JPH095620A - Automatic focusing device and automatic focusing method for image pickup device - Google Patents

Abstract

PURPOSE: To provide an automatic focusing device and an automatic focusing method for an image pickup device capable of obtaining rapid and smooth automatic focusing operation and realizing miniaturization and the reduction of cost. CONSTITUTION: An image projected by an optical system consisting of a photographing lens 1, a polarizing filter 10, and a double refraction plate 11 is converted into a video signal by an image pickup element 2, and a high frequency component is fetched from the video signal by a 1st filter means consisting of a filter 12 and a BPF 14 and a 2nd filter means consisting of a filter 13 and a BPF 15, changed to an absolute value by detection circuits 16 and 17, and compared by a microcomputer 7 so as to decide a focusing state. A motor 9 is driven in accordance with the result of the decision, so that the lens 1 is driven in a focusing direction. The 1st and the 2nd filter means have characteristic that the largeness of the quantity of the high frequency component being their output is inverted in the vicinity of a focusing point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjustment device for an image pickup apparatus and an automatic focus adjustment method for an image pickup apparatus, in which a moving amount of a taking lens is adjusted by using a video signal obtained from an image pickup device. It is about.

[0002]

2. Description of the Related Art Conventionally, as a device of this type, a high-frequency component contained in a video signal is extracted by a bandpass filter or the like, or the sharpness of the edge portion of the object is extracted by a differentiating circuit or the like to obtain a video image of the subject. A method is known in which the focus state is determined and the position of the lens is moved so that the extracted amount is maximized to obtain the in-focus state of the video signal. This method is described in detail in NHK Technical Research, Vol. 40, No. 17, "Automatic Focusing of Television Camera by Mountain Climbing Servo Method" by Ishida et al. Hereinafter, this will be briefly described.

In FIG. 15, 1 is a lens, 2 is an image pickup element, 3 is a preamplifier, 4 is a process circuit, 5 is a bandpass filter (hereinafter abbreviated as BPF), 6 is a detection circuit,
Reference numeral 7 is a microcomputer (hereinafter referred to as a microcomputer), 8 is a motor drive circuit, and 9 is a motor.

An image of a subject is projected on the image pickup surface of the image pickup device 2 by the lens 1, and a video signal converted into an electric signal is obtained by the image pickup device 2. This video signal is amplified to an appropriate level by the preamplifier 3 and the process circuit 4 outputs the NT signal.
It is converted into a standardized video signal such as SC. The output of the preamplifier 3 is also applied to the BPF 5, the high frequency component included in the video signal is extracted, and the detection circuit 6 obtains an output corresponding to the absolute amount of this high frequency component.

The lens 1 projected on the image pickup surface of the image pickup device 2.
The resolution of the projected image varies depending on the focus state. That is, the resolution becomes maximum when the focus of the projected image of the lens 1 is on the image pickup surface of the image pickup element 2, and the longer the distance the focus is from the image pickup surface (hereinafter, referred to as defocus amount), the resolution. Will fall.

FIG. 16 shows changes in the MTF curve when the lens 1 is in focus, small blur, and large blur. As shown in FIG. 16, the closer the focus state of the lens 1 is to the focused state, the higher the spatial frequency is resolved. The closer to the large blur state, the lower the spatial frequency that can be resolved. This relationship directly corresponds to the relationship between the output amplitude of the video signal and the frequency. That is, the closer the focus state of the lens 1 is to the focused state, the larger the amplitude of the high frequency component included in the video signal, and the closer to the large blur state, the smaller the amplitude of the high frequency component.

Therefore, the output of the detection circuit 6 changes depending on the amount of extension of the lens 1 as shown in FIG. 17, and has a maximum value at a certain position. This is because when the amount of extension of the lens 1 changes, the focus state of the image projected on the surface of the image pickup element 2 changes, and the sharpness of the picked-up image becomes maximum in the in-focus state, that is, when the image is in focus. This is because when converted into a video signal in 2, the high frequency component contained in the video signal becomes maximum.

