JPH0363722B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for driving an autofocus lens that performs focus detection based on the contrast of a subject image. 2. Description of the Related Art Autofocus devices have been put to practical use in single-lens reflex cameras and the like, which utilize the principle that the contrast (difference between brightness and darkness) of a subject image formed by a photographic lens is maximized when in focus. However, while conventional autofocus devices based on the above-mentioned principle have the advantage of being able to measure distances (focus) regardless of the type of photographic lens, they are difficult to use when shooting subjects with low contrast or low brightness. This has the disadvantage that it is not possible to properly instruct the driving means of the photographing lens in the direction of movement of the photographic lens. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problem that focusing on a low-contrast object or a low-luminance object becomes uncertain. Therefore, in the present invention, the contrast distributions at positions equidistant in front and behind the focal plane where the subject image is formed are detected, the lens is moved until one of the contrast distributions shows a peak value, and then the lens is moved at both positions. The contrast values are compared and the lens is moved in the direction where they become equal. Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings. FIG. 1 conceptually shows a distance measuring optical system. In the same figure, the film surface 1 of the camera
The light splitter 2 placed in front of (planned focal plane)
A half mirror 2a that passes 1/2 of the light that has passed through the photographic lens 3 and reflects 1/2 downward, and a total reflection mirror 2b that directs the light reflected by the half mirror 2a toward the film surface 1. On the back side thereof, there is an optical sensor 3F that receives the transmitted light of the half mirror 2a, and the total reflection mirror 2.
An optical sensor 3R is attached to receive the reflected light of b. As mentioned above, the contrast value of the subject image formed by the photographic lens 3 is maximum at the in-focus position, so for example, when the film surface 1 is in focus as shown in the figure, 3
The contrast of the subject image at the positions F and 3R is slightly lower than that at the film surface 1. Since the sensors 3F and 3R are arranged at equal distances from the front and back of the film surface 1,
In this case, the contrast values at the installation positions of both sensors are equal. On the other hand, when the sensor 3F position is in focus, the contrast value at this position shows the peak value, and the contrast value at the other sensor 3R position decreases, and the sensor 3R position is out of focus. If they match, the above will be reversed. Therefore, the contrast distribution at the installation position of each of the sensors 3F and 3R is expressed by curves a and 2 in FIG.
It changes in the manner shown in b. The optical sensors 3F and 3R described above have a configuration in which a plurality of photoelectric conversion elements are arranged in a predetermined direction (perpendicular to the page), and in this embodiment, MOS, CCD,
A solid-state image sensor such as CID is used. The automatic focusing lens driving method according to the present invention detects the contrast distributions at the installation positions of the optical sensors 3F and 3R based on the output signals of the optical sensors 3F and 3R, until one of the contrast distributions shows a peak value. Move the photographic lens,
After this, the contrast values of each contrast distribution are compared and the photographic lens is moved in the direction where the contrast values become equal, thereby focusing on the film surface 1. Figure 3 shows how this method is carried out. An example of a device for this purpose is shown. In the figure, a distance measuring optical system 10 includes the light splitter 2 and optical sensors 3F and 3R shown in FIG. The constituent light receiving element arrays are scanned. Sample hold/contrast detection circuit 30
samples the different time-series photoelectric conversion signals obtained by scanning the optical sensors 3F and 3R during the "H" level period of the clock pulse, and holds them during the "L" level period. The function is to obtain a signal indicating the contrast value at the installation position of each sensor 3F, 3R based on the value of the photoelectric conversion signal for each bit. That is, after holding the value of the photoelectric conversion signal for each bit of each sensor 3F, 3R, the absolute value of the difference between the signal values of adjacent bits or the signal values of arbitrary bits is detected. The absolute value obtained in this way indicates the magnitude of the amount of light received between adjacent bits or arbitrary bits, that is, the contrast, and therefore indicates the sample hold/contrast.
The contrast detection circuit 30 connects each sensor 3F, 3
Based on the time-series photoelectric conversion signals outputted from R, contrast signals for the subject images formed on these sensors are detected and outputted in time-series. Next, an example of the sample and hold circuit will be explained based on FIG. This circuit consists of an operational amplifier 3 that functions as an emitter follower with a gain of 1.
