JPH0378604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device used in a video camera or the like.

Hitherto, various types of focus adjustment devices of this type have been proposed and are actually incorporated into video cameras and the like. It is well known that these various methods can be roughly divided into active type distance measuring devices called so-called active methods and passive type distance measuring devices called so-called passive methods. The former type of active automatic focus adjustment involves emitting light rays or sound waves from the camera side toward the subject, and using the reflected light as an information source.
Although it is possible to obtain some kind of signal from the reflected light of an extremely common object that exists within a distance range of up to around m, and determine the object distance, the reflected light, etc. from objects further away will be at a low level. becomes undetectable.

Therefore, in a conventional video camera equipped with this type of active type automatic focus adjustment device, when shooting a subject at a distance where the emitted light beam or sound wave does not return, the lens involved in focus adjustment of the photographic lens The group was stopped at a predetermined position. The limit distance at which this light beam or reflected light of sound waves, etc. can be detected is called the reaching distance.If this reaching distance is beyond the near point of the hyperfocal distance, the result will be from the specified closest distance. No matter where the subject is located within the infinite distance, no problem will occur because the subject will be within the depth of field.

For example, focal length f=35mm, aperture FNo.=F2.8,
In a 35mm camera with a circle of least confusion diameter δ = 0.03,
The near point of this hyperfocal distance is 7.3 m from H/2=f ² /(2δF), and if the reachable distance is 10 m, focusing will be possible over the entire area. However, here f=60
If we consider a video camera with mm, aperture F No. = F1.8, and minimum circle of confusion diameter δ = 0.03 mm, H/2 = 33 m, and realizing a camera that can focus over the entire area is as follows:
This is extremely difficult due to the type and size of the electrode elements.

Many of the known active distance measuring devices are capable of focusing on most subjects in practice, but when the aperture is set relatively wide open, it is difficult to focus on distant objects such as fireworks or neon signs at night. It is necessary to manually adjust the focus. For example, the above f=60
For a video camera with a mm lens, if the travel distance of light rays, etc. is 10 m, then 10000 = 60 ² /
From (2・0.03・F), F=6, and if you shoot at a wider aperture than F6, the image may be out of focus.

On the other hand, with the latter passive automatic focus adjustment device, distance measurement is theoretically impossible unless the subject has some discernible contrast. For this reason, if the subject is a wall with no contrast, or if the subject is under low illuminance and there is almost no difference in contrast, it has the disadvantage that distance measurement is impossible. However, unlike the active method described above, the passive method has the advantage of being able to measure distances over the entire distance range as long as the object has discernible contrast. In other words, active distance measuring devices are better for close objects, and passive distance measuring devices are better for distant objects, and they do not compensate for each other's shortcomings. I can say that it is.

For the above-mentioned reasons, camera distance measuring devices that have both active and passive methods are known, but the conventional ones do not fully consider the hyperfocal distance and reach distance as described above. Therefore, if the aperture is relatively narrow and the photographing lens is stopped at the hyperfocal distance device at that aperture or wide open aperture, the passive distance measurement device will be able to measure the distance even under focused conditions. If the lens moves continuously and the captured moving image becomes difficult to see, or if a subject with no contrast enters the distance measurement field due to panning, etc., the lens enters the so-called search mode of the passive method and the lens moves significantly. There is also a risk that this will happen. For this reason, when a conventional autofocus device that uses two types of distance measurement methods is used mainly for moving images, there is a drawback that the screen may become unsightly in some cases.

An object of the present invention is to eliminate the drawbacks of the conventional example described above, to use two different types of distance measuring devices, and to stop the photographing lens at a fixed position under certain conditions to avoid wasteful distance measuring. The purpose is to provide an automatic focus adjustment device that eliminates the need for a focus adjustment device, and its gist is to provide an automatic focus adjustment device that includes a light projecting means for projecting light toward a subject, and a first light receiving means for receiving the light reflected from the subject. a first focusing device that adjusts focus by moving a lens of a photographing lens based on a light receiving state of the first light receiving device; and a second light receiving device that receives photographing light of the photographing lens; a second lens for adjusting the focus by moving the lens based on the light receiving state of the light receiving means;
An automatic focus adjustment device for a photographing device having a focus adjustment device, wherein the detection means detects the brightness of the subject, and the first focus adjustment device determines that the subject is far away. When the detection means detects that the subject brightness is higher than a predetermined level, the operation of the first focusing device is stopped and the lens is placed at a predetermined fixed position. control means for operating the second focus adjustment device instead of operating the first focus adjustment device when the detection means detects that the subject brightness is lower than the predetermined level while moving the subject; It is characterized by comprising the following.

