30) are input to the OR circuit (OR). Here, the signal (SHEN) from the microcomputer (30) is a signal for permitting the generation of the shift pulse by the shift pulse generation circuit (34), and the generation of the shift pulse (SH) is prohibited (for example, the photoelectric conversion circuit). (During the data dump from (20) to the microcomputer (30) and during the data calculation by the microcomputer (30)) become “Low”, but then become “High” to open the AND circuit (AN). Therefore, when this signal (SHEN) is “high”, the signal (TINT)
Occurs, the AND circuit (AN) outputs a “High” signal (TIN
T) is output. The OR circuit (OR) outputs this signal (TINT) or signal (SHM) to the shift pulse generation circuit (34), and in response, the shift pulse generation circuit (34) generates a shift pulse (SH). A transfer clock generation circuit (36) generates a transfer clock (φ ₁ ) and (φ ₂ ) in response to a clock pulse (CL) from the microcomputer (30), and outputs a signal (TINT) or a signal (TINT) from an OR circuit (OR). When (SHM) is received, it is reset to the initial state, and regardless of the phase of the previous transfer clock (φ ₁ ) and (φ ₂ ), generation of new (φ ₁ ) and (φ ₂ ) starts (this Is to synchronize the shift pulse (SH) with the transfer clocks (φ ₁ ) and (φ ₂ ).) The signal (SH) output from the microcomputer (30) is a pixel which is captured by the peak hold circuit (24). This is a sample and hold signal for designating the signal (DOS ').

The microcomputer (30) is circuit-connected to the display circuit (38) and the lens driving device (40), and displays the focus adjustment state of the photographing lens (2) obtained by calculation as described later.
, And the lens driving device (40) drives the photographing lens based on the display. In this embodiment, the focus adjustment state of the photographing lens (2) calculated by the microcomputer (30) is represented by the defocus amount and the defocus direction. Therefore, the photographing lens (2) by the lens driving device (40) is used. The driving amount and driving direction in 2) are determined. The lens driving device (40) drives the photographing lens (2) according to the driving amount and the driving direction, and outputs a signal indicating the lens driving amount executed by the microcomputer (30),
The microcomputer (30) outputs a signal for stopping the lens driving to the lens driving device when the executed lens driving amount reaches the driving amount calculated by the calculation.

In FIG. 1, S1 is an AF start signal switch (AF switch). The focus detection operation is started when the AF start signal switch S1 is closed, and the focus detection operation is stopped when the AF start signal switch S1 is opened. Is done.

S2 is a release signal switch. When the release signal switch S2 is closed, the camera itself shifts to a release operation and exposure control is performed, but the focus detection circuit temporarily closes the release signal switch S2 for mirror operation at the time of release. At the same time, the operation is stopped.

SOC is one-shot AF mode, continuous AF
Mode changeover switch So, mode changeover switch So
c sets the one-shot AF mode when closed and the continuous AF mode when opened. The continuous AF mode has already been described.In the one-shot AF mode, the lens position adjustment is completed once the in-focus state has been detected during the focus detection operation, and the AF mode that performs AF lock is effective for still subjects. AF operation.

The switch Swn is a focus detection sensitivity range changeover switch. When this switch is closed, the focus detection sensitivity range becomes the central spot-like sensitivity range B in the camera view frame 42 shown in FIG. The focus detection sensitivity range is A.

Next, before describing the operation of the automatic focus detection device for a camera whose configuration has been described above, the correlation calculation and interpolation calculation used in this embodiment will be described.

The correlation calculation used here is the line sensor (15) in FIG.
Is calculated using the photoelectric conversion element rows l _{1 to} l ₄₀ and r _{1 to} r ₄₈ of the above. l ₁ 8-bit data of ~l _40, r ₁ ~r _48, first, the difference data Dl _n to add restrictions to the spatial frequencies detected as detailed in JP-A-60-4914, Dr _{n (where, Dl n = l n -l n} + 4, Dr n = r n -r n + 4, Dl 1 ~Dl 36, Dr 1 ~Dr
₄₄ ) is converted. Subsequently, calculation of all contrast values is performed. The contrast value C is obtained from the sum of the absolute values of the differences between the adjacent difference data of the reference portion (L) as follows.

