JPH087318B2 - Auto focus device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device in an image pickup device such as a video camera, and more particularly to an autofocus device for performing focus adjustment using a video signal.

[Prior Art] Conventional autofocus devices of this type can be roughly classified into active type and passive type.

Among them, the active type has an infrared method and an ultrasonic method.In recent years, infrared light is emitted from the camera side, a spot image is formed on the subject, and the reflected light is detected by a light receiving element on the camera side. and, although the infrared method of performing focusing is commonly used because of the high ranging accuracy, this method requires a interlocking mechanism for moving the light receiving element or the like according to the object distance, therefore inevitably structure complicated Moreover, complicated adjustments are required, and there are drawbacks such as poor assembly and adjustment efficiency.

On the other hand, with regard to the passive type, there are some that use a video signal and some that do not. Among them, those that do not use video signals include the Honeywell method and so-called Canon SST (Solid St
ate Triangulation) method, but these also require optical components that are not necessary for the imaging system, and require advanced adjustment technology.

On the other hand, the autofocus device using the video signal has an advantage that no dedicated optical component for autofocus is required and high-level adjustment is not required. FIG. 4 shows the configuration of a conventional autofocus device using such a video signal. In the figure, an image passing through a photographing lens (focusing lens) 1 is converted into an electric signal by an image pickup element 2, and this electric signal is amplified by a preamplifier (preamplifier) 3.
The video signal amplified by the preamplifier 3 passes through the process circuit 4 and is input as a video signal to a monitor (not shown) or a video tape recorder. At the same time, the video signal amplified by the preamplifier 3 is limited to only high frequency components by a high-pass filter (hereinafter referred to as HPF) 5, and further a predetermined image range (for example, a focused image range) to be focused when displayed on a monitor or the like (for example, After passing through the gate circuit 6 for extracting only the signal corresponding to the central portion of the screen), the absolute value circuit 7 and the integrating circuit 8 convert the signal into a quantity (voltage value) indicating the focus state. The amount indicating the focus state has a relationship with the defocus amount (defocus amount) of the lens system as shown in FIG. 5, and according to this relationship, the motor drive system 9 indicates the amount indicating the focus state (hereinafter, focus amount). The imaging lens 1 is driven to a position where f) (which will be referred to as the amount) becomes maximum.

Further, the operation of the drive system 9 of the above motor will be described.
It is assumed that the focus state at the start of distance measurement is at the position A in FIG. Further, the focus position when the focusing lens 1 is moved very slightly by rotating the motor in a certain direction is designated as B in FIG. The focus amount f _{(A) at} the position A and the focus amount f _(B) at the position B are compared by the motor drive system 9, and if f _(B) > f _(A) The focusing lens is moved in the direction of the focal point x _o by rotating the motor in the same rotation direction and reversing the rotation direction of the motor if f _(B) <f _(A) .

[Problems to be Solved by the Invention] However, when the difference between the above-described focus amounts f _A and f _B is almost unchanged and comparison is not possible, the focus amount is kept rotating in the same direction until the comparison becomes possible. Are sequentially detected. After that, when the lens 1 hits the movable end, the direction of the motor is reversed and the detection of the focus amount is repeated in the same manner as described above. In this detection method, however, the same place is compared twice and the focus amount is compared and determined. Because while passing
There is a drawback that the time until the inclination of the focus amount can be detected is delayed, and as a result, it is slow to bring the lens 1 closer to the focal point. Such a drawback becomes a big problem in the above-described automatic focusing device using the video signal, and even in the above-mentioned active type or passive type automatic focusing device, when the focus adjustment state cannot be detected, the same problem occurs. There was a drawback.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional drawbacks, to provide an autofocus device capable of detecting the inclination of the focus amount more quickly and bringing the imaging lens system closer to the in-focus point.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a focusing lens for forming a subject image, a determination means for determining a focus state of the focusing lens, and a determination by the determination means. In an autofocus device having a lens driving mechanism that moves the focusing lens system based on a result, a detection unit that detects the position of the focusing lens, and an initial position before the movement of the focusing lens that is detected by the detection unit. Storage means for storing
The lens driving mechanism is operated to move the focusing lens in a predetermined direction to perform the determination operation by the determination means, and the focusing lens is moved to the closest end or infinity while the determination by the determination means is disabled. When reaching, the determination operation of the determination means is stopped, and the control means for returning the focusing lens to the initial position stored by the storage means by the lens driving mechanism is provided. is there.

[Operation] In the present invention, the first start position of the lens system for forming an image of a subject is detected by the detection means and stored in the storage means.
Next, the image forming state of the lens system is sequentially judged by the judging means while moving the lens system by the lens driving mechanism, and the lens system is moved to the in-focus position based on the judgment result. At this time, when the judgment by the judgment means is impossible, the lens drive mechanism moves the lens system in a predetermined direction, and when the lens system reaches the closest end or infinity while the judgment by the judgment means is impossible, control is performed. The determination operation of the determination means is stopped by the means, the lens system is quickly returned to the start position stored by the storage means by the lens drive mechanism, and the detection and determination operation is restarted from the returned start position in the opposite direction to the previous time. Therefore, since it is not necessary to determine the image formation state of the lens system twice at the same place, it is possible to bring the lens system closer to the focal point more quickly.