Next, the present invention will be explained in more detail based on illustrated embodiments.

FIG. 1 shows a system outline diagram of the first embodiment of the present invention. Reference numeral 1 denotes a photographing lens held by a distance ring 2. This photographing lens 1, more specifically, the lens group involved in focus adjustment, is According to the drive of the electric motor 3, the gear 4 allows the lens to move forward and backward relative to the fixed lens barrel 5 in the optical axis direction. The object image obtained from the photographing lens 1 through the image pickup tube 6 is converted into a TV signal and sent to a processing circuit (not shown). The luminance signal EV, which is the output thereof, is input to the sequencer 8. Also,
A position detection circuit 9 is provided for detecting the position of the photographic lens 1, and its output is input to a sequencer 8. In the sequencer 8, in combination with the luminance signal EV, The output of is connected to operate any one of the active distance measuring device 10, the passive ranging device 11, and the fixed focus device 12, and these devices 10,
The outputs of 11 and 12 are configured to drive the motor 3 via a motor drive circuit 13. Note that the timer signal of the timer 14 is input to the sequencer 8 as necessary, and the sequencer 8 is configured to operate taking into account the presence or absence of the timer signal.

Therefore, the information from the brightness detection circuit 7 and the position detection circuit 9 are both transmitted to the sequencer 8, and as a result of the judgment within this sequencer 8, the active rangefinder 10, the passive rangefinder 11, or the fixed rangefinder One of the fixed focus devices 12 that maintains the stop position is selected, and the electric motor 3 drives the photographing lens 1 via the gear 4 according to a command from the motor drive circuit 13 according to the output of the selected device. By adjusting the position, the subject image is focused on the imaging surface of the imaging tube 6.

In this first embodiment, as described above, brightness information and lens position information are used to determine whether to use an active range finder or a passive range finder. Note that, as will be described later, the fixed focus device 12 for holding the photographic lens 1 at a fixed focus can be considered to be included in the active distance measuring device 10. Here, the role of the timer 14 is to prevent the problem described below from occurring if distance measurement is continued using only the passive method when the mode is set to passive distance measurement.
While the passive distance measuring device 11 is in operation, the active distance measuring device 10 is driven at a predetermined time period. Additionally, the timer 14 indicates that the fixed focus device 12 has ceased operation and that the active distance measuring device 10
It also serves as a timing adjustment for switching.

As is known from FIG. 1, in this embodiment, the active distance measuring device 1 is used for objects at close range.
0, when measuring a long distance object using the passive distance measuring device 11, by incorporating lens position information and further incorporating object brightness information corresponding to aperture information, it is possible to Passive distance measuring device for distant objects 1
1, the lens is stopped at a predetermined stop position without performing distance measurement. Table 1 shows distance measurement modes depending on the combination of subject conditions.
The two positions of can be detected by the position detection circuit 9,
Further, as the brightness information, the brightness detection circuit 7 can detect a "bright state" and a "dark state" with a predetermined aperture aperture as a boundary.

Table 1 Lens position Brightness Mode Far distance Dark Passive Far distance Bright Fixed focus Close distance Dark Active Close distance Bright Active As shown in Table 1, the aperture is open for dark and far objects, so the hyperfocal distance f ² /(δF)
[However, f is constant at the telephoto end] increases,
It is best to measure distance in passive mode in order to exceed the reach of the light beam. Also, when photographing bright, long-distance subjects, for example, the video lens mentioned above
If you stop down from f/6, there is no need for passive distance measurement, and the lens only needs to stay at a position where the focal length is the hyperfocal distance. Furthermore, within the range, active distance measurement can be performed regardless of the aperture state. The sequencer 8 that controls these operations can be realized by hardware such as a logic circuit, but in this embodiment, it is operated by software as will be described later.

