JPH0325984B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device, and in particular to a camera device such as a video camera, which performs focus adjustment so that the amount of high frequency signal components contained in a video signal is maximized. The present invention relates to an automatic focus adjustment device using a servo control method.

FIG. 1 shows a conventional automatic focusing device.
In the figure, 1 is a zoom lens, and 2 is a focus lens, which together with the zoom lens 1 constitute an imaging lens. 3 is an iris that adjusts the aperture aperture, 4 is an image sensor such as a CCD, and 5
1 is a video amplifier circuit, 6 is a focus amount detection circuit, 7 is a maximum value detection circuit, 8 is a servo amplifier circuit, 9 is a motor, and 10 is a sampling pulse generation circuit.

In the camera device shown in FIG. 1, light from a subject passes through a zoom lens 1, a focus lens 2, and an iris 3 and is incident on a photoelectric conversion surface of an image sensor 4. The optical image on the photoelectric conversion surface is converted into a video signal by the image sensor 4, and the video signal is sent to the next stage video amplification circuit 5.
is amplified to an appropriate amplitude by the focus amount detection circuit 6.
is input. The focus amount detection circuit 6 is composed of a high-pass filter, a detection circuit, a DC amplification circuit, etc. (not shown), and extracts a high frequency signal component from the video signal from the video amplification circuit 5, rectifies and amplifies it, and generates a focus amount signal. Output.

As shown in FIG. 2, this focus amount signal becomes smaller when the focus ring moves from the focusing position to either the close-up side or the limitless side, and it forms a chevron with respect to the position of the focus ring 1. Show characteristics. Further, the shape of the mountain-shaped characteristic of this focal amount signal is such that the slope of the mountain becomes steep when the depth of focus is shallow, and the slope of the mountain becomes gradual when the depth of focus is deep. Note that the depth of focus becomes deeper as the focal length of the imaging lens becomes shorter, and as the aperture of the iris becomes smaller and the F-number becomes larger.

The focus amount signal having the above-mentioned characteristics is then input to the maximum value detection circuit 7, and the focus amount Vt ₁ of t seconds ago and the current focus amount are determined according to the period t of the sampling pulse output from the sampling pulse generation circuit 10. The focal amount Vt ₂ is compared. If Vt ₂ is larger than Vt ₁ , the motor 9 is
continues to rotate in the same direction as the current rotation direction, and conversely, if Vt ₁ is greater than Vt ₂ , the motor 9 is rotated in the opposite direction. In other words, it constantly checks whether the direction in which the focus lens 2 is currently moving is toward the in-focus position (the top of the mountain), and if it is moving in the opposite direction to the in-focus position, the motor The rotation direction of 9 is reversed to move the focus lens 2 in the focusing direction. In addition, the first
In the camera device shown in the figure, a sampling pulse generation circuit 10 receives a synchronization pulse synchronized with a video signal, is driven while maintaining a certain synchronization state with the video signal, and generates a sampling pulse that is synchronized with the video signal and has a certain frequency. Output.

In such conventional automatic focus adjustment devices, the sampling period is fixed to a constant value, and the focus amount signal generally contains low-frequency noise, so the focus amount changes when the depth of focus is deep. The inclination of the mountain becomes gentle and the level of the focal amount signal also becomes small, resulting in a disadvantage that the precision of focus adjustment is reduced and focus adjustment is not performed normally. This will be explained in detail with reference to FIG. 3. Since the focus amount signal includes low frequency noise, it becomes a curved line with a certain width as shown in the figure.
Therefore, for example, in characteristic B when the depth of focus is shallow, the sample from t seconds ago is taken from the intersection b ₁ of the outer peaks generated due to noise, and the current sample is taken from the intersection b ₂ of the inner peaks. and let the respective sample values be V _fb1 and V _fb2 , V _{fb2 is} smaller than V fb1
is larger, and the relationship between each sample value matches the slope direction of the mountain, so correct mountain climbing control can be performed. However, in characteristic A when the depth of focus becomes deep and the slope of the mountain becomes gradual, even though the slope of the mountain near each sample point is upward to the right, the sample value t seconds ago
V _fa1 (the focal amount of the intersection point a ₁ of the outer peaks) is larger than the current supplement value V _fa2 (the focal amount of the intersection point a ₂ of the side peaks), that is, V _fa1 > V _fa2 , and the focus shifts further. False signals are generated that cause the lens to move.

