JP2003287673A - Focusing state detecting device for photographic lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographic lens whose focusing state can be detected with high precision without malfunction even during telephotography or extender insertion, etc. <P>SOLUTION: The photographic lens 12 equipped with a device which picks up an image of subject light by imaging elements A, B, and C for focusing state detection and detects the focusing state according to the high-frequency component of an obtained luminance signal has its focusing state detected by converting the frequency of the luminance signal by an electric filter according to a photographic state. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus state detection device for a photographing lens, and more particularly to a focus state detection device for a photographing lens applicable to focus detection in autofocus control of the photographing lens.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a method for detecting a focus state (front focus, rear focus, focus) of a photographing lens by using a plurality of image pickup elements having different optical path lengths (Japanese Patent Laid-Open No. 55-7).
6312, Japanese Patent Publication No. 7-60211). For example, two focus state detection image pickup devices that pick up images in the same shooting range with respect to an image pickup device (video image pickup device) that picks up a video image have longer optical path lengths than those of the video image pickup device. Place it in a position that shortens the position.

Then, a focus evaluation value for each image pickup surface of each focus state detection image pickup device is obtained and compared based on the high frequency components of the video signal obtained from these focus state detection image pickup devices. Thereby, the focus state on the image pickup surface of the image pickup device for image pickup from the magnitude relation of the focus evaluation value,
That is, it is detected which of the front focus state, the rear focus state, and the in-focus state. Such a focus state detection method can be applied to focus detection for autofocus.

[0004]

However, when the zoom lens is telephoto or when the extender is inserted, the focal length becomes long and the frequency component of the image becomes coarse, so that the contrast caused by the electric signal from the focus state detecting image pickup device is increased. There is a problem that the difference becomes small and it becomes difficult to detect the in-focus position. That is, 10 when wide
There are many 12 MHz frequency components, but 2-3 during tele
The frequency component of mega Hz increases and the contrast difference decreases.

Further, there is a similar problem when the illuminance of the image forming screen is low or when the image contains many blue components (Bch) and red components (Rch).

However, an effective measure is taken in the conventional focus detection method in which a plurality of focus state detecting image pickup devices are arranged at positions where the optical path length is longer and shorter than the image pickup device, respectively. Was not obtained.

The present invention has been made in view of the above circumstances, and provides a photographing lens capable of performing highly accurate focus state detection without malfunction even during telescopic operation or insertion of an extender or the like. With the goal.

[0008]

In order to achieve the above object, the present invention provides a subject light for focus state detection from a subject light for a video which passes through a photographing lens and is incident on a video image pickup device of a camera body. Is generated, and the generated subject light for focus state detection is imaged by the focus state detection image sensor,
In a focus state detection device for a photographing lens that detects a focus state based on a high-frequency component of a luminance signal obtained from the focus state detection image pickup device, the focus state detection device uses the electric filter to adjust the luminance according to the photographing state. Provided is a focus state detection device for a photographing lens, wherein a frequency of a signal is converted to detect a focus state.

According to the present invention, the frequency of the luminance signal is converted by the electric filter even when the focal length becomes long at the time of telephoto, insertion of an extender, etc., and the electric signal from the image sensor for focus state detection is converted. Because of the contrast difference due to, a highly accurate focus state detection can be performed without malfunction.

In the present invention, it is preferable that the focus state detecting device has a plurality of types of electric filters, and the electric filters are selectively used according to the focal length. This is because the effect of the present invention can be further exerted if the optimum electric filter corresponding to the focal length is selected and used.

Further, in the present invention, it is preferable that the focus state detection device includes a plurality of focus state detection image pickup elements arranged at positions having different optical path lengths. If the present invention is applied to such an optical system, the effect can be further exhibited.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a photographing lens according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a configuration diagram showing the configuration of a television camera system using a taking lens according to the present invention.
The television camera system shown in FIG.
The camera body 10 is composed of a photographic lens 12 and the like which can be exchanged with 0. Necessary circuits etc. are built in.

On the other hand, the taking lens 12 is the camera body 10.
As is well known, the zoom lens that is detachably mounted on the front side of the taking lens 12 includes a fixed focus lens F ′, a movable focus lens F, a zoom system and a correction system from the front end side as is well known. Z, an iris I, and a relay lens (relay optical system) including a front relay lens R1 and a rear relay lens R2 are arranged. It should be noted that the configuration of each lens in the figure is simplified, and there is also one in which a lens group including a plurality of lenses is shown as one lens.