FIG. 2 shows an embodiment of the position detection circuit 9 for determining the stop position information of the lens, in which the operating contact piece 16 of the leaf switch 15 is integrally provided on the outer periphery of the distance ring 2 that holds the photographic lens 1. The cam portion 17 is driven by contacting the cam portion 17, and is connected to the fixed contact piece 18. In FIG. 2a, the switch is open, and in FIG. 2b, as the distance ring 2 rotates, the cam part 17 pushes down the operating contact piece 16, and the switch is closed. The two positions detected in this way may be, for example, a short distance area in FIG. 2 and a long distance area in FIG. 2b. In addition, the distance between the switching point between these two positions may be set near the reachable distance of the light beam of the active distance measuring device 10, or depending on other design intentions, for example, the reachable distance may be set to the near point when the telephoto end is open. good.

FIG. 3 shows an active distance measuring device 10 of a type suitable for use in this embodiment. Note that in this embodiment, it is of course possible to use an active distance measuring device of a type other than that shown here. In FIG. 3, the microprocessor 20 instructs the infrared light drive circuit 21 to emit pulsed light at a constant cycle based on a command from the sequencer 8, and the infrared light emitting diode 22 periodically emits near infrared light. Light projection lens 2
3 toward the subject. The projected light beam is diffusely reflected by the subject S and forms an image on the light receiving element 25 via the light receiving lens 24. At this time, FIG. 3 shows the focused state, and since the light beam to the light receiving element 25 forms an image centered on the boundary between the two areas 25a and 25b of the light receiving element 25, the areas 25a and 25b
The output difference (A-B) between outputs A and B has become zero. For example, when the subject S approaches, the center of the spot on the light receiving element 25 moves toward the area 25b, the output of B increases, and (A-B)<0, the rear focus is detected and the front In the case of focus, the opposite is true. Signals A and B are transmitted through amplifiers 26a and 26b, respectively.
After amplification, AC noise components are removed by integrators 27a and 27b and sent to a differential amplifier 28,
The difference signal (A-B) is processed by the microprocessor 20, and the rotational direction of the electric motor 3 is set. For example, in the case of rear focus, the photographing lens 1 moves to the left on the screen, and the photographing optical axis and light emitting/receiving lens 23,
The optical axes of 24 will intersect on the object at the new distance.

FIG. 4 shows a passive distance measuring device 11 suitably used in this embodiment. Here, the output from a solid-state image sensor 30 such as a CCD, which corresponds to an image pickup tube, is processed by a processing circuit 3 having circuits such as a preamplifier, gamma correction, blanking mixing, and linear clip.
In addition to being converted into a TV signal by 1, only the signal within the distance measuring field at the center of the screen is extracted by a gate 33 operated by a microprocessor 32 for automatic focus adjustment, and this signal is passed through a high-pass filter 34.
Only the high frequency components pass through and are extracted by the detector 35. On the other hand, focus modulators 36 and 37
two optical elements and a vibrating body 38 that drives them
obtains a frame period signal from the counter 39 and CCD drive 40, and changes the imaging position for each frame. As a result, the phase sensing detector 41 detects front focus and rear focus from the output of the detector 35 and the positions of the focus modulators 36 and 37 at that time.
The magnitude and sign indicate the magnitude and direction of the focus error, and the motor drive circuit 13 is driven via the focus servo circuit 42.

FIG. 5 is a diagram showing the principle of the passive distance measuring device 11 of this method. Figure 5a shows the contrast of the subject; in the out-of-focus state, the Y signal is as shown in b, and its differential signal is only a small output as shown in c. On the other hand, in the focused state, the Y signal becomes as shown in d, and the differential signal e shows c
The peak is much larger than that of Therefore, it can be seen that the position where the differential signal peaks should be set as the in-focus position.

