JPS62133412A - Focus detecting system - Google Patents

Abstract

PURPOSE:To speed up an operation time required for focus detection by making an arithmetic range in which the 1st and 2nd signals are relatively displaced narrower than a normal arithmetic range after the 2nd frame of continuous photographing in a continuous photographing mode. CONSTITUTION:Since it is expected in the continuous photographing mode that focus detection should be executed within a short period shorter than that of a single photographing mode and the change of defocusing value of an object is not generated so much, a relative displacement value (kc) in a comparatively small arithmetic range, i.e. k1=-kc and k2=kc, is set up to speed up the arithmetic operation. Since a range for the execution of correlative operation, i.e. the arithmetic range, is reduced at the continuous photographing mode, the time required for the focus detecting processing is shortened and focus detection corresponding to high speed continuous photographing can be attained. Since operation similar to normal photographing (single photographing) is executed in the 1st frame of the continuous photographing and the size of the range to be displaced is set up to the relative displacement value (kc) in the 2nd frame and after, probability generating the failure of focus detection is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in a focus detection method for detecting a focus state from the relative positional relationship between two images of an object.

(Background of the Invention) Conventionally, one type of camera focus detection device divides the exit pupil of a photographic lens and observes the relative positional displacement of two images formed by the light beams that have passed through each pupil area. For example, an aerial image formed on a predetermined focal plane (plane equivalent to a film plane) by two parallel imaging optical systems is guided to two sensor planes. , there is a secondary imaging method that detects the displacement of the relative positions of the two images.

JP-A-55-118019, JP-A-55-155
It is disclosed in Publication No. 331 and the like.

A schematic view of the secondary imaging type focus detection device is shown in FIG. 3. A field lens 3 is arranged on the same optical axis 2 as the photographing lens 1 whose focus is to be detected. Behind it, two secondary imaging lenses 4a are placed at symmetrical positions with respect to the optical axis 2,
4b is placed.

Furthermore, photoelectric conversion element rows 5a and 5b are arranged behind it. Apertures 6a, 6b are provided near the secondary imaging lenses 4a, 4b.
is provided. The field lens 3 forms an image of the exit pupil of the photographing lens 1 approximately on the pupil plane of the two secondary imaging lenses 4a and 4b. As a result, the light beams incident on the secondary imaging lenses 4a and 4b respectively correspond to the secondary imaging lenses 4a and 4b on the exit pupil plane of the photographic lens 1. They are emitted from areas of equal area that do not overlap each other. An aerial image formed near the field lens 3 is converted into photoelectric conversion element arrays 5a, 5 by secondary imaging lenses 4a, 4b.
When the image is re-formed on the plane b, the two images on the photoelectric conversion element arrays 5a and 5b change their positions based on the displacement of the aerial image position in the optical axis direction. Fig. 4 shows this situation. As shown in Fig. 4 (^), at the time of focusing, the two images are located at the center of the photoelectric conversion element arrays 5a and 5b, and as shown in Fig. 4 (B). As shown, when the rear focus is on, the two images move in a direction away from the optical axis 2, and as shown in FIG. 4 (CC), when the front focus is on, the two images move in a direction toward the optical axis 2. The focal state of the photographic lens 1 can be detected by photoelectrically converting this image intensity distribution and detecting the displacement (shift) of the relative positions of the two images through electrical signal processing.

A method for processing the photoelectric conversion signals output from the photoelectric conversion element arrays 5a and 5b is disclosed in Japanese Patent Application Laid-open No. 58-14230.
No. 6, US Pat. No. 4,333,007, etc. are disclosed. in particular.

The number of photoelectric conversion elements constituting the photoelectric conversion element row 5a or 5b is N, and the first (i≠0....., N-1)
The image signals from the photoelectric conversion element arrays 5a and 5b are A(i)
, B(i), the following formula %( is calculated for kI≦≦2. Note that M is (M =
The number of pixels to be calculated is expressed as N-1kl-1). A
(i) OB (D is an operator for A(i), BU), for example, A (i) mouth BN) = l A(i) −B(DI
(2) m.

A(i)OBU)=l A(i)-BU)I (
3) A(i)OB(j)=max [A(i).

B(Dl (4)A(i)OBU
)=m l n [A(i).