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

FIG. 1 shows the configuration of an autofocus device according to an embodiment of the present invention. In the figure, 10 is a control circuit having a memory function for controlling a motor drive circuit 11 which is a lens drive mechanism, and 12 is a detection means for reading an absolute address of a focusing lens 1 which is a lens system for forming an image of a subject. Sensor. The control circuit 10 has a function of a determination unit that determines the image formation state of the lens 1, and a storage unit that stores the initial start position of the lens 1 detected by the sensor 12. The other structure is the same as that of the conventional example shown in FIG. 4, and therefore the detailed description thereof is omitted.

FIG. 2 is a flowchart showing the control procedure of the above-mentioned control circuit 10 in this example, which is stored in advance in the program memory in the control circuit 10. FIG. 3 is a diagram showing the relationship between the movement of the focusing lens 1 and the focus amount in this example. Next, with reference to FIG. 2 and FIG. 3, an operation example of the embodiment apparatus of FIG. 1 will be described.

First, assuming that the focusing lens 1 is located at the point A in FIG. 3, the absolute address of the lens 1 is the sensor.
It is detected by 12 and read into the control circuit 10 and is stored in advance in the internal memory (storage means) of the control circuit 10 (S
1) Next, the control circuit 10 causes A to the near end position C.
The absolute address of the point is compared with a fixed fixed fixed focus position (S2). Here, assuming that the common in-focus point B is closer to the close end C than the point A, the control circuit 0 first controls the motor drive circuit 11 to move the focusing lens 1 in the direction of the close end (S4). .

At this time, when the inclination of the focus amount f measured by the integrating circuit 8 is so small that it cannot be detected (S5), it directly hits the closest end C (S6). In that case, although the moving direction of the focusing lens 1 is reversed, it is known that the inclination of the focus amount has already been detected between the closest end C and the point A, and the inclination cannot be detected. , The motor is set to the maximum speed via the motor drive circuit 11 without detecting the inclination of the focus amount (determination operation of the image formation state),
Return to point A read from the internal memory (S7),
The lens 1 is moved from the point A to the infinity end D while detecting the inclination of the focus amount again (S8, S9, S10).

Even when the first point A is located closer to the closest end C than the normal focusing point B, only the rotation direction of the first motor is reversed (S4), and the focusing lens is adjusted by the same algorithm (control procedure) as described above. Focusing control of 1 can be performed.

Note that in step S10, when it again hits the near end C or the infinity end D, an undetectable display is displayed on a display means (not shown), or the lens 1 Is returned to the common focusing point B at the maximum speed, and the motor is stopped (S11, S12). Also, step S5
Alternatively, in step S9, when the inclination of the focus amount can be detected and the in-focus point E can be detected, the motor is stopped via the motor drive circuit 11 (S11, S12).

In this embodiment, an autofocus device using a video signal has been described, but it goes without saying that the present invention can be implemented with other types of active / passive autofocus devices.

EFFECTS OF THE INVENTION As described above, according to the present invention, when the focusing lens reaches one end of the lens and is inverted while the focus determination is impossible, the focus determination cannot be performed. Since the focusing lens is forcibly and appropriately moved to the initial position before the movement of the focusing lens without performing the determination operation again in the area, the area where the focus determination cannot be performed is not determined twice, and the useless lens It is possible to reduce the movement and the time, and it is possible to obtain an effect that a quick and highly reliable focus determination operation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic focusing device according to an embodiment of the present invention, FIG. 2 is a flow chart showing an operation example of the device shown in FIG. 1, and FIG. 3 is a movement of a focusing lens shown in FIG. And FIG. 4 is a characteristic diagram showing the relationship between the focus amount and the focus amount. FIG. 4 is a block diagram showing a configuration of a conventional automatic focusing device using a video signal. FIG. 5 is a position of a focusing lens and a focus amount in the conventional device of FIG. It is a characteristic view which shows the relationship with. 1 ... Imaging lens, 2 ... Imaging element, 3 ... Preamplifier, 4 ... Process circuit, 5 ... High-pass filter, 6 ... Gate circuit, 7 ... Absolute value circuit, 8 ... Integrator, 10 ... … Control circuit, 11 …… Motor drive circuit, 12 …… Sensor.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H04N 5/232 H (72) Inventor Naoya Kaneda 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Tamagawa Plant (72) Inventor Yoichi Iwasaki, Tamano Plant, 770 Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Canon Inc. (56) Reference JP 59-221081 (JP, A)

Claims (1)

[Claims] 1. A focusing lens for forming a subject image, a judging means for judging a focusing state of the focusing lens, and a lens driving mechanism for moving the focusing lens system based on the judgment result of the judging means. In an automatic focusing device having, a detecting means for detecting a position of the focusing lens, a storing means for storing an initial position of the focusing lens detected by the detecting means before the movement starts, and a lens driving mechanism for operating the lens driving mechanism. The determination operation is performed by the determination means while moving the focusing lens in a predetermined direction, and when the focusing lens reaches the closest end or infinity while the determination by the determination means is impossible, the determination means of the determination means Stop the judgment operation and move to the initial position stored by the storage means. Autofocus apparatus characterized by comprising a control means for returning the focusing lens by said lens drive mechanism.