FIG. 6 is a flowchart of this embodiment for operating the sequencer 8, and the luminance detection circuit 7
The distance measurement mode is switched based on the luminance signal EV from , and the lens position information from the position detection circuit 9.
The photographing lens 1 is moved to the in-focus position by the outputs A and B from the light receiving element 25. At the start of distance measurement, the active distance measurement device 10 is activated to start distance measurement in active mode. The reason for this is that if the photographing lens 1 is in a long-distance focusing state at the beginning of shooting, and the subject is at a close distance and is in passive mode, and for some reason it becomes impossible to measure distance in passive mode. The lens 1 is in a hyperfocal position until active distance measurement is activated by the timer signal from the timer 14 shown in FIG. However, this problem can be solved if the camera is in active mode at the beginning of shooting. Conversely, even if the subject is in close focus and the subject is far away and distance measurement is not possible in active mode, the photographing lens 1 will move in the direction of long distance focusing and switch to another mode. There is no problem as it can be switched.

Therefore, at the start of distance measurement, the infrared light emitting diode is turned on in step 1 and distance measurement is performed in the active mode, regardless of brightness information or lens position information. As a result, two regions 25 of the light receiving element 25
If the output difference (A-B) from a and 25b is determined to be greater than a certain level V1 in step 2, front focus is determined. If it is determined in step 3 that the photographing lens 1 is at close range based on the lens position information, the photographing lens 1 is retracted in step 4 for focusing, and the active mode of step 1 is maintained. If it is determined that the area is far away in step 3, the process goes to step 5. If the brightness EV value is less than a predetermined value N, the process goes to passive mode in step 6. If the EV value is N or more, the process goes to step 7 and 8 to fix the area. It becomes focus mode.

On the other hand, in step 2, (A-B)<-V1
In this case, it is determined that the camera is in rear focus, and in step 9 it is determined whether the photographing lens 1 is at the N end. If not, in step 10 the photographing lens 1 is extended for focusing, and the active mode of step 1 is maintained. Note that, as shown in FIG. 7, -V1<(A-
B) A dead zone width is provided so that focus is determined in the region of <V1. Therefore, in step 2, (A
-B) is between -V1 and +V1, and in step 11, both A and B have outputs above a certain level V2, that is, if it is determined that there is reflected light from the subject, the focus is determined in step 12. However, in the case of a moving image, the subject position changes, so the active distance measurement in step 1 is restarted. In step 11, A≦V2, B≦
If V2, the process proceeds to step 3, and it is determined whether to proceed to step 4 or step 5 based on the lens position information.

During distance measurement in passive mode, the step
At step 13, it is determined whether or not there is a timer signal from the timer 14. If not, the passive mode is maintained, and if there is a timer signal, the process returns to the active mode of step 1. That is, during the passive mode, active distance measurement is performed at intervals determined by the timer 14. this is,
For example, this is to prevent distance measurement from becoming impossible if an object with no contrast suddenly appears at a close distance while measuring a relatively distant object in the passive mode.

In the fixed focus mode, the photographing lens 1 is moved to the F end in steps 7 and 8. Note that in the case of this fixed focus mode, the photographing lens 1 is not necessarily set at F.
It may be moved to a hyperfocal position without moving to the edge. After the photographing lens 1 is moved to the F end, it is determined in step 14 whether or not there is a timer signal from the timer 14. If there is a timer signal, the mode returns to the active mode of step 1, and if not, the fixed focus mode is maintained. In reality, there is a time delay caused by the timer 14 from the fixed focus mode to the distance measurement in the active mode, thereby preventing unnecessary loss of infrared light emission energy. When switching from fixed focus mode to active mode, if the subject conditions do not change, the mode will return to fixed focus mode after going through step 2, step 11, step 3, and step 5. No movement occurs at all.

FIG. 8 shows a second embodiment using a zoom lens. In the first embodiment shown in FIG. 1, the position information and brightness information of the distance ring 2 are used as elements for selecting active mode, passive mode, and fixed focus mode, and the lens position information is used to determine whether the lens is on or off. The switching focusing distance is, for example, the range in active mode, and as mentioned above, f = 60 mm, open F
If the distance is 10m with No.=1.8 and δ=0.03,
The aperture on/off switch was around F6. Here, similarly, if the reach distance is 10 m and F=1.8 is a constant, then f≈33 mm due to 10000=f ² /(2・0.03・1.8). Therefore, in the second embodiment shown in FIG. 8, the focal length information of the zoom lens is turned on and off with 33mm as the boundary based on this idea.
As shown in Table 2 below, when the focal length information from the focal length detection circuit 50 is on the wide-angle side of the boundary, the mode is set to fixed focus mode, and when it is on the telephoto side, the mode is set to passive mode.