The microcomputer 7 takes in the output of the detection circuit 6 and calculates the driving direction and the driving speed of the motor 8 such that the output becomes large, and the rotation direction and the rotating speed of the motor 9 are calculated via the motor driving circuit 8. To control. Then, the motor 8 is stopped at the position where the output of the detection circuit 6 becomes maximum.

As described above, the focus amount is automatically obtained by controlling the repetition amount of the lens of the video camera.

By the way, in this system, for example, if the lens is first extended to the position indicated by point A in FIG. 17, in order to extend the lens to the point B at the in-focus position, the lens is first moved to the infinity direction. The driving direction must be determined by moving the lens in either the, or the closest direction. That is, when the lens is driven in the infinity direction at the point A in FIG. 17, the lens can be driven as it is to the point B. However, when the lens is driven in the close direction, it is confirmed that the output of the detection circuit 6 decreases and then the direction is changed. Must be reversed.

Further, even if the driving direction of the lens is toward the point B, it cannot be determined that the point B is the maximum value immediately after reaching the point B. Therefore, once the point B is passed, the detection is performed at the point C. It is necessary to confirm that the output of the circuit 6 has decreased and then to return to the point B.

In the above operation, if the lens is driven and the change in the output of the detection circuit 6 is not observed, it may be in focus or out of focus in the infinity direction (hereinafter referred to as the rear focus state).
However, it is out of focus in the close-up direction (hereinafter referred to as the front focus state).
This is an operation that is necessarily performed because it is not known, and it is an unfavorable operation for automatically and smoothly obtaining a focused state.

In contrast to the above-mentioned method, a part of the lens system or a drive system different from the drive system for performing the focusing operation of the image pickup device is used to perform minute vibrations in a specific cycle in the optical axis direction (hereinafter referred to as wobbling operation). A method for determining the focus state of a subject image on the image pickup surface and automatically obtaining the in-focus state is proposed, for example, as described in JP-A-58-188965 (Kitamura et al.). Has been done. In this method, it is possible to determine whether the lens is in focus, is in the front focus state, or is in the rear focus state without driving the lens system with a motor, so that the focusing operation can be performed efficiently and smoothly as compared with the above-described method. However, the mechanism for vibrating the lens system or the image pickup device in the optical axis direction becomes complicated and expensive.

On the other hand, at present, there is a method in which a drive system such as a stepping motor which is relatively easy to perform position control is used as a drive system for performing a focusing operation, and the above-mentioned wobbling operation is also simultaneously performed by this drive system. It is becoming mainstream.

[0015]

However, in the above-mentioned conventional example, the wobbling operation for discriminating the focus state of the optical system is performed with a small vibration amplitude that is difficult to understand on the image screen observed by the photographer. Although it must be performed, the video signal is accompanied by noise in no small amount, so wobbling is performed for a long time and averaged in order to reliably identify the front pin, the rear pin, etc. with the minute vibration width as described above. It is necessary to judge after obtaining the detection result. Since the focusing operation involves a process of driving the lens in the focusing direction after the result is obtained, it takes a long time to focus as a whole, which is not preferable. Especially,
In the vicinity of the focus, even if the wobbling operation is performed with a slight vibration amplitude, the picked-up image is sensitively affected, and a good image may not be obtained in some cases.

Further, since the position of the subject is changing every moment even after the optical system is brought into the in-focus state, the wobbling operation is continuously or regularly continued to determine whether or not the in-focus state is maintained. There must be. Such an operation is unfavorable because it is necessary to constantly supply power to the drive system, which requires large power consumption. Furthermore, the drive system for performing the operation involving wobbling as described above is required to have a drive speed, a drive torque, a drive accuracy, and the like commensurate with the operation, so that it is difficult to miniaturize and the price is also low. It becomes expensive.

The present invention has been made under such circumstances, and a fast and smooth automatic focusing operation can be obtained.
An object of the present invention is to provide an automatic focus adjustment device for an image pickup apparatus and an automatic focus adjustment method for an image pickup apparatus, which can be downsized and reduced in cost.

