JPH03237416A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To accurately obtain a focusing state within a short time by adjusting the position of a focusing optical system, then adjusting the position of the focusing optical system by the output of a signal forming means. CONSTITUTION:After adjusting the position of the focusing optical system in accordance with distance information, the position of the optical system is adjusted again by the output of the signal forming means. In a stage for moving a focusing lens 10 in accordance with the output of a distance measuring circuit 40, the lens 10 is moved to a position shifted to the side of an image pickup element 42 by a prescribed distance. While moving the lens 10 stepwise in each prescribed distance, a system control circuit 60 stores the outputs of a detector 58 at respective moving points in an internal memory, detects the point of the maximum output, and moves the lens 10 up to the position. Thus, the real focusing state can be rapidly and accurately obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eye movement focusing device, and more specifically to an automatic focusing device in an imaging device equipped with an electronic imaging device.

[Prior Art] FIG. 3 shows a configuration block diagram of a conventional example of an automatic focusing device in an imaging device equipped with an electronic imaging device. 10 is a concave focusing lens (group), and 12 is a convex variable power lens (group) for changing power during zooming. Note that the focusing lens 10 is configured to adjust its position during zooming in order to correct the movement of its focal point.

Reference numeral 14 denotes a holding frame to which the focusing lens 10 is fixed on the inner surface, and a male helicoid 14a is attached to one end of the outer peripheral surface.
is formed, and a gear 14b is formed at the other end. 1
Reference numeral 6 denotes a cylindrical moving cylinder having a female helicoid 16a formed on its inner periphery and helicoidally coupled to the holding frame 14 by meshing with the male helicoid 14a. Reference numeral 18 denotes a holding frame to which the variable magnification lens 12 is fixed on the inner surface.

2.0 is a cylindrical fixed barrel fixed to a camera body (not shown), and 22 is a cylindrical zoom ring having an inner circumferential surface inscribed in the outer circumferential surface of the fixed barrel 20. Note that the zoom ring 22 is rotatably attached around the optical axis along the outer periphery of the fixed barrel 20 without moving in the optical axis direction. Zoom ring 2
A gear 22a is formed at one end of the outer peripheral surface of the gear 22a.

Bins 2 are provided on the outer peripheral surfaces of the movable cylinder 16 and the holding frame 18, respectively.
These pins 24 and 26 pass through straight grooves of the fixed barrel 20 and are fitted into cam grooves of the zoom ring 22, respectively. That is, when the zoom ring 22 rotates, the movable barrel 16 and the holding frame 18 are not restricted in the optical axis direction by the linear grooves of the fixed barrel 20, but are moved by a corresponding distance in the optical axis direction by the corresponding cam grooves of the zoom ring 22. Moving. This configured eye body is well known as a zoom mechanism. Moving cylinder 1
6, that is, the focusing lens 10 is replaced with the variable magnification lens 12
The reason for linking is to correct the focus movement during zooming.

28 is a zoom motor, and a gear 30 is fixed to its shaft 28a, and the gear 30 meshes with the gear 22a of the zoom ring 22. 32 is a focusing motor, and a gear 34 is fixed to its shaft 32a, and the gear 34 meshes with the gear 14b of the holding frame 4. 36 is a position sensor that detects the rotational position (or rotation) of the motor 32; 38 is a motor drive circuit that drives the motor 32; 40 is a position sensor that detects the rotational position (or rotation) of the motor 32; 40 is a motor drive circuit that drives the motor 32; The ρI distance spreader circuit 42 that measures the distance to is an image sensor that converts an optical image produced by a photographing optical system including a lens group 1O12 into an electrical signal.

44 is a distance signal from the distance measuring circuit 40 and the position sensor 3
This is a system control circuit that not only controls the motor 32 according to the output of the motor 6, but also controls the entire system. Specifically, the system control circuit 44 takes into consideration the gear ratio of the gear 34 and the gear 14b of the holding frame 14, and the pitch of the helicoids 14a and 16a.
From the distance signal from the distance measuring circuit 40, the rotational direction and amount of rotation of the motor 32 to bring the desired subject into focus are calculated, and the motor drive circuit 38 rotates the motor 32 by the rotational direction and amount of rotation.