Table 2 Lens position Focal length Mode Long distance Telephoto Passive Long distance Wide angle Fixed focus Close distance Telephoto Active Close distance Wide angle Active Figures 9a and b show focal length detection suitable for use in the second embodiment shown in Figure 8. It shows the mechanism. In the first embodiment, the leaf switch 15 for knowing the position of the distance ring 2 is turned on and off following the cam portion 17 of the distance ring 2, as shown in FIG. It was set up. In contrast, in this embodiment, the leaf switch 15 is attached to the distance ring 2 and is rotatable together with the distance ring 2. A cam portion 51 for turning on and off the leaf switch 15 is integrated with a zoom operation ring 52 and extends forward.

With the configuration of this second embodiment, the focusing distance at the boundary between the close range and far range of the range ring 2 changes depending on the focal length. This is intended to limit the active operation area to the closer side when the depth of field becomes deeper due to the wide-angle side. This brings the boundary point between the area and the far area closer to the close side. The biggest advantage of such a configuration is that it eliminates the need to keep measuring distances to objects within the depth of field in situations where the aperture is small and the aperture is wide and the depth of field is increased. It is.
Note that in this case, when the aperture is open, the distance measurement area in the passive mode increases compared to the first embodiment.

As explained above, the automatic focus adjustment device according to the present invention has both an active method and a passive method automatic focus adjustment device, thereby improving the distance measurement accuracy of the entire device by taking advantage of mutual advantages. Furthermore, by using lens focusing distance information and subject brightness information or focal length information, etc., especially when the photographing lens is at a long distance, the brightness of the subject is high, or the focal length of the zoom lens is wide-angle. In this case, the photographing lens is fixed, which contributes to power saving.

[Brief explanation of drawings]

The drawings show an embodiment of the automatic focus adjustment device according to the present invention, FIG. 1 is a block circuit diagram of the first embodiment, FIGS. 2a and 2b are diagrams of the distance detection means, and FIG. FIG. 4 is a block circuit diagram of the active range finder used in the first embodiment; FIG. 4 is a block circuit diagram of the passive range finder used in the first embodiment;
FIG. 5 is an explanatory diagram of the passive distance measuring device of FIG. 4, FIG. 6 is a flowchart of the first embodiment, and FIG. 7 is an explanatory diagram of the dead zone of the active ranging device of the first embodiment. FIG. 8 is a block circuit diagram of the second embodiment, FIG. 9a is a cross-sectional view of a focal length detection mechanism used in the second embodiment, and FIG. 9b is a vertical cross-sectional view thereof. 1 is a photographing lens, 2 is a distance ring, 3 is an electric motor, 7 is a brightness detection circuit, 8 is a sequencer, 9 is a position detection circuit, 10 is an active range finder, 11 is a passive range finder, 12 is a fixed focus device , 13 is a motor drive circuit, 14 is a timer, 15 is a leaf switch, 17 and 50 are focal length detection circuits, 51 is a cam portion, and 52 is a zoom operation ring.

Claims (1)

[Claims] 1. It has a light projecting means for projecting light toward a subject and a first light receiving means for receiving the light reflected from the subject, and moves the lens of the photographic lens based on the light receiving state of the first light receiving means. and a second light receiving means for receiving the photographing light of the photographing lens, and the lens is moved based on the light receiving state of the second light receiving means to adjust the focus. An automatic focus adjustment device for a photographing device having a second focus adjustment device that performs When the detection means detects that the brightness of the subject is higher than a predetermined level, the first focusing device stops operating and the lens is moved to a fixed position. while moving the lens, if the detection means detects that the subject brightness is lower than the predetermined level, the second focus adjustment device is activated instead of the first focus adjustment device. An automatic focus adjustment device characterized by comprising: control means for controlling the focus.