1 and 32, an analog switch 33 interposed between these amplifiers 31 and 32, and a hold capacitor _C31 connected to the input terminal of the amplifier 32. If the time-series photoelectric conversion signals sequentially output from each light-receiving element of the sensor 3F or 3R are input to the amplifier 31, when the analog switch 33 is turned on by the timing clock, a charge corresponding to the value of the photoelectric conversion signal will be generated. is charged in the capacitor _C31 , and when the analog switch 33 is turned off, the charged charge is held. Therefore, at the output end of the amplifier 32, the held photoelectric conversion signal is outputted in time series. Note that as the analog switch 33, it is possible to apply an electronic switch element such as a transistor, junction FET, or MOS-FET. The peak hold circuit 40 connects the optical sensors 3F, 3
The peak value of the time series contrast signal output from the sample hold/contrast detection circuit 30 during one scanning period of R is held. The contrast hold circuit 50 serves to hold the peak values of the contrast signals for the optical sensors 3F and 3R that are output in time series from the peak hold circuit 40, respectively. The contrast peak detection circuit 60 detects contrast peak signals (hereinafter referred to as A contrast signal Ac and B contrast signal Bc) for each of the sensors 3F and 3R that are held in the hold circuit 50 every time the optical sensors 3F and 3R are scanned. )
Based on this, it is detected that these contrast signals have reached a maximum. Further, the focus logic circuit 70 forms a direction indicating signal, which will be described later, based on the A contrast signal Ac and the B contrast Bc, and the focus instruction circuit 80 also generates a direction display signal based on the output signal of the contrast peak detection circuit 60 and the focus logic. Based on the output signal of the circuit 70, etc.
It outputs a focus instruction signal that instructs the stopping or moving direction of the photographing lens 3. The specific configurations of the focus logic circuit 70 and the focus instruction circuit 80 of the contrast peak detection circuit 60 will be described below with reference to FIG. The contrast peak detection circuit 60 has a terminal T ₁
An amplifier 62 and an analog amplifier 62 to which the A contrast signal Ac inputted from the terminal _T2 is inputted via an analog switch 61a, and the B contrast signal Bc inputted from the terminal T2 is inputted via an analog switch 61b interlocked with the analog switch 61a. Contrasts C ₆₁ and C ₆₂ are respectively connected to the output terminal of this amplifier 62 via switches 63a and 63b, and amplifiers 64 and 65 are inputted with the terminal voltages of capacitors C ₆₁ and C ₆₂ , respectively. and a comparator 66 for comparing the output voltages of 65. Note that the analog switches 63a and 63b are operated in synchronization with the output pulses of the timing clock generator 20. Further, the amplifier 62, analog switches 63a and 63b, capacitors C ₆₁ and C ₆₂ , and amplifiers 64 and 65 constitute two peak hold circuits (see FIG. 4). Now focus instruction signal Sx= from focus instruction circuit 80
“0” and Sy=“1” are output, whereby a motor drive circuit 90 (to be described later) operates a lens moving motor 100 to move the photographing lens 3 from the short distance side to the infinity direction. When the analog switches 61a and 61b are closed and opened, respectively, as shown in the figure. When the photographing lens 3 is moved from the short distance side to the infinity direction, the A contrast signal Ac based on the output signal of the optical sensor 3F gradually increases from the short distance side as shown by the curve in FIG. After reaching a peak value, it drops again. The contrast peak detection circuit 60 detects that the A contrast signal Ac has reached its peak. That is, the A contrast signal Ac inputted from the terminal _T1 is held in the capacitor C61 via the switch 63a, and then this switch 63a is held in the capacitor _C61 .
A is opened and switch 63b is closed, and at the same time, the other capacitor C ₆₂ is held. In addition,
This series of operations always starts with the switch 63a, and after the hold of the switch 63b is completed and before the next operation starts, the charges stored in the capacitors C ₆₁ and C ₆₂ are discharged by a switch (not shown) and returned to the initial state. . Assuming that the hold value of capacitor C ₆₁ due to the above-mentioned hold operation is An and that of capacitor C ₆₂ as A _o+1 , the comparator 66 compares these hold values, and if An<A _o+1 , the signal is Sc＝“0” An＞
In the case of A _o+1 , a signal Sc="1" is output.
