JPS63193775A - Autofocusing device for video camera - Google Patents

Abstract

PURPOSE:To obtain the miniaturized autofocusing device at low cost by providing a focusing mechanism after a zoom lens system variator lens group and motor-driving the focusing mechanism in such a way that the polarity and the amplitude of a detection signal is detected for focusing. CONSTITUTION:The autofocusing device has the focusing mechanism after the variator lens group, and focusing, in which a motor is driven in such a way that the high-pass frequency component of an image pickup signal becomes maximum, is executed by shifting a part of, or the whole master lens, or a part of, or the whole compensator lens, or an image pickup element, and a driving circuit 16 drives the motor so that they are microscopically fluctuated with a prescribed period while they are shifted. Thus, a system sharing the focusing mechanism and an optical path fine motion mechanism can be realized, and the autofocusing device can easily be constituted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a focus device for a video camera, an electronic still camera, etc., and in particular detects a high frequency component (focus voltage) from a video signal. The present invention relates to an autofocus device suitable for use in a TTL video system that controls the lens position so that the focal voltage is maximized.

[Conventional technology]

The optical path length between the subject and the light-receiving surface of the image sensor is slightly varied using a signal of a predetermined reference frequency, a high frequency component signal is extracted from the video signal obtained from the image sensor, and the predetermined minute signal is extracted from the nuclear high frequency component signal. A fluctuating frequency component signal is obtained, and this signal is compared with the optical path length minute fluctuation period base single frequency signal, the focusing direction is determined based on the signal obtained by the comparison, the focusing device of the lens is driven, and the high-frequency component signal is A TTL image type autofocus device in which a feedback circuit is configured to maximize the frequency component signal is disclosed in, for example, Japanese Patent Laid-Open No. 60-42725, or National Technical Review), Vol. 51, No. 6,
It is proposed as described in December 1985, pages 65 to 67. According to the above-mentioned patent application No. 60-42723, a vibrating prism is provided in front of the image pickup element as an optical path length minute variation device, and a piezoelectric element attached to the prism is vibrated by an electric signal of a predetermined reference frequency. A method of slightly changing the optical path length in the optical axis direction of a lens system,
A method is described in which the optical path length is slightly changed by vibrating a lens other than the 7 Orcas single lens via a piezoelectric element as described above, and a specific practical example of the latter is described in the above-mentioned document. .

As shown in FIG. 3, a zoom lens system 1 in a video camera or the like generally includes a focusing lens (front lens) group 2, a variator lens group 3, a convencator lens group 4, an aperture device 1C5, and an imaging lens (master lens). )
Group 6 forms the basic structure. As is well known, in this basic configuration, the focusing lens group 1 has the function of focusing on a desired photographic subject located at an arbitrary distance, and the variator lens group 3 has the function of changing the magnification for zooming. , convencator lens 1fP
Numeral 4 moves with zooming, and has a correcting function to prevent defocusing of the object desired to be photographed during zooming, and imaging lens 6 has a function of forming an optical character image on image sensor 7 .

The examples shown in the above-mentioned documents include a lens system 1 having such a basic configuration, in which a prism or f! ' (Mask) This is achieved by providing an optical path length minute variation mechanism that moves the lens 6 using a piezoelectric element.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, the focusing device of the lens is very loose, so mechanical flaws such as assembly precision of the focusing device
An advantage is that even if the angle is rough, an automatic focusing device with good focusing accuracy can be realized.

However, as described above, the conventional technology requires a small optical path length imaging mechanism using a piezoelectric element, and therefore, its mounting requires structural innovation in consideration of long-term stability, such as a supporting method. In addition, driving a piezoelectric element requires a driving voltage of several tens of volts or more, so in the case of devices that operate on low-voltage batteries, such as video cameras, it is necessary to provide an extra means to generate such a relatively high voltage. There is a need.