[0018]

In order to achieve the above object, according to the present invention, an automatic focus adjusting device for an image pickup apparatus is as follows (1) and an automatic focus adjusting method for an image pickup apparatus is as follows (2). Configure as follows.

(1) A photographing lens, a polarizing filter arranged after this photographing lens, a crystalline transmission plate having birefringence development arranged after this polarizing filter, and a light transmission plate arranged behind this transmission plate. Of the image sensor, a first filter means for extracting the high frequency component from the video signal by the image sensor, a second filter means for extracting the high frequency component from the video signal by the image sensor, and a first filter means. Discriminating means for discriminating the focus state of the optical system including the taking lens by comparing the output with the output of the second filter means, and driving means for driving the taking lens in the focusing direction based on the output of the discriminating means. And the first
The above-mentioned filter means and the above-mentioned second filter means are automatic focus adjusting devices for an image pickup apparatus, in which the magnitude relation of the high frequency components of the respective outputs is inverted in the vicinity of the focal point.

(2) The focus state of the optical system including the taking lens is discriminated by the video signal obtained by the projection image by the ordinary ray of the birefringence phenomenon and the projection image by the extraordinary ray projected on the image pickup surface of the image pickup device. Then, an automatic focus adjusting method for an image pickup apparatus, which drives the taking lens in a focusing direction based on a result of this determination.

[0021]

With the constructions of (1) and (2), the photographing lens is formed by the image signals obtained by the projection image by the ordinary ray and the projection image by the extraordinary ray of the birefringence phenomenon which are projected on the image pickup surface of the image pickup device. The focus state of the optical system is discriminated, and the photographing lens is driven in the focusing direction based on the discrimination result.

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples.

(Embodiment 1) FIG. 1 is a block diagram showing the arrangement of an "imaging device" according to the first embodiment.

In FIG. 1, 1, 2, 3, 4, 7, 8,
Each element 9 is the same as that of the conventional example shown in FIG. 10
Is a polarization filter, 11 is a crystalline transmission plate having a birefringence phenomenon (hereinafter referred to as a birefringence plate), and 12 is an image of an image projected by an extraordinary ray from an image signal of the image projected on the image sensor 2. A filter for canceling the signals and extracting only the video signal of the image projected by the ordinary ray, 13 is the image sensor 2
The image projected by the ordinary ray by canceling the image signal of the image projected by the extraordinary ray from the image signal of the image projected by the ordinary ray while including more high frequency components of the image signal of the image projected on A filter that extracts the video signal of
Reference numerals 14 and 15 are BPFs (band pass filters) for extracting high frequency components from the respective input signals, and 16 and 17 are detection circuits. Note that the birefringent plate that is normally inserted immediately before the image sensor 2 as an optical low-pass filter is not included in the configuration in this embodiment. The filter 12 and the BPF 14 are the first in claim 1.
The filter 13 and the BPF 15 correspond to the second filter means of claim 1.

The subject image projected by the lens 1 and the polarization filter 10 of FIG. 1 forms two overlapping images on the image pickup surface of the image pickup device 2 via the birefringent plate 11. This process is shown in Figure 2.
This will be described with reference to FIG.

In FIG. 2, reference numeral 10 denotes a polarization filter, and 11
Is a birefringent plate, 2 is an image sensor, A is an incident ray, A ₁ is an ordinary ray of A in the birefringence phenomenon, and A ₂ is an extraordinary ray of A in the birefringence phenomenon. When the incident light ray A that has passed through the polarization filter 10 enters the birefringent plate 11, the incident light ray A is polarized in different directions, the ordinary ray A ₁ and the extraordinary ray A ₂
Divided into

In the case of birefringence of general incident light that is not polarized, the light amount of the ordinary ray and the light amount of the extraordinary ray are equally divided, and the respective light amounts become equal, but in the case of this embodiment, the polarization filter 10 is used. Since the incident light A is polarized, the light quantity of the ordinary ray A _{1 and} the light quantity of the extraordinary ray A ₂ differ depending on the polarization direction and extinction ratio of the polarization filter 10. Here, the light quantity of the ordinary ray A ₁ is F ₁ , and the light quantity of the extraordinary ray A ₂ is F
₂ , assuming that the extinction ratio of the polarization filter 10 is k and the polarization direction of the polarization filter 10 is equal to the polarization direction of the ordinary ray A _1.

