JPH0553042A - Focusing device - Google Patents

Abstract

PURPOSE:To derive the best focal position of an arbitrary area of a screen with high accuracy by a simple constitution without having complicated and enormous correction data by executing driving control of a photographic lens, based on a peak value of an MTF value. CONSTITUTION:By a sensor (CCD) 3 being orthogonal to two directions, a luminous flux of an object to be photographed which passes through a photographic lens 2 is photodetected, and in an arithmetic part 17, a peak of an MTF value is derived, based on to kinds of output of the CCD 3, and in a driving control part 14, driving control of the photographic lens 2 is executed, based on this peak value. That is, while driving the photographic lens 2, a position in which an integral value (MTF signal) of a video signal which passes through a digital filter becomes a peak, the photographic lens 2 is stopped in its position and it becomes a focused position. An encoder circuit converts a driving amount of the photographic lens 2 driven by the driving control part 14 to the number of pulses. A CPU can know the present lens position by counting the number of pulses sent from the encoder circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to correction of focus detection error due to aberration (particularly astigmatism) in an apparatus capable of detecting focus on a region of a screen position.

[0002]

2. Description of the Related Art Focusing devices disclosed in JP-A-63-172209 and JP-A-63-47711 include:
The shooting screen is divided into a plurality of areas and a plurality of automatic focus detection elements arranged in the respective areas, and outputs of the plurality of focus detection elements are arithmetically processed according to a predetermined algorithm to output a focus detection signal. A calculating means, a means for outputting a plurality of correction data relating to the aberration of the photographing lens corresponding to each area of the photographing screen divided into the plurality of areas built in the interchangeable photographing lens, and output from the calculating means Correction calculation means for correcting the focus detection signal by the correction data relating to the aberration, and variable the weighting of the correction data when correcting the focus signal according to predetermined information input from the outside. It is a thing.

[0003]

However, the conventional focusing device has the following drawbacks.

(1) Since it is necessary to store the correction coefficient of the aberration in accordance with a plurality of areas of the screen, the correction coefficient becomes huge when the number of areas and the number of lens types increase, and the man-hour for determining the coefficient is very large. In addition, the ROM capacity becomes very large. (2) Since focus detection is performed by extracting an image signal in one direction of a predetermined area of the screen, focus detection accuracy is degraded depending on the subject.

The focusing device of the present invention has been made in view of such a problem, and its purpose is to obtain the best focus of an arbitrary area of the screen without complicated and enormous correction data. The purpose is to obtain the position with high accuracy with a simple configuration.

[0006]

In order to solve the above-mentioned problems, a focusing device of the present invention receives a light flux of a subject which has passed through a photographing lens, and sensor means which are orthogonal to each other in two directions. It comprises an arithmetic means for obtaining a peak of the MTF value based on the two kinds of outputs, and a drive control means for controlling the drive of the photographing lens based on the peak of the MTF value.

[0007]

According to the present invention, the two predetermined areas of the screen are orthogonal to each other.
The MTF value in the direction is calculated for each predetermined defocus interval, the peak positions of the MTF in the two directions of the screen are detected, and the best focus position is obtained from the two peak positions.

[0008]

First, the basic concept of the focusing device according to the present invention will be described. As shown in FIG. 1, the present invention receives an object light flux that has passed through a photographing lens 2 by an orthogonal sensor 3 which is orthogonal to two directions, and based on two kinds of outputs of this sensor 3, an MTF (Modulation Transfer Function). A calculation unit 17 for obtaining a peak of a value and a drive control unit 14 for controlling the driving of the photographing lens based on the peak of the MTF value are provided. Here, the orthogonal sensor 3 corresponds to a CCD as an image pickup device described later, and the calculation unit 17 is a CP described later.
The U15 and the digital filter 8 are included, and the drive control unit 14 corresponds to a motor drive circuit described later. Embodiments of the present invention will be described below with reference to FIGS.

FIG. 2 is a block diagram of an electronic circuit of a focusing device showing an embodiment of the present invention. In the figure, the subject light that has passed through the diaphragm 1 and the taking lens 2 that is moved to the in-focus position by the motor drive circuit 14 is C
An image is formed on the CCD 3 as an image pickup element driven by the CD drive circuit 15. Then, the image pickup signal photoelectrically converted by the CCD 3 is subjected to level stabilization processing by the AGC circuit 4. Further, the video signal processing circuit 5 performs processes such as color separation, white balance, and γ correction, and the video signal recording circuit 6 and an electronic viewfinder (referred to as EVF).
Sent to 7. Although the present embodiment is applied to an electronic image pickup camera, the video signal recording circuit 6 is not necessary when applied to a conventional silver halide camera.

