JP2575607B2 - Focus detection device - Google Patents

Description

Description: TECHNICAL FIELD The invention of the present application relates to an apparatus for performing focus detection based on an output signal of an imaging unit, and particularly, performs high-precision focus detection in accordance with an increase in sensitivity of a video camera or the like. The present invention relates to a focus detection device which can be used.

(Prior art) As a so-called TTL-passive type automatic focusing device mainly used for a video camera and performing focus detection from a luminance signal in a video signal, it is known as "NHK Technology Research" Vol. 17 No. 1 (Vol. 86 ) (Issued in 1965), various papers have been proposed, including a paper on "Automatic Focus Adjustment of TV Cameras Using the Climbing Servo System". Many of these methods utilize the phenomenon that the higher the sharpness of the image of a subject, the higher the high-frequency component in the luminance signal.The high-frequency component is extracted by some kind of signal processing means, and the position at which this peak occurs is focused. It is based on the principle of doing.

By the way, as will be described in detail later, in the conventional video camera, since the depth of field becomes deep on the short focus side, even if there is a high probability of a near-far conflict on the short focus side, FIG. 10 and FIG. Although a fixed distance measurement field of view was set as indicated by 24 in the figure, it has become necessary to obtain an accurate focus even on the short focal length side with an increase in the sensitivity of the camera.

(Object) In order to address the above-described problems, the invention of this application is directed to a focus detection apparatus that performs focus detection based on an output signal of an imaging unit, and a perspective view that tends to occur under a fixed distance measurement field of view. It is an object of the present invention to provide means capable of reducing erroneous distance measurement due to a competing subject and performing highly accurate focus detection.

It is another object of the present invention to provide a unit capable of setting the size of a distance measurement field of view according to a photographer's drawing intention and subject conditions.

Also, at the start of the focus detection operation, first, the distance measurement area is changed, and then the drive direction of the lens is determined, and the direction determination operation based on the accurate focus signal obtained from the optimal distance measurement area can be performed. It is an object of the present invention to provide a focus detection device which can be used.

(Explanation by Examples) Hereinafter, means taken in the invention of the present application to achieve the above object will be described with reference to the illustrated examples. The following description is directed to an example in which the invention of this application is applied to a focus detection device of a type that performs focus detection from a high-frequency component of a luminance signal in an output signal of a two-dimensional image sensor. Of the focus detection device of the first embodiment and the zoom ring information detection and transmission device in the first embodiment.

(Conventional focus detection device) (FIGS. 1 to 11) FIGS. 1 to 4 schematically explain the principle of focusing on a position where a high-frequency component in a luminance signal reaches a peak. Things. FIG. 1 shows a state of an image on an image forming plane when a subject having black and white stripes is picked up by a video camera, and a portion where a vertical line is drawn in the drawing corresponds to a black portion. . When the image is focused on the image forming surface, the image becomes as shown in FIG. 7A, but when the image is out of focus, the black and white boundary of the subject becomes blurred as shown in FIG. FIG. 2 shows a luminance signal (Y signal) during the output of the image sensor in each of the above states, and the output difference depending on the position in the in-focus state (A) is naturally larger than that in (B). That is, the contrast increases as the focus approaches. Several proposals have been made for this Y signal processing means. For example, when this signal is differentiated and converted into an absolute value, the peak of the differentiated signal is obtained at the in-focus position as shown in FIGS. 3 (A) and 3 (B). Has been proposed which utilizes the fact that the maximum value of the differential signal is maximized. However, in order to further improve the S / N ratio, a method may be employed in which the differential signal is squared and then integrated.

FIG. 4 shows the output of the high-frequency component detected as described above on the vertical axis, and the stop position of the lens group involved in focus adjustment among the photographing lenses on the horizontal axis. At the in-focus position A, the high-frequency component shows a peak, and at the out-of-focus position B, the peak deviates.