[0028]

[Equation 1]

Is as follows. At this time, the angle formed by the ordinary ray A ₁ and the extraordinary ray A ₂ is θ, and the thickness of the birefringent plate 11 is t.
When is _h, the distance w between the ordinary ray A ₁ and extraordinary ray A ₂ when it reaches the imaging plane of the imaging element 2 is _{w = t h · tanθ .................. (} 2) Further, the ordinary ray A ₁ And the optical path length difference ΔL between extraordinary ray A ₂ is

[0030]

[Equation 2]

It is represented by

Considering the above process in the optical system shown in FIG. 1, the process is as follows. FIG. 3 shows in detail the part of the optical system shown in FIG. In FIG. 3, 1 is a lens, 10 is a polarizing filter, 11 is a birefringent plate, 2 is an image sensor, A ₁ is a light flux of an object image by an ordinary ray, and A ₂ is a light flux of an object image by an extraordinary ray. Show. As shown in FIG. 3, the subject image projected by the lens 1 passes through the polarizing filter 10, split into two by the birefringent plate 11, the projected image by the ordinary ray A ₁ is imaged on a point P ₁ in FIG. 3 , the projected image by the extraordinary ray a ₂ is imaged at point P _2. At this time, as described above, since the optical path length of the extraordinary ray A ₂ is longer than the optical path length of the ordinary ray A ₁ by ΔL, the position of the image forming point P ₂ is closer to the lens 1 by ΔL than P ₁ .
That is, if the projection image of the ordinary ray A ₁ is in focus on the image pickup surface of the image pickup element 2, the projection image of the extraordinary ray A ₂ is in the front focus state by ΔL.

FIGS. 4 to 8 show the image formation states of the projection image of the ordinary ray A _{1 and} the projection image of the extraordinary ray A ₂ in various focus states. 4 to 8,
Each element shown in 2, 10, and 11 is the same as that shown in FIG.

FIG. 4 shows the case of the same focus state as in FIG. 3 in more detail. Here, the scanning direction of the scanning line of the image sensor 2 is the direction of arrow M, the light quantity of the projected image by the ordinary ray A ₁ is F ₁ , and the light quantity of the projected image by the extraordinary ray A ₂ is F ₂ , and F ₁ > F ₂ , The image projected on the image pickup surface of the image pickup element 2 is an image in which the two images are overlapped with each other by shifting by w to the left and right as shown in FIG. The image on the left side is ΔL front-focused, and the image on the left side is brighter by F ₁ / F ₂ than the image on the right side.

It is assumed that such a projected image is represented by a video signal output when the scanning line in the direction indicated by the arrow M is scanned, that is, an output function f ₀ (t) of the preamplifier 3 shown in FIG. This f ₀ (t) is expressed by f ₀ (t) = h ₀ (t) + k · g {h ₀ (t−Δt)} (4) Here, h ₀ (t) represents a video signal waveform of only the projection image of the ordinary ray A ₁ when the projection image of the ordinary ray A ₁ is in focus, and k is the ordinary ray A
The ratio of the amount F ₂ of the projected image relative to the amount of light F ₁ and the extraordinary ray A ₂ of the projected image by _1, that is, _{k = F 2 / F 1 (} <1), t {} is ΔL only previous focus state In this case, it is a function representing the attenuation of the high frequency component of the video signal due to the change of the MTF curve, and Δt is the time for scanning the section w of the image pickup surface of the image pickup device 2. Therefore, k · g {h ₀ (t−Δt)}
Represents the video signal waveform of only the projection image by the extraordinary ray A ₂ .