In Fig. 7, the relationship An _{<A o+1 indicates the state where the value of the A contrast signal Ac is increasing, and the relationship An>} A _o+1 indicates the state where the value of the same signal is decreasing. and therefore from An<A _o+1
This means that the A contrast signal reaches its peak at the time when it switches to An>A _o+1 . Note that the focus instruction signal Sx is sent from the focus instruction circuit 80.
When =1 and Sy=0 are output and the photographing lens 3 is moved from an infinity position to a short distance direction, the switch 61b is closed and the B contrast signal Bc is applied to the capacitors C ₆₁ and C ₆₂ . held,
The hold values Bn and B _o+1 of these capacitors are compared in the same manner as described above. and comparator 66
When the logic level at the output terminal of B changes from "0" to "1", the B capacitor signal Bc shown in FIG.
exhibits a peak value. On the other hand, the focusing logic circuit 70 compares the magnitudes of the A contrast signal Ac and the B contrast signal Bc input from the terminals _T1 and _T2 , and when the former is larger than the latter, a logic level "0" signal is output. The comparator 71 outputs a signal "0", and analog switches 72a, 72b, 72c, and 72d each enter the operating state shown in the figure when the comparator 71 outputs a signal "0". Now, if the A contrast signal Ac and the B contrast signal Bc are Ac>Bc, the A contrast signal Ac will be switched to switch 7.
2a, is applied to one input terminal of the differential amplifier 74 via the amplifier 73 and the resistor R ₇₁ , and the above-mentioned signal Bc is applied to the other input terminal of the differential amplifier 74 via the switch 72d, the amplifier 73' and the resistor R ₇₃ . added to the input end. On the contrary, each contrast signal Ac, Bc is Ac
<When the relationship is Bc, the comparator 71
Since the logic level of the output terminal becomes "1", each switch 72a to 72d is switched, thereby applying signals Ac and Bc to the other input terminal and one input terminal of the differential amplifier 74, respectively. . Therefore, the values of resistors R ₇₁ and R ₇₃ are set to R ₇₁ = R ₇₃ , and the resistance
Since the values of R ₇₂ and R ₇₄ are set to R ₇₂ =R ₇₄ , the differential amplifier 74 outputs the absolute value of the difference between the signals Ac and Bc |Ac-Bc|. A signal indicating this absolute value |Ac-Bc| is input to a window comparator 76 composed of operational amplifiers 75, 75' and resistors R ₇₅ and R ₇₆ . This window comparator 76 has an absolute value |Ac−
Bc | is the reference voltage Vth set by resistors R ₇₅ and R ₇₆
When the relationship is 0<|Ac-Bc|<Vth, the amplifiers 75 and 75' both act to output the signal "1", and when the relationship is |Ac-Bc|>Vth, the amplifier 75 outputs the signal The amplifier 75' functions to output a signal "0" and the amplifier 75' outputs a signal "1". Therefore,
When |Ac−Bc|<Vth and the output signal Sc of the comparator 66 of the contrast peak detection circuit 60 is “1”, a signal “0” is output from the NAND circuit 77, which causes the finder display section (not shown) to be output. The light emitting diode _D71 constituting the camera is turned on and the so-called in-focus state can be known. Also, the output signal Sc is “1”, |Ac−Bc|<Vth and Ac>
If Bc, the signal S _A = “0” from the NAND circuit 78
is output, thereby lighting up the light emitting diode _D72 , and the so-called front pin state can be known. In addition, under the same conditions as described above, when Ac<A _B , a signal S _B of "0" is output from the NAND circuit 78'.
is output, which lights up the light emitting diode _D73 , making it possible to know the so-called rear pin state. Next, the focus instruction circuit 80 will be explained based on FIG. 7. This circuit 80 receives the peak detection signal Sc output from the comparator 66 of the contrast peak detection circuit 60, the direction display signals S _A and _SB output from the NAND circuits 78 and 78', and the switches SW _N and SW. Based on the open/close signals _{S N} , S _F and S _AF of F and SW _AF (“1” when open, “0” when closed), the logical operations shown in the formula and table below are performed, and the flip-flop 81 and inverter 82
a to 82e, AND circuits 83a to 83e, and OR circuits 84a and 84b. Note that the mark X in the table below indicates that it may be either "1" or "0".

[Table] Note that the switch SW _N is closed when the photographic lens 3 is moved to the close distance position, and the switch SW _F is closed when the photographic lens 3 is moved to the infinity position. Furthermore, the switch SW _AF is
It is located on the lens side and is closed by manual operation. The motor drive circuit 90, as shown in FIG.