B(j)] (5) and other calculation formulas are considered, where formula (2) calculates the absolute value of the difference between A(i) and B (D), formula (3) calculates the power value thereof, and formula (4) is A(i)
, B(D) represents the extraction of the larger one, and equation (5) represents the extraction of the smaller one. According to the above definitions,
Vs (k) and V2 (k) can be regarded as correlation quantities in a broad sense. Furthermore, according to equation (1), Vl(k) is actually the correlation amount according to the above definition at a displacement of (k-1), and similarly, v2(k) is the correlation amount at a displacement of (k+ 1), respectively. It means. Gatte, Vt.
(k) , V2 (k) The evaluation amount V (
k) is the image signal A(i), B at the relative displacement amount k
It represents the change in the amount of correlation in (i). Since the amount of change at the peak of the correlation amount is -rQJ, V(k) -V(k+ 1) < 0
(8) Considering that there is a peak of the correlation amount at +13 in the interval [k, and interpolating the values of v(k) and v(k+t), You can know the amount of deviation. Figure 5 shows the number of photoelectric conversion elements, 16 (N=
16), image signals A(i) and B(i) of 21 are shown. In this case, there is a deviation amount of P. 6th
The figure shows the evaluation amount V (k) according to the above equation (2) when the relative displacement amount k is changed within the calculation range of -N/2≦≦N/2. As mentioned above, V(k)−V(k+1)<0
The deviation amount P can be obtained by linearly interpolating the values of V(k) and V(k+1). Furthermore, in FIG. 7, the relative displacement amount k
Each evaluation amount V (
The correspondence relationship between image signals A(i) and B(i) when calculating k) is diagrammatically shown, and the shaded area is the photoelectric conversion element to be subjected to the correlation calculation.

In the above calculation of the evaluation amount V (k), the calculation time varies greatly depending on the calculation range for the relative displacement amount. Therefore, it is desirable to perform calculations in a small range if possible, but if it is too small, the amount of deviation between the two images when the TI shadow lens is largely defocused will deviate from the calculation range of the amount of relative displacement. Accurate focus detection was sometimes not possible. Therefore, normally, the lower limit value of the calculation range is 1 and the upper limit value is 2, which corresponds to the number of photoelectric conversion elements in the photoelectric conversion element array (the number of pixels of the sensor), k, = -N/2゜k2= N/2
Because of this, it takes a considerable amount of calculation time to perform the focus detection calculations, and when high-speed operation is required, such as during continuous shooting, this significantly impairs continuous shooting performance. there were.

(Object of the Invention) An object of the present invention is to provide a focus detection method capable of solving the above-mentioned problems and performing focus detection compatible with high-speed continuous shooting.

(Features of the Invention) In order to achieve the above object, the present invention provides that, in continuous shooting mode, the calculation range for relatively displacing the first and second signals is changed from normal calculation at least after the second frame of continuous shooting. It is characterized in that it is made smaller than the range, thereby speeding up the calculation time required for focus detection.

(Embodiments of the Invention) The present invention will be described below in detail based on illustrated embodiments.

FIG. 1 is a block diagram showing an example of a camera focusing device suitable for implementing the present invention. PH1 is the control circuit of the camera.For example, there is a CPU (central processing unit) inside,
It is an l-chip microcomputer in which RAM, ROM, EEFROM (electrically erasable programmable ROM), input/output board, etc. are arranged, and the ROM and EEFROM are arranged.
A series of camera control software and parameters including AF control are stored in the EFROM.

DBUS is a data bus, and SHT is a data bus DBU while the control signal C3HT is input from the control circuit PR3.
The shutter control circuit APR accepts data input via S and controls the running of the shutter leading and trailing curtains (not shown) based on the data, and the APR connects the data bus DBUS while the control signal CAPR is input. The aperture control circuit, which receives data input via the data bus DBUS and controls an aperture mechanism (not shown) based on the data, receives data input via the data bus DBUS while the control signal CD5P is input. A display circuit for displaying various photographic information based on the data, and SWS are a group of switches (not shown) such as a release switch, a continuous shooting mode switch, and switches for setting various information.

SPC is a photometric circuit, and its output analog photometric signal 5SPC is sent to the control circuit PR3, where it is A/D converted and used to control the shutter control circuit SHT and aperture control circuit APR. Used as photometric data. LCOM is a lens communication circuit that accepts data input via the data bus DBUS while the control signal CLCOM is input, and performs serial communication with the lens unit described later based on the data, and synchronizes with the clock signal LCK. data DCL for driving the lens is transmitted to an internal lens control circuit to be described later, and at the same time, lens information DLC such as the maximum defocus amount of the photographing lens (described later) is serially input from the internal lens control circuit. B.S.
Y is a signal to inform the camera that the photographing lens is moving, which will be described later. When this signal is generated, the serial communication is not performed.