The change in the MTF curve shown in FIG. 16 can be regarded as an optical low pass filter (hereinafter abbreviated as LPF). Therefore, the electrical L corresponding to the above-mentioned g {}
Consider the PF, which upon the LPF1, the recursive filter shown in FIG. 12, in the formed signal from the video signal h ₀ of the image projected by the ordinary ray A ₁ (t), the extraordinary ray A ₂
Image signal k · g {h ₀ (t−Δ
t)} can be canceled to extract the video signal h ₀ (t) of only the projected image by the ordinary ray A ₁ from the original video signal output f ₀ (t).

In FIG. 12, 111 is a subtractor, and 112
Is a multiplier, 113 is the above-mentioned LPF 1, and 114 is a delay circuit that delays the input signal by Δt. Assuming that the output of the subtractor 111 is the image signal h ₀ (t) of the image projected by the ordinary ray, the output of the delay circuit 114 is Δ
It is delayed by t and becomes h ₀ (t−Δt). This is because the high frequency component is reduced by LPF1, and g {h ₀
(T−Δt)}. Further, in the multiplier 113, k (k <
1) It is multiplied to become a video signal k · g {h ₀ (t−Δt)} of only the projection image by the extraordinary ray A ₂ . By subtracting this from the original signal f ₀ (t) by the subtractor 111,
A video signal h ₀ (t) of only the projection image by the ordinary ray A ₁ is obtained.

The filter 12 shown in FIG. 1, such be composed of a recursive filter, is output from the preamplifier 3, a video signal projected image is superimposed by the extraordinary ray A ₂ to the projection image by the ordinary ray A ₁ From this, a video signal of only the projection image of the ordinary ray A ₁ is extracted and output to the process circuit (corresponding to the signal processing means of claim 1) 4. The process circuit 4 converts this signal into a standardized video signal such as NTSC and outputs it.

In FIG. 5, the object image projected by the lens 1 is divided into two by the birefringent plate 11, and the ordinary ray A ₁
From the imaging surface of the image sensor 2 on the optical axis by ΔL /
An image is formed at a point P ₁ apart from the lens 1 in the opposite direction by _{2 and} a projection image of the extraordinary ray A ₂ is separated from the image pickup surface of the image pickup element 2 by ΔL / 2 on the optical axis at a point P ₂ apart from the lens 1. This shows the case where an image is formed on the. In such a case, the image projected on the image pickup surface of the image pickup device is 2 as shown in FIG.
The two images overlap left and right by w, and the left image is Δ
L / 2 rear pin, right image is ΔL / 2 front pin,
Furthermore, the image on the left is brighter by F ₁ / F ₂ than the image on the right. As for the images, if the amount of defocus is the same, there is almost no difference between the front focus and the rear focus, and the two images have the same blur amount but different brightness. The video signal output when such a projected image is scanned by the scanning line in the direction shown by the arrow M is similarly represented by the function f ₁ (t). This f ₁ (t)
Is represented by f ₁ (t) = h ₁ (t) + k · h ₁ (t−Δt) (5). Here, h ₁ (t) represents a video signal waveform of only the projection image of the ordinary ray A ₁ when the projection image of the ordinary ray A ₁ is back-focused by ΔL / 2. The video signal waveform of only the projected image by the extraordinary ray A ₂ is ΔL / 2
Is the front pin only, and k · h ₁ (t
-Δt).

[0040] For the signal f ₁ (t), the recursive filter shown in FIG. 13, the signal formed from the video signal h ₁ of the image projected by the ordinary ray A ₁ (t), the extraordinary ray A ₂ Video signal of projected image k · h ₁ (t−Δ
It is possible to cancel out t) and extract the video signal h ₁ (t) of only the projection image by the ordinary ray A ₁ from the original video signal output f ₁ (t).

