JP2745010B2 - Auto focus method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an autofocus method used for various video cameras and the like. (Prior Art) Conventionally, focusing on the fact that the voltage level of a high-frequency component of a video signal obtained by photographing a subject corresponds to the definition of a reproduced image, gain control is performed on the voltage of the high-frequency component. After that, the focus voltage is extracted as a focus voltage, and a focus lens is driven so that the focus voltage becomes a maximum level, thereby performing focusing such that the position of the lens coincides with the just focus position. Such a focusing method is known as a so-called hill-climbing servo method. This method is described in NHK Technical Research Report 40, Vol. 17, No. 1, No. 86
No. 21 page, or the literature such as the Television Society Technical Report ED No. 675 published in November 1982. (Problems to be Solved by the Invention) By the way, when the position of the focus lens at the start of focusing is far from the just focus position, the frequency component of the subject is small, and the level of the base of the focus voltage is small. In such a case, that is, when photographing a bird flying in the sky immediately after photographing a short distance, there is a problem that it takes time to reach the bottom of the focal voltage as described above. (Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an autofocus method capable of solving the above problems and realizing faster focusing. Aim. In order to achieve this object, the present invention takes out a predetermined high-frequency component of a video signal obtained by photographing a subject while moving the focusing member in the optical axis direction as a focal voltage, and moves the focusing member. An auto-focus method for performing focusing by moving the focusing member in a predetermined direction based on a change in the focus voltage accompanying the detection of the current position of the focusing member at the start of focusing. The data and the data of the predetermined position having the highest probability of becoming the preset focus position are compared by the comparing means to calculate the positional relationship with the predetermined position, and the focusing member is moved from the current position based on the calculation result. The auto fork is characterized in that it is moved in the direction of the predetermined position. There is provided a scan method. (Operation) According to the autofocus method as described above, there is a large probability that the focusing member moved at the same time as the start of focusing reaches the base of the focal voltage due to the initial movement, or the direction of the initial movement is equal to the direction of the just focus position. Become. Therefore, the time required for focusing can be reduced. (Embodiment) Hereinafter, a preferred embodiment according to the present invention will be described with reference to FIG.
This will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an autofocus apparatus for realizing an autofocus method according to the present invention. This autofocus apparatus includes an afocal lens 5 and a focus lens (master) as a focusing member in the present embodiment. System lens 1). Focusing is performed by moving the focus lens 1 in a predetermined direction (the direction of arrow A or B) in the optical axis direction by the pulse motor 2, and the focus lens 1 is described later simultaneously with the start of focusing. The focus lens 1 is moved in a predetermined direction.
It is supplied to the microcomputer 3 as position information S ₁ is detected by the rotary encoder provided in the pulse motor 2. In addition, the imaging light from the subject which is incident through the optical system 6 as described above is a CCD that is an imaging unit in the present embodiment.
Is photoelectrically converted into an electrical video signal S ₂ in the imaging element 7 using the (charge coupled device) or the like. Then, the video signal S ₂ is supplied to the camera circuit, not shown is amplified by the amplifier 8 is supplied to a band pass filter (BPF) 9, the bandpass filter 9, from the video signal S ₂ A predetermined high frequency component is extracted and supplied to an automatic gain control circuit (AGC) 10. Then, the automatic gain control circuit 10 controls the gain so that the high-frequency component falls within a predetermined level, and then supplies the high-frequency component to a detector (DET) 11. Figure 2 on the focus voltage En as shown is thus obtained which corresponds to a predetermined high-frequency component of the video signal S _2. The focus voltage En is digitized by an A / D (analog / digital) converter 12 and supplied to the microcomputer 3. Then, the microcomputer 3 controls the focus lens 1
Is sequentially sampled every field from the start of focusing. Further, the microcomputer 3 includes a plurality of reference voltages SEn (1 ≦
n ≦ max) and a unique number (corresponding to n) for each reference voltage SEn. Then, the microcomputer 3 sequentially compares the levels of the reference voltages SEn with the focus voltages detected as described above,
When they match, only the number unique to the matching reference voltage is read. Here, the microcomputer 3 stores the magnitude relationship between the numbers unique to each reference voltage, and when the newly read number is larger than the number read before that, the force lens 1 There it is judged that does not reach the just-focus position P, and the control signal S ₃ that the focus lens 1 continues as it is moving motor driving circuit
Supply 13 As described above, the autofocus device according to the present embodiment can read the number unique to each reference voltage SEn and continue to move the focus lens 1 based only on this number, so that the difference between the respective focus voltages is actually obtained. Even when the voltage becomes smaller than the detection limit value, reliable focusing can be performed. On the other hand, the microcomputer 3 when the Asemise voltage En of the respective reference voltage SEn ... the same level ... is detected, taking the position information S ₁ indicating the position of the focus lens 1 at that time. In this embodiment, the focus voltage is taken into the microcomputer 3 as discrete information for each field.
