JPS6090316A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To compensate merits and demerits of two different type distance measuring devices by constituting so that an active distance measuring device is operated after a prescribed time has elapsed, when a passive distance measuring device is operated. CONSTITUTION:A luminance signal and position information are inputted to a sequencer 8 from a photographed object luminance detecting circuit 7 for detecting a disphragm state to an image pickup tube 6 from a photographic lens 1, and a position detecting circuit 9 for detecting a position of the photographic lens 1, respectively, and an output from the sequencer 8 is connected so as to operate one of an active distance measuring device 10, a passive distance measuring device 11 and a fixed focus device 12. In this state, as for an object to be photographed of a closest focusing distance, the distance is measured by the active distance measuring device 10, and as for an object to be photographed of a long distance, the distance is measured by the passive distance measuring device 11, so that the active distance measuring device 10 is driven in some prescribed time period when the passive distance measuring device 11 is being operated, and a distance measuring accuracy of the whole device is raised by making the most of each merit.

Description

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

Conventionally, various methods have been proposed for this type of focus adjustment device.
It is actually incorporated into video cameras and the like. It is well known that these various methods can be roughly divided into active distance measuring devices called active methods and passive distance measuring devices called passive methods. The former active automatic focusing method emits light or sound waves from the camera side toward the subject and uses 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 and know the distance to the object, the reflected light, etc. for objects further away will be at a low level and cannot be detected.

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 IiY that is involved in focus adjustment among the photographic lenses 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. Even if a subject is located at an infinitely far distance, no problem will occur because the subject will be within the depth of field.

For example, focal length f4 f = 35 mm, open FN
o = F2,8, minimum circle of confusion diameter δ - 35m of 0,03mm
For m cameras, the near point of this hyperfocal distance is H/2=
f'/(26F) gives a distance of 7.3 m, and if 10 m can be achieved, it will be possible to focus over the entire area. However, if we consider a video camera with f=60mm, aperture FNo.=F1.8, and minimum circle of confusion diameter δ=0.03mm, H
/ 2 = 33 m, and it is extremely difficult to realize a camera that can focus over the entire area due to the type and size of the power elements.

Many of the known active distance measuring devices are capable of focusing on most subjects in practice, but when the aperture is relatively open, it is difficult to focus on distant objects such as fireworks or neon signs at night. , manual focusing is required. For example, in the aforementioned video camera having a lens of f=60 mm, if the travel distance of the light beam, etc. is 10 m, then 1
Since 0000=602/(2ψ0.030F), F=6, and when photographing at a wider aperture than F6, it may become out of focus by one degree.

On the other hand, with the latter passive automatic focus adjustment device, distance measurement is in principle impossible unless the subject has some discernible contrast. For this reason, if the subject is a wall with no contrast, or if it is under low illumination 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 perform contrast distance measurement that allows the subject to be identified. In other words, the active distance measuring device is used for close objects, and the passive distance measuring device 1 is used for long distance objects.
Moreover, it can be said that they compensate for each other's shortcomings.

For two reasons, camera distance measuring devices with both active and passive methods are known; Because the aperture is relatively narrow, if the photographic lens is stopped at the hyperfocal distance position at that aperture or wide open aperture, the passive distance measuring device can be used even under in-focus conditions. When distance measurement is continued and the lens moves minutely, making it difficult to see the captured video, or when a subject with no contrast enters the distance measurement field of view due to panning, etc., the lens enters a passive search mode. There is also a risk that there will be a significant shift. For this reason, when an autofocus device that uses both conventional distance measurement methods is used mainly for moving images, there is a drawback that the screen may become unsightly depending on the situation.

The purpose of the present invention is to eliminate the drawbacks of the conventional example described above, use two different types of distance measuring devices, compensate for the advantages and disadvantages of both distance measuring devices, and ensure more accurate accuracy even during passive distance measuring. The purpose is to provide an automatic focus adjustment device capable of distance measurement, and its gist is to provide a first method using different methods for automatically detecting the distance to an object. It has a second distance measuring device, the first distance measuring device measures a distance to an object at a relatively short distance, and the second distance measuring device measures a distance to an object at a relatively short distance.
The distance measuring device is designed to measure relatively far objects,
The present invention is characterized by having a control device that operates the first distance measuring device at a predetermined time after the second distance measuring device is activated.