In FIG. 13, 121 is a subtractor and 122
Is a multiplier, and 124 is a delay circuit that delays the input signal by Δt. Assuming that the output of the subtractor 121 is the image signal h ₁ (t) of the image projected by the ordinary ray, the output of the delay circuit 124 is delayed by Δt from this,
h ₁ (t−Δt). Further, in the multiplier 123, k (k
<1) It is multiplied to become the video signal k · h ₁ (t−Δt) of only the projection image by the extraordinary ray A ₂ . This is the original signal f ₁
By subtracting from (t) by the subtractor 121, the video signal h ₁ (t) of only the projected image of the ordinary ray A ₁ is obtained.

The filter 13 shown in FIG. 1 is composed of such a recursive filter, and is a video signal in which the projection image of the extraordinary ray A ₂ is superimposed on the projection image of the ordinary ray A ₁ output from the preamplifier 3. From, the video signal of only the projection image by the ordinary ray A ₁ is extracted.

On the other hand, in the focus state as shown in FIG. 4, the output h ₀ ′ (t) of the filter 13 is h ₀ ′ (t) = f ₀ (t) −k · h ₀ ′ (t− Δt) = h ₀ (t) + k · g {h ₀ (t−Δt)} − k · h ₀ ′ (t−Δt) = h ₀ (t) + k · [g {h ₀ (t−Δt)} -H ₀ '(t-Δt)] ............ (6). Here, if k << 1, then h ₀ '(t−Δt) ≈h
_{It is 0} (t-Δt), and the value in [] of the equation (6) is the image signal of the image defocused by only ΔL minus the image signal of the in-focus image. Only the high frequency components included in the video signal of are left. Therefore, when the focus state is as shown in FIG. 4, the filter 1 of FIG.
The output of 3 contains more high frequency components than the output of the filter 12.

The BPF 14 and BPF 15 respectively extract the high frequency components from the outputs of the filter 12 and the filter 13, and the detecting circuit 16 and the detecting circuit 17 respectively detect the BP.
F14, obtained from the output of BPF15 to output D _1, D ₂ corresponding to the absolute amount of the high-frequency component. In the focus state as shown in FIG. 4, these outputs are D ₁ <D ₂ .

As for this relationship, the projected image by the ordinary ray A ₁ as shown in FIG. 4 is obtained by the ordinary ray A ₁ as shown in FIG. 6 even if the projected image by the ordinary ray A ₁ is not in focus on the image pickup surface of the image pickup device 2. The same is true in the front pin state, where the output of the filter 13 contains more high frequency components than the output of the filter 12, and D ₁ <
It becomes D ₂ .

In contrast to the focus state shown in FIG. 4, in the case of the focus state shown in FIG. 5, the output of the filter 13 is the above-mentioned h ₁
The output of the filter 12 is represented by (t) h ₀ '(t)
Is h ₀ ′ (t) = f ₁ (t) −k · g {h ₁ ′ (t−Δt)} = h ₁ (t) + k · h ₁ (t−Δt) −k · g {h ₁ “(T−Δt)} = h ₁ (t) + k · [h ₁ (t−Δt) −g {h ₁ ′ (t−Δt)}] ... (7) Here, if k << 1, then h ₁ '(t−Δt) ≈
h ₁ (t−Δt), and the value in [] of the equation (7) is obtained by subtracting the video signal corresponding to the image defocused by ΔL from the video signal of the image defocused by ΔL / 2. Only the high frequency component included in the video signal of the image defocused by ΔL / 2 remains. Therefore, FIG.
In such a focus state, the output of the filter 12 in FIG. 1 contains more high frequency components than the output of the filter 13. Therefore, in the focus state as shown in FIG. 5, the outputs of the detection circuit 16 and the detection circuit 17 are D ₁ > D ₂ .

In FIG. 7, the object image projected by the lens 1 is divided into two by the birefringent plate 11, and the extraordinary ray A ₂
A projected image formed by is formed on the image pickup surface of the image pickup element 2, and the ordinary ray A
_The projected image by ₁ is ΔL on the optical axis from the image pickup surface of the image pickup element 2.
This shows a case where an image is formed at a point P ₁ which is separated from the lens 1 in the opposite direction. In such a case, as shown in FIG. 11, the images projected on the imaging surface of the image sensor 2 overlap with each other with the two images left and right displaced by w, the right image is in focus, and the left image is ΔL. At the rear focus, the image on the left side is brighter by F ₁ / F ₂ than the image on the right side. The video signal output when such a projected image is scanned by the scanning line in the direction indicated by the arrow M is similarly represented by the function f ₂ (t).