Therefore, in this embodiment, the value taken in is the value of each reference voltage SE.
The focus voltage En detected at the time when the value n exceeds n for the first time has reached the reference voltage value SEn.
n and is adapted to take in the position information S _1. Further, in the above-described autofocus device, as shown in FIG. 3, when a unique number is detected twice consecutively in the reference voltage value SEmax taken as having reached the maximum reference voltage SEmax, , The just focus position P is located between the two detection positions. Therefore, when the same number is read twice, if the focus lens 1 is moved to an intermediate position between the two detection positions, the position of the focus lens 1 coincides with the just focus position P. Can be done. Therefore, in such a case, the microcomputer 3 moves the focus lens 1 in the opposite direction (the direction of the arrow B) to the position information.
The control signal S ₃ that is moved by a predetermined amount based on the S ₁ by supplying to the motor drive circuit 13 performs focusing by rotating the pulse motor 2 in the opposite direction. On the other hand, as shown in FIG. 4, when the number read as described above is at a lower level than the number read before it, the previous detection position is the just focus position P.
It turns out that. Therefore, in such a case, the focus lens 1 can be made to coincide with the just focus position P by returning the focus lens 1 to the previous detection position. Even in this case, the microcomputer 3 as in the above-described control signal S ₃ that moves the focus lens 1 in the opposite direction is supplied to the motor drive circuit 13, to perform focusing. Further, the microcomputer 3 is always with confirming the current position of the focus lens 1 by the position information S _1, position on the highest optical axis probability of just focus position (hereinafter referred to as "predicted just focus position" ) Is remembered. The microcomputer 3 determines the initial movement direction at the start of focusing based on the positional relationship between the data of the current position at the start of focusing and the data of the preset expected focus position. The direction is the direction toward the expected just focus position. Thus, useless movement of the focus lens 1 during focusing, that is, movement in the direction opposite to the jaspint position can be minimized, and more rapid focusing is realized. The predicted just focus position may be obtained experimentally, or may be appropriately replaced by the microcomputer 3 with a position having the highest frequency of the just focus position. The expected just focus position in the present embodiment is determined as follows. That is, the focal length f and the just focus position corresponding to the subject distance u have a relationship as shown in FIG.
In principle, the just focus position is shifted to one side (left side in the figure) of the movable range 1 of the focus lens 1 as is apparent from FIG. Therefore, in this embodiment, the subject distance is an intermediate distance,
The just focus position P 'when the focal length is intermediate is set as the expected just focus position. In addition, this expected sharp focus position is set to the focal length f.
And the microcomputer 3 may set the just-in-focus position as the most frequently used position so far. In this embodiment, the initial movement direction in the case where the focusing is once completed and then the focusing is performed again to check the just focus position is the moving direction immediately before the end of the previous focusing. That is, as shown in FIG. 6, the focus voltage E1 detected while actually moving the focus lens 1 in the direction A in FIG.
Is delayed by an electrical error from the true focus voltage E2 detected while stopping the focus lens 1 at the detection position. That is, for example, the light is photoelectrically converted and stored in an imaging device such as a CCD after a predetermined time.
Therefore, it is delayed by the time required for photoelectric conversion. When the focus lens 1 moves, for example, in the direction B in the drawing, the focus voltages E1 and E2 are determined by the motor 2 controlled by the microcomputer 3 and the focus lens 1 driven by the motor 2. The focus voltages E3 and E4 are shifted from each other by an amount corresponding to the mechanical coupling error. If the focus lens 1 is moved to the sixth
If focusing is started from point A in the figure and moves rightward in the figure and passes through points B and C, which are the same voltage, and if it is detected that the just focus position is an intermediate position, the moving direction is changed to the left (B ) Change to the direction and stop at point D as the just focus position. In this case, when the just focus position is checked by performing the focusing again, the point E of the focus voltage E3 in the moving direction immediately before the end of the previous focusing, that is, the left (B) direction in the drawing is set to the just focus position. Becomes The point E is located in the left direction in the figure with respect to the point D, that is, in the moving direction immediately before the end of the previous focusing. In this case, if the initial movement direction is the right direction different from the movement direction immediately before the end of the previous focusing, that is, the A direction, it is long before reaching the point E as shown by a dashed line in FIG. take time. Therefore, a quick check operation can be realized by setting the initial movement direction in the check operation as the movement direction immediately before the end of the previous focusing as described above. Also, in this embodiment, when the focus voltage accompanying the movement of the focus lens 1 passes the reference voltage from top to bottom in FIG. 6, that is, when the focus lens 1 moves away from the just focus position, The focus lens 1 is forcibly returned to the focusing start position without performing a level comparison between the focus voltage and the reference voltage, and is moved in the direction opposite to the initial movement direction to realize accurate and quick focusing without malfunction. be able to. That is, in FIG. 6, focusing starts from point G, moves to the left in the figure, passes through points H and I, and when it is determined that the subject is away from the just focus position, it is immediately turned to the opposite direction (right in the figure). In this case, the reference voltage below the point I may be crossed at the point J, and the direction of the movement may be reversed again to move leftward in the drawing. Malfunction. Therefore, when it is determined that the focus lens 1 is moving away from the just focus position as described above, such a malfunction can be prevented by forcibly returning the focus lens 1 to the focusing start position (point G) immediately. By the way, in the present invention, the initial movement direction at the start of focusing is determined by the positional relationship between the current position of the focus lens 1 and the expected just focus position.