Furthermore, in the conventional type, since the sampling period t is a constant value, as the depth of focus becomes shallower, the amount of overshoot during focusing increases near the top of the mountain of focus amount, that is, near the in-focus point, resulting in high accuracy. Focusing is not performed. That is, as shown in FIG. 4, V _fa1 −V _fa2 <<V _fb1 −V _fb2 , and the amount of overshoot becomes extremely large when the depth of focus is shallow and the characteristics near the top of the mountain are sharp.
Therefore, if there is no device to stop the focus adjustment motor when it reaches the top of the mountain, the screen will repeatedly move between the near side and the infinity side with the top as the center, making the screen very unsightly.

In view of the above-mentioned problems with the conventional type, an object of the present invention is to improve the accuracy of focus adjustment and prevent malfunctions in focus adjustment based on the concept of changing the sampling period according to the depth of focus in an automatic focus adjustment device. The purpose is to prevent it.

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

FIG. 5 shows the configuration of an automatic focus adjustment device according to an embodiment of the present invention. In the figure, a zoom lens 1, a focus lens 2, an iris 3, an image sensor 4, a video amplification circuit 5, a focal length detection circuit 6, a local maximum detection circuit 7, a servo amplification circuit, and a motor 9 are the same as in FIG. and the same reference numerals are used. Further, 11 is a sampling pulse generation circuit, 12 is an aperture value detection circuit, and 13 is a focal length detection circuit.

In the apparatus shown in FIG. 5, when the zoom lens 1 is not driven and the aperture value provided by the iris 3 is constant, the operation is the same as that of the apparatus shown in FIG. However, when the zoom lens 1 is driven and its focal length changes, a voltage corresponding to the focal length is applied to the sampling pulse generation circuit 11 by the focal length detection circuit 13 composed of, for example, a potentiometer.
The period of the sampling pulse is changed. In other words, when the focal length becomes shorter (wide side), when the depth of focus becomes deeper and the slope of the peak of the focal amount becomes slower, the frequency of the sampling pulse is controlled to be lower, that is, the period becomes longer; As the focal length becomes longer (on the telephoto side) and the depth of focus becomes shallower, the slope of the peak of the focal amount becomes steeper, the frequency of the sampling pulse becomes higher and the sampling cycle is controlled to become shorter.

On the other hand, when the iris 3 moves to a small aperture side with a deep depth or an open aperture side with a shallow depth depending on the brightness of the subject, the amount of movement can be determined by adjusting the deflection angle of an iris motor (not shown) using, for example, a potentiometer or a built-in iris motor. The aperture value detection circuit 12, which includes a Hall element or the like, detects the aperture value. A detection signal corresponding to this movement amount is sent to the sampling pulse generation circuit 11.
The frequency of the sampling pulse is adjusted. In other words, when the iris 3 is set to a small aperture and the slope of the peak of the focal amount becomes slow, the frequency of the sampling pulse becomes low, and conversely, when the iris 3 is driven to the open side and the slope of the peak of the focal amount becomes steep, the frequency of the sampling pulse becomes low. The frequency is controlled to be high.

In this way, by providing the aperture value detection circuit 12 and the focal length detection circuit 13, the frequency of the sampling pulse is controlled in accordance with the degree of focus depth caused by changes in the state of the zoom lens 1 or the iris 3. This improves the accuracy of focus adjustment and prevents malfunctions.

FIG. 6 shows a circuit configuration for generating sampling pulses when potentiometers are used in the aperture value detection circuit 12 and the focal length detection circuit 13, respectively. In the figure, 14 is a potentiometer whose slider moves according to the movement of the zoom lens 1, 15 is a potentiometer whose slider moves according to the deflection angle of the iris motor, and 16 is a differential amplifier circuit. , 17 is a voltage frequency conversion circuit, 18 is a waveform shaping circuit, and 19 is a sampling pulse output terminal.