Further, as shown in the figure, on the optical path of the subject light between the front relay lens R1 and the rear relay lens R2 of the relay optical system, approximately 45 degrees with respect to the optical axis O of the taking lens 12. A half mirror 24, which is a light splitting unit that splits the subject light (light flux) into transmitted light and reflected light, is arranged.

Of the subject light incident from the front end side of the taking lens 12, the transmitted light that has passed through the half mirror 24, that is, the subject light for video, is emitted from the rear end side of the taking lens 12, and the camera body 10 takes an image. It is incident on the portion 20. Although the configuration of the image capturing unit 20 is omitted, the subject light incident on the image capturing unit 20 is decomposed into three colors of red light, green light, and blue light by, for example, a color separation optical system, and the image pickup device (image Incident on the image pickup surface of the image pickup device). As a result, a color image for broadcasting is shot. The focusing surface 22 in the figure shows an optically equivalent position on the optical axis O of the taking lens 12 with respect to the image pickup surface of each image pickup device.

On the other hand, the reflected light reflected by the half mirror 24, that is, the subject light for focus state detection, is used for focus state detection along an optical axis O'substantially perpendicular to the optical axis O of the taking lens 12. It is guided to the imaging unit 26. Here, the subject light is in a state of substantially parallel light between the front relay lens R1 and the rear relay lens R2, and the subject light reflected by the half mirror 24 has the same character as the rear relay lens R2. The light passes through the relay lens R3 for and enters the imaging unit 26 for focus state detection. In the following description, when the optical axis O and the optical axis O'are particularly distinguished, the optical axis O is called the optical axis O of the photographing optical system, and the optical axis O'is the optical axis of the focus state detecting optical system. It is called axis O '.

FIG. 2 is a block diagram showing the structure of the image pickup unit 26. As shown in the figure, the image pickup unit 26 includes three prisms P1, P2, and P3 that form a light splitting optical system and three image pickup devices (two-dimensional CCD) A for focus state detection.
It is composed of B and C. Half mirror 24 as described above
The subject light that has been reflected by and traveled along the optical axis O ′ first enters the first prism P1 and is split into reflected light and transmitted light by the half mirror surface 40 of the first prism P1. Of these, the reflected light is incident on the image pickup surface of the focus state detection image pickup element C.

On the other hand, the transmitted light is then transmitted to the second prism P2.
And is further split into reflected light and transmitted light by the half mirror surface 42 of the second prism P2. Of these, the reflected light is incident on the image sensor B for focus state detection. On the other hand, the transmitted light passes through the third prism P3 and enters the focus state detection image pickup device A. In addition, the image sensor A for focus state detection,
The subject light is split by the half mirror surface 40 of the first prism P1 and the half mirror surface 42 of the second prism P2 so that the light quantities of the subject light incident on B and C become equal. Further, these focus state detecting image pickup devices A,
In the present embodiment, B and C are CCDs for picking up a monochrome image.

When the optical axes of the subject light incident on the focus state detecting image pickup devices A, B, and C (optical axis of each image pickup device) are shown on the same straight line, as shown in FIG. 3, each focus state detection is performed. The optical path length of the focus state detecting image sensor B is the shortest and the optical path length of the focus state detecting image sensor C is the longest with respect to the subject light until it enters the image capturing elements A, B, and C. The optical path length of the image sensor A for state detection is an intermediate length between the optical path lengths of the image sensor B for focus state detection and the image sensor C for focus state detection. That is, the image pickup surfaces of the focus state detection image pickup device B and the focus state detection image pickup device C are arranged in parallel at positions equidistantly in front of and behind the image pickup face of the focus state detection image pickup device A.

The image pickup surface of the focus state detecting image pickup device A is ideally the focus surface 22 of the camera body 10 (see FIG. 1).
The optical path length for the subject light incident on the taking lens 12 is the same as the image pickup surface of the image pickup element of the camera body 10. The light splitting optical system that splits the subject light into the focus state detecting image pickup devices A, B, and C is not limited to the configuration using the prisms P1 to P3 as described above.

With the optical system configured as described above, the subject light incident on the taking lens 12 is located near a position conjugate with the focusing surface 22 of the camera body 10 and detects three focus states with different optical path lengths. The image is picked up by the image pickup devices A, B, and C.

Next, an outline of autofocus control based on focus state detection will be described. As shown in FIG. 1, three focus state detection image pickup devices A, B and C of the focus state detection image pickup unit 26 are shown in FIG. The image captured by is captured by the signal processing unit 28. Signal processing unit 28
The focus state detecting image pickup devices A, B,
Based on the high frequency components of the image acquired from C, the position (focus position) of the focus lens F where the focus state of the taking lens 12 is in focus with respect to the focus surface 22 of the camera body 10 is obtained.