Taking these points into consideration, if it is possible to move the 7-occurring lens group shown in FIG. 3 or the above-mentioned known document while performing micro-imaging using a motor, the above-mentioned optical path length micro-imaging mechanism can be installed separately. Since this is not necessary, the configuration may be simplified. However, generally a DC motor is used to drive the focus, and with such a motor,
It is extremely difficult to move a relatively heavy focusing lens group so slightly that it cannot be detected by the human eye due to the influence of inertia, etc. Also, from the viewpoint of the lifespan of the motor, it is difficult to make the motor constantly perform photographing (reversing) motion. However, it is extremely difficult to put it into practical use.

The present invention has realized a device that can perform both optical path length micro vibration and focusing without installing a piezoelectric element-based optical path length micro-imaging device by moving the lens while moving it in a single motion. By doing so, it is possible to obtain an effect effectively equivalent to that of the prior art, and to provide a low-cost, simple automatic focusing device.

[Means for solving the problem] The above purpose is to have a focusing mechanism after the variator lens group, and the focusing mechanism for driving the image so that the high frequency component of the imaging signal is maximized is a part of the master lens. , or all of the compensator lens, or a part or all of the compensator lens, or the image pickup device, and is achieved by driving a motor to move the compensator lens while slightly changing it at a predetermined period.

[Effect]

In a general zoom lens system 1 shown in Figure 3, the position of the focusing lens group 2 is fixed, and part or all of the master lens group 6 or the camera lens 7 can be moved to achieve close-up. In principle, it is possible to adjust the focus on any subject from the distance to infinity. In this case, the focusing function is provided in the variator lens group 3 and beyond, so if the zoom position changes during zooming, the focus will shift even for subjects at the same distance. The image sensor position changes. However, in the autofocus device configured as described above, the feedback circuit is configured so that the high frequency component of the photographing signal is maximized, in other words, the blur of the photographed lff1I image is detected and the blur is minimized. Since it is an autofocus device, it can perform auto 2 orcus operation even when zooming, making it suitable for shooting F! You can always get the picture. In addition, in recent years, image sensors have become a commodity, and small-area solid-state image sensors have been put into practical use and have become mainstream. Such a solid-state image sensor has a small m@ amount (2 of) compared to the focusing lens group 2 shown in FIG.
~49). On the other hand, the master lens group 6 also has a light weight smaller than the focusing lens group 2, and only a portion of the lenses are required for focusing, for example, one or two lenses of the lens group 6. The weight is at most 1f to 2faK. [The inertia is small, and by driving the motor, it is possible to move the master lens or the image sensor while slightly changing the desired amount to adjust the focus. Furthermore, a low-torque motor can be used to drive such a lightweight focusing mechanism. Therefore pulse motors, ultrasonic motors and brushless motors.

It is now possible to use a motor that can be driven by pulses, and the inertia of the motor itself is small, making it easier to control the displacement by a predetermined amount, making it possible to make slight fluctuations by the desired and appropriate amount, and greatly improving the lifespan.

As explained above, the master lens or image sensor
By using a focusing mechanism and moving the camera while making slight movements at a predetermined period, the video signal obtained from the camera can be of the same quality as that of the prior art. Therefore, there is no need for a special optical path length fine adjustment mechanism, and the conventional 7-focus (front lens) lens can be fixed, making it possible to realize a simple and low-cost autofocus device.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to Figure @1. 1st
In the figure, 1 is an imaging lens system, 2' is a fixed lens group that corresponds to the conventional front lens group but is not moved, 3 is a variator lens group, 4 is a convencator lens group, 5 is an aperture device, and 6' is a master lens. Group 7 is an image sensor. 1
9 is means for holding and moving the master lens group 6'.

