JP2893727B2 - Focus control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contrast detection type focus control circuit used for auto focus of a video camera, for example.

[Summary of the Invention] The present invention provides a focus control circuit for detecting a spectral component in a video signal and performing focus control, wherein a control signal for wobbling the focus lens by a signal obtained by modulating a predetermined wobbling signal with a predetermined voltage is provided. Providing wobbling means for outputting to the focus motor, moving the focus lens to the focus position side, obtaining evaluation values at regular intervals, stopping at a position beyond the focus position based on the comparison result of each evaluation value, and then focusing The lens is returned to the in-focus position while being wobbled by the wobbling means, the evaluation value is obtained at regular intervals, and the lens is stopped at the in-focus position based on the comparison result of each evaluation value. Since it is not necessary to refer to the number of pulses of the frequency generator, Focus control can be performed without using a number generator and without considering the amount of backlash.

[Related Art] The video camera's autofocus method includes a distance measurement method and a focus detection method when classified based on the principle of a focusing method. The distance measuring method measures the distance to a subject and controls the position of a lens in accordance with the distance. The focus detection method detects focus on an imaging surface and controls the position of a lens at a position where focus is achieved.

One of the focus detection methods is a contrast detection method. The contrast detection method performs focus control using the fact that the edge of a captured image becomes clearer as the lens approaches a focus position. The fact that the edge of the imaging screen becomes clear corresponds to an increase in high frequency components in the video signal. FIG. 6 shows a conventional example of an autofocus circuit using this contrast detection method.

In FIG. 6, a focus lens 2 is displaced by a focus motor 1 and light from a subject is irradiated to an image pickup device 3 via the focus lens 2. Image sensor 3
Converts light from a subject into a video signal, which is output to a band-pass filter (BPF) 6 via a signal processing system circuit 4 and an amplifier 5. Bandpass filter 6
For example, a component having a frequency of 200 KHz to 2 MHz is passed, and the output of the band-pass filter 6 is supplied to the detector 7. Detector 7
Rectifies the input signal in both waves, and the output of the detector 7 is supplied to the A / D converter 8. The A / D converter 8 A / D converts only the signal corresponding to the focus area based on the sampling clock sent from the microcomputer 10, and supplies this digital signal to the integration circuit 9. The integration circuit 9 integrates the digital signal of the A / D converter 8, and the output of the integration circuit 9 is supplied to the microcomputer 10 as a focus evaluation value.
The microcomputer 10 searches the position of the focus lens 2 at which the output of the integration circuit 9 becomes maximum by the algorithm of the hill-climbing control, and positions the focus lens 2 at the focus position as described below.

That is, the microcomputer 10 outputs a constant voltage to the focus motor 1 via the drive circuit to move the focus lens 2 to the in-focus position at a constant speed. During this movement, the evaluation value sequentially sent from the integration circuit 9 is compared with the previous evaluation value, and when the evaluation value becomes larger than the previous evaluation value, the output pulse of the frequency generator 15 is counted from this point. In order to prevent the peak value from being erroneous due to the fluctuation of the evaluation value due to the nozzle, after that, when the evaluation value from the integrating circuit 9 is larger than the previous one, it is determined that the peak value has been exceeded if the continuous two or three times. The motor 1 is stopped. And
The focus motor 2 is driven in the reverse direction and stopped by the amount obtained by subtracting the count number corresponding to the backlash amount from the count number of the output pulse of the frequency generator 15, thereby positioning the focus lens 2 at the focus position.

[Problems to be Solved by the Invention] However, according to the above-described structure, since the number of pulses of the frequency generator 15 is used as a reference to return to the peak point, the frequency generator 15 is necessary and the amount of backlash is taken into consideration. In this case, the return amount of the focus motor 1 must be determined.

Therefore, the present invention, without providing a frequency generator,
It is another object of the present invention to provide a focus control circuit capable of performing focus control without considering a backlash amount.

