JPS60242414A - Automatic focus controller - Google Patents

Abstract

PURPOSE:To perform speedy focusing control without unnecessary range finding operation by setting a lens at a position of over-focal length when a subject position is extremely at distance and a lens position is at distance. CONSTITUTION:When the lens position is at a distant side and the subject position is extremely at distance, the output of a lens position detecting circuit 2 is large and the quantity of light incident on photodetecting elements 8 and 9 is small. The output of a summing amplifier 20 is small and a comparator 22 generates an H-level output. The output of an AND gate 69 goes up to the level H and the output of a monostable multivibrator 70 is held at the level H for a specific time. The output of an OR gate 64 goes up to the level H to turn a switch 65 on and a switch 18 off. A signal corresponding to a half of over focus distance from a summing amplifier 38 and a signal corresponding to a half of the signal of a lens position detecting circuit 2 are inputted to a differential amplifier 67, whose output drives an electric motor 1 to set the photographic lens at a position of over-focal length.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device used, for example, in a camera equipped with a zoom lens.

A camera that projects light onto a subject from a light projecting optical system and receives the reflected light by a light receiving optical system to perform focusing is disclosed, for example, in Japanese Patent Application Laid-open No. 78327/1983. Although it is desirable for automatic focus adjustment to be