It has a configuration in which a lens driving motor 100 is connected between the connection points of the transistors Q ₁ and Q ₃ and the transistors Q ₂ and Q ₄ connected in series, and operates as follows. That is, the logic states of the signals Sx and Sy output from the direction indicating circuit 90 are "1" and "0", respectively.
When , transistors Q ₁ and Q ₄ conduct and motor 1
00 flows in the direction of the solid line arrow, thereby moving the lens 3 from the infinity direction to the short distance direction. Further, when the above-mentioned signals Sx and Sy are "0" and "1", respectively, the transistors Q ₂ and Q ₃ are conductive, and a current flows in the direction of the dashed arrow in the motor 100, thereby causing the photographing lens 3 to The object is moved in a long distance direction opposite to that described above. Note that when the signals Sx and Sy are "0" and "0", no current flows through the motor 100, so the photographing lens 3 stops. In the device of this embodiment, when the power is turned on, when the switch S _AF is not operated, that is, in the open state, the first truth in the table shown above holds, so that Sx, Sy becomes "1" and "0", and therefore the photographing lens 3 is moved toward a close distance. Then, when the photographing lens reaches close range, switch SW _N is closed, so the second truth in the table is established, and Sx and Sy become "0" and "0". .
In other words, the photographing lens 3 stops moving. Here, when switch SW _AF is closed, the third truth in the same table holds true, so Sx, Sy
becomes "0" and "1", and the photographing lens 3 is moved from close range to infinity. This shooting lens 3
As the A contrast signal Ac outputs from the contrast hold circuit 50 increases as shown in FIG. 6, the analog switch 61a shown in FIG. 5 is closed as shown in FIG. Therefore, the A contrast signal Ac is input to the contrast peak detection circuit 60. Note that at this time, A output from the hold circuit 50
Contrast signal Ac and Bcontrast signal Bc are
Since there is a relationship of Ac>Bc, the inverter 79 of the focusing logic circuit 70 outputs the signal "1", and the signal
The absolute value of the difference between Ac and Bc |Ac−Bc| is |Ac−Bc|
>Vth, the NAND circuit 77 of the same circuit 70 outputs a signal of "1". However, at this point, the comparator 6 of the contrast peak detection circuit 60
6 outputs the signal Sc="0", and the output of the NAND circuit 78 becomes "1", so the light emitting diode
D ₇₂ is in the off state. When the photographing lens 3 is further moved to the infinity side and the contrast signal Ac takes on a peak value,
Since the sixth truth in the above table holds true, the light emitting diode _D72 lights up and the photographing lens 3 is further moved toward infinity. Therefore, the A contrast signal Ac and the B contrast signal Bc are |Ac−Bc|
When the relationship becomes <Vth, a signal "0" is output from the NAND circuit 77 of the focusing logic circuit 70, so the fifth truth in the above table is established, and therefore the light emitting diode D ₇₂ is turned off. At the same time, the light emitting diode _D71 indicating the in-focus state is turned on, and at the same time, the movement of the photographing lens 3 is stopped. In this state, since the film surface 1 shown in FIG. 1 is in focus, a clear image of the subject can be photographed by operating a shutter (not shown). By the way, when the signal Sc="1" indicating the peak value of the contrast signal is output, the flip-flop 81 shown in FIG. 7 is set. Therefore, after the signal Sc becomes "1", even if the subject is moving, the photographing lens 3 follows the movement of the subject in a manner described later. In other words, when the object is brought into focus in front of the optical sensor 3F shown in FIG. If the focus is brought to the rear of position 4 shown in the figure due to the movement, the seventh truth in the table above holds true, and therefore the photographing lens 3 is moved in a short distance direction. Note that number 8 in the above table shows the truth when focusing at close range. Furthermore, if the switch SW _AF is opened, the flip-flop 81 is reset and the first and second truths in the above table are established in sequence.