LNSU is a lens unit, and LPRS is an in-lens control circuit that drives the motor MTR based on serially input data DCL to move the photographing lens LNF. It has a ROM that stores information such as values. The ENC detects, for example, a pulse signal generated as a lens barrel holding the photographing lens LNF moves, and transmits the encoder pulse signal EPL as a position signal of the photographing lens LNF to the in-lens control circuit LPRS.
The encoder circuit SDR outputs to the control circuit PR
According to each signal input from S, two sensor arrays SAA,
Line sensor SN, such as COD, with SAB
This is a sensor drive circuit that controls S.

Next, the operation will be explained with reference to the flowchart shown in FIG. Note that the operations of the shutter control circuit 5) (T, aperture control circuit APR1, display circuit DSP, and photometry circuit SPC) are not directly related to the present invention, and will therefore be omitted here.

[Step l] Drive the line sensor SNS via the sensor drive circuit SDR to generate two image signals A(i),
Obtain B(i). To briefly explain the operations of the control circuit PR3, sensor drive circuit SDR, and line sensor SNS at this time, when the accumulation start signal STR is generated in the control circuit PR3, the sensor drive circuit SDR outputs a clear signal CL to the line sensor SNS. Then, the charges in each photoelectric conversion section of the sensor arrays SAA and SAB are cleared. Then, the line sensor SNS uses the secondary imaging lens, etc. (first
Although not shown in the figure, photoelectric conversion and charge accumulation operations of the optical images formed on the sensor arrays SAA and SAB are started by the sensor arrays arranged as shown in FIG. 3). When a predetermined period of time has elapsed after the start of the above operation, the sensor drive circuit SDR transfers the transfer signal S) (to the line sensor SNS).
The charge accumulated in the photoelectric conversion section is transferred to the CCD section. At the same time, the sensor drive circuit SDR outputs an accumulation end signal END to the control circuit PR3.
Wait for CCDCD drive clock C to change from CC
When DCD drive clock C is applied, sensor drive circuit SD
R generates CCD drive signals φl and φ2 and outputs the signals to the line sensor SNS. CCD drive signal φ1,
When φ2 is input, the line sensor SNS outputs an analog image signal 5SNS to the control circuit PR3 in accordance with this signal. As a result, the control circuit PR3 A/D converts the analog image signal 5SNS in accordance with the CCDCD drive clock C,
The two image signals A(i) and B(i) are stored at a predetermined address in the RAM.

[Step 2] Check the status of the continuous shooting mode switch in the switch group SWS, and if it is in continuous shooting mode, step 13
If not, proceed to step 3.

[Step 3] Communicate with the lens unit/unit LNS U via the lens communication circuit LCOM, obtain the maximum defocus amount MD of the currently attached photographic lens LNS from the lens information DLC, and calculate the relative displacement according to this value. If the quantity k is within the calculation range of −MD≦≦MD, that is, 1=−
MD, set 2=MD.

[Step 4] For example, a correlation calculation such as the above-mentioned equations (2) to (5) is performed to obtain focus detection information, that is, the amount of shift P between the two images at this time.

[Step 5] Even if the shift amount P can be detected, if the contrast of the signal is low and the reliability of the result is poor, the focus cannot be detected, so in such a case, go to Step 10.
If the focus can be detected, the process moves to step 6.

[Step 6] Compare the absolute value of the amount of deviation P with a predetermined value, and if the amount of deviation P is smaller than the predetermined value, that is, the amount of change that can be considered to be in focus, proceed to step 9; otherwise, proceed to step 9. moves to step 7.

[Step 7] Check whether the subject is in front or rear focus based on the sign (positive or negative) of the shift amount P, and send the data to the display circuit DSP to display the focus state at that time.

[Step 8] Calculate the amount of movement of the photographing lens LNS based on the shift amount P obtained in Step 4, and send the data to the in-lens control circuit LP via the lens communication circuit LCOM.
Output to R3. To briefly explain the operation on the lens unit LNSU side at this time, the in-lens control circuit LPR
3 drives the motor MTR to move the photographic lens LNS to a position corresponding to the data, that is, until the number of encoder pulse signals EPL input from the encoder circuit ENC matches the data.

[Step 9] Data indicating that the focus is in focus is sent to the display circuit DSP, and the data is displayed.