Finally, the calculation is performed by the following equation while shifting the correlation value YM / C (I) of the reference part (L) and the reference part (R) by one pixel.

However, I = 1 to 9.

As a result, the correlation value YM / C (I) decreases as the degree of correlation increases. And find the point where the degree of correlation is maximum,
When the I value is 5, focusing is achieved. When I is smaller than 5, the camera is in a front focus state, and when I is larger than 5, the camera is in a rear focus state.

The correlation value obtained in this manner is a line sensor (1
Since it is obtained discretely by the output of 5), an interpolation operation is performed to obtain a fine precision, and a calculation of a focal point is performed.

Although various interpolation calculations have been proposed in Japanese Patent Application Laid-Open No. 59-126517 and the like, they are performed in steps # 100 to # 106 of the flowchart shown in FIG.

First, the minimum YM (1M) among the correlation values is detected.

Next, the value YM (1M) is normalized by the contrast value C, and the value YM (1M) / C is less than a predetermined value (YM (1M) / C <0.
Different methods are used for the case 1) and the case where the value is equal to or more than a predetermined value (YM (1M) /C≧0.2). First, in the former case, the minimum value YM (lM) / C
Is determined to be highly reliable, and when YM (lM + 1) ≧ YM (lM-1), When YM (lM + 1) <YM (lM-1) Becomes

In this method, when considered in an ideal state, the correlation curves are mutually different.
Based on orthogonality with a 45 ° slope. When considered in an ideal state, the reference part (L) and the reference part (R) are l _n = r
Outputs exactly the same value as _{n + 4} . Thus the difference data thereof Dl _n = D _{n + 4.} Where the contrast value C is It is.

On the other hand, the minimum correlation value is The correlation value on both sides is As long as the value of | Dl ₁ −Dr ₄ |, | Dl ₃₆ −Dr ₄₁ | is sufficiently small with respect to the overall contrast C, the correlation curves are orthogonal at 45 ° to each other. This interpolation calculation method has conventionally been a more accurate interpolation method than the interpolation method proposed in Japanese Patent Application Laid-Open No. 59-126517. However, the minimum correlation value YM (1M) normalized by the contrast value YM (1M) / C
Becomes larger than a predetermined value, the minimum correlation value becomes a large value due to some influence, for example, a subject of centrifugal competition or electric noise, resulting in poor reliability. Therefore, when this value YM (lM) / C is equal to or more than a predetermined value, the minimum value is not used and the correlation value on both sides thereof is used. To obtain an interpolation value. Considering that this value YM (lM) / C varies in the interpolation value at the threshold level, a hysteresis is provided, and once the former interpolation method is used, this value YM (lM) / C becomes 0.2 or more. Until the former interpolation method is used.

Next, for an embodiment in which the line sensor (15) is divided into blocks as shown in FIG. 2 and next in the table, refer to the flowcharts in FIGS. 4 (a) and 4 (b). I will explain while.

Note that the line sensor (15) is in between an intermediate separation zone, the reference unit including pixels l ₁ to l ₄₀ (L) and the pixel r ₁ ~r
_And a reference section (R) consisting of ₄₈ parts. Reference part (L)
The first block to the pixel l ₁ ~l ₂₀ (I), the pixel l ₁₁ ~
second block up to l ₃₀ (II), is divided into blocks by overlapping so that the third block (III) to the pixel l ₂₁ to l _40. Interval between the two image formed respectively reference unit (R) and the reference portion (L), when the focus is achieved, a predetermined distance L _2.

