JPH0389683A - automatic focus adjustment device - Google Patents

Abstract

PURPOSE:To attain quick focusing even when focusing is applied within a range of a very short distance by using position information of a focusing lens and a focus voltage so as to apply focus position prediction thereby applying a limit to the moving range of the focusing lens. CONSTITUTION:A prediction circuit 8 fetches position information of a focus lens and a focus voltage outputted from a sample-and-hold circuit 7 to predict whether or not an object exists in a macro area. The result of prediction is inputted to a motor direction discrimination circuit 9 to decide the direction of rotation of a motor 12. That is, the motor direction decision circuit 9 applies focusing as it is in a macro area when the existence of the object is predicated in the macro area. When no existence of the object in the macro area is predicted, the focusing lens is reversed and focusing is continued at a normal area. Thus, quick focusing is attained even to an object at a very short distance range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus detection device suitable for use in video cameras and the like.

[Prior Art] An automatic focus detection device conventionally used in video cameras and other video cameras extracts high frequency components from a video signal obtained from a tit image element, and shoots images so that this high frequency component is maximized. A so-called hill-climbing automatic focusing method is known in which focusing is performed by driving a lens.

Such an automatic focus adjustment method does not require a special optical member for focusing WRm, and has advantages such as being able to focus accurately regardless of the distance of the subject whether it is far or near. This type of automatic focus adjustment method will be explained using FIG. 5.

A focusing lens 1 is moved in the optical axis direction by a lens drive motor 12 to perform focusing. The light passing through this lens forms an image on the imaging surface of the image sensor 2, undergoes photoelectric conversion, and is output as a video signal. This video signal is amplified to a predetermined level by an amplifier 3, inputted to a process circuit (not shown) of the camera, converted into a standard television signal, and inputted to a bandpass filter (BPF) 4. The BPF 4 extracts high frequency components from the video signal, and the gate circuit 5 extracts only the video signal corresponding to the focus detection area set in a part of the screen, which is detected by the detector 6 and then sent to the sample hold circuit 7.
Sample and hold is performed at intervals synchronized with an integral multiple of the vertical synchronization signal (hereinafter, this sampled and held value will be referred to as a focal voltage value). Based on this focal voltage value, the motor speed judgment circuit 9 determines the degree of focus. Focusing motor 1 according to
Set the speed of 2. That is, the motor driver 13 is instructed to vary the motor speed so that it is fast when the blur is large and slow when the blur is small. Further, the motor direction determining circuit 9 sets the motor drive direction in the direction in which the focal voltage value is maximized. However, since the motor direction determination circuit 9 does not initially know the direction in which the focal voltage value is maximum, it moves the motor 12 in an appropriate direction and continues turning it until it can determine the direction in which the focal voltage value is maximum. . If the lens l hits an edge during this time, the edge detector 14 determines this and reverses the motor. Therefore, the direction in which the motor is initially rotated is opposite to the direction in which the focal voltage value is maximized, as shown in FIG. 6, and the focal point XI [
The initial position of lens l at the start is far from the focal point,
When the direction of the peak of the focal voltage value cannot be determined because the focal voltage value is low, a search operation is performed in which the lens moves to the - termination and then returns, so it takes some time to bring it into focus.

By the way, this type of device is generally configured to focus on subjects within a range of 1.2 m from the camera to infinity, or if there is a desire to focus on objects even closer. To answer this, it is only necessary to increase the amount of movement of the focusing lens compared to the conventional one, so that it is possible to photograph objects at a close distance of 1.2 m or less, which is relatively easy in terms of lens design. For example, if you double the amount of movement of the focusing lens, it will move from infinity to 0.
．． Capable of shooting up to 6m. Furthermore, by positioning the focusing lens at the rear end or in the middle of the zoom lens, it is possible to bring the minimum photographing distance close to just in front of the photographic lens.

