JPS6381308A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To make a master lens group or a part of it perform minute modulating operation and focusing operation by providing a driving element that moves a movable lens in the direction of the optical axis while giving the lens minute vibration. CONSTITUTION:A master lens group 11 that forms a zoom lens with a focus ring 12 can be moved freely in the direction of optical axis by a driving element 13 having a rotor 15. By switching the electrode of a stator 14 of a surface waveform ultrasonic motor, being a driving element 13, the direction of rotation of the rotor 15 is changed, and the master lens group 11 causes minute vibration longitudinally, and the focus position on the image pickup face of an image pickup device 16 changes minutely, and the higher harmonic component of video signals causes minute change periodically. The amount and direction of out-of-focus is calculated by a signal processing circuit 17, and the master lens group 11 is vibrated minutely by the driving element 13 and at the same time, the amount of amplitude is made larger in the direction of out-of-focus, and thereby, the master lens group 11 is moved in the direction of focusing. Thus, the focusing can be made automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an autofocus device using a sharpness modulation method based on minute fluctuations in optical path length.

2. Description of the Related Art Conventionally, this type of autofocus device uses a master lens group (1) as a minute modulation means, as shown in FIG.
By slightly vibrating the rear lens (9) in the optical axis direction with the drive element 00, the focus position on the imaging surface of the imaging device (3) is slightly changed, and the high frequency component of the video signal is periodically slightly changed. The signal processing circuit (force) calculates the amount and direction of out-of-focus, and the motor (6) rotates the focus ring (5) to perform autofocus operation.

Problems to be Solved by the Invention However, in the case of this configuration, as shown in FIG. A dedicated motor (6) must be provided to rotate (5).

Furthermore, since a piezoelectric element is used as a driving element, the outer diameter becomes large, which has the disadvantage of hindering miniaturization.

The present invention eliminates these drawbacks and improves mastering/reduction.
The object of the present invention is to provide an excellent autofocus device in which the lens group or a part thereof has both fine modulation operation and focusing operation.

Means for Solving the Problems The present invention makes the master lens group or a part thereof movable in the optical axis direction, and is provided with a drive element that moves the movable lens in the optical axis direction while causing minute vibrations. A surface wave type ultrasonic motor is used as the driving element.

For this reason, the drive element can be miniaturized because it also serves as microvibration and focus adjustment.

Example An embodiment shown in FIG. 7 will be explained below.

α℃ is the master lens group that forms the focus ring (I3 and the zoom lens), the stator 14, the rotor 1
It is made movable in the optical axis direction by a drive element α3 (surface waveform ultrasonic motor) having a drive element α3 (surface waveform ultrasonic motor). [Note that the surface wave type ultrasonic motor itself is well known, and a description of its specific configuration will be omitted. ] In this case, the light rays in front of the master lens group (1 degree Celsius are set to become parallel rays), and even if the master lens group σ is moved in the optical axis direction, the change in image magnification is kept at a constant value (±5%). ).In other words, even if the master lens group (1) 1 is moved, the image magnification does not change.
Only the focus will be blurred.

The stator α4, which forms part of the surface wave type ultrasonic motor serving as the driving element 13, is fixed to a part of the lens barrel α, and the rotary movement of the rotor (L9) is controlled by an intervening device such as a helicoid screw mechanism or a cam mechanism. This causes the master lens group I to move linearly in the optical axis direction.

The stator of the surface wave type ultrasonic motor which is the driving element 13 (
By switching the electrode 14J, the rotation direction of the rotor α is switched, and the master lens group <1)+ is slightly vibrated back and forth. This minute vibration causes the imaging device α to
The focus position of θ on the imaging surface changes slightly as in the case of FIG. 2, and the harmonic components of the video signal periodically change slightly. On the other hand, the out-of-focus amount and direction of out-of-focus are calculated using the signal processing circuit α corresponding to the force shown in Fig. 2.
The drive element α3 (surface waveform ultrasonic motor) causes the master lens group α°C to vibrate minutely as shown in Figure 3 (bl), and at the same time focuses the master lens group α°C by increasing the amplitude in the direction of blur. If you move the camera in that direction, it will automatically focus.

Effects of the Invention The above has been explained by way of embodiments, but according to the present invention, a master lens group forming a part of a zoom lens is composed of a micro vibrator and a microvibrator.
Since it is also used for focusing, and the surface waveform ultrasonic motor is also used as the driving element, the number of parts can be reduced, such as eliminating the need for a conventional focusing motor.

Further, by using a surface waveform ultrasonic motor, it is possible to drive the device coaxially with the optical axis, so that the device including the lens can be made smaller, which is advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an autofocus device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional autofocus device, and FIG. 3 is a comparison diagram of the conventional device of the present invention. (1))... Master lens group, (13... Drive element (surface waveform ultrasonic motor), αO... Imaging device,
o2...Focus ring. Name of agent Patent attorney Satoshi Nakao One male figure Figure 3 (EI) (b

Claims (3)

[Claims] (1) Autofocus in which all or part of the master lens group forming the zoom lens is movable in the optical axis direction, and a drive element is provided that can cause the movable lens to minutely vibrate and simultaneously move in the optical axis direction. Device. (2) The autofocus device according to claim 1, wherein the lens that moves minutely is provided with means for supplying parallel light rays. (3) The autofocus device according to claim 1, wherein a surface wave type ultrasonic motor is used as the drive element.