JPS62247314A - Automatic focus controlling device - Google Patents

Abstract

PURPOSE:To eliminate the need for conventional movable parts and to improve reliability by providing two faces shifted longitudinally in the direction of optical axis on the image forming face of an image pickup element and making automatic focus control utilizing the difference of contrast of the two faces. CONSTITUTION:Constitutional elements of image forming face at the center 11 of the image forming face are provided in unit of one horizontal line shifting longitudinally in the direction of optical axis. The image pickup output from a CCD image pickup element 13 is supplied to a sampling gate circuits 14F and 14B. On the other hand, a gate signal generating circuit 15 is provided, and the image pickup output from the constitutional element 12F of the line is obtained from the gate circuit 12F, and the image pickup output from the constitutional element 12B of the line is obtained from the gate circuit 14B, and supplied respectively to contrast detecting circuits 16F and 16B. The difference of contrast is found by a comparator circuit 17, and the output of the difference is supplied to a focus controlling circuit 18, and the output of the circuit 18 is supplied to a motor for driving a focus ring.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an autofocus control device suitable for use in an autofocus mechanism of a video camera, for example.
related.

(Summary of the Invention) The present invention forms a subject image at two adjacent partial positions in the image forming plane of an image sensor with a substantial difference in optical path length. This system uses contrast information for autofocus control, and does not require the RIJ moving part to obtain the autofocus control signal, making it highly reliable. It has various advantages such as not requiring space.

[Conventional technology]

Conventionally, the following is known as an example of an autofocus control device for a video camera.

This is done by moving the master lens of the zoom lens back and forth in the optical axis direction using a piezoelectric element such as a piezo element, for example, at 15Hz.
The change in the contrast of the object image on an image pickup device such as a COD is detected at that time, front blur and back blur are detected from this, and focus control is performed based on this.

In other words, as shown in Figure 8, when the vertical axis represents the contrast and the horizontal axis represents the position in the optical axis direction, the contrast is at its maximum at the position where the in-focus state is achieved, but as shown by the imaging range d1 in the same figure, When the master lens is vibrated, the contrast decreases when the master lens is swung to the left in the diagram, and the contrast increases when it is swung to the right, so the master lens is controlled to move to the right in the diagram. Conversely, when the master lens is swung back and forth at a position within the vibration range d2 in the same figure, the control is performed so that it does not move to the left in the figure where the contrast increases. and,
When you swing the lens back and forth at the in-focus position, the contrast at the positions before and after the swing is almost the same, which indicates that the focus was successful.

[Problem that the invention seeks to solve]

However, in the case of a degree-based autofocus mechanism, the master lens of the zoom lens is mechanically moved back and forth in the optical axis direction using a piezoelectric element, so (i) the piezoelectric element,
(11) It is difficult to ensure reliability due to the presence of moving parts; (iii) Special space is required for installing mechanical parts for the driving structure; etc. There are drawbacks.

The object of the present invention is to provide an autofocus control device that does not have these drawbacks.

[Means for solving problems]

In this invention, adjacent first and second
means for forming a subject image at the imaging portion positions (12F) and (12B) by substantially different light vIt lengths, and the first and second imaging portion positions (12F) (12
@l and a second contrast detector m(
16F) and (16B), a comparison means (17) for comparing the outputs of the first and second contrast detection means (16F) and (16B) to find the difference between the two, and the comparison means Ii
& (17) is provided, and means (18) is provided for controlling the focus so that the above-mentioned difference becomes approximately zero.

[Effect]

First and second imaging portion positions (12F) and (12B)
Since the optical path length from the subject is different, the contrast of the subject imaged at the first imaging part position (12F) and the second
By detecting the difference between the contrast of the subject image formed at the imaging part position (12B), front blur and back blur can be detected as explained in Fig. 8, and the difference between the two contrasts can be detected. By making sure that there is no focus, it is possible to bring the camera into focus.

〔Example〕

An embodiment of the device of the present invention will be described by taking as an example a case where it is applied to a video camera using COD as an image sensor.

In the example shown below, the autofocus control signal is obtained from the center portion (11) shown with diagonal lines, for example, in the entire CCD imaging focus 0 imaging plane (10) as shown in FIG. I am trying to use it as an area for

FIG. 1 is an example of this, and the figure shows a sectional view of an image sensor.

In this example, the components of the image forming surface at the center (11) of the image forming surface are shifted back and forth in the optical axis direction by one horizontal line. Imaging self-configuration of every other horizontal line 11! ! (12F) and the remaining horizontal line imaging plane components (12B)
) and the optical path length! ! ! It is formed so that it is shifted by d. This can be formed, for example, by an etching process.

In this case, the optical path length ip, d is set to a value within the depth of focus of the imaging lens and within the range from which blur information can be obtained, for example, d=50μ.

FIG. 3 is a block diagram showing focus control using such a CCD image sensor, and in the figure (13) is a CCD II image sensor. The image output from this CCD image sensor (13) is the sampling gate II!
1 path (14F) and (14B).