[Problems to be Solved by the Invention] However, when a conventional automatic focus adjustment device is used for such a lens with a short minimum photographing distance,
This will cause some inconvenience. First, since the amount of movement of the first e-focusing lens increases, the responsiveness of the automatic focusing device deteriorates. For example, conventionally from the infinite end to the nearest end (1
, 2m) Now, if the lens speed is about 3 seconds, the closest end is 0.
．． By extending the distance to 6 m, it takes approximately 6 seconds for the lens to move from the closest end (0.6 m) to the infinity end. As described above, at this motor speed, if a search operation is performed due to a mistake in the initial motor direction, the lens movement range is doubled, so approximately twice as much time is required, which poses a practical problem in terms of responsiveness.

A second disadvantage is a focusing malfunction caused by false resolution of the lens. False resolution means that when the focus of the lens is shifted, the phase is 18 for a subject with a high spatial frequency.
This is an imaging phenomenon that is shifted by 0°. By the way, automatic focus adjustment devices that use video signals determine that focus is achieved when the high-frequency components in the video signal reach a maximum value, so even in this state of false resolution, the maximum value is reached. . Therefore, the lens is determined to be in focus in a state of false resolution and the lens stops. This phenomenon occurs more frequently as the amount of defocus of the lens increases. In other words, the minimum shooting distance is 1.2, which is the same as before.
m, even if false resolution does not occur due to the depth of field, if the minimum shooting distance is extended to 0.6 m, false resolution will occur and the camera will stop in focus or out of focus. Sometimes.

[Object 1] The object of the present invention is to solve the above-mentioned problems and provide an automatic focus adjustment device that can quickly focus not only on a normal distance range but also on a subject in a very close range. Our goal is to provide the following.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides an extraction means for extracting a signal according to the degree of focus from an imaging signal, and a signal extracted by the extraction means. a driving means for driving the focusing lens based on the focusing lens; a predicting means for predicting the focusing position based on the position information of the focusing lens and the signal extracted by the extracting means; It is characterized by comprising a limiting means for limiting.

[Operation] This uses the position information and focal voltage value of the focusing lens to predict whether or not there is a subject in the macro area that is not normally used, and when it is predicted that there is no subject in the macro area, the focusing lens By limiting the movement range of the focusing lens to only the normal area, the search time is shortened, and poor response due to false resolution in the macro area is prevented. Conversely, when it is predicted that a subject exists in the macro area, the movement range of the focusing lens is reduced. By expanding the focus over the entire range, it becomes possible to quickly perform automatic focusing from short distances to infinity.

[Example] Hereinafter, an example of the automatic focus Wy5 device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic focus adjustment device according to the present invention.

In this figure, the same reference numerals are used for the same components as in the conventional example of the ft44 diagram, and the explanation thereof will be omitted. Reference numeral 11 is a focus encoder, which determines the position of the focus lens (closest end/macro area (0.6 m to 1.2 m).
m)/normal area (1,2m~oo)/infinite end). The prediction circuit 8 that predicts the focal voltage value in the macro area takes in the position information of the focus lens from the focus encoder 11 and the focal voltage value output from the sample/hold circuit 7, and determines whether a subject exists in the macro area. Predict. FIG. 3 shows this prediction circuit 8.
This shows a prediction method based on The focusing lens ranges from the normal range (1,2 m to oO) to the macro range (0
, 6 m to 1.2 m), if the focal voltage is increasing, it is predicted that there is a subject in the macro area. 1. If the focal voltage is in a phenomenon or does not change when entering the macro area from the normal area. It is determined that the subject does not exist in the macro area. This prediction result is input to the motor direction determination circuit 9, and the direction of the motor 12 is determined according to the algorithm shown in the flowchart of FIG. That is, in the motor direction determination circuit 9, when entering the macro area from the normal area, if it is predicted that a subject exists in the macro area (the focus voltage is increasing), the motor direction determination circuit 9 performs the focusing operation directly in the macro area, and When it is predicted that there is no subject, the focusing lens is reversed and the focusing operation continues in the normal area.