This f ₂ (t) is f ₂ (t) = g {h ₀ (t)} + k · h ₀ (t−Δt) (8) At this time, the output h ₂ 'of the filter 13 (T) is h ₂ ′ (t) = f ₂ (t) −k · h ₂ ′ (t−Δt) = g {h ₀ (t)} + k · h ₀ (t−Δt) −k · h ₂ ′ (t−Δt) = g {h ₀ (t)} + k · [h ₀ (t−Δt) −h ₂ ′ (t−Δt)] (9) Here, if k << 1, then h ₂ '(t-Δt) ≈g
{H ₀ (t−Δt)}, and the value in [] of the expression (9) is the image signal of the image in the focused state minus the image signal of the image defocused by ΔL. Only the high-frequency component contained in the video signal of the image is left.

Next, the output h _{2 of the} filter 12 is: h ₂ (t) = f ₂ (t) -k · g {h ₂ (t−Δt) = g {h ₀ (t)} + k · h ₀ ( t-Δt) -k {g ₂ (t-Δt)} = g {h ₀ (t)} + k [h ₀ (t-Δt) -g {h ₂ (t-Δt)}] … (10). Here, if k << 1, h ₂ (t−Δt) ≈g
{H ₀ (t−Δt)}, and [] in the equation (9) corresponds to the image signal of the focused image defocused by ΔL from the image signal of the focused image further defocused by ΔL. Since it is a video signal that is subtracted from the video signal, the higher frequency component included in the video signal of the focused image remains. Therefore, in the focus state as shown in FIG.
The output of the filter 12 in FIG. 1 contains more high frequency components than the output of the filter 13. Therefore, in the focus state as shown in FIG. 7, the outputs of the detection circuit 16 and the detection circuit 17 are D ₁ > D
It becomes ₂ .

[0050] This relationship, the projected image by the extraordinary ray A ₂ as shown in FIG. 7, may not in focus on the imaging surface of the imaging element 2 of the image pickup element 2, the extraordinary ray A ₂ as shown in FIG. 8 The same is true even if the projection image by the lens is in the rear focus state, and the output of the filter 12 contains more high frequency components than the output of the filter 13 and D ₁ > D ₂ .

FIG. 14 shows the output levels D ₁ of the detection circuits 16 and 17 with respect to the defocus amount of the image forming point of the ordinary ray A ₁ including the image forming states shown in FIGS. 4 to 8. , D ₂ and the respective differences D ₂ −D ₁ are shown. As shown in FIG. 14, when the defocus amount at the image formation point of the ordinary ray A ₁ is back by about ΔL / 4, D ₂
-D ₁ = 0, that is, D ₂ = D ₁ . Further, when the front pin is more than this, D ₁ <D ₂ , and when the rear pin is more than this, D ₁ > D ₂ .

In the microcomputer 7 shown in FIG.
The outputs of the two detection circuits 16 and 17 are A / D-converted and fetched for calculation, and when D ₁ <D ₂ , the motor drive circuit 8
The motor 9 is driven via the to move the position of the lens 1 in the infinity direction. On the contrary, when D ₁ > D ₂ , the motor 9 is driven through the motor drive circuit 8 to move the position of the lens 1 in the closest direction.

Here, the diameter of the circle of confusion of the image projected on the image pickup surface of the image pickup device 2 by the ordinary ray A ₁ generated by the defocus amount of ΔL / 4 is the diameter of the circle of confusion which can be regarded as the focus, that is, the minimum circle of confusion. If it is smaller, the microcomputer 7 may stop the lens 1 at a position where D ₁ = D ₂ . If the diameter of the circle of confusion is larger than the minimum diameter of circle of confusion, D ₂ > D
_The lens 1 may be stopped at the position of 1.