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, in which 1 is a photographing lens held by a distance ring 2;
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). A subject brightness detection circuit 7 for detecting the aperture state of a6 is provided, and its output, a brightness signal EV, is input to a sequencer 8. In addition, a position detection circuit 9 for detecting the position of the photographic lens l is installed, and its output is inputted to the sequencer 8. In the sequencer 8, in combination with the luminance signal EV, The output from the sequencer 8 is the active range finder ff,
The outputs of these devices lo, ll, 12 drive the electric motor 3 via the upper motor drive circuit 13. is configured to do so. In addition,
A timer signal from a timer 14 is inputted to the sequencer 8 as necessary, and the sequencer 8 operates taking into consideration 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 distance measurement bag FIT 10, the passive distance measurement device 11, or the fixed Any one of the fixed focus devices 12 holding the stop position is selected, and the selected device 1! In response to a command from the motor drive circuit 13 in response to the output of
The image will be formed on the imaging plane.

In this first embodiment, as described above, brightness information and lens position information are used to determine whether to use an active distance measuring device or a passive distance measuring device. Note that, as will be described later, the fixed focus device 12 for holding the photographing lens l 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 later from occurring if distance measurement using only the passive method is continued when the mode is set to passive distance measurement. While the device 11 is in operation, the active distance measuring bag #lO is driven at a predetermined time period. Furthermore, the timer 14 also has the role of adjusting the timing when the fixed focus device 12 stops operating and switches to the active distance measuring bag wlO. In cases where the active distance measuring device 10 measures distances for long-distance objects, and the passive distance measuring device 11 measures distances for long-distance objects, by incorporating lens position information and further incorporating object brightness information corresponding to aperture information, In some cases, the passive distance measuring device 11 does not perform distance measurement on a distant object, but instead stops the lens at a predetermined lens stop position. Table 1 shows distance measurement modes depending on the combination of subject conditions. In this embodiment, the photographing lens 1 is set to a fixed subject, and the brightness information is set to a fixed aperture aperture, and the brightness detection circuit 7, it is possible to detect a "bright state" and a "dark state."

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, long distance subjects, so hyperfocal length 111 [1:f2/(δF
) [However, if f is constant at the telephoto end, it becomes large, and it is best to measure the distance in passive mode in order to exceed the reach of the light beam. In addition, when photographing a bright, long-distance subject,
For example, with the video lens described above, if the aperture is smaller than F6, active distance measurement can be performed without depending on the aperture state within passive distance measurement. 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 described later.

FIG. 2 shows an embodiment of the position detection circuit 9 for determining the stop position information of the lens. The cam portion 17 is driven by contacting the cam portion 17, and is connected to the fixed contact piece 18. In FIG. 2(a), the switch is open, and in FIG. 2(b), as the distance ring 2 rotates, the cam portion 17 pushes down the operating contact piece 16, and the switch is closed. The two positions detected in this manner may be, for example, a short-distance area in FIG. 2(a) and a long-distance area in FIG. 2(b). In addition, the distance between the switching points of these two positions may be set close to the reaching pressure a and fI of the light beam of the active distance measuring device 10, or depending on other design intentions, for example, the reaching distance may be set close to the reaching distance with the telephoto end open. It may also be a point.

FIG. 3 shows an active ranging device lO of a type suitable for use in this embodiment. Note that, of course, in this embodiment, an active distance measuring device of a type other than that shown here may be used. In FIG. 3, a microprocessor 20 instructs an infrared light drive circuit 21 to emit pulsed light at a constant cycle according to a command from a sequencer 8, and an infrared light emitting diode 22 periodically emits near-infrared light. optical 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, Figure 3 is in focus,
The light flux to the light receiving element 25 is divided into two regions 25 of the light receiving element 25.
Since the image is centered on the boundary between a and 25b, the output difference (A-B) between the outputs A and H of the regions 25a and 25b is zero. For example, when the subject S approaches, the spot center on the light receiving element 25 moves toward the area 25b, and
The output becomes large and becomes (A-B) 0 to detect rear focus, and vice versa when front focus is detected. Signals A and B are amplified by amplifiers 26a and 26b, respectively, and then sent to an integrator 27.
AC noise components are removed by the signals a and 27b and sent to the differential amplifier 28, and the difference signal (A-B) is processed by the microprocessor 20 to determine the direction of rotation of the motor 3, etc. 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 the optical axes of the light projecting and receiving lenses 23 and 24 intersect on the subject at a new distance.