4 (a) and 4 (b), the microcomputer (30) first starts operation at # 20,
The start block (zone) designation of the focus detection calculation is set to the second block, and the shift amount restriction flag of the defocus amount calculation is set.
Reset ZF and reset lens drive flag SF Set to. The lens driven flag SF is a flag indicating whether or not the subject exists near the in-focus position. At the start of the focus detection calculation, the position of the subject has not been detected. Set. Then, it waits for the input of the AF operation start signal (# 1). When the AF switch S1 is closed and the start of the AF operation is instructed, first, the line sensor (15) is initialized, and then the image information accumulation of the line sensor (15) is started (# 2). When the charge accumulation of the line sensor (15) is completed to a predetermined level, the accumulated charges are transferred in parallel to the analog shift register by the shift pulse, and thereafter, the charges are synchronized with the transfer clocks (φ ₁ ) and (φ ₂ ). Transfer and data dump (# 3) are performed. When the data dump of all the pixels required for the focus detection calculation is completed, the microcomputer (30) first converts the pixel data into difference data (# 4). This is to remove a spatial frequency component which is not necessary for the focus detection calculation and is an obstacle.

After calculating the difference data, the microcomputer (30) performs sensing of the focus detection sensitivity changeover switch Swn in order to determine whether or not the focus detection sensitivity range is restricted. Focus detection sensitivity range switch Swn is set to OF
When in the F state, in # 21, the entire focus detection sensitivity range, that is, the first to third blocks (I) and (I) in FIG.
In order to perform the focus detection calculation in I) and (III), 3 is set to the zone calculation counter j. Conversely, when the focus detection sensitivity range changeover switch Swn is in the ON state, in # 22, Second
The zone calculation counter j is set to 1 in order to perform focus detection calculation for the focus detection sensitivity range of only the block (II), and n = n in order to set the zone designation to the second block (II).
Set to 2.

Next, in step # 61, the microcomputer (30) sets the lens driven flag SF to SF = Is determined. Before the focus detection calculation starts, SF = Therefore, the microcomputer (30) starts the focus detection calculation. In this case, since zone designation n = 2 and defocus amount restriction flag ZF = 0, # 23 to # 27
First, in # 29, the respective correlation function calculations are performed for the entire shift range of the second block (II), and in # 30 in FIG. 4B, the correlation function YM2 / C2 (k) is calculated. Is obtained, that is, the image interval lM2 having the highest correlation is obtained. Interpolation calculation is performed at # 31 based on the lM2, YM2 / C2 (lM2) and the correlation values before and after, and the image interval XM2, YM2 / C2
(XM2).

Next, LO-CON determination is performed on this value in # 32, and if the obtained XM2 is not reliable, the image shift amount P2 is calculated and stored in # 33 from the image interval if the obtained XM2 is reliable. . Further, in order to speed up the correlation calculation of the subsequent blocks, only the image shift larger than this image shift amount is calculated. Therefore, the defocus restriction flag ZF is set to 1 at # 34.
And 1M2-15 is stored as the limit value Pmin. This is because the correlation value of the pitch shift on both sides is necessary for the interpolation operation with a value smaller by one than the line sensor pitch image interval at which the degree of correlation is maximum. The LO-CON determination is described in Japanese Patent Application No. 60-7687.

Thereafter, the routine counter is checked. At this stage, when the focus detection sensitivity range changeover switch Swn is set to the ON state, and when the focus detection sensitivity range is set only in the second block (II), j = 1 is set in advance. Therefore, the counter j becomes φ by passing through the step of j = j-1 of # 35, and at the time when the focusing detection calculation of the second block (II) is completed, the process proceeds from # 36 to the lens driving routine of # 38.

On the other hand, a wide focus detection sensitivity range is selected, and the focus detection sensitivity range changeover switch Swn is set to j = 3 in advance in an OFF state, and j = j-1 =
2 ≠ 0, n = n + 1 = 2 + 1, and the third block (III) is selected as the next focus detection zone, and the third block (I
Return to the correlation function calculation for II) (# 25, # 41 to # 4)
Four). In the correlation operation of the third block (III), the second
If it is determined that the block is not LO-CON in block (II), the second block (I
Correlation calculation is performed only with an image shift amount larger than the image shift amount detected in I). When the LO-CON is determined in the second block (II), the correlation operation is performed in the third block (III) under the whole image shift amount. Thus the second block (II)
As shown in FIG. 4 (b), as shown in FIG. 4 (b), calculation of lM3 (# 45), calculation of XM3, YM3 / C3 (XM3) by interpolation calculation (# 46), and LO-CON determination (# 47) If not LO-CON, the image shift amount P3 is stored in the memory (# 48), the defocus limit Pmin = 1M3-25 is stored, and the flag ZF = 1 is set (# 49). It is conceivable that P3 obtained here is smaller than P2 by a difference within one pitch, but Pmin at that time becomes the same value, and Pmin cannot be reduced.