The operation shown in FIG. 3 will be briefly explained. By energizing the zoom motor 28, the zoom ring 22 rotates about the optical axis via the gear 30.22a.

As the zoom ring 22 rotates, the bins 24 and 26 move along the cam grooves of the zoom ring 22, while being restricted from moving in the optical axis direction by the linear grooves of the fixed barrel 20. As a result, the movable cylinder 16 and the holding frame 18 move in the optical axis direction. The movement of the holding frame 18 causes the variable power lens 12 to move in the optical axis direction, thereby performing variable power. As the movable barrel 16 moves, the holding frame 14 and the focusing lens 10 also move in the optical axis direction, and this is to correct the focus movement that accompanies zooming.

The automatic focusing operation is as follows. System control circuit 4
4 determines the rotational direction and rotational speed of the motor 32 from the stored data regarding the gear ratio of the gear 34 and the gear 14b of the holding frame 14, the pitch of the helicoids 14a and 16a, and the output of the ranging circuit 40. The motor 32 is rotated by the motor drive circuit 38 in the direction and amount of rotation. The amount of rotation of the motor 32 can be known from the output of the position sensor 36. Until the focusing lens 1o reaches the target position, the system control circuit 44 supplies acceleration, deceleration, and brake control signals to the motor drive circuit 38. When the motor 32 rotates, the holding frame 14 rotates around the optical axis by the gear 34.14b, and the helicoid 14a
, 16a, the focusing lens 10 is moved in the optical axis direction. In this way, the focusing lens 10 is driven to the in-focus position.

[Problems to be Solved by the Invention] As the image sensor 42, for example, a type using a charge-coupled device (CCD) is used, but in recent years, the size has increased from 2/3 inch to 1/2 inch, and even further. The size has been reduced to 1/3 inch. As the size becomes smaller, the permissible diameter of the circle of confusion on the imaging surface also becomes smaller, and therefore, high precision is required for positioning in the optical axis direction during zooming and focusing.

In addition, photographic lenses have also become smaller, and as a result, the focus sensitivity of each lens group (i.e., the ratio of the amount of focus movement of the imaging plane to the displacement of each lens group in the optical axis direction) has increased.
High precision is also required for lens positioning.

In conventional configurations of automatic focus control, focus control is affected by backlash in the drive system, wobbling of the lens holding frame, expansion and contraction of the lens holding frame due to changes in temperature and humidity, and changes in the refractive power of the lens itself. It has been difficult to obtain sufficiently high accuracy.

Therefore, an object of the present invention is to provide a highly accurate automatic focusing device.

[Means for Solving the Problem] The automatic focusing device according to the present invention includes a distance measuring means for measuring the distance to a subject, an imaging means for converting an image of the subject into an electrical signal, and a method for converting the electrical signal from the imaging means into an electrical signal. , a signal forming means for forming a signal for focus determination, a driving means for driving the focusing optical system of the photographing optical system, and a signal forming means after adjusting the position of the focusing optical system according to the distance information from the distance measuring means. It is characterized by comprising a control means for adjusting the WR position of the focusing optical system based on the output of the means.

[Function] First, the focusing optical system is adjusted using the output of the distance measuring means, and then the focusing optical system is adjusted using the output signal of the imaging means. The former type of adjustment includes ranging errors and mechanical errors in the transmission system, and is fast but not very accurate. On the other hand, although the latter adjustment is more accurate, it has the disadvantage that the farther out of focus it is, the more difficult it becomes to detect focus, and the longer it takes to reach the in-focus state. By combining the two in this way, even with a relatively simple configuration, it becomes possible to control the focus state accurately in a short time.

[Example code] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of an embodiment of the present invention. The same components as in FIG. 3 are given the same reference numerals. 5
2 is a camera circuit that converts the output signal of the image sensor 42 into a video signal; 54 is a gate circuit that extracts a signal used for distance measurement, that is, a video signal within the distance measurement area from the video signal output from the camera circuit 52; 56; is a bypass filter (HPF) that extracts high frequency components from the output of the gate circuit 54.
, 58 is a detector for detecting the output of the HPF 56.

The output of the detector 58 represents the definition of the subject image. 60 is a system control circuit that controls the entire system.