FIG. 5 shows an example of a sequence for executing the focus detection operation shown in FIGS. Simultaneously with the start of the distance measurement, a Y signal of a portion corresponding to the distance measurement field of view is extracted by means to be described later, and the high frequency component thereof is extracted. Next, the lens is driven in a minute amount, that is, in the reentrant direction in this example (in general, focusing on a distant subject is performed by reentrantness). In FIG. 5, the symbol “→ F” indicates that the lens is driven in the reentrant direction, and the symbol “→ N” indicates that the lens is driven in the reentrant direction. In this state, high-frequency components are extracted again. The reason why the high-frequency components at the two lens positions are taken out at the start of the distance measurement is to detect the direction (front focus or rear focus), and these two signals are compared.

FIG. 6 shows the relationship between the magnitudes of the high-frequency components A and B extracted in and above and the state of the focus detection system. In FIG. In this state, the lens needs to be further re-introduced (). In FIG. (B), since A ≒ B, it can be regarded as an in-focus pin (), and in FIG. Since it is in a pin state, it is necessary to further draw out the lens (). As a result of the direction detection as described above, the high-frequency component is taken out again at the new position where the lens is driven, and compared with the value before the driving (). At this time, since the current value is used for comparison in the next cycle, it is sampled and held (S / H), taken out at the next high frequency component extraction, and used for comparison. In this way, it is determined that focusing has been achieved when A 段 階 B, and driving of the lens is stopped.

FIG. 7 shows an example in which the means for extracting the Y signal is incorporated in an actual camera. In FIG. 7, reference numeral 10 denotes a lens group involved in focus adjustment among photographing lenses, and reference numeral 11 denotes a zoom system. The lens group normally includes a variator lens and a compensator lens, and 12 is a lens group of an imaging system. 13 is an image sensing type solid-state imaging device composed of, for example, a CCD, 14 is a clock signal generator, 15 is a frequency divider,
16 is a CCD drive circuit, 17 is a horizontal and vertical synchronization signal generator, 1
Reference numeral 8 denotes an analog gate, and reference numeral 19 denotes an automatic focus adjustment circuit. Specifically, as described above, it is assumed that direction detection is performed using a high-frequency component. Reference numeral 20 denotes a microprocessor, and a motor drive circuit 21 operates based on the instruction to drive a motor 22.

In the above configuration, the clock signal generated by the clock signal generator 14 is frequency-divided by the frequency divider 15 to be NTSC or PAL.
A signal that determines the read timing of one horizontal period of the CCD 13 is formed so as to produce a screen in one field of 1/60 second based on a standard television signal in a system or the like. The optical information stored on the CCD 13 is sequentially read out by the CCD drive circuit 16 based on this signal. The read signal is superimposed with a synchronizing signal by an adder circuit 17 and further processed by a processing circuit (not shown) as is well known to form a video signal.

On the other hand, the frequency divider 15 simultaneously outputs a signal to open the gate only at a position corresponding to a predetermined distance measurement field of view (for example, a position indicated by 24 in FIG. 8). Only Y signal of automatic focus adjustment circuit 19
Sent to Subsequent operations are as described above.

FIG. 9 shows an example of a signal at each position of D to G in FIG. 7. (D) shows a raw signal just read from the CCD 13, and (E) shows an adder 17A to this signal. (F) shows a synchronizing signal for automatic focusing, and (G) shows a signal corresponding to the distance measurement field 24 taken out for automatic focusing. Each signal is shown.

FIG. 10 and FIG. 11 show images in the finder screen when the subject 32 is photographed by the video camera configured as described above. Is a case where the subject 32 is photographed with a focal length shorter than the short focus. As can be seen from this figure, in general, when shooting at a short focal length, the proportion of the subject in the screen is often smaller than when shooting at a long focal length. Further, even when photographing at a long focal length, if the subject is small, the subject distance is often far. Considering these facts, if the position of the distance measurement field of view 24 is set to the extent shown in FIGS. 10 and 11, when shooting on the long focal length side, erroneous distance measurement due to perspective conflict will occur. Is unlikely to occur, but tends to occur on the short focal length side. In the drawing, reference numeral 23 denotes an imaging field of view.