Next, in steps # 50 to # 59, similarly, n = n + 1
= 4, and the correlation operation of the first block (I) is performed.

When the wide focus detection sensitivity range is thus selected, an image shift range larger than the image shift amount of the block previously obtained by the correlation operation in the first to third blocks (I), (II), and (III). After the focus detection calculation is performed in step (3), the zone counter becomes j = 0, and the flow shifts to the lens drive routine of # 38.

Here, the focus detection sensitivity range changeover switch Swn is turned ON and O again.
The same routine is performed regardless of FF.

First, it is determined whether there is a zone that is not LO-CON (# 39). Here, the focus detection sensitivity range switch Sw
If n is ON and a narrow focus detection sensitivity range of only the second block (II) is selected, it goes without saying that the determination is made only for the second block (II). # 1 at # 39
When it is determined that the third blocks (I), (II), and (III) are LO-CON, the process returns to # 1 from # 10, # 11, and # 76, and the taking lens (2) is in the closest state. Move the entire area at least once from to ∞ and move to LO-CON SCAN where focus detection calculation is performed and drive the lens. During this operation, focus detection calculation is performed several times, all become LO-CON, and when LO-CON SCAN is completed, the lens operation is stopped at the closest lens end point ∞, and the lens operation is stopped. As long as the ON state of the AF switch S1 continues, the LO-CON display is performed while driving the image sensor and performing focus detection calculation (# 12), and waits until a subject state appropriate for focus detection is reached.

When a zone other than LO-CON is detected, a zone having the largest image interval among them, that is, an image shift amount and a zone of a zone including the closest subject among the subjects are extracted (# 40). The image shift amount Pi is converted by taking the product of the defocus amount and a constant (# 13), and n = zone number i
As a memory. The obtained defocus amount is converted into a lens drive amount by multiplying a product of a defocus amount and a lens drive amount coefficient that is different for each photographing lens (2) (# 14). If the lens drive amount is extremely small, In-focus display is performed (# 17). In other cases, lens drive is performed (# 1).
6).

Next, the lens drive completed flag SF cleared at # 20 at the start of the AF operation is set to 1 at # 72. This lens driven flag SF indicates that the probability that the subject exists near the in-focus position is high. Thereafter, the focus detection device performs reintegration of the image sensor, obtains new image information, and repeats the focus detection calculation. Here, in the case of SF = 1, the image interval having the highest correlation is predicted in advance because the probability that the subject exists near the in-focus position is high. Therefore, a correlation value is obtained only for the five image intervals of -2, -1, 0, 1, and 2 from the focused image interval (# 62). As a result, when the image interval for obtaining the highest correlation is any of −1, 0, and 1, the interpolation calculation is performed according to the value to perform the LO-CON determination (# 63, # 64, # 6
5) When the value is determined to be high in reliability, the lens driving is repeated according to the interpolated image interval XMn. That is, after calculating the image interval shift amount Pn in # 66 of FIG. 4A from the interpolated image interval XMn, the image interval shift amount Pn is defocus amount in # 13 of FIG. 4B. Is converted to On the other hand, when it is determined as LO-CON in # 65, including the case where the maximum correlation image interval is 2 or -2, at that time, the same correlation calculation as in the first time is performed. Finally, the LO-CON
If it is determined in step # 76 that the lens drive completion flag SF has been cleared, the routine does not follow this routine, and all defocusing is performed as in the first focus detection calculation until the focus is detected again. The focus detection calculation is repeated for all blocks in the amount range. When the in-focus state is detected, in the case of the one-shot AF, the lens driven flag SF is set at # 74.