[Means for Solving the Problems] To achieve the above object, a focus control circuit according to the present invention comprises: an imaging unit for converting an optical signal from a subject into a video signal; and a spectrum in the video signal output by the imaging unit. Spectrum detection means for detecting the components, evaluation value calculation means for obtaining an evaluation value by summing the spectrum components in the focus area detected by the spectrum detection means, and evaluation value output from the evaluation value calculation means for the previous evaluation. And a focus control circuit for controlling a focus motor based on the comparison result of the comparison means to position the focus lens at a focus position, wherein a predetermined wobbling signal is modulated by a predetermined voltage. A wobble for outputting a control signal for wobbling the focus lens according to a signal to the focus motor; Coarse means for moving the focus lens to the in-focus position side, obtaining an evaluation value at regular intervals, and stopping at a position beyond the in-focus position based on the result of comparing the evaluation values. After the adjustment, the focus lens is returned while being wobbled to the in-focus position by the wobbling means, and an evaluation value is obtained for each extreme value of the wobbling cycle of the focus lens. Is used to perform focus control.

[Operation] In the coarse adjustment, the focus lens is moved to the in-focus position side, the evaluation value is obtained at regular intervals, the peak point of the evaluation value is searched, and in the fine adjustment, the focus lens is wobbled to the in-focus position by the wobbling means. Then, an evaluation value is obtained for each extreme value of the wobbling cycle of the return focus lens, and the process stops at the peak point.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 5 show an embodiment of the present invention,
This embodiment shows a case where the focus control circuit of the present invention is applied to a video camera.

In FIG. 1, the position of a focus lens 2 is changed by a focus motor 1, and a subject is imaged on an image sensor 3 via the focus lens 2. The image sensor 3 converts light from a subject into a video signal, and the output of the image sensor 3 is supplied to a signal processing circuit 4. The signal processing circuit 4 is, for example, R,
G, B signals are added at a predetermined ratio to create a luminance signal,
This signal is sent to the band pass filter 6 via the amplifier 5. The band-pass filter 6 serving as a spectrum detecting means is a filter that passes a component having a frequency of, for example, 200 KHz to 2 MHz. The band-pass filter 6 extracts all the spectral components other than the DC component and the noise component in the luminance signal. The output of the band pass filter 6 is a detector 7
And the detector 7 rectifies the output of the band-pass filter 6 in both waves. The output of the detector 7 that has been subjected to the double-wave rectification is supplied to an A / D converter 8 and digitized by a sampling clock. This sampling clock is output from the microcomputer 10, and this sampling clock is different between the coarse adjustment and the fine adjustment, and A / D converts only the video signal corresponding to the focus area. An integrating circuit 9 as an evaluation value calculating means integrates the digital signal of the A / D converter 8, and an output of the integrating circuit 9 is supplied to a microcomputer 10 as a focus evaluation value. The microcomputer 10 has comparison means for comparing the evaluation value output from the integration circuit 9 with the previous evaluation value.
The flowchart shown in the figure is executed. The detailed control of the microcomputer 10 will be described in the section of operation. The drive signal of the microcomputer 10 is supplied to the drive circuit 12 via the adder 11.
Is output to The wobbling signal generation circuit 13 is a microcomputer
The sine wave wobbling signal is output to the adder 11 and supplied to the microcomputer 10 in response to the start signal from 10.
Also, the output of the wobbling signal is stopped by the stop signal from the microcomputer 10.

 Hereinafter, the operation of the above configuration will be described with reference to FIG.

When the photographing is started, the microcomputer 10 executes the coarse adjustment mode, and the microcomputer 10 drives the constant voltage by comparing the evaluation value when the focus lens 2 is at the maximum position or the minimum position, or when the focus lens 2 is at the intermediate position. A focus signal is output by driving the focus motor 1 to move the focus lens 2 to the focus position side. Further, the microcomputer 10 outputs the frequency of the color subcarrier to the A / D converter 8 as a sampling clock, for example, and takes in the evaluation values (N ₀ , N ₁ , N _2, ...) Sequentially transmitted from the integration circuit 9. The second evaluation value (N _x (x ≧ 1)) is compared with the previous evaluation value (N _x−1 ). If the evaluation value (N _x ) is larger than the previous evaluation value (N _x−1 ), the next evaluation value is fetched and the comparison is sequentially repeated. When the evaluation value (N _x ) becomes smaller than the previous evaluation value (N _x−1 ) and this state continues a plurality of times, the focus motor 1 is stopped. The case where the evaluation value (N _x ) is smaller than the previous evaluation value (N _x-1 ) and this state is repeated a plurality of times is referred to as a fifth case.
As shown by the arrow A in the drawing, it means that the focus position (peak value) has been exceeded, and the focus lens 2 is stopped at a position beyond the focus position, and the coarse adjustment ends.