The focus lens 1 may be moved to the expected just focus position when the power is turned off in advance. (Effects of the Invention) As is clear from the above description, in the present invention, at the start of focusing, the current position of the focusing member is detected, and the data of this current position and the predetermined probability that the preset focus position is the highest are set. The position data is compared with the position data by the comparing means to calculate the positional relationship with the predetermined position, and based on the calculation result, the focusing member is moved from the current position to the direction of the position having the highest probability of being the just focus position. By doing so, useless movement of the focus lens, that is, movement in the direction opposite to the just focus position can be minimized. Thereby, according to the present invention, more rapid focusing can be realized. Further, in particular, by setting the initial movement direction in the check operation to the movement direction immediately before the end of the preceding focusing, the initial movement direction in the check operation can be almost surely matched with the correct direction. Further, when the initial movement direction is not the correct direction, malfunction can be prevented by forcibly returning to the focusing start position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment according to the present invention, FIG. 2 is a graph showing a focus voltage, and FIGS. 3 and 4 are relationships between a focus voltage and a reference voltage. FIG. 5 is a graph showing the relationship between the focal length and the just focus position according to the distance of the subject, and FIG. 6 is a graph showing the focus voltage for explaining the operation state. 1. Focusing member (focus lens) 3. Microcomputer 7. Focusing member (imaging element)

Claims (1)

(57) [Claims] A predetermined high-frequency component of a video signal obtained by photographing a subject while moving the focusing member in the optical axis direction is extracted as a focus voltage, and the focusing member is moved based on a change in the focus voltage accompanying the movement of the focusing member. An autofocus method for performing focusing by moving in a predetermined direction, wherein at the start of focusing, the current position of the focusing member is detected, and the data of the current position and a predetermined probability that the preset focus focus position is the highest are set. The position data is compared with the position data by a comparing means to calculate the positional relationship with the predetermined position, and the focusing member is moved from the current position to the direction of the predetermined position based on the calculation result. Auto focus method. 2. A predetermined high-frequency component of a video signal obtained by photographing a subject while moving the focusing member in the optical axis direction is extracted as a focus voltage, and the focusing member is moved based on a change in the focus voltage accompanying the movement of the focusing member. An autofocus method for performing focusing by moving in a predetermined direction, wherein at the start of focusing, the current position of the focusing member is detected, and the data of the current position and a predetermined probability that the preset focus focus position is the highest are set. The position data is compared with the position data by the comparing means to calculate the positional relationship with the predetermined position. Based on the calculation result, the focusing member is moved from the current position in the direction of the predetermined position to end the focusing, and the focusing is performed again. To check the just focus position. An autofocus method, wherein the initial movement direction of the focusing member when performing focusing is the movement direction immediately before the end of the previous focusing. 3. A predetermined high-frequency component of a video signal obtained by photographing a subject while moving the focusing member in the optical axis direction is extracted as a focus voltage, and the focusing member is moved based on a change in the focus voltage accompanying the movement of the focusing member. An autofocus method for performing focusing by moving in a predetermined direction, wherein at the start of focusing, the current position of the focusing member is detected, and the data of the current position and a predetermined probability that the preset focus focus position is the highest are set. Comparing the position data with the predetermined position by comparing the position data with the comparing means, and when the focusing member is moved from the current position in the direction of the predetermined position based on the calculation result, the moving direction is the When the direction is determined to be away from the position, An autofocus method, wherein the focusing member is forcibly returned to a position at the time of starting focusing and is moved in a direction opposite to the moving direction.