Here, an example is shown in which refocus detection is performed after lens driving is completed.However, it is also possible to repeat focus detection while driving the lens, and in such an example, the lens drive completion flag SF indicates the focus detection. It can be set only at the time.
Here, the correlation value calculation image shift amount at the time of simple focus detection is
The five points of 2,1,0, −1, −2 are the values depending on the adjustment accuracy between the AF sensor and the re-imaging lens, etc., and if sufficient accuracy is secured, 1,0, − 3 points of 1, or 1,0, -1, -2,
Needless to say, four points of 2,1,0, -1 are also possible.

Finally, in FIG. 4 (a) and FIG. 4 (b), the ON / OFF discriminating unit of the focus detection sensitivity range changeover switch Swn is set to the ON / OFF discrimination of the mode changeover switch SOC to continue. It is also possible to switch between a wide and narrow focus detection sensitivity range by ass AF and one-shot AF.

According to the present invention, the shift amount is limited to the vicinity of the shift position corresponding to the in-focus state after the photographing lens has been driven at least once, so that the time for the focus detection calculation can be reduced. Yes, the AF operation cycle is shortened, and the ability to follow a moving subject is improved. Further, at this time, the focus detection sensitivity range for the subject is not changed (that is, all signals corresponding to the focus detection sensitivity range output from the photoelectric conversion element array are used). There is no inconvenience that the focal point changes and the focus is lost.

[Brief description of the drawings]

FIG. 1 is a block diagram of an automatic focus adjustment circuit, FIG. 2 is an explanatory diagram showing a pixel array of an image sensor, FIG. 3 is an explanatory diagram of switching of a focus detection sensitivity area within a field of view of a camera, FIG. 4 (a) and 4 (b) are flowcharts of the operation of the automatic focus adjustment circuit of FIG. 1, FIG. 5 is a flowchart showing an example of interpolation calculation, FIG. 6 is an explanatory diagram of a focus detection optical system, FIG. FIG. 7 is an explanatory diagram showing the positions of two images in focus detection, and FIG. 8 is an explanatory diagram for explaining problems of the conventional automatic focus detection device. Reference numeral 1 denotes a subject light beam, 2 denotes a photographing lens, 9,11 denotes two images, 12,14 denotes a photoelectric conversion element array. 15 ...... line sensors, 20a ...... photoelectric conversion circuit, 30 ...... microcomputer, S ₁ ...... AF switch, Soc ...... mode switch, Swn ...... focus detection sensitivity range selector switch. SF ... Lens driven flag.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Nobuyuki Taniguchi 2-30 Azuchicho, Higashi-ku, Osaka City International Building Minolta Camera Co., Ltd. Document JP-A-59-9611 (JP, A) JP-A-59-123810 (JP, A)

Claims (1)

(57) [Claims] 1. A subject light beam which has passed through each of a first and a second area of a taking lens which is symmetrical with respect to an optical axis is re-imaged to form two images into a first image and a second image. It is formed on a photoelectric conversion element array, and the mutual positional relationship between the two images is obtained from signals indicating the illuminance distribution from the first and second photoelectric conversion element arrays, thereby detecting the focus adjustment state of the taking lens. In the automatic focusing device for a camera, the shift position at which the best correlation is obtained by relatively shifting the positions of the two photoelectric conversion element arrays from the signal representing the illuminance distribution output from the first and second photoelectric conversion element arrays. Calculating means for obtaining; a detecting means for detecting a focus adjustment state based on the shift position; a driving means for driving the taking lens to a focus position based on the detected focus adjustment state; Control means for repeating focus detection operation by means and detection means and focus adjustment operation by drive means; and changing the focus detection sensitivity range for the subject after driving of the photographing lens by the drive means at least once. Instead, all of the signals output from the photoelectric conversion element array and corresponding to the focus detection sensitivity range are used, while the shift amount of the shift in the arithmetic means is limited to the vicinity of the shift position corresponding to the focus state. An automatic focusing device for a camera, comprising: a quantity limiting unit;