Next, the microcomputer 10 executes the fine adjustment mode, and
Numeral 10 outputs a low-speed voltage in the opposite direction (the direction of the arrow B in FIG. 5) to drive the focus lens 2 at a very low speed as compared with the above. Further, the microcomputer 10 outputs a start signal to the wobbling signal generation circuit 13, and the wobbling signal generation circuit 13 outputs a wobbling voltage. Accordingly, as shown in FIG. 2, a combined voltage (c) obtained by combining the low-speed voltage (a) and the wobbling voltage (b) is supplied to the drive circuit 12, and the focus lens 2 wobbles (oscillates) to the in-focus position. Moved) and returned. Further, based on the wobbling signal, the microcomputer 10 converts the sampling clocks at the timings t _A and t _{B in} FIG. 2 which are the extreme values (maximum value, minimum value) of the wobbling cycle of the focus lens 2 into the A / D converter 8. And the timing evaluation values n _A , n
Capture _B sequentially. Since the focus lens 2 is wobbling, if Shimese in Figure 3 _{A 1 → B 1 → A 2} → B 2 → Go A ₃ → ... in the order of, A ₁ at the timing of t _A, A ₂ ... evaluation value n of _A receives the evaluation values n _B of B ₁ , B ₂ ,... At the timing of t _B. Then, by comparing the n _A and n _B of the evaluation value, if n _B is greater than n _A, and outputs a stop signal to the wobbling signal generating circuit 13 while stopping the output of the low-speed voltage. Then, the wobbling signal generation circuit 13 stops outputting the wobbling voltage, and the focus motor 1 stops,
The focus lens 2 is located at the focus position (peak point).

In this embodiment, the wobbling operation and the return operation are performed simultaneously to return to the peak point. However, the return operation and the wobbling operation are performed alternately, and the evaluation value is taken for each extreme value of the wobbling cycle. It may be configured as follows.

[Effects of the Invention] As described above, according to the present invention, the focus lens is moved to the in-focus position side, evaluation values are obtained at regular intervals, and a position exceeding the in-focus position from the comparison result of each evaluation value is obtained. Then, the focus lens is returned to the in-focus position while wobbling, the evaluation value is obtained at regular intervals, and the focus lens is stopped at the in-focus position based on the comparison result of each evaluation value. It is not necessary to use the number of pulses of the frequency generator as a reference to return to the peak point, so that there is an effect that focus control can be performed without using a frequency generator and without considering the amount of backlash.

[Brief description of the drawings]

1 to 5 show an embodiment of the present invention. FIG. 1 is a block diagram of a focus control circuit, FIG. 2 is an output waveform diagram of each part at the time of fine adjustment, and FIG. 3 is a focus lens at the time of fine adjustment. FIG. 4 is a flowchart showing a relationship between a position and an evaluation value to be taken, FIG. 4 is a flowchart, and FIG.
FIG. 6 is a block diagram of a conventional focus control circuit. 2 focus lens, 3 image pickup device (imaging means), 6 bandpass filter (spectrum detection means), 9 integration circuit (evaluation value calculation means), 10 microcomputer (comparison means).

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G02B 7/36 G03B 3/00

Claims (1)

(57) [Claims] 1. An imaging device for converting an optical signal from a subject into a video signal, a spectrum detection device for detecting a spectral component in a video signal output by the imaging device, and a focus area detected by the spectrum detection device. Evaluation value calculation means for obtaining an evaluation value by summing the spectral components of the above, and comparison means for comparing the evaluation value output by the evaluation value calculation means with the previous evaluation value, based on a comparison result of the comparison means A wobbling means for outputting to the focus motor a control signal for wobbling the focus lens with a signal obtained by modulating a predetermined wobbling signal with a predetermined voltage in a focus control circuit for controlling the focus motor to position the focus lens at a focus position. The focus lens is moved to a focus position side, and is A coarse adjustment is performed to obtain an evaluation value and stop at a position beyond the in-focus position from the comparison result of each evaluation value, and after this coarse adjustment, returning the focus lens to the in-focus position by the wobbling means while wobbling the focus lens, A focus control circuit, wherein an evaluation value is obtained for each extreme value of a wobbling cycle of a focus lens, and focus control is performed by fine adjustment of stopping at a focus position based on a comparison result of case evaluation values.