On the other hand, the distance measurement field of view 24 shown in FIGS. 10 and 11 can be made smaller in order to prevent perspective conflict, but in this case, the part without contrast of the subject is mainly measured on the long focal length side. It is not preferable because the probability of distance increases. Therefore, in the conventional video camera, since the depth of the subject becomes deep on the short focal length side, even if the probability of a near-far conflict occurring on the short focal length side is high, the distance measurement visual field position of the size indicated by 24 described above is required. You have set. However, with the increase in the sensitivity of cameras, it has become necessary to obtain accurate focus even on the short focal length side if possible.

(One Embodiment of the Focus Detection Apparatus of the Invention of this Application) (FIGS. 12 to 14) The invention of this application eliminates the above-mentioned disadvantages of the conventional focus detection apparatus and provides a fixed distance measurement field of view. This reduces erroneous ranging due to a subject that is likely to occur in the near-far conflict and enables high-precision focus detection.The size of the ranging field can be adjusted according to the photographer's drawing intention and subject conditions. It is possible to set the height.

Fig. 25 in Fig. 12 shows an example of the distance measurement visual field position on the short focal length side when the invention of this application is carried out. Has become smaller.

FIG. 13 shows an embodiment of the focus detection device of the invention of the present application. Portions having basically the same configuration and function as the device of FIG. 7 are denoted by the same reference numerals as in FIG. Detailed description is omitted. In FIG. 13, reference numeral 26 denotes a programmable logic array (PLA) which is an example of a gate control circuit, and controls a signal for selecting a distance measurement field of view. Reference numeral 27 denotes a zoom position detecting means, which includes, for example, a detecting unit and a microprocessor unit for determining a distance measuring position based on the information,
The instantaneous focal length is detected, and information based on the size of the distance measurement field determined thereby is output to the PLA 26. The PLA 26 changes a control signal supplied to the gate 18 according to the distance measurement field information. That is, for example, the on / off timing of the synchronization signal for extracting the luminance signal shown in F of FIG. 9 is changed so that the on-period is shortened on the short focal length side and is increased on the long focal length side.

FIG. 14 shows an example of a sequence of a focus detection operation when the invention of the present application is carried out. Compared with the sequence of the conventional apparatus shown in FIG. 5, a zoom position detection step and measurement based on the information are shown. Distance area selection step,
And have been added. First, at the start of distance measurement, the zoom position, that is, the focal length, is detected, and then the distance measurement area determined thereby is selected. Hereinafter, the direction is detected in the process described with reference to FIG.
After driving (10) in the figure, the high-frequency components are extracted again as described above through the steps of zoom position detection and distance measurement area selection.

(Zoom ring information detection and transmission device in the embodiment of the invention of this application) (FIGS. 15 and 16) As means for detecting the zoom position described above, measurement is performed using a conventionally known gray code or potentiometer. In addition to changing the distance visual field very finely, the distance field may be divided into two or three stages by a leaf switch or the like.

FIG. 15 shows an example of two divisions as an example of the latter. The rotation of the zoom operation ring 33 changes the position of the lens 11 and changes the focal length of the taking lens. Specifically, for example, two cams are cut into a cam ring fitted on the inner periphery of the fixed lens barrel, and the positions of the variator lens and the compensator lens are changed in conjunction with the zoom operation ring 33. On the outer periphery of the zoom operation ring 33, cam portions 34, 35, 36 are formed, while a leaf switch constituted by two contact pieces 37, 38 is turned on in a wide range and turned off in a tele range. . The position shown in the figure is an intermediate state and is a switching point between the above-mentioned ON and OFF.

