JPH03237417A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To obtain accurate focusing control by changing an optical axis direction interval from an image pickup mean stepwise and comparing the outputs of a signal forming means at respective interval points to control the image pickup means in a focusing state. CONSTITUTION:The optical axis direction interval from the image pickup means 42 is changed stepwise and the outputs of the signal forming means respective optical axis direction intervals are compared with each other to control the means 42 in the focusing state. After zooming based upon a motor 28, a system control circuit 60 moves the element 42 in one direction of the optical axis direction stepwise by means of a motor driving circuit 49 and a motor 48. Namely, the movable range of the element 42 is divided into plural areas based upon the allowable blur circle of an image pickup face and focal depth calculated from a stop value at the time of photographing and the element 42 is moved to the representative points of respective areas in steps. The outputs of a detector at respective representative points are stored in an internal memory and the element 42 is moved to the representative point having the maximum output of the detector 58.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic focusing device, and more particularly 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 adapted to be adjusted in position W during zooming in order to correct the movement of the 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.

20 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 22
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 a corresponding distance in the optical axis direction by the corresponding cam grooves of the zoom ring 22. Moving. This configuration itself 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.

A zoom motor 28 has a gear 30 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 14. 36 is a position sensor that detects the rotational position (or amount of rotation) of the motor 32, and 38 is a motor drive circuit that drives the motor 32. 40, for example, the principle of triangulation,
A distance measuring circuit measures the distance to the object by detecting reflected waves of ultrasonic waves, and 42 is an image sensor that converts an optical image produced by a photographing optical system including a lens group 1012 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 are calculated so that the dot is aligned with the desired subject, 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 zoom motor 28, zoom ring 22 rotates about the optical axis via 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 tube 16 and the holding frame 18 are moved 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 rotation direction and rotation speed of the motor 32 from the gear ratio of the gear 34 and the gear 14b of the holding frame 14, the stored data regarding the pinch 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 10 reaches the target position, the system control circuit 44 supplies acceleration, deceleration, and braking control signals to the motor drive circuit 38. When the motor 32 rotates, the holding frame 14 rotates around the optical axis by the gears 32a and 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 (COD) is used, but in recent years, the size has increased from 273 inches to 1/2 inch and even 1 inch. /3 inches. 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 goldfishing.

In addition, taking lenses have become smaller, which has increased 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).
High precision is also required for lens positioning.

In the conventional configuration of an automatic focusing device, there are many problems such as failure of the drive system, insufficient resolution of the position sensor 36, wobbling of the lens holding frame, distortion of the lens holding frame during driving, and temperature and temperature fluctuations.
It has been difficult to obtain sufficiently high precision in focusing control due to expansion and contraction of the lens holding frame due to changes in humidity and changes in the refractive power of the lens itself.

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

[Means for Solving the Problems] An automatic focusing device according to the present invention includes an imaging device that converts a subject image into an electrical signal, and an electrical signal from the imaging device.
a signal forming means for forming a signal for focus determination; an adjusting means for adjusting the distance in the optical axis direction between the photographing optical system and the imaging means; It is characterized by comprising a control means that changes the interval in the optical axis direction in steps and controls the in-focus state by comparing the output of the signal forming means at each interval in the optical axis direction. The present invention also provides an imaging means for converting a subject image into an electrical signal, a signal forming means for forming a signal for focus determination from the electrical signal by the imaging means, and a drive for moving the imaging means in the optical axis direction. By means and said driving means! A control means for changing the interval in the optical axis direction between the photographing optical system and the imaging means in steps, and controlling the in-focus state by comparing the output of the signal forming means at each interval in the optical axis direction. Features.

[Operation] Since the above means determines the in-focus point by video signal processing, it is possible to precisely control the in-focus state without being influenced by various error factors of the photographing optical system. Furthermore, since the lens of the photographing optical system is not moved during focusing, slight movement in the optical axis direction of each photographing lens group due to vibration occurs, which also leads to accurate focusing control.

[Example 3 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. In this embodiment, instead of using a configuration in which focusing is controlled by moving the lens constituting the photographing optical system in the optical axis direction, a configuration in which the image sensor 42 and the eye body are moved in the optical axis direction is adopted. Therefore, the focusing lens 1 shown in FIG. 3 is provided with a drive system for driving the focusing lens.
The first lens (group) 62 corresponding to No. 0 is fixed to a holding frame 64 corresponding to the movable barrel 16, and the bottle 24, which fits into the cam groove of the zoom ring 22, is planted on the outer peripheral surface of the holding frame 64. ing. The other elements of the photographic optical system are the same as in FIG. 3 and are given the same reference numerals.