In the example shown in FIG. 1, the entire master lens group 6' is held;
Although it is designed to move, it may also be part of the master lens group. A gear 18 is driven by the motor 17 and meshes with teeth provided on the moving hand installation 9, and is connected to the master lens group 6.
' is moved in the optical axis direction at a predetermined period while being slightly varied by a predetermined amount. 16 is a signal from the control circuit 12 to the motor 1.
This is a drive circuit for driving 7. 13 is a reference signal generation source that generates a reference frequency signal for slightly varying the master lens at a predetermined period, and a control signal generation circuit 14
4 and the signal is input to the synchronous detection circuit 15. The control signal generation circuit 14 includes a reference signal generation source 13 and a synchronous detection circuit 1.
5, the master lens group 6 is slightly fluctuated at the above-mentioned reference frequency, and a control signal is outputted to move and focus while changing the lens by a degree that cannot be detected by the human eye. Give to 16. The output voltage of the image sensor 7 changes in response to slight fluctuations in the master lens group 6'. The output signal obtained by the image sensor 7 is amplified by a preamplifier circuit 8, and a camera signal is generated by a camera circuit 9. 10 is a high frequency component extraction circuit that extracts high frequency components from the video signal. The output signal of the high-frequency component extraction circuit 10 contains a component of the change since the focus is slightly changed. Reference numeral 11 denotes a detection circuit for detecting the changing component, that is, the slightly fluctuating reference frequency component.The detection signal is input to the synchronous detection circuit 15, and synchronous detection is performed using the original single frequency a signal. As a result, the polarity and amplitude of the detected reference frequency component signal are detected, and in addition to the control signal generation circuit 14, the image sensor 7
The motor 17 is driven so that the amplitude of the high frequency portion of the image is maximized, that is, focusing is performed. Next, the output voltage of the high frequency component of the image sensor 7 and the motor drive circuit 16
The zero control method will be explained using FIG. lens 1
The focusing device, that is, the master lens group 6', is moved from the close focusing distance to the infinity focusing distance, and the distance is now 11fI.
Assuming that there is a PoK object, the amplitude of the high frequency component exhibits a mountain shape that reaches its maximum at position fIPo, as shown in FIG. 21 indicates slight fluctuations of the motor; when the object is located close to the subject, a signal with the polarity 22 is sent; when the object is located far away, the signal with the polarity 23 is sent to the detection circuit 1.
1 output.

The motor 17 is moved to infinity by the signal obtained by synchronously detecting the signal of 22.
Since the motor 17 is driven toward the nearest direction using the signal obtained by synchronously detecting the signal 23, it is stabilized at the maximum value of the amplitude of the high frequency component, that is, at the top of the mountain in FIG.

As explained above, the motor moves the master lens group 6' slightly to adjust the focus. However, according to the present invention, since all or a part of the lightweight master lens group 6' is slightly moved, the inertia It should be possible to change the lid focus appropriately so that it is so small that it cannot be detected by the eye.

A second embodiment of the invention is shown in FIG. In FIG. 2, the same reference numerals as in FIG. 1 have the same functions and operations as in the embodiment of FIG. The difference from the embodiment shown in FIG. 1 is that in FIG.
' However, in the embodiment shown in FIG.
is movable so as to move and focus while slightly moving the image sensor 7. In this case, the master lens group 6 is fixed.

According to the embodiment shown in FIG. 2, the feedback circuit system is connected to the image sensor 7.
', a preamplifier circuit 8, a high-frequency component extraction circuit 10, a detection circuit 11 for detecting a slight fluctuation reference frequency component, a control circuit 12, a motor drive circuit 16, a motor 17, a gear 18, and an image sensor moving means 19. . In other words, since the feedback circuit system is configured separately from the lens system 1, there is no need for any movable parts in the lens system other than the zooming mechanism, and there is less influence on lens design, making it possible to realize an even simpler autofocus device. .

Above is the first part. In the embodiment shown in FIG. 2, since the lens or image sensor moved by the motor is small and light, the type of motor 17 is not particularly limited, but a pulse drive motor such as a stepping motor or an ultrasonic motor may be used. This is preferable because the inertia of the rotor is small and fine movements can be appropriately controlled.

In addition, since such a motor is a non-contact type, it has a long life and can be easily controlled in speed, making it possible to provide a more excellent autofocus device.