FIG. 4 shows a passive distance measuring device 11 suitably used in this embodiment. Here, the CO equivalent to the image pickup tube is
The output from the solid-state image sensor 30 such as D is converted into a TV signal by a processing circuit 31 having circuits such as a preamplifier, gamma correction, blanking correction, and linear clip.
A gate 33 operated by a microprocessor 32 for automatic focus adjustment extracts only the signal within the distance measurement field of view at the center of the screen, and this signal passes only high frequency components through a high-pass filter 34 and is extracted by a detector 35. It will be done. On the other hand, the two optical elements of the focus modulator 36 and 37 and the vibrating body 38 that drives them are connected to the counter 39, the COD
A frame period signal is obtained from the drive 40, and the imaging position is changed for each frame. As a result, the phase sensitive detector 41 detects the front focus and the rear focus from the output of the detector 35 and the position of the focus modulators 36 and 37 at that time, and the magnitude and sign indicate the magnitude and direction of the focus error. , electric I! via the focus servo circuit 42. The drive circuit 13 is now driven.

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

FIG. 6 is a flowchart of this embodiment for operating the sequencer 8, in which the distance measurement mode is switched based on the luminance signal EV from the luminance detection circuit 7 and the lens position information from the position detection circuit 9, and the light receiving Output A from element 25,
B moves the photographing lens 1 to the in-focus position. At the end of pressure measurement, the active distance measuring device 10 is activated to start distance measurement in active mode. The reason for this is that if the shooting lens 1 is in a long-distance focusing state at the beginning of shooting, and the subject is at a close distance, it is in passive mode, and for some reason it becomes impossible to measure distance in passive mode. , the photographing lens l 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 object is in focus at close range and the subject is far away and distance measurement in active mode is impossible, the photographing lens 1 will start moving in the direction of focusing at long distance. There is no problem because it switches to the mode.

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 the brightness information or lens position information. As a result, the output difference (
If A-B) is determined to be constant and larger than bell v1 in step 2, front focus is determined. If it is determined in step 3 that the photographing lens 1 is at a close distance 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 continued. Furthermore, if it is determined in step 3 that it is a far area, the process proceeds to step 5, if the moderation EV value is less than or equal to the predetermined value N, the process proceeds to step 6, passive mode, and if the EV value is greater than or equal to N, the process proceeds to step 7.8. Fixed focus mode.

On the other hand, in step 2, if (A-B) <-Vl, it is determined that the rear focus is on, 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 changed for focusing. , and maintain the active mode of step 1. Furthermore, as shown in Fig. 7, -
A dead zone width is provided so that focus is determined in the region of Vl<(A-B)<Vl. Therefore, in step 2 (
If A - B) is between -v1 and +v1, and in step 11 it is determined that the output is constant at A, B or C and is equal to or higher than bell v2, that is, there is reflected light from the subject, step 12 is in focus, and the objective is achieved, but
In the case of a moving image, since the subject position changes, active distance measurement in step 1 is restarted. In step 11, when A≦v2 and B≦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, it is determined in step 13 whether or not there is a timer signal from timer 14, and if there is no timer signal, the passive mode is maintained, and if there is a timer 4i+, it returns to the active mode in step 1. ing. That is, during passive mode, active distance measurement is performed at intervals determined by the timer 14. This is to prevent distance measurement from becoming impossible if an object with no contrast appears on the close side #1 of the printing press while measuring a relatively distant object in the passive mode, for example.