Looking at the flowchart in FIG. 4, when the focusing lens l is driven in either direction at the start of the automatic focusing operation, the position of the focusing lens is determined from the detection output of the focusing lens encoder 11 in 5 tepl, and the focusing lens The movement position of is 1.2
When it is detected that the normal region of m to ■ has shifted to the macro region of 0.6 m to 1.2 m, it is determined in step 5 whether or not the focal voltage output from the sample hold circuit 7 is in an increasing state. is determined. If the focal voltage is increasing, it is determined that the subject is within the macro area, and the 5te
Proceeding to step p4, the focusing lens is directly moved to the macro area and a focus adjustment operation is performed within the macro area.

If the focal voltage decreases or does not change at 5tep2, it is determined that there is no subject in the macro area, and 5tep2
After reversing the focusing lens with p3, 5tep4
The focus adjustment operation is performed within the normal region.

Then, the automatic focus adjustment operation is performed until the focal point is reached at step 5, and when the focal point is reached, the focusing lens is stopped at step 6. After that, if the focus state changes at 5 tep 7 and the camera deviates from the in-focus point and requires restarting, the process returns to 5 tep 7 and the above-described flow is repeated.

FIGS. 2A and 2B are diagrams showing the movement range of the focusing lens, changes in focal voltage, and the trajectory of movement of the focusing lens until the subject is brought into focus. The horizontal axis shows the lens movement range, and the vertical axis shows the focal voltage. Second
Figure (A) is a diagram showing the movement locus of the focusing lens when the focusing lens l is initially positioned in the normal area and is brought into focus on a subject in the macro area. Figure 2 (B) shows the case where the focusing lens is initially positioned in the normal area, and it is predicted that there is no subject in the macro area, and the focusing lens is reversed to focus on the normal area further from the initial position to infinity. This is the movement trajectory of the focusing lens in .

In the above embodiment, the macro area is 0.6 m to 1.2 m.
Although the description has been made assuming that the normal area is 1.2 m or more, the macro area is not limited to this, and it is possible to widen or narrow the macro area, or increase the number of area divisions by increasing the number of divisions of the focus encoder 11. By increasing the resolution of the encoder and predicting the focus position more precisely, it is also possible to control the movement range of the focusing lens with high precision. Further, by dividing the area into smaller areas, it is possible to configure a structure in which movement restrictions are applied to the normal area instead of applying movement restrictions to the macro area.

[Effects of the Invention] As described above, according to the automatic focusing device of the present invention, one in-focus position is predicted using the focusing lens position information and the focal voltage, and the movement range of the focusing lens is restricted. This allows for quick focusing not only at normal distance ranges, but also when focusing on very close ranges, so there is no wasted movement of the focusing lens, and the time it takes to reach the in-focus point is reduced. In addition, it is possible to reliably prevent malfunctions such as erroneous focusing on false resolution, etc., and it is possible to realize a high-speed, high-precision, and highly reliable automatic focusing device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the invention, FIG. 2 is a diagram showing the operation of the embodiment of the invention, and FIG. 3 is a diagram showing a prediction method according to the invention. FIG. 4 is a flowchart showing the algorithm of the focus adjustment operation of the present invention. FIG. 5 is a block diagram showing an example of a conventional automatic focusing device, and FIG. 6 is a diagram showing the operation of the conventional example shown in FIG. 7men nin 7L varnish” Tsutaro□□□ Tani■2 ＋

Claims (1)

[Scope of Claims] Extracting means for extracting a signal according to the degree of focus from an image pickup signal, driving means for driving a focusing lens based on the signal extracted by the extracting means, and position information of the focusing lens. an automatic focusing device comprising: a prediction means for predicting a focus position based on the signal extracted by the extraction means; and a restriction means for restricting the operating range of the focusing lens by the prediction means.