JPH0614237A - Focus adjusting method and device therefor - Google Patents

Abstract

PURPOSE:To prevent a hunting and out-of-focus stoppage by changing the moving speed of a focus adjusting element, and returning the focus adjusting element to the peak value when the present sharpness is less than the maximum sharpness by more than a prescribed value. CONSTITUTION:The information of a photographing lens 10 to be used is set for a focus adjustment, and the focus adjustment is started by a hill-climbing operation #1. When the differential value of a sharpness signal supplied from a BPF 50 is less than a prescribed threshold value TH1, the hill-climbing operation #1 is continued by judging that an object is changed due to a panning or the like, or that the level of the sharpness signal is small, and the position is at the foot of the hill. When the differential value is more than the threshold value TH1, a hill-climbing operation #2 at a lower speed is started. The sharpness peak value and a position (peak value address) where the sharpness becomes the peak value are updated until the hill can be crossed. When the hill is crossed, and the present sharpness obtained from the output of an encoder 38 is less than the sharpness peak value by more than a threshold value TH2, a focusing lens 20 is step-moved to the stored peak value address by a motor 30 through a driving circuit 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjusting method and apparatus for a camera, and more particularly to a focus adjusting method and apparatus for detecting a focus by a video signal and adjusting a focusing lens.

[0002]

2. Description of the Related Art In a camera having an image pickup device for converting an optical image into an electric signal, such as a video camera, the sharpness of a picked-up image is detected from a video signal of a subject image so as to maximize the sharpness. A focus adjustment method that adjusts the focusing lens of the photographic optical system is used.

As the sharpness evaluation signal, for example, the strength of a high frequency component extracted from a video signal of a photographed image or the strength of a blur width signal obtained by differentiating the video signal is used. This is because in a normal subject, the high-frequency component and the blur width signal are small in a defocused state, increase as the focus is increased, and are maximum at the in-focus point.

In focus adjustment, it is necessary to accurately reach the in-focus point at high speed. In the conventional example, normally, when the sharpness is small, the focusing lens is moved at a high speed, is moved at a low speed as the sharpness is increased, and is stopped at the maximum value. However, in order to know the maximum value, it is necessary to confirm that the sharpness once decreases beyond the maximum value. This operation is generally referred to as hill climbing control or hill climbing operation.

[0005]

However, in a focus adjusting device using a video signal, the dependence on the subject is high, and it is very difficult to control the speed of the focusing lens near the in-focus point. If the speed is too high, the focus may be overcome and the hunting operation may fluctuate near the focus.

Further, in the conventional example, since the focusing lens is driven by the DC motor, in order to stop the focusing lens at the top of the mountain (the maximum value of the sharpness) with high accuracy, just before the top of the mountain, You need to slow down and be prepared for a stop at the top of the mountain. However, this is also very difficult in reality unless the top of the mountain is known in advance.

It is an object of the present invention to provide a focus adjusting method and apparatus that solves the above problems.

[0008]

According to the present invention, there is provided a focus adjusting method and device for adjusting the position of a focus adjusting element of a photographing optical system by a hill climbing operation so that the sharpness of an image signal of a subject is maximized. The moving speed of the focusing element is changed according to the function of the sharpness. Then, the position of the focus adjusting element at which the sharpness is maximized during the hill climbing operation is stored as a peak position, and when the current sharpness is smaller than the maximum sharpness by a predetermined value or more, the focus adjustment is performed at the peak position. Control the drive means of the focusing element to bring the element back.

[0009]

The peak position of the focus adjusting element is stored, and when the mountain is descended by a predetermined amount, the focus adjusting element is returned to the peak position, so that the focus adjusting element can be adjusted to an accurate focusing point.

Further, since the control speed is changed according to the function of the sharpness, it is possible to control the in-focus point at high speed even for an object having a low contrast, for example.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the schematic arrangement of an embodiment of the present invention applied to a video camera equipped with a zoom lens.

Reference numeral 10 denotes a photographing lens, which is a fixed front lens 1.
2, a zooming lens 14, a diaphragm 16, a fixed lens group 18, and a focusing lens 20. 22
Is a motor for moving the zooming lens 14 in the photographing optical axis direction, 24 is a motor drive circuit for driving the motor 22, 26 is a galvanometer for opening and closing the diaphragm blades of the diaphragm 16, and 28 is a drive current applied to the galvanometer 26. Drive circuit, 30 is a motor for moving the focusing lens 20 in the photographing optical axis direction, and 32 is the motor 30.
Is a motor drive circuit for driving the.

Reference numeral 34 is a zooming encoder for outputting a signal indicating the position of the zooming lens 14 in the photographing optical axis direction, 36 is an aperture encoder for outputting a signal indicating the openness of the aperture 16, and 38 is a focusing lens 20. This is a focusing encoder that outputs a signal indicating the position in the shooting optical axis direction.

Reference numeral 40 designates an image pickup element for converting an optical image of the subject by the taking lens 10 into an electric signal, and 42 designates an image pickup element 40.
Is a preamplifier that amplifies the output of the preamplifier to a predetermined level, and 44 is a video signal processing circuit that subjects the output of the preamplifier 42 to known video signal processing such as γ correction and color balance adjustment to generate a video signal. A diaphragm control circuit 46 controls the diaphragm 16 via the galvanometer 26 and the drive circuit 28 according to the output of the preamplifier 42 so that the output level of the preamplifier 42 becomes constant.

Reference numeral 48 is a gate circuit for extracting a portion necessary for focus adjustment (for example, a signal within a distance measuring area at the center of the screen) from the output of the preamplifier 42, and reference numeral 50 is for extracting a predetermined high frequency component from the output of the gate circuit 48. It is a bandpass filter (BPF).

Reference numeral 52 is a control circuit that controls the focusing lens through the drive circuit 232 and the motor 30 according to the output of the BPF 50 to adjust the focus. Control circuit 5
The output of the encoder 38 is applied to 2, so that the control circuit 52 can always know the current position of the focusing lens 20.

Incidentally, the outputs of the encoders 34 and 36 are also applied to the control circuit 52, and the zooming lens 14 is also controlled via the drive circuit 24 and the motor 22, but this is not directly related to the present invention. A description of the control of the zooming lens 14 will be omitted.

The operation of this embodiment will be described with reference to FIGS. FIG. 2 shows an operation flowchart of this embodiment, and FIG. 3 shows the relationship between the position of the focusing lens 20 and the sharpness signal. Here, the motor 30 is assumed to be a step motor. Further, in the present embodiment, two types of hill climbing motions are prepared in terms of speed, the one moving the focusing lens 20 at high speed is designated as hill climbing motion # 1, and the one moving at low speed is designated as hill climbing motion # 2.

First, information (focal length information, diaphragm information, etc.) of the photographic lens 10 to be used is set for focus adjustment (S1), and first, focus adjustment is started in hill climbing operation # 1 (S2). It is checked whether the difference value of the sharpness signal supplied from the BPF 50 is less than or equal to a predetermined threshold value TH1 (S3). If the sharpness difference value is TH1 or less, it is determined that the sharpness signal level is low because of a change in the subject due to panning or the like, or the level of the sharpness signal is low, and the mountain climbing operation # 1 is continued.

When the difference value of the sharpness signal exceeds the predetermined threshold value TH1 (S3), the slower hill climbing operation # 2 is performed (S4). In the mountain climbing operation # 2, a peak of sharpness is detected. That is, the current sharpness is compared with the peak value of the past sharpness (S5), and if the current value is larger, the sharpness peak is updated (S6). At the same time, the current position (address) of the focusing lens 20 is stored as a peak value address (S6).

When the current sharpness becomes smaller than the peak sharpness value, it means that the mountain is crossed. Therefore, the difference between the sharpness peak value and the current sharpness (the sharpness peak difference value) is the threshold value T.
When it becomes larger than H2 (S7), the hill climbing operation # 2 is exited, and the operation shifts to a more precise operation of the step motor 30 in steps. That is, the current address (position of the focusing lens 20) obtained from the output of the encoder 38 is compared with the peak value address (S8). At this point of time, the two do not usually coincide with each other, and therefore, the current address (the position of the focusing lens 20) and the peak value address are compared, and then the step through the drive circuit 32 is performed.
One drive pulse in the direction approaching the peak value address is applied to the motor 32 (S9, 10, 11).

When the current address becomes equal to the peak value address due to the pulse driving in the direction approaching the peak value address (S8), the focus adjustment operation is terminated because the in-focus point is reached. Of course, if it is determined by the subsequent focus detection that the focus state is lost, S1 and subsequent steps are repeated.

In FIG. 2, after the maximum value of the sharpness signal is exceeded, the maximum value of the sharpness signal is returned to the maximum value. However, after the maximum value of the sharpness signal is exceeded, the movement amount to return from the current address to the peak value address is shown. The focusing lens 20 may be calculated and moved by the moving amount. FIG. 4 shows a flowchart of the operation.

In FIG. 4, S21 to S27 are the same as S1 to S7 in FIG. When the sharpness peak difference value becomes larger than the threshold value TH2 in the hill climbing operation # 2 (S27),
After the mountain climbing operation # 2, the difference A between the current address (position of the focusing lens 20) and the peak value address is calculated (S28). If the difference A is negative (S29), A driving pulses for moving the focusing lens 20 in the infinity direction are applied to the motor 30 via the driving circuit 32 (S30), and A is positive ( Or (0) (S29), the motor 30 is moved through the drive circuit 32 to move the focusing lens 20 in the close-up direction A.
Individual drive pulses are applied (S31). As a result, the focusing lens 20 reaches the in-focus point, and the focus adjusting operation ends. Of course, when it is determined by the focus detection thereafter that the focus state is lost, S21 and subsequent steps are repeated.