In FIG. 6, the output of the potentiometer 14 on the zoom lens side is connected to the non-inverting input terminal of the differential amplifier circuit 16, and the output of the potentiometer 14 on the iris side is connected to the non-inverting input terminal of the differential amplifier circuit 16.
The output of 5 is applied to the inverting input terminal. Therefore, the output of the differential amplifier circuit 16 becomes smaller as the depth of focus, which is changed by the zoom lens or iris, becomes deeper, and conversely becomes larger as the depth of focus becomes shallower. FIG. 7 shows the relationship between the depth of focus and the output voltage of the differential amplifier circuit 16. The output of such a differential amplifier circuit 16 is input to a voltage frequency conversion circuit 17 to perform voltage frequency conversion. Voltage frequency conversion circuit 1
As shown in FIG. 8, the characteristic of No. 7 is that the frequency increases as the input voltage increases, that is, as the depth of focus decreases. The output of the voltage frequency conversion circuit 17 is waveform-shaped in a waveform shaping circuit 18 and sent to an output terminal 19.
output as a sampling pulse. Therefore, in the circuit shown in Fig. 6, when the depth of focus is shallow, the frequency of the sampling pulse becomes high;
Conversely, when the depth of focus is deep, the frequency becomes low, and a sampling pulse having a frequency corresponding to the degree of depth of focus is generated.

Note that in the above description, the frequency of the sampling pulse is adjusted according to the degree of the depth of focus, but the frequency of the sampling pulse can also be adjusted, for example, according to the magnitude of low-frequency noise of the focal amount signal. That is, by automatically controlling the sampling period to increase the sampling period when the noise is large and conversely shorten the sampling period when the noise is small, it is also possible to realize an automatic focus adjustment device that does not malfunction.

As described above, according to the present invention, by adjusting the sampling period according to the degree of the depth of focus, it is possible to prevent malfunctions of the automatic focus adjustment device, and to reduce the amount of overshoot at the focused point. This makes it possible to obtain high focusing accuracy.

[Brief explanation of drawings]

Figure 1 is a block circuit diagram showing a conventional automatic focus adjustment device, Figure 2 is a graph showing the characteristics of the focus amount signal when the depth of focus is deep and shallow, and Figure 3 is noise contained in the focus amount signal. FIG. 4 is a graph showing the focus amount signal characteristics mainly taken into consideration. FIG. 4 is a graph showing the excessive amount of the focus amount signal characteristics near the in-focus point. FIG. 5 is a graph showing an automatic focus adjustment device according to an embodiment of the present invention. Block circuit diagram, Figure 6 is
A block circuit diagram showing details of the vicinity of the sampling pulse generation circuit in the device shown in the figure, Figure 7 is a graph showing the output voltage characteristics of the differential amplifier circuit in Figure 6, and Figure 8 is the voltage frequency conversion circuit in Figure 6. 2 is a graph showing the input/output characteristics of DESCRIPTION OF SYMBOLS 1...Zoom lens, 2...Focus lens, 3...Iris, 4...Imaging element, 5...Video amplifier circuit, 6...Focus amount detection circuit, 7...Local maximum value detection circuit, 8... Servo amplifier circuit, 9... Motor, 10, 11... Sampling pulse generation circuit, 12... Aperture value detection circuit, 13... Focal length detection circuit, 14... Zoom lens side potentiometer, 15... Iris side potentiometer,
16... Differential amplifier circuit, 17... Voltage frequency conversion circuit, 18... Waveform shaping circuit, 19... Sampling pulse output terminal.

Claims (1)

[Scope of Claims] 1. An automatic focus adjustment device for a camera device that periodically samples high frequency signal components contained in a video signal and performs focus adjustment so that the high frequency signal components are maximized. A depth of focus detection means for generating a signal corresponding to the depth of focus of the camera device in the device, and a sampling period of the high frequency signal component is increased as the depth of focus becomes deeper in accordance with the signal from the depth of focus detection means. An automatic focus adjustment device characterized by being provided with a means for changing the focus. 2. The depth of focus detection means includes a device for detecting the focal length of the imaging lens in the camera device,
2. The automatic focus adjustment device according to claim 1, wherein the sampling period is shortened as the focal length of the imaging lens becomes longer, and the sampling period is lengthened as the focal length of the imaging lens becomes shorter. 3. The depth of focus detection means includes a device for detecting the aperture aperture of the iris in the camera device, and shortens the sampling period when the aperture becomes large, and lengthens the sampling period when the aperture becomes small. An automatic focus adjustment device according to claim 1 or 2.