Reference numeral 46 denotes a holding member that holds the image sensor 42, and has a nut portion extending in the optical axis direction formed therein, into which a feed screw 47 is screwed. A feed screw 47 is coaxially fixed to the shaft of a stepping motor 48. 49
50 is a drive circuit for the motor 48, and 50 is a position sensor that detects the position of the holding member 46, that is, the image sensor 42 in the optical axis direction.

52 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. After zooming by the motor 28, the system control circuit 60 causes the motor drive circuit 49 and the motor 48 to step drive the image sensor 42 in one direction along the optical axis. That is, the movable range of the image sensor 42 is divided into a plurality of regions based on the depth of focus calculated from the permissible circle of confusion of the imaging surface and the aperture value at the time of photographing, and the image sensor 42 is moved stepwise to the representative point of each region. let

FIG. 2 is a diagram showing the output of the detector 58 with respect to the position of the image sensor 42 in the optical axis direction and how the movable range is divided into regions. The vertical axis is the output voltage of the detector 58, and the horizontal axis is the image sensor 4.
2 shows the position in the optical axis direction.

A is the infinite position and B is the 4th position. In order to cope with changes in the temperature of the lens barrel and changes in the refractive index of the lens, the movable range of the image sensor 42 is set from a little towards infinity than A to a little closer to d than B. DI-C4 is a representative point of each region Cl-C4 when the movable range is divided. Each region Cl-C4 and its representative point DI-D4 is included in the region corresponding to the distance within the depth of field when the image sensor 42 is located at the representative point DI-D4. It is set as follows. A curve 66 shows the output of the detector 58 when the image sensor 42 is continuously moved.

In the initial state, the image sensor 42 is located at DI, and the system control circuit 60 stores the output of the detector 58 at that time in the internal memory. The system control circuit 60 moves the image sensor 42 to the next representative point D2 by the motor 48, and stores the output of the detector 58 at that time in another address in the internal memory. In this way, the output of the detector 58 at each representative point DI-D4 is sequentially stored in the internal memory, and the output of the detector 58 at each representative point DI-D4 is stored in the internal memory.
The image sensor 42 is moved to the representative point (in the example of FIG. 2, C2) where the output of . This completes the ring movement,
You are now ready to take pictures. Of course, the image sensor 42 is not moved step by step to each representative point, but the output of the detector 58 is compared, and when the output of the detector 58 becomes small, the representative point where the output of the detector 58 reaches its peak is determined. The image sensor 42 may be moved and stopped at the same time.

[Effects of the Invention] As can be easily understood from the above explanation, according to the present invention, since focusing control is performed based on the image signal of the object that has passed through the photographing optical system, accurate focusing can be performed taking into account errors in the photographing optical system. If the focus is on! Can perform I+. In addition, since the focusing operation is performed by moving the imaging means rather than the photographing optical system, there is no vibration of the lens group due to lens movement.
Accurate focusing control becomes possible, and the photographing optical system can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is an output voltage characteristic diagram of the detector 58, and FIG. 3 is a diagram of the conventional example.
It is a block diagram. 10: Frame-cushing lens (group) 12: Variable magnification lens (group) 14.18.64: Holding frame 14a, 16
a: Helicoid 14b, 22a 30.34: Gear 16/Movable cylinder 20: Fixed cylinder 22: Sum ring 24,
26: Pin 28: Zoom motor 28a, 32a:
Shaft 32 Focusing motor 36: Position sensor 38: Motor drive circuit 40: Distance measurement circuit 42:
Image sensor 44, 60: System control circuit 52 Power camera circuit 54: Kate circuit 56 bypass filter
58: Detector

Claims (2)

[Claims] (1) Distance in the optical axis direction between an imaging device that converts a subject image into an electrical signal, a signal forming device that forms a signal for focus determination from the electrical signal from the imaging device, and a photographic optical system and the imaging device The adjustment means adjusts the distance between the photographing optical system and the imaging means in a stepwise manner, and the output of the signal forming means at each interval in the optical axis direction is compared. 1. An automatic focusing device comprising: control means for controlling to a focused state. (2) an imaging means for converting a 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 driving means for moving the imaging means in the optical axis direction. , a control means for controlling the focusing state by causing the driving means to change the interval in the optical axis direction between the photographing optical system and the imaging means in a stepwise manner, and comparing the output of the signal forming means at each interval in the optical axis direction; An automatic focusing device comprising: