JPH05134163A - Focus control device - Google Patents

Abstract

PURPOSE:To keep the in-focus state even if the zoom direction is reversed by absorbing a slippage of a correction curve caused by a difference in the zoom direction at the time of reversing the zoom direction in an inner type focus adjusting device. CONSTITUTION:In a lens system which has a magnification changing function and adapted to change the image formation position according to the focal distance, when it is once put in the in-focus state, an object distance is calculated from the zoom position and the position of a focus adjusting lens 2, and hereinafter, the focus adjusting lens 2 is little displaced only for a designated slippage correction amount immediately after changing the zoom direction in such a manner as to absorb a slippage of a correction curve caused corresponding to the moving direction of the zoom lens 1 while the focus adjusting lens 2 is moved to the lens position determined according to the correction curve prepared for every object distance and the focal distance to keep the in-focus state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens adjusting device for a lens system, which has a function of varying magnification and whose image forming position changes depending on the focal length.

[0002]

2. Description of the Related Art Focusing systems used in video cameras and the like, depending on the type of lens to be moved, use a front lens system that uses the frontmost lens group (position most distant from the image pickup element), and other front lens systems There is a so-called inner method using a lens group. A major difference between these two methods is the behavior in the zooming operation that changes the focal length.

In the front lens system, a mechanism such as a cam is generally used, so that a focus shift due to a zoom operation does not occur even when the focusing lens group is fixed. On the other hand, in the inner method, for example, as shown in Japanese Patent Publication No. 52-15226 (G02B7 / 04), it is necessary to move the focusing lens group along with the zoom operation in order to maintain the focus. Become.

However, in recent years, since the entire lens system can be downsized as compared with the front lens system and the driving lens for focusing is small, power saving and quick operation can be realized. The inner method is used for awards.

Here, this inner method will be described with reference to FIG. FIG. 3 is a circuit block diagram of the focus control device according to the present embodiment. In the figure, 1 is a lens group that controls the focal length and has a zoom function, 2
Is a focusing lens having a focusing function, 3 is a zoom motor that displaces the lens group 1 in the optical axis direction, and 4 is a focus motor that displaces the focusing lens 2 in the optical axis direction.

At 6, the incident light passing through each lens group is imaged,
A CCD that is converted into an electric signal, 7 is a signal processing circuit that creates a video signal from an image pickup signal obtained from the CCD 6, and 8 is a focus that outputs a focus evaluation value that is a criterion for determining the degree of focus using the imaged video signal. It is an evaluation value generation circuit.

The focus evaluation value generating circuit 8 is specifically
As shown in FIG. 4, a focus area extraction circuit 40 that receives the image pickup luminance signal output from the signal processing circuit 7 as an input and extracts only the luminance signal in the focus area arranged in the center of the image pickup screen in a time division manner. And the HPF 41 that extracts only the high frequency component of this output, and 1 of this HPF output.
It is composed of a digital integrator 42 that digitally integrates the field portion and outputs it as a focus evaluation value. When the focus operation is performed, the focus evaluation value sequentially output for each field from the integrator is adjusted to a position where the maximum value is obtained. The focus motor 4 from the microcomputer 10 is moved so that the focusing lens 2 is moved and stopped.
Is supplied with a drive control signal. The above-described focusing operation using the principle that the high frequency component of the luminance signal is maximum in the focused state is a technique known as a so-called hill-climbing autofocus method.

Reference numeral 9 denotes a potentiometer for detecting a focal length, that is, a zoom area from the position of the lens group 1 in the optical axis direction, and specifically, a conductive contact piece 20 interlocking with the lens group 1 and a power supply voltage + B. It is composed of a resistor 21 inserted between grounds, and the contact piece 20 is displaced in conjunction with the lens group 1,
The voltage value at this contact changes, and this voltage is
Is applied to the zoom position and the zoom position from the telephoto to wide angle is detected by this voltage value.

A motor 5 detects the rotation state of the focus motor 4 and issues N rotation detection pulses for one rotation of the motor and a signal indicating the rotation direction (near point direction or far point direction). Rotation detector 1 attached to 4
In response to the output from 3, the rotation detection pulse is counted up when the focusing lens 2 is moved in the direction of the near point, and conversely when the focusing lens 2 is moved in the direction of the far point, the rotation detection pulse is counted down. , The microcomputer 10 using this count value as the current lens position of the focusing lens 2.
It is a counter to supply to.

The operation of the image pickup apparatus constructed as described above will be described. First, the subject is subjected to the above-mentioned hill-climbing focusing operation at an arbitrary zoom position to reach a focused state. In this focused state, the distance from the video camera to the subject (subject distance) from the lens position indicated by the count value of the counter 5 and the current zoom position from the potentiometer 9.
Is calculated.

From this in-focus state, the zoom position is set to TELE.
When the zoom operation for changing to the (telephoto) side or the WIDE (wide angle) side is performed, the position correction operation of the focusing lens 1, that is, the zoom focus operation is required accordingly. For example, as shown in FIG. 5, it is necessary to make a correction along the curve L1 for a subject with an infinite subject distance, and to make a correction along the curve L2 for a subject with a subject distance of 1 m. is necessary. The correction curves of L1 and L2 differ depending on the subject distance, and these straight lines are prepared for each subject distance in advance when the lens unit is designed, and each curve is stored in the memory 11 for supplying data to the microcomputer 10. ing.

Therefore, as described above, the focus correction is performed by selecting a correction curve from the memory based on the object distance calculated at the end of the hill climbing focusing operation from the memory and inputting the focal length corresponding to the zoom position. The amount (correction amount for keeping the imaging position constant) is calculated by the microcomputer. By shifting the focusing lens in the optical axis direction by this correction amount, it becomes possible to correct the lens position for automatically continuing the focused state by following the zoom operation.

[0013]

In a lens system having a variable power function, such as the zoom lens described above, when the variable power operation direction (zoom direction) is reversed due to the variation in the clearance that is structurally inevitable. The focus position may change. This phenomenon often appears especially in the inner focus type lens.

[0014]

SUMMARY OF THE INVENTION According to the present invention, a focal length changing means for changing a zoom magnification by displacing a first lens group for controlling a focal length, a second lens group for performing focusing control, and Lens position holding means for holding the lens positions of the two lens groups as position data, a correction curve prepared for each subject distance, and the second lens group so that the position data coincides with the lens position determined by the difference in the focal length. The focusing means for displacing the focusing state and the second correction amount by a predetermined correction amount when changing the focal length by the focal length varying means so as to absorb the deviation of the correction curve generated according to the changing direction of the focal length.
It is characterized in that the lens group is displaced.

[0015]

Since the present invention is configured as described above, the shift of the in-focus position when the zoom direction is reversed can be easily corrected and the in-focus state can be maintained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The circuit block diagram of the focus control apparatus according to the present embodiment is the same as that of the prior art FIG.
The hill-climbing focus operation at 0 and the zoom focus operation are exactly the same, and the only difference is that a rattling correction operation is added in addition to these operations. This rattling correction operation is shown in the flowchart in FIG. ..

In FIG. 1, the backlash correction operation is executed for each field after the hill-climbing focusing operation. First, whether or not the zoom operation is being executed, and if the zoom operation is being executed, in the TELE to WIDE direction. It is determined from the output change of the potentiometer 9 whether the zoom is going toward the zoom or the zoom going from the WIDE to the TELE direction (step 5).
1) When the zoom operation is not performed, it is determined whether the ZM flag is set or reset (step 5).
2) During zooming in the WIDE direction, or when zooming is completed in this direction, the ZM flag is reset (step 53), and conversely, zooming in the TELE direction or zooming in this direction is completed. If so, the ZM flag is set (step 54).

When the ZM flag is reset, it is 1 until the count value K of the GATA counter becomes 0.
Decrement for each field (step 55), Z
If the M flag is set, the count value K of the GATA counter is incremented for each field until it reaches the upper limit value N (step 56).

Here, for a subject with a certain subject distance (infinity in the example of FIG. 2) as shown in FIG. 2, the correction curve when the zoom direction is from TELE to WIDE is L
If it is set to 3, the correction curve when the zoom direction goes from the WIDE to the TELE side for the same subject at the same subject distance becomes L4 due to the structural clearance of the zoom lens group, and the zoom position on the curve L3. When the focusing lens position at y is X, the focusing lens position at the zoom position y becomes X-D when the zoom direction is reversed. That is, it is necessary to shift the position of the focusing lens 2 by D in order to maintain the focused state only by reversing the zoom direction.

Further, the shift of the in-focus position due to the reversal of the zoom direction usually takes several msec to several hundred msec, and continuously shifts. Therefore, when the shift correction is performed at the moment when the zoom is reversed, a time lag is generated between the actual shift and the actual shift, and the image is instantaneously out of focus when reversed. Therefore, it is necessary to correct the shift of the focusing lens due to the reversal in the same way as the shift of the focusing position, and it is necessary to continuously move it over several msec to several hundred msec.

Here, the backlash correction routine shown in the flow chart of FIG.
6.7 msec), and if the time during which the in-focus position shifts during zoom reversal is usually about 334 msec, the upper limit value N of the number of corrections is 334 msec / 16.
7 msec = 20 times. At this time, if the movement amount (deviation amount) of the focusing lens necessary for the deviation correction is D, D = N /
The value of M may be determined so that it becomes M. Here, the normal deviation amount D is about several μm to several tens of μm.

In consideration of the above, in the backlash correction routine, the correction amount d for one field of the backlash correction operation is d =
K / M is set (step 57), and the backlash is gradually corrected by moving the focusing lens to Xd based on the correction amount d thus determined (step 58).

Therefore, when the zoom direction is the TELE direction or when the zoom is completed by zooming in the TELE direction, the count value K is incremented, and the correction amount d is 1 / M for each field. Increased,
If K = 0 in the initial state, d = N / after N fields
It becomes M, which corresponds to the amount of play.

Further, when the zoom direction is the WIDE direction or when the zoom is completed in the WIDE direction and the zoom is completed, the count value K is decremented, so the correction amount d is 1 / M for each field. It decreases, and finally d = 0.

The backlash correction based on the backlash correction amount d thus determined is executed at the same time as the movement of the focusing lens according to the change of the zoom position along the correction curve L3, that is, the zoom focus operation.

In the above-described embodiment, the hill climbing method is used as the focusing operation method, but it goes without saying that another method such as an infrared distance measuring method may be used instead. Further, when a backlash amount exists in the drive system of the focusing lens due to a speed reduction mechanism or the like, the shift amount D should be an amount including the backlash amount.

[0028]

As described above, according to the present invention, the inner
In the focusing system of the system, when the zoom direction is reversed,
The shift of the correction curve caused by the difference in the zoom direction can be easily corrected, and the in-focus state can be maintained even after reversing the zoom direction.

[Brief description of drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

FIG. 2 is a diagram showing a shift of a position correction curve of a focusing lens during zoom focusing.

FIG. 3 is a block diagram of a focus control circuit of the image pickup apparatus.

FIG. 4 is a block diagram of a main part of a focus control circuit of the image pickup apparatus.

FIG. 5 is a diagram showing a position correction curve of a focusing lens at the time of zoom focusing.

[Explanation of symbols]

 1 lens group 3 zoom motor 2 focusing lens 5 counter 4 focus motor 10 microcomputer

Claims (1)

[Claims] 1. In a lens system having a function of varying a magnification and in which an image forming position changes in accordance with a focal length, a first lens group for controlling a focal length is displaced to change a focal length. Means, a second lens group for focusing control, a lens position holding means for holding the lens position of the second lens group as position data, a correction curve prepared for each subject distance, and a focal length. Focusing means for displacing the second lens group so that the position data coincides with the lens position, and for absorbing the deviation of the correction curve caused by the difference in the changing direction of the focal length. Further, the focus control device is characterized in that the second lens group is displaced by a predetermined correction amount when the focal length is changed by the focal length changing means.