The video signal of the AGC circuit 4 is digitized by the A / D conversion circuit 9 and stored in the memory of the video RAM 10. Focus frame selection circuit 11
A video signal corresponding to the focus frame selected by, for example, the frame (FR) in FIG. 3 is sent to the digital filter 8 via the CPU 15. The digital filter 8 is a circuit for separating a signal having a band frequency suitable for focus detection from a video signal. The video signal filtered by the digital filter 8 is input to the CPU 15 again, and the focus detection calculation described later is performed. As the focus detection method in this embodiment, a so-called hill climbing method, which is a basic method of a known contrast method, is used. That is, while driving the taking lens 2, the position where the integrated value of the video signal that has passed through the digital filter (hereinafter referred to as the MTF signal) reaches a peak is detected, and the taking lens 2 is stopped at that position to focus. It is a position-based method. The encoder circuit 13 is a circuit that converts the drive amount of the taking lens 2 driven by the motor drive circuit 14 into a pulse number. The CPU 15 can know the current lens position by counting the number of pulses sent from the encoder circuit.

The focus frame selected by the focus frame selection circuit 11 is designated and displayed on the EVF 7 by the focus frame display circuit 13. FIG. 4 shows an astigmatism diagram. The horizontal axis is the deviation from the paraxial focus, and the vertical axis is the height from the intersection 0 of the optical axis with the CCD 3. As shown in FIG. 4, since the focus position is different between the meridional surface (M) and the sagittal surface (S), the meridional surface is in focus, the sagittal surface is in focus, or an intermediate position depending on the pixel arrangement of the CCD 3. It is in focus. For example, if the MTF peak position of the sensor output arranged in the S direction in FIG. 4 is focused, the M direction may be out of focus. Further, if the image contrast in the S direction is low, the focusing accuracy in the S direction itself will be poor. In view of this point, the present invention seeks the best focus position from the MTF peak positions in two orthogonal directions within a predetermined area of the screen.

FIG. 5 is an MTF curve in which the horizontal axis is the lens position and the vertical axis is the MTF. In FIG. 5, solid line 1 is the MTF of the meridional surface, solid line 2 is the MTF of the sagittal surface, dotted line 3 is the MTF in the X direction (see FIG. 5), and dotted line 4 is the MTF in the Y direction.
Represents. The best focus position over a predetermined coefficient peak position of the first curve and second curve Request (l _o). However, since it is generally difficult to arrange the sensors in the M direction and the S direction in FIG. 5, actually, the MTF peak positions l _x and l _y in two directions orthogonal to each other in the X direction and the Y direction in FIG.
In this way, the best focus position (l _o ) is obtained.

FIG. 6 is a diagram showing the position of the focus frame selected by the focus frame selection circuit, and FIG. 7 is a pixel array (x ₁ , x ₂ ... x _n ) in the X direction in the focus frame shown in FIG. And the pixel array in the Y direction (y
₁ , y ₂ ... Y _n ).

FIG. 7 shows another embodiment showing a method for extracting a sensor output. The two-dimensional pixel signals S _ij are added in the amount of n pixels in the X direction and the Y direction to obtain 1 in the Y direction and the X direction, respectively.
Corresponds to output for pixels. Hereinafter, the focus detection procedure will be described in detail with reference to the flowcharts of FIGS.

In step S1 of FIG. 8, when the automatic return type switch SW1 is turned on, focus detection operation (hereinafter referred to as AF
(Referred to as operation) starts. Next, the CPU 15 activates the motor drive circuit 14 so that the photographing lens 2
Is started (step S2). Next, the CPU 15
The position of the focus frame designated by the focus frame selection circuit 11 is read by (step S
3). Next, the video signals in the focus frame are sequentially read from the video RAM 10 into the RAM of the CPU (step S4). For example, in the case of the extraction method of FIG. 7, _first , x ₁ , x ₂ ... X _n in the X direction are sequentially read. Then C
The PU 15 sends this signal to the digital filter 8 and, after filtering, inputs the filter output signals x ′ ₁ , x ′ ₂ ... X ′ _n to the CPU 15 again (step S
5).

[0016] Next, in _{CPU15, x'1, x'2 ...} x
′ _N addition output, X _t = Σx ′ _i is obtained (step S
6). This is the MTF output in the X direction. The Y direction is also digitally filtered (step S7), and the MTF output, Y _t = Σy ′ _i is obtained (step S8).

[0017] Next, detecting a peak value X _pt of X _t (step 9). If the peak value of X _t is detected, the lens position l _{x at} which X _pt is obtained is stored in the RAM in the CPU 15 (step S10). If step S9
In, X peak value X _pt of _t is subjected to detection of a peak value Ypt the next Y _t is not detected (step S11), and wherein Y _t lens position l of if Y _p long by detecting the peak value of
_y is stored in the CPU 15 (step S1)
2). If the Y _t peak value is not detected in step S11, the process returns to step S4. On the other hand, step S
If the peak Y _pt of Y _t is already detected in 13, the lens peak positions in the two directions are detected, and the lens drive is stopped next (step S15). In step S13, if no peak position of the peak Y _pt of Y _t is still detected, the processing proceeds to step S11. If the peak X _pt of X _t has been detected in step S14, the lens driving is similarly stopped next,
If _Xpt is not detected in step S14, the process returns to step S4.