The operation shown in FIG. 1 will be explained. First, as explained in the conventional example, the system control circuit 60 rotates the motor 32 according to the output of the distance measurement circuit 40, and starts from a position corresponding to the distance to the subject determined by the distance measurement circuit 40 (designed focus position). The focusing lens 10 is moved to a position shifted by a predetermined amount in the optical axis direction. This is to shorten the time required to move the focusing lens 10 in one direction for the next step of focus detection.

Thereafter, the system control circuit 60 moves the focusing lens 10 using the motor 32 so that the output voltage of the wave detector 58 is maximized, and stops it at that spot. FIG. 2 shows the detector 5 relative to the position of the focusing lens 10.
8, the vertical axis shows the output voltage of the detector 58, and the horizontal axis shows the position of the focusing lens 10 in the optical axis direction.

Point A is the designed position where the image is in focus (that is, the designed focus position), and point B is the position where the image is truly in focus. In the step of moving the focusing lens 10 according to the output of the distance measuring circuit 40, it is driven from the original target point A to a position C shifted by a predetermined amount E toward the image pickup element 42.

The shift amount E is determined by taking into account control errors due to distance measurement errors, lens frame play, position errors of each lens group during zooming, backlash of the transmission gear, etc. Focus B is always focusing lens 1
The shift amount E is determined so as to be positioned in the feeding direction of 0.

Next, the system control circuit 60 moves the focusing lens 10 in steps by a predetermined amount from point C to point F, which is a distance E in the lens extending direction from point A. The step movement amount is the amount of extension of the focusing lens corresponding to the depth of focus calculated from the aperture value at the time of photographing, or a value smaller than this. Since the focusing lens 10 is not moved in steps, the system control circuit 60 stores the output of the detector 58 at each moving point in the internal memory 10.
I remember these 5 things.

When the focusing lens reaches point F, the system control circuit 60 compares the data stored in the internal memory and
The point at which the maximum value is reached (point B in the example of FIG. 2) is detected, and the focusing lens 10 is moved to that position B.

However, if the L1 focusing lens 10 is simply returned from F to B, errors will occur due to the hacklannons of the gears 14b and 34 and the gaps of the helicoids 14a and 16a. After driving by a predetermined amount, B
drive and stop. Since the focusing lens 10 is driven in the same direction as when detecting the output voltage of the wave detector 58, the above-mentioned error due to the drive system can be eliminated. The output voltage of the detector 58 may be detected by moving the focusing lens 10 to a designed focusing position according to the output of the distance measuring circuit 40 and moving the focusing lens 10 back and forth in the optical axis direction.

[Effects of the Invention] As can be easily understood from the above explanation, according to the present invention, after rough adjustment using distance information from a distance measuring means, fine adjustment is performed using a focus determination signal obtained by video signal processing. As a result, a true in-focus state can be obtained quickly and accurately.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention, FIG. 2 is an output voltage characteristic diagram of a detector 58, and FIG. 3 is a configuration block diagram of a conventional example. 107 Orcusing Lens (group) 12. Variable magnification lens (group) 14, 18: Holding frame 14a16a: Helicoid 14b, 22a, 30.34, Gear 16 Movable barrel 20/Fixed barrel 22 Zoom ring 24.26/Bin
28: Zoom motor, 28a, 32a: Shaft 3 Cushing motor 36 Position sensor drive circuit 40: Distance measurement circuit 42 44.60 Niji system control circuit 52 Circuit 54 Gate circuit 56: Bypass router 58:
detector

Claims (2)

[Claims] (1) A distance measuring means for measuring the distance to the subject, an imaging means for converting the subject image into an electrical signal, a signal forming means for forming a signal for determining focus from the electrical signal from the imaging means, and a photographing means. A driving means for driving a focusing optical system of the optical system, and a control means for adjusting the position of the focusing optical system based on the output of the signal forming means after adjusting the position of the focusing optical system according to distance information from the distance measuring means. An automatic focusing device characterized by: (2) The automatic system according to claim 1, wherein the control means moves the focusing optical system to a position shifted by a certain amount from the position according to the distance information, according to the distance information from the distance measuring means. Focusing device.