On the other hand, a gate signal generation circuit (15) is provided, which generates every other line component (
A gate signal GF that opens the gate circuit (14F) during the horizontal period when the imaging output is read out from the gate circuit (12F) is supplied to this gate circuit (14F), and the remaining every other line component (12B) A gate signal GB is supplied to the gate circuit (14B) to open the gate circuit (14B) during a horizontal period when the imaging output is more visible.

Therefore, the imaging output from the line component (12F) is obtained from the gate circuit (14F), and the gate circuit (
148), the imaging output from the line component (12B) is obtained, and the contrast detection circuit (16F) is obtained from the line component (12B).
) and (18B).

In the contrast detection circuits (16F) and (16B), contrast is detected depending on the amount of high frequency components of the respective human power imaging outputs. In other words, the closer the image is to the in-focus position, the more clearly defined the image is obtained, the more high frequency components there are, and the higher the contrast becomes.

These contrast detection circuits (16F) and (
The output of 16B) is supplied to a comparison circuit (17) to determine the difference in contrast, and the output of the difference is supplied to a focus control circuit (18).
The output is supplied to the focus ring drive motor.

As shown in Fig. 4, when the focus ring position at that time is in front of the in-focus position P1,
As is clear from FIG. 4, the contrast of the imaging output from the component (12F) is lower than that from the component (12B), and the positive difference signal from the comparison circuit (17), for example, is used for focus control. It is supplied to the circuit (18).

On the other hand, at P2, which is in the background blur state, as is clear from FIG. 4, the contrast of the imaging output from the component (12F) is greater than that from the component ff1 (t2B), A negative difference signal is supplied from the comparison circuit (17) to the focus control circuit (18).

In the focus control cycle VpI (18), the direction of the focus ring is determined without moving based on the positive and negative difference signals.
A motor control signal is generated that determines the amount of movement of the focus ring based on the magnitude of the difference fWt, and is supplied to the focus ring drive motor.

Focus control is performed so that the difference signal from the comparison circuit 11 (17) becomes almost zero.The fact that the difference signal from the comparison circuit (17) is zero means that the contrast is the constituent element m(12p) and ( 12B) is the same, and this is the in-focus position P3 as shown in FIG.

In the above example, the imaging plane components of every l line are configured with an optical path length difference d, but the optical path length i! d may be added to constitute the imaging plane component of the central portion (11).

In addition, as shown in FIG. 5, the image forming surface component in the center part (11) of the image forming surface is divided into two in the vertical or horizontal direction,
This two-part imaging plane configuration is necessary: A (20F) and (20B)
The optical path length! l! It may be shifted by d.

Further, instead of processing the image forming surface itself as in the above example, a filter can be placed in front of the image forming surface to obtain the same effect.

FIG. 6 shows the case where an optical path length difference d is provided between the imaging plane components of every other line, and in the central part (11),
Line imaging plane components (12F) and (1
2B) is left in the same direction as the imaging plane (10), and the thickness in the optical axis direction of the filter (21) placed in front of component # (12F) and component (128) is By changing the optical path length difference d.

Figure 7 shows the hook corresponding to the example in Figure 5. In this example, the filter (
As 22), the imaging plane component (12) of the central part (11)
), the optical path length, [d
has been realized.

Note that the present invention is applicable not only to CCD imaging devices but also to image pickup tube type imaging devices.

〔Effect of the invention〕

This invention provides at least two image forming surfaces of the image sensor that are substantially shifted back and forth in the optical axis direction, and uses the difference in contrast between the two surfaces to perform autofocus control. This eliminates the need for such a driving section, improving reliability. Further, there is an advantage that a space for providing a movable mechanism is not required and cost is reduced. Second, it has the advantage that the flange panchromatic circumference of the lens can be easily adjusted.

[Brief explanation of drawings]

Fig. 1 shows an example of the essential parts of this invention, Fig. 2 is a diagram for explaining this invention, Fig. 3 is a block diagram of an example of the inventive device, and Fig. 4 shows details of this invention. FIG. 5, FIG. 6, and FIG. 7 are diagrams for explaining other examples of essential parts of the present invention, and FIG. 8 is a diagram for explaining the operation of the conventional device. (12F) and (128) are imaging plane components at positions shifted in the optical axis direction, (16F) and (16B) are contrast detection circuits, and (17) is a comparison circuit.

Claims (1)

[Scope of Claims] 1. Means for forming a subject image at adjacent first and second imaging portion positions within an imaging plane with substantially different optical path lengths; The first and second parts detect the contrast by detecting the high frequency component of the imaging output from the position of the imaged part.
a contrast detecting means, a comparing means for comparing the outputs of the first and second contrast detecting means to find the difference between the two, and a focusing means that is supplied with the output from the comparing means and focuses so that the difference becomes approximately zero. an autofocus control device comprising: means for controlling; 2. As a means for forming a subject image at the first and second imaging portion positions within the imaging plane with different optical path lengths, the first
and an autofocus control device according to claim 1, using an imaging surface in which the position of the second imaging portion is shifted in the optical axis direction. 3. The autofocus control device according to claim 1, wherein a filter is used as a means for forming an image of a subject at the first and second imaging portion positions in the imaging plane with different optical path lengths.