As described above, in this embodiment, the focusing lens 20 is moved at a low speed in a place where the difference in sharpness is small, so that the sharpness signal does not draw a steep mountain with respect to the position of the focusing lens. The top of the mountain can be accurately detected even for a subject with contrast. Also,
Even if the detected top is crossed, the detected focusing lens position is stored, so that the focusing lens 20 can be accurately returned to the top of the mountain, that is, the focal point. That is, hunting and blur stop do not occur.

In the above embodiment, the position of the focusing lens 20 in the optical axis direction is detected by the encoder 38, but the position of the focusing lens can be accurately detected by counting the drive pulse applied to the step motor 30. Therefore, the count number of the drive pulse may be used as the current address and the peak value address in FIGS. 2 and 4.

In the above embodiment, the moving speed of the focusing lens 20 is controlled in two steps according to the sharpness difference, but it may be controlled in three steps or more or continuously. Nor. In addition to the sharpness difference, the moving speed may be controlled according to the ratio of the sharpness difference to the sharpness or the sharpness level to the average image level, or according to a combination thereof. .

The embodiment in which the focusing lens of the photographing lens is moved in the optical axis direction to adjust the focus has been described.
It goes without saying that the present invention can also be applied to an image pickup apparatus in which the image pickup element 40 is moved in the optical axis direction to adjust the focus.

[0030]

As can be easily understood from the above description, according to the present invention, it is possible to accurately control the photographing optical system without causing hunting or blur stop. Also,
The focus can be controlled at high speed.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of the present embodiment.

FIG. 2 is an operation flowchart of this embodiment.

FIG. 3 is an explanatory diagram of hill climbing control according to the present embodiment.

FIG. 4 is another operation flowchart of the present embodiment.

[Explanation of symbols]

10: Photographic lens 12: Front lens 14: Zooming lens 16: Aperture 18: Fixed lens group 20: Focusing lens 22: Motor 24: Motor drive circuit 26: Galvanometer 28: Drive circuit 30: Motor 32: Motor drive circuit 34 : Zooming encoder 36: Aperture encoder 38: Focusing encoder 40: Image sensor 42: Preamplifier 4
4: Video signal processing circuit 46: Aperture control circuit 48:
Gate circuit 50: Bandpass filter 52: Control circuit

Claims (7)

[Claims] 1. A focus adjusting method for adjusting the position of a focus adjusting element of a photographing optical system by a hill climbing operation so that the sharpness of an image signal of an object is maximized, and the focus is adjusted according to a function of the sharpness. While changing the moving speed of the adjusting element, the position of the focus adjusting element that maximizes the sharpness during the hill climbing operation is stored as a peak position, and when the current sharpness becomes smaller than the maximum sharpness by a predetermined value or more. A focus adjusting method, wherein the focus adjusting element is returned to the peak position. 2. The focus adjusting element is moved by an amount corresponding to the distance between the current position of the focus adjusting element and the peak position after the current sharpness becomes smaller than the maximum sharpness by a predetermined value or more. The focus adjusting method according to claim 1, further comprising: 3. The focus adjusting method according to claim 1, wherein the focus adjusting element is step-moved to the peak position after the current sharpness becomes smaller than a maximum sharpness by a predetermined value or more. 4. A focus adjusting device for adjusting the position of a focus adjusting element of a photographing optical system by a hill climbing operation so that the sharpness of an image signal of an object is maximized, and a driving means for driving the focus adjusting element. A position detecting means for detecting the position of the focus adjusting element, and a position of the focus adjusting element that maximizes the sharpness during the hill climbing operation is stored as a peak position, and the current sharpness is determined to be higher than the maximum sharpness. A focus adjusting device comprising: a control unit that returns the focus adjusting element to the peak position when the value becomes smaller than a value. 5. The drive means, after the current sharpness becomes smaller than the maximum sharpness by a predetermined value or more, by an amount corresponding to the distance between the current position of the focus adjusting element and the peak position. The focus adjusting device according to claim 4, wherein the focus adjusting element is moved by means of. 6. The control means causes the drive means to move the focus adjustment element stepwise to the peak position after the current sharpness becomes smaller than a maximum sharpness by a predetermined value or more. Item 5. The focus adjustment device according to item 4. 7. A focus adjusting device for adjusting the position of a focus adjusting element of a photographing optical system by a hill climbing operation so that the sharpness of an image signal of a subject becomes maximum, and the focus is adjusted according to a function of the sharpness. A focus adjusting device comprising a control means for controlling a moving speed of an adjusting element.