The photographing lens 3 is automatically moved to a close distance position and stopped. Further, region b in FIG. 6 indicates a focusing region where the contrast signals Ac and Bc satisfy |Ac-Bc|<Vth, and at this time, the light emitting diode D ₇₁ for in-focus display is lit. In addition, in areas a and c in the figure, the above signals are Ac>Bc, |Ac−Bc|
＞Vth and Ac<Bc, |Ac ₋ Bc _| Each is lit. In the above embodiment, the taking lens 3 is moved from the close distance side to focus, but by slightly changing the logic shown in the table above, the taking lens 3 can be started from the infinite distance side. Of course, this is also possible, and in that case, the photographing lens 3 is extended based on the fourth truth in the above table. Further, in the above embodiment, the motor 100 is operated in an analog manner, but a pipe signal is used as a direction indicating signal, and thereby the motor 100 is operated in an analog manner.
0 may be driven intermittently. Furthermore, a speed control function is added to the focus instruction circuit 80, so that the photographic lens is fast-forwarded until a contrast peak is found, and after the peak is searched, that is, after the signal Sc becomes "1", the photographic lens is advanced. It is also possible to reduce the speed. In the present invention, the contrasts at positions equidistant in front and behind the focal plane are detected, the photographing lens is moved until one of the contrasts reaches its peak value, and then the photographing lens is moved in a direction where the intensities of both contrasts are equal. is being moved.
Therefore, the photographing lens can be accurately moved in the focusing direction even for a low-luminance subject or a low-contrast subject. Furthermore, by configuring as in the embodiment, the present invention can be effectively applied to moving subjects.

[Brief explanation of drawings]

Fig. 1 is a diagram conceptually showing the configuration and operating principle of the distance-measuring optical system, Fig. 2 is a graph illustrating the relationship between the amount of extension of the photographing lens and the contrast intensity, and Fig. 3 is the method of the present invention. Fig. 4 is a circuit diagram showing an example of the configuration of a sample and hold circuit, and Fig. 5 shows a specific configuration of a contrast peak detection circuit and a focusing logic circuit. The illustrated circuit diagram, FIG. 6, is a graph for explaining the operation of the device shown in FIG. 3, and FIG.
The figure is a logic circuit diagram illustrating a specific configuration of a focus instruction circuit, and FIG. 8 is a circuit diagram illustrating an example configuration of a motor drive circuit. 1...Film surface (planned focal plane), 3...Photographing lens, 3F...First optical sensor, 3R...Second
optical sensor, 30... sample hold/contrast detection circuit, 60... contrast peak detection circuit, 70... focusing logic circuit (arithmetic circuit), 8
0... Focus instruction circuit, 90... Motor drive circuit (drive means).

Claims (1)

[Scope of Claims] 1. Detecting the contrast distribution of the subject image at positions equidistant in front and behind the planned focal plane of the photographing lens, moving the photographing lens until one of the contrast distributions shows a peak value, and then A method for driving an autofocus lens, characterized by comparing contrast values at and moving a photographing lens in a direction where the contrast values become equal. 2. First and second optical sensors arranged at equal distances in front and back of the expected focal plane of the photographic lens and each comprising a plurality of photoelectric conversion elements arranged, and based on the optical signals output from each of the optical sensors. a contrast detection circuit that detects the contrast distribution of the subject image at the front and rear equidistant positions; a contrast peak detection circuit that detects the peak value of each contrast distribution obtained from the contrast detection circuit; and a contrast peak detection circuit that detects the peak value of each contrast distribution obtained from the contrast detection circuit; a calculation circuit that calculates a difference; and a contrast peak detection circuit that moves the photographing lens in a predetermined direction until it detects a peak value, and after detecting the peak value, the contrast peak detection circuit moves the photographic lens in a predetermined direction based on the calculation result of the calculation circuit. 1. A drive device for an autofocus lens, comprising: a focus instruction circuit that outputs an instruction signal for moving the photographing lens in a direction in which contrast values at equidistant positions are equalized. 3. A patent characterized in that the focus instruction circuit is provided with a driving means for driving a photographing lens located at an arbitrary position to an infinite distance position or a close distance position according to a logical state determined by contrast signals obtained from both contrast distributions. An autofocus lens driving device according to claim 2. 4. The focus instruction circuit displays an instruction signal in accordance with the logic state determined by the contrast signals obtained from both contrast distributions in the viewfinder, and clearly indicates the in-focus state of the photographing lens and the direction of movement of the photographing lens. 3. The automatic focusing lens driving device according to claim 2, wherein the driving device functions as a display signal for a display unit.