Further, in the zoom ring information presentation device of FIG. 15, a switch board P is provided, and information by contact or non-contact of the contact pieces 37 and 38 is transmitted through the switch board P to the zoom position detecting means 27 of FIG. Is transmitted to the microprocessor section.
In the switch board P, 39 and 40 are input terminals, 4
1, 42, 43 are annular fixed conductor pieces, 44, 45 are output terminals, 46 is a movable conductor piece rotatable about a shaft 47, each arm of which is annular, and each tip end thereof. The contacts 46a and 46b form contacts, and the contacts 46a and 46b are in contact with the fixed conductor pieces 42 and 43 at the positions shown in the figure. The movable conductor piece 46 is provided with holes 48 and 49, and the operation knob 51 in FIG. 16 is fixed to these holes 48 and 49 by means such as screwing, and if the knob 51 is operated, the movable conductor piece 46 And rotate together. Knob
The pointer 51 is provided with a pointer 52, and indicators 53, 54 and 55 indicating “automatic”, “large” and “small” described later are provided around the knob 51, respectively. In FIG. 15, reference numeral 39a denotes a conductor for connecting the terminal 39, the conductor piece 41 and the terminal 44, and 40
a is a conductor for connecting the terminal 40 to the conductor piece 43; 45a is a conductor for connecting the terminal 45 to the conductor piece 43; and 50 is an operation rod of the zoom operation ring 3.

In the above configuration, the illustrated positions of the movable conductor piece 46 and the knob 51 are "automatic" positions, and the terminals 44, 4
The output from 5 corresponds to ON and OFF of the contact pieces 37 and 38 constituting the leaf switch. That is, a signal corresponding to the focal length of the zoom lens system 11 is output. Next, when the knob 51 is rotated clockwise from the illustrated position by about 30 degrees and the pointer 52 reaches the position of the `` large '' indicator 54, the contact 46a and the conductor piece 42 and the contact 46b and the conductor piece 43 Since the contact is broken, the output from the terminals 44 and 45 is turned off regardless of whether the contact pieces 37 and 38 are on or off. When the knob 52 is further rotated clockwise about 30 degrees and the pointer 52 reaches the position of the "small" index 55, the contact
46a and the conductor piece 43, and the contact 46b and the conductor piece 41 are in contact with each other, the terminals 44 and 45 are short-circuited by these fixed and movable conductor pieces, and the output from these terminals is a contact piece.
It turns on regardless of whether 37 or 38 is on or off.

Therefore, as described above, in general, the distance measurement field of view is relatively large and the distance measurement field of view is relatively wide and the distance measurement field is small (automatic mode). The focus detection range can be switched to "small" when teleconferencing is intense even in telephoto, and to "large" when there is no contrast and focus detection is impossible even in wide. Can be raised.

In the above-described embodiment, a two-dimensional image sensor is used as the imaging means. However, in practicing the invention of this application, a one-dimensional image sensor can be used. Alternatively, the focus detection may be performed by using output signals of one or a part of columns of the interline CCD. Further, the invention of this application divides the position corresponding to the distance measurement field of view in the image sensor into two parts, and compares the outputs of these parts to perform focus detection. Can also be applied. Also the thirteenth
Other gate control circuits can be used in place of the programmable logic array shown.

(Effects) As described above, according to the invention of this application, in a device that performs focus detection based on an output signal of an imaging unit, the focal length of an imaging optical system is detected, and the focal length of the imaging unit is determined in accordance with the focal length. Since the output signal extraction range is made variable, erroneous ranging due to a subject of distance conflict that is likely to occur under a fixed ranging field of view can be reduced, and highly accurate focus detection can be performed. .

Also provided is a means for setting the output signal extraction range of the imaging means to a specific range regardless of the focal length, so that in general, it is possible to change the distance measurement field of view according to the focal length and take a picture. The size of the distance measurement field of view can also be set according to the user's drawing intention, subject conditions, and the like.