As described above, in this embodiment, since the focusing direction at each lens position can be determined, a faster and smoother automatic focusing operation can be performed as compared with the conventional hill climbing servo system. Also, since no wobbling operation is involved, a good image can be obtained even in the vicinity of the in-focus point. Also, since no wobbling is performed, the lens drive system does not require such high drive speed, drive torque, drive accuracy, etc., and is relatively small. The device can be constructed at low cost.

(Embodiment 2) In Embodiment 1, only the video signal of the projection image by the ordinary ray is canceled by canceling the video signal of the projection image by the extraordinary ray on the basis of the video signal of the projection image by the ordinary ray of the birefringence phenomenon. Is extracted and output as a video signal standardized to NTSC, but the reverse is also possible. The present embodiment is an example of this "reverse". That is,
Align the polarization direction of the polarization filter with the polarization direction of the extraordinary ray, make the amount of light projected by the extraordinary ray larger than that of the image projected by the ordinary ray, and project the image projected by the ordinary ray based on the video signal of the image projected by the extraordinary ray. By canceling the signals, only the video signal of the projection image due to the extraordinary ray is extracted and the video signal standardized to NTSC is output.

In this way, also in this embodiment, the same effect as that of the first embodiment can be obtained.

[0057]

As described above, according to the present invention,
A fast and smooth automatic focusing operation can be performed, and since no wobbling operation is involved, a good image can be obtained even in the vicinity of the in-focus point. Further, since the lens drive system does not need to be wobbled, it does not require such high drive speed, drive torque, drive accuracy, etc., and can be configured with a relatively small and inexpensive device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment.

FIG. 2 is a diagram showing light rays passing through a birefringent plate.

[Figure 3] Detailed view of the optical system

FIG. 4 is a diagram showing an imaging example 1.

FIG. 5 is a diagram showing an imaging example 2;

FIG. 6 is a diagram showing imaging example 3;

FIG. 7 is a diagram showing imaging example 4;

FIG. 8 is a diagram showing imaging example 5;

FIG. 9 is a diagram showing a projected image example 1;

FIG. 10 is a diagram showing a projected image example 2;

FIG. 11 is a diagram showing a projected image example 3;

FIG. 12 is a diagram showing a recursive filter for extracting a video signal h ₀ (t).

FIG. 13 is a diagram showing a recursive filter for extracting a video signal h ₁ (t).

FIG. 14 is a diagram showing the relationship between the defocus amount of an ordinary ray and the output level of a detection circuit.

FIG. 15 is a block diagram showing a configuration of a conventional example.

FIG. 16 is a diagram showing a spatial frequency characteristic of a lens.

FIG. 17 is a diagram showing the output characteristic of the detection circuit 6 of the conventional example.

[Explanation of symbols]

 1 Photographic lens 2 Image sensor 7 Microcomputer 9 Motor 10 Polarizing filter 11 Birefringent plate 12 Filter 13 Filter 14 BPF 15 BPF

Claims (2)

[Claims] 1. A photographing lens, a polarizing filter arranged after the photographing lens, a crystalline transmission plate having birefringence development arranged after the polarizing filter, and a crystalline transmission plate arranged after the transparent plate. Image pickup element, first filter means for extracting a high frequency component from a video signal by the image pickup element, second filter means for extracting a high frequency component from a video signal by the image pickup element, and output of the first filter means Discriminating means for discriminating the focus state of the optical system including the taking lens, and driving means for driving the taking lens in the focusing direction based on the output of the discriminating means. The first filter means and the second filter means are characterized in that the magnitude relation of the high frequency components of the respective outputs is inverted near the in-focus point. Automatic focus adjustment device for imaging device. 2. A focus state of an optical system including a taking lens is discriminated by a video signal obtained by a projection image of an ordinary ray of a birefringence phenomenon and a projection image of an extraordinary ray projected on an image pickup surface of an image pickup device. An automatic focus adjusting method for an image pickup apparatus, characterized in that the photographing lens is driven in a focusing direction based on a result of this determination.