Then, a control signal for instructing the movement of the focus lens F to the focus position is output to the focus motor drive circuit 30. The focus motor drive circuit 30 drives a focus motor (not shown), and a focus lens F via a power transmission mechanism 32 including gears.
Is moved to set the focus lens F to the focus position instructed by the signal processing unit 28. The autofocus is controlled by continuously performing such processing.

Next, the structure of the signal processing unit 28 and the focus state detection processing will be described. FIG. 4 is a block diagram showing the configuration of the signal processing unit 28. As shown in the figure, the image of the subject imaged by each focus state detection image pickup device A, B, C for focus state detection is output as a video signal of a predetermined format, and each focus state detection image pickup device A, Switching elements 57, 67, 77 and high-pass filters 50, 60, 7 having the same configurations for B and C.
0 (or low pass filters 58, 68, 78), A / D
Converters 52, 62, 72, gate circuits 54, 64, 7
4 and the adders 56, 66 and 76 convert the signals into focus evaluation value signals indicating the sharpness of the image (contrast of the image) and input to the CPU 82.

The process for obtaining the focus evaluation value will be described with reference to the circuit provided for the focus state detecting image sensor A. The focus state detecting image sensor A according to the present embodiment will be described.
Is a CCD that captures a black and white image, the video signal output from the focus state detecting image sensor A is output as a brightness signal indicating the brightness of each pixel forming the screen.

Since the switching element 57 is set on the high-pass filter 50 side in a normal state, the luminance signal output from the focus state detecting image pickup element A is
First, the high-pass filter (HPF) 50 is input and the high frequency components of the luminance signal are extracted. HPF50
The signal of the high frequency component extracted by the A / D converter 52
Are converted into digital signals by.

Then, within a predetermined focus area (for example, in a predetermined focus area of the digital signal for one screen (for one field) of the image picked up by the focus state detecting image pickup device A).
After only the digital signal corresponding to the pixel in the central portion of the screen) is extracted by the gate circuit 54, the values of the digital signals in the extracted range are added by the adder 56. Thereby, the sum of the values of the high frequency components of the luminance signal in the focus area is obtained. Adder 56
The value obtained by is a focus evaluation value indicating the level of sharpness of the image in the focus area.

The synchronizing signal generating circuit 8 shown in FIG.
Various sync signals from 0 to the image sensor A for focus state detection,
B, C, and gate circuits 54, 64, 74 and the like are provided to each circuit to synchronize the processing of each circuit. Further, a vertical synchronizing signal (V signal) for each field of the video signal is given from the synchronizing signal generating circuit 80 to the CPU 82.

The CPU 82 determines the current focus state of the taking lens 12 with respect to the focus surface 22 of the camera body 10 based on the focus evaluation values obtained from the focus state detecting image pickup devices A, B and C as described above. To detect. FIG. 5 is a diagram showing the state of the focus evaluation value with respect to the focus position when a certain subject is photographed, with the focus position of the taking lens 12 on the horizontal axis and the focus evaluation value on the vertical axis. A curved line a shown by a solid line in the figure shows a focus evaluation value obtained from the focus state detecting image pickup device A at a position conjugate with the focus surface 22 of the camera body 10 with respect to the focus position. Curved lines b and c indicated by dotted lines show focus evaluation values obtained from the focus state detection image pickup devices B and C, respectively, with respect to the focus position.

In the figure, the focus position F3 where the focus evaluation value of the curve a is maximum (maximum) is the focus position, but the focus position of the taking lens 12 is now set to the position F1 in the figure. And At this time, the focus evaluation value obtained from each of the focus state detection image pickup devices A, B, and C is a value corresponding to the focus position F1 by the curves a, b, and c. At this time, at least the focus evaluation value obtained from the focus state detection image pickup device B is larger than the focus evaluation value obtained from the focus state detection image pickup device C, so that the focus position is higher than the focus position F3 which is the focus position. It can be seen that is the state set to the close side, that is, the state of the front pin.

On the other hand, if the focus position of the taking lens 12 is set to the position F2 in the figure, the focus evaluation values obtained from the focus state detecting image pickup devices A, B and C are the curves a and b. , C are values corresponding to the focus position F2. At this time, at least the focus evaluation value obtained from the focus state detection image pickup device C is larger than the focus evaluation value obtained from the focus state detection image pickup device B, so that the focus position is more than the focus position F3 which is the focus position. Is set to the infinity side, that is,
You can see that it is in the state of the rear pin.

The focus position of the taking lens 12 is F in the figure.
If the focus position is set to 3, the focus evaluation value obtained from each of the focus state detection image pickup devices A, B, and C is a value corresponding to the focus position F3 by the curves a, b, and c. . At this time, since the focus evaluation value obtained from the focus state detection image sensor B and the focus evaluation value obtained from the focus state detection image sensor C are equal, the focus position is set to the focus position F3, that is, You can see that it is in focus.

As described above, based on the focus evaluation values obtained from the focus state detecting image pickup devices A, B, and C, the focus state at the current focus position of the taking lens 12 is the front focus, the rear focus, and the focus. Either of them can be detected. On the other hand, in such a focus state determination method, only the focus evaluation values obtained from the focus state detection image pickup devices B and C are sufficient, and the focus evaluation values obtained from the focus state detection image pickup device A are unnecessary. Therefore, in the present embodiment, three focus state detection image pickup devices A,
The focus evaluation values obtained from B and C are effectively used, and the focus position at which focus is achieved is directly detected as follows.

In FIG. 5, the curves a, b, and c for the focus evaluation values obtained from the focus state detecting image pickup devices A, B, and C have substantially the same shape, and therefore the focus state at a certain focus position. The focus evaluation value obtained from the detection image pickup devices B and C can be regarded as the focus evaluation value of the focus state detection image pickup device A at the focus position displaced from the focus position by a predetermined shift amount. For example, in the curve a of the focus evaluation value of the image sensor A for focus state detection shown in FIG. 6, it is assumed that the focus position is set to F4 in the figure. At this time,
The focus evaluation value obtained from the focus state detection image sensor A indicates the value of the point P _A on the curve a.

On the other hand, the focus evaluation value obtained from the focus state detecting image pickup device B is a focus position F5 which is displaced from the focus position F4 to the infinity side by a predetermined shift amount.
The focus evaluation value obtained from the focus state detecting image sensor C is a value at a point P _B on the curve a in the curve a, and the focus evaluation value obtained from the focus state detecting image sensor C is a curve a at the focus position F6 displaced by a predetermined shift amount to a position closer to the focus position F4. The value of the upper point P _C is shown.

The difference between the focus position F4 and the focus position F5, that is, the focus state detecting image sensor B
The shift amount with respect to the focus evaluation value obtained from is equal to the difference between the focus position of the maximum point of the curve b and the focus position of the maximum point of the curve a in FIG.
The difference between the focus position F4 and the focus position F6, that is, the shift amount for the focus evaluation value obtained from the focus state detection image sensor C is shown in FIG. Equal to the difference in the focus position of the points.

On the other hand, the curve a can be approximated by a predetermined function (for example, a quadratic curve). Therefore, three points P _A , P _B obtained from the respective focus state detecting image pickup devices A, B, C,
The curve a can be specifically specified from the focus evaluation value at P _C, and the focus position F3 at which the focus evaluation value is maximum can be obtained on the curve a.

In this way, the CPU 82 of FIG. 1 detects the focus position on the basis of the focus evaluation values obtained from the focus state detecting image pickup devices A, B, and C, and becomes the focus position. As described above, the control signal is transmitted to the focus motor drive circuit 30 to move the focus lens F. As a result, autofocus control is performed.

Next, a description will be given of the control of autofocus in a state where the focal length tends to be coarse in the image and the focal length is long (for example, at the time of tele). In FIG. 1, a potentiometer (not shown) for detecting the focal length is arranged in the taking lens 12, and the signal from the potentiometer is taken into the signal processing unit 28 to calculate the focal length. It

In FIG. 4, the CPU 8 of the signal processing unit 28
The type of electric filter corresponding to the focal length is stored in advance in the storage device 83 connected to No. 2, and a control signal is transmitted to each of the switching elements 57, 67, 77 according to the focal length. As a result, the switching elements 57, 67, 77 have high-pass filters 50, 60, 7 respectively.
The connection of 0 is switched to the low pass filters 58, 68, 78.

In the configuration of FIG. 4, the electrical filters are high-pass filters 50, 60 and 70 and low-pass filter 58,
Only two kinds of 68 and 78 are provided, but three or more kinds are provided,
It may be used by switching according to the focal length.

The configuration of FIG. 4 can be applied in addition to selecting the type of electrical filter in accordance with the focal length. For example, even when the illuminance of the image formation screen is low, or when there are many blue components (Bch) or red components (Rch) in the image, each switching element 57, 67 and 77 may be switched to select the optimum type of electrical filter.

As described above, by selecting the optimum type of electric filter, the contrast of the video signal is increased, and as a result, the focus position can be easily detected.

As described above, in the above embodiment, the camera body 1
When the focus state detecting image pickup devices B and C are arranged at positions before and after the image pickup face is optically equidistant with respect to the focus state detecting image pickup device A arranged at a position conjugate with the 0 focus plane 22. The focus state detection image pickup devices A, B, and C are arranged so that the optical path lengths are different, and the optical path length is longer than the position conjugate with the focus surface 22 of the camera body 10. It is sufficient if at least one of the focus state detecting image pickup devices A, B, and C is arranged at each of the shortened positions.

That is, as described above, for focus state detection at a focus position obtained by displacing the focus evaluation value obtained from the focus state detection image pickup devices B and C at a certain focus position by a predetermined shift amount. When the focus evaluation value of the image sensor A is considered, the shift amount may be set based on the distance between the focus state detection image sensors B and C with respect to the focus state detection image sensor A. Further, as a method of obtaining the shift amount, for example, the focus position is changed while shooting a fixed subject, and the focus position at which the focus evaluation value obtained from each of the focus state detection image pickup devices A, B, and C becomes maximum. To detect. Then, with respect to the focus position where the focus evaluation value obtained from the focus state detecting image sensor A is maximum,
The displacement amount of each focus position where the focus evaluation value obtained from each of the focus state detecting image pickup devices B and C is maximum is detected, and the displacement amount is set as the shift amount.

Further, in the above-described embodiment, the three focus state detecting image pickup devices A, B and C for focus state detection are arranged in the image pickup unit 26, but two focus state detecting image pickup devices B are arranged. , C are arranged before and after the position conjugate with the focus surface 22 of the camera body 10,
It may be possible to detect whether the focus state is the front focus, the rear focus, or the in-focus state, and to control the autofocus based on the detection result. On the contrary, four or more focus state detecting image pickup devices having different optical path lengths are used, and at least one focus position is provided at each of the position where the optical path length becomes longer and the position where the optical path length becomes shorter than the position conjugate with the focus surface 22 of the camera body 10. The focus detection position may be detected more accurately by arranging the state detection image pickup element.

Further, in the above embodiment, the case where the detected focus state is applied to the autofocus has been described, but the present invention is not limited to this, and the present invention can be used for other purposes, for example, for displaying the focus state.

[0049]

As described above, according to the taking lens of the present invention, the frequency of the luminance signal is converted by the electric filter even when the focal length becomes long at the time of telephoto or insertion of the extender or the like. And the contrast difference due to the electric signal from the focus state detection image sensor is added,
It is possible to detect a focus state with high accuracy without malfunction.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a television camera system using a taking lens according to the present invention.

FIG. 2 is a configuration diagram showing a configuration of an imaging unit for detecting a focus state.

FIG. 3 is a diagram showing the focus state detection image pickup devices A, B, and C on the same optical axis.

FIG. 4 is a block diagram illustrating a configuration of a signal processing unit that performs a focus state detection process.

FIG. 5 is a diagram showing a state of focus evaluation values in each focus state detecting image sensor with respect to a focus position when a certain subject is photographed.

FIG. 6 is an explanatory diagram used for explaining a focus state detection process by three focus state detection image pickup devices.

[Explanation of symbols]

10 ... Camera body, 12 ... Photographing lens, F ... Focus lens, R1 ... Front relay lens, R2 ... Rear relay lens, R3 ... Relay lens, 24 ... Half mirror (light splitting means), 26 ... Imaging unit, A, B, C ... Image sensor for focus state detection, 28 ... Signal processing unit, 50, 60, 70 ... High-pass filter (electrical filter), 58, 68, 78
... Low-pass filter (electrical filter)

Claims (3)

[Claims] 1. A subject light for focus state detection is generated from a subject light for video that passes through a photographing lens and is incident on a video image sensor of a camera body, and the generated subject light for focus state detection is focused. Image with the image sensor for state detection,
In a focus state detection device for a photographing lens, which detects a focus state based on a high-frequency component of a luminance signal obtained from the focus state detection image pickup device, the focus state detection device comprises: A focus state detection device for a photographing lens, wherein the frequency of a signal is converted to detect a focus state. 2. The focus state detection device for a photographing lens according to claim 1, wherein the focus state detection device has a plurality of types of electric filters, and the electric filters are selectively used according to a focal length. 3. The focus state detection of a photographing lens according to claim 1, wherein the focus state detection device includes a plurality of focus state detection image pickup elements arranged at positions having different optical path lengths. apparatus.