In the fixed focus mode, the photographing lens l 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 does not necessarily need to be moved to the F end, but may be moved to a hyperfocal position. 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 process 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 actep mode, if the subject conditions do not change, the process goes through step 2, step 11, step 3, and step 5, and then returns to fixed focus mode. 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 on.・For example, the range of active mode is used as the off switching focusing pressure, and as described above, f = 6
0 mm, open FNo.=1.8, .delta.=0.03, and Te(7) distance of 10 m, the aperture on/off switching was around F6. Here, similarly, the reach distance is lo
and F=1. ,．． 8 is a constant, 1OOOO=f
2/(2-0,03-1,8) gives f: 33mm. Therefore, in the second embodiment shown in FIG. 8, based on this idea, the focal length information of the zoom lens is turned on and off with 33 mm as the boundary, and the focal length detection circuit is configured as shown in Table 2 below. When the focal length information from 5o 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 Mote long distance Telephoto Passive long distance Wide angle Fixed focus close distance Telephoto Active close distance 1111m Wide angle Active Figures 9(a) and (b) are suitable for the second embodiment shown in Figure 8. 2 illustrates a focal length sensing mechanism that can be used. 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 all 17 of distance #Jl 2 as shown in FIG.
The punch 15 was fixed at a predetermined location. On the contrary,
In this embodiment, the leaf switch 15 is attached to the distance ring 2 and is rotatable together with the distance ring 2. Cam portion 51 for turning on and off this leaf switch 15
is integrated with the zoom operation ring 52 and extends forward.

With the configuration of this second embodiment, the focal length of the boundary between the close range telescope and the far range of the range ring 2 changes depending on the focal length. This is when the depth of field becomes deeper due to the wide-angle side.
This is intended to limit the active operating area to the closer side, and in comparison with the previous example, on the wide-angle side than f = 33 mm, the boundary point between the near area and the far area is brought closer to the near side. Become. 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. In this case, when the aperture is wider than in the first embodiment,
This increases the distance measurement area in passive mode.

As explained above, the automatic focus adjustment device according to the present invention has
By having both active and passive automatic focusing devices, the system takes advantage of the mutual advantages to improve the distance measurement accuracy of the entire device. When the passive distance measurement device is activated, the active distance measurement device starts after a certain period of time. The distance measuring device operates to compensate for the shortcomings of the passive distance measuring device, ensuring accurate distance measurement at all times.

[Brief explanation of the drawing]

The drawings show an embodiment of an automatic focusing device according to the invention,
Figure 1 is a block circuit configuration diagram of the first embodiment, Figure 2 (
a) and (b) are block diagrams of the distance detection means, FIG. 3 is a block circuit diagram of the active distance measuring device used in the first embodiment, and FIG. 4 is the passive ranging device used in the first embodiment. 5 is an explanatory diagram of the puffive ranging device of FIG. 4, FIG. 6 is a flowchart of the first embodiment, and FIG. 7 is a diagram of the active ranging device of the first embodiment. An explanatory diagram of the dead zone, FIG. 8 is a block circuit diagram of the second embodiment, FIG. 9(a) is a cross-sectional view of the focal length detection mechanism used in the second embodiment, and FIG. 9(b) is a vertical cross-section thereof. It is a diagram. 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, and 12 is an active range finder.
13 is a fixed focus device, 13 is a motor drive circuit, 14 is a timer, 15 is a leaf switch, 17.50 is a focal length detection circuit, 51 is a cam portion, and 52 is a zoom operation ring. Figure 5 Figure 7 Figure 8 Figure 9) (b)

Claims (1)

[Claims] 1. A first distance measuring device and a second distance measuring device with different methods are provided for automatically detecting the distance to an object, and the first distance measuring device 1 is used to detect a relatively short distance. t
The automatic focusing device is configured to range-find an object at a relatively long distance, and has a control device that activates the first range-finding device at a predetermined time after the second range-finding device is activated. The automatic focusing device according to claim 1, wherein the adjusting device 62 and the first distance measuring device are of an active type, and the second distance measuring device is of a passive type. 3. The automatic focus adjustment device according to claim 1, wherein the operation of the first distance measurement device while the second distance measurement device is in operation is performed by an interruption by a signal from a timer.