51i9 fl) to (3) show how the master lens group 6 or the image sensor 7 is moved while being slightly moved by a motor that performs pulse drive such as a stepping motor. This is an example in which the amount of movement from an infinite distance to a close distance is one step, that is, one pulse is used to move 1/n. The solid line shows the time t, after 1 cycle (Tf) micro-movement, 1
The broken line is an example of a system configured to move while repeating step changes.The broken line shows an example in which the system is configured to move while repeating three step changes after one cycle of slight movement. Figure 5 +21 (3
) shows an example of the timing of the pulse sent to the motor for each step; (2) corresponds to the operation shown by the broken line in FIG. 5 fl), and (3) corresponds to the operation shown by actual measurements. By arbitrarily setting the amount of shift in this way, the focusing time can be set arbitrarily. Note that the amount of fine movement in one cycle is the amount that changes the focus so much that it cannot be detected by the eye, but by increasing the number of drive pulses at a predetermined period (Tt) circle, the change characteristics as shown in a in Fig. 5 are obtained. If controlled, the amount of slight change can be set arbitrarily.

□ In the example described above, a case was described in which the master lens group or the image sensor is moved once and the lens is doubled at once, but although it will not be described in detail, the case can be applied to a compensator lens group (this can also be implemented in the same way).

When such an N1 example is used, the lens system can be made smaller and lighter because there is no need for a mechanism for hollowing out the front lens (front lens), which was required in the past. In addition, in the past, the macro 7 focus function was usually realized by moving the compensator lens group, but in this example, focusing up to the macro range can be easily achieved by moving the master lens group or the image sensor. Therefore, the macro focus mechanism becomes simple, and a compact, low-cost autofocus device can be realized. Furthermore, there are many advantages, such as the ability to implement macro autofocus functions that were previously impossible.

〔Effect of the invention〕

According to the present invention, without installing a special optical path length fine adjustment mechanism in addition to the autofocus focusing mechanism, the optical path length can be effectively finely adjusted, that is, the focus can be slightly changed to an imperceptible degree, and the focus can be adjusted to the same level. can have a focusing function. In other words, it is possible to realize a system that combines a focusing mechanism, which has conventionally been provided separately, and an optical path fine movement mechanism. An autofocus device can be easily configured.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram showing an embodiment of wJl of the present invention, Fig. 2 is a partial system configuration diagram of an embodiment of theory 2,
Fig. 3 is a configuration diagram showing an example of a general zoom lens Q used in a video camera, Fig. 4 is a graph showing the level characteristics of high frequency components obtained from an image sensor with respect to the focal position, and Fig. 8g5 shows the operation of the embodiment. It is an explanatory prisoner to explain. 1... Lens system, 2... Front lens group, 3... Variator lens group, 4... Compensator lens group,
5... Aperture device, 6... Master lens group, 7...
Image sensor, 8... Preamplifier circuit, 9... Camera circuit, 10... High frequency component signal extraction circuit, 11...
Reference frequency component signal detection circuit, 12...control circuit, 1
3... Fundamental frequency signal generation source, 14... Control signal generation circuit, 15... Synchronous detection circuit, 16... Motor drive circuit, 17... Motor. 1. Country 5: Mask Shin, ゛° shore, odor sentry, haze, 5th Country

Claims (1)

[Claims] 1. A T comprising a feedback circuit that extracts a high frequency component signal from a video signal obtained from an image sensor and adjusts a focusing mechanism so that the high frequency component signal is maximized.
In a TL image type autofocus device, a focusing mechanism is provided after a zoom lens system variator lens group, and the focusing mechanism is moved while slightly fluctuating at a predetermined reference frequency, and the fine fluctuation component of the reference frequency is detected from the high frequency component. An autofocus device for a video camera, characterized in that the focusing mechanism is driven by a motor so as to detect a signal, detect the polarity and amplitude of the detection signal, and adjust the focus. 2. The autofocus of a video camera according to claim 1, wherein the focusing mechanism moves all or a part of the master lens group while making slight fluctuations at a reference frequency to adjust the focus. Device. 3. The autofocus device for a video camera according to claim 1, wherein the focusing mechanism moves and focuses the image sensor while making slight fluctuations at a reference frequency. 4. The autofocus device for a video camera according to claim 1, wherein the focusing mechanism moves all or a part of the compensator lens group with slight fluctuations at a reference frequency to adjust the focus. . 5. The above autofocus mechanism uses a stepping motor,
Alternatively, the autofocus device for a video camera according to any one of claims 1 to 4 is characterized in that the position is controlled by a motor driven by a pulse signal, such as an ultrasonic motor.