[Step 10] Compare the maximum defocus amount MD obtained in step 3, which was determined to be unable to detect the focus in step 5, with the fixed defocus amount MS, and
If D>MS, the process moves to step 12; if MD≦MS, the process moves to step 11.

[Step 11] If MD≦MS, it means that the maximum defocus value of the currently attached photographic lens LMS is relatively small, and in this case, the photographic lens LM
Move S by a predetermined amount 1 to perform a so-called search operation,
Even if focus detection is performed again, the contrast cannot be expected to increase because the amount of defocus is small to begin with, and as a result, the probability that focus will be detected next time is low.Therefore, in such a case, the search operation is not performed and the display Data indicating that the focus cannot be detected is output to the circuit DSP, and the data is displayed. After that, the process moves to step 1 again.

[Step 12] When MD>MS, contrary to the case when MD≦MS, there is a high probability that the focus can be detected by a search operation, so a search operation is performed.

[Step 13] Determine whether it is the first frame of continuous shooting,
- If it is a piece, the process moves to step 3; otherwise, the process moves to step 14.

[Step 14] In continuous shooting mode, focus detection must be performed in a shorter time than in single shooting mode,
Since it is expected that the defocus of the subject will not change much during continuous shooting, the relative displacement amount kc is set in a relatively small calculation range, i.e., = -kc, and 2 = k.
Set c to speed up the calculation.

[Step 15] Correlation calculation is performed to obtain focus detection information within the calculation range set in step 14.

[Step 16] As in step 5, it is determined whether focus detection is possible or not. If focus detection is not possible, performing a search operation during continuous shooting is not recommended in terms of continuous shooting performance. etc., so the process moves to step 11 to display an inability display. If the focus can be detected, the process moves to step 6 to determine the focus. After that, as described above, step 9 or step 7 → step step Move to 8.

According to this embodiment, in the continuous shooting mode, the range in which the correlation calculation is performed, that is, the calculation range, is made small.
The time required for focus detection processing is shortened, making it possible to perform focus detection compatible with high-speed continuous shooting. In addition, the first frame of continuous shooting performs the same operation as during normal shooting (single shooting), and the size of the range to be displaced for the first time after the second frame is set as the relative displacement amount kc. , the probability that focus cannot be detected is reduced.

(Modified Example) In this embodiment, the first frame of continuous shooting is performed in the same manner as in normal shooting, but in continuous shooting mode, the process immediately moves to step 14, that is, the size of the calculation range is changed. It may be set to the relative displacement amount kc. If this is done, the probability that the focus will be detected becomes low, but it becomes possible to take pictures that meet the original purpose of selecting the continuous shooting mode.

(Effects of the Invention) As explained above, according to the present invention, in the continuous shooting mode, the calculation range for relatively displacing the first and second signals is changed from the normal range at least after the second continuous shooting frame. Since the calculation range is made smaller than the calculation range, thereby speeding up the calculation time required for focus detection, focus detection corresponding to high-speed continuous shooting can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a camera focus adjustment device implementing the present invention, FIG. 2 is a flowchart thereof, and FIG.
The figure is a layout diagram showing the optical system of a general secondary imaging type focus detection device, Figure 4 is a diagram showing the relationship between the focus detection state and image blur in the secondary imaging type, and Figure 5 is a diagram showing the relationship between the focus detection state and image blur in the secondary imaging type. A diagram showing an example of the image signal output from two sensor arrays in the imaging method, FIG. 6 is a diagram showing changes in the evaluation amount in the secondary imaging method, and FIG. 7 is a diagram showing focus detection in the secondary imaging method. FIG. 7 is a diagram showing a correspondence relationship between two images during calculation. . PH1...control circuit, LCOM...lens communication circuit, LNSU...lens unit,
SDR...Sensor drive circuit, SNS...
・Line sensor, k...Relative displacement amount. Patent Applicant Canon Co., Ltd. Representative Minoru Nakamura Figure 5 Figure 6

Claims (1)

[Claims] 1. The optical system forms first and second images whose relative positional relationship changes depending on the focal state of the imaging optical system to be detected, and corresponds to the first and second images. The first and second signals that have been photoelectrically converted are obtained by a plurality of photoelectric conversion means, and correlation information is calculated by relatively displacing the first and second signals, and the correlation information is In the focus detection method, in which the focus state of the imaging optical system is detected by determining the relative positional relationship between the first and second images based on the A focus detection method characterized in that a calculation range for displacing the image is made smaller than a normal calculation range at least after the second frame of continuous shooting.