Now, if the lens drive is stopped,
In S16 of FIG. 10, it is determined whether (X _pt ≤C _o and Y _pt ≤C _o ). If (X _pt ≤C _o and Y _pt ≤C _o ), the contrast is very low and the reliability of focus detection is low, and an unfocusable display is displayed on the EVF 7 (step S).
17). If (X _pt ≤C _o and Y _pt ≤C _o ), then (X _pt ≤C _o and Y _pt > in step S18.
C _o ), if yes, M in Y direction
TF only drives the lens as reliable location of l _y (step S19). If in step S18 (X
_{If pt} ≤C _o and Y _pt > C _o ), step S2
It is determined whether 0 (X _pt > C _o and Y _pt ≦ C _o ).
When (X _pt > C _o and Y _pt ≦ C _o ), set the lens to l _x
Is driven to the position (step S21). As described above, when the lens is driven to l _x or l _y , it is determined whether or not the release switch SW2 is turned on (step S
22) If it is released, the exposure control operation is performed thereafter. It should be noted that the video camera does not require the exposure control operation after step S22.

On the other hand, if it is not (X _pt > C _o and Y _pt ≤C _o ) in step S20, that is, (X _pt > C _o and Y _p +> C _o ), as shown in FIG. , The lens is driven to the position of (l _x + l _y ) / 2 (step S
25). FIG. 12 shows another embodiment of FIG. 11 in which the position of the center of gravity (X
_{pt · l y + Y pt ·} l x) / ( driving the X _pt + Y _pt) lens at the position of (step S26).

In the flow after step S22 in FIG. 10, the position of the focus frame is automatically returned to near the center of the screen after the exposure control in step S23 is completed (step S24). FIG. 12 shows another embodiment of the present invention.
This is a method of driving the lens to the peak position of the added value of the MTF outputs in the X and Y directions shown in FIG.

From (SW1 ON) to (filter output addition,
Up to Y _t = Σy _i ) is the same as in FIG. If not detecting a peak value of X _t + Y _t in step ST9 of FIG. 12 returns to step ST4. Now, if the detected peak value of X _t + Y _y in step ST9, X _t + Y _t is the peak lens position l _{x, y}
Is stored in the RAM of the CPU (step ST10), and the lens driving is stopped (step ST11). Next, in step ST12, it is detected whether or not X _t + Y _t ≤C _o ,
If X _t + Y _t ≤C _o , the unfocusable display is displayed on the EVF (step ST13), and the focus frame is initialized (the focus frame is returned to the vicinity of the center of the screen) (step ST14).

If X _t + Y _t ≤C _{o is} not _satisfied in step ST12, then the lens is driven to the position of l _{x, y} (step ST15). Next, in step ST16,
If the release switch SW2 is turned on, after exposure control is performed (step S17), the focus frame is initialized and the process ends. In the embodiment of FIG. 12, FIG.
It is not necessary to individually detect the MTF peak positions in the X direction and the Y direction as in the embodiment described above, which facilitates control.

Although the contrast method is used as the focus detection method in the above embodiment, the best focus position in two directions is obtained from the phase difference between two images in two orthogonal directions even in the known phase difference method. The best focus position can be determined by the method of the present invention.

[0024]

As described above in detail, according to the present invention, it is not necessary to have complicated and enormous correction data, and the best focus position of an arbitrary area of the screen can be obtained with high accuracy by a simple structure. It is possible to provide a focusing device capable of performing the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic concept of the present invention.

FIG. 2 is a block diagram of an electronic circuit of a focusing device according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a selected focus frame.

FIG. 4 is a diagram showing astigmatism.

FIG. 5 is an MTF in which the horizontal axis is the lens position and the vertical axis is the MTF.
The figure which shows a curve.

FIG. 6 is a diagram showing a position of a focus frame selected by a focus frame selection circuit.

7 is a diagram showing a pixel array in the X direction and a pixel array in the Y direction in the focus frame shown in FIG.

FIG. 8 is a diagram showing another example of a sensor output extraction method.

FIG. 9 is a part of a flowchart for explaining a focus detection procedure according to the present invention.

FIG. 10 is a part of a flowchart for explaining a focus detection procedure according to the present invention.

FIG. 11 is a diagram showing an embodiment in which a part of the flowchart of FIG. 10 is modified.

FIG. 12 is a diagram showing an embodiment in which a part of the flowchart of FIG. 9 is modified.

FIG. 13 is a flowchart for explaining another embodiment of the focus detection procedure according to the present invention.

[Explanation of symbols]

1 ... Aperture, 2 ... Shooting lens, 3 ... Quadrature sensor (CC
D), 4 ... AGC circuit, 5 ... video signal processing circuit, 6 ... video signal recording circuit, 7 ... EVF, 8 ... digital filter,
9 ... A / D conversion circuit, 10 ... Video RAM, 11 ... Focus frame selection circuit, 12 ... Focus frame display circuit, 13 ... Encoder circuit, 14 ... Drive control section (motor drive) Circuit), 15 ... CPU, 16 ... CCD drive circuit, 17 ... arithmetic unit.

Claims (1)

[Claims] 1. A sensor means for receiving a light flux of a subject which has passed through a taking lens, orthogonal to two directions, an arithmetic means for obtaining a peak of an MTF value based on two kinds of outputs of the sensor means, and the MTF. A focusing device comprising: a drive control means for controlling the drive of the taking lens based on a value peak.