At the start of the focus detection operation, the distance measurement area is first changed, and then the direction is determined. Therefore, it is possible to perform the direction determination operation based on the accurate focus signal obtained from the optimal distance measurement area. You can do it.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory views schematically showing states of a subject image on an image forming plane of an image pickup apparatus at the time of focusing and at the time of out-of-focus, respectively, and FIGS. 3B is an explanatory diagram showing a luminance signal being output from the image sensor in the states of FIGS. 1A and 1B, and FIGS. 3A and 3B are respectively FIGS. 2A and 2B. FIG. 4 is an explanatory diagram showing a signal obtained by differentiating the signal shown in FIG. 4B and FIG. 4B. FIG. 4 is a diagram showing a relationship between a lens position of the imaging device and a high-frequency component in an output of the image sensor. FIGS. 6A, 6B and 6C are explanatory diagrams showing an example of the sequence, and are explanatory diagrams showing the relationship between the state of the focus detection system and the high-frequency component in the output of the image sensor, respectively, and FIG. FIG. 8 is a block diagram of a conventional focus detecting device, FIG. 8 is an explanatory diagram showing a standard distance measuring visual field position, and FIG. D), (E), (F) and (G)
Fig. 10 is a waveform diagram showing signals at points D, E, F and G in Fig. 7, respectively. Fig. 10 shows a case where a subject is photographed at a focal length longer than a relatively long focal point in an imaging device using a conventional focus detection device. Explanatory diagram showing the state of the image in the finder screen
FIG. 12 is an explanatory view showing the state of an image when the image is taken at a focal length relatively shorter than the short focus, and FIG. 12 shows the size of the distance measurement field on the short focus side in the imaging apparatus embodying the present invention. FIG. 13 is a block diagram of an embodiment of the focus detection device of the invention of this application, FIG. 14 is an explanatory diagram showing an example of a focus detection operation sequence in the embodiment of FIG. 13, and FIG. FIG. 16 is a configuration diagram of a zoom ring information detecting and transmitting device applied to the embodiment of the invention of the application, and FIG. 16 is a plan view of a knob for operating the device of FIG. DESCRIPTION OF SYMBOLS 11: lens group constituting a zoom system, 13: two-dimensional image sensor as an example of imaging means, 18: analog gate, 24, 2
5: distance measurement field of view; 26: programmable logic array as an example of a gate control circuit; 27: zoom position detection means; 3
3: Zoom operation ring, 34, 35, 36: cam section, 37, 38: contact piece, 51: operation knob, P: switch board.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-67505 (JP, A) JP-A-58-219505 (JP, A) JP-A-57-116311 (JP, A) JP-A 58-219 188965 (JP, A) JP-A-58-188966 (JP, A) JP-A-48-12615 (JP, A) JP-B-39-5265 (JP, B1)

Claims (1)

(57) [Claims] 1. A focus detection device for detecting a focus based on an output signal of an image pickup means, comprising: a detection means for detecting a focal length of an image pickup optical system; A gate circuit for extracting a signal corresponding to the inside of the distance measuring field used for focus detection; and focus detecting means for detecting a focus state from an image signal corresponding to the inside of the distance measuring field formed by the gate circuit. A distance measuring step of controlling the opening / closing timing of the gate circuit in accordance with the focal length of the imaging optical system detected by the detecting means to change the size of the distance measuring visual field in the screen in a plurality of steps; Field-of-view control means, direction discriminating means for discriminating the driving direction of the imaging optical system from a change in the output of the focus detection means when the imaging optical system is driven back and forth by a small amount in the optical axis direction, Operating the ranging field control means in response to the start of the operation, changing the size of the ranging field according to the focal length of the imaging optical system detected by the detection means, Control means for operating a discriminating means to determine a driving direction of the imaging optical system, and controlling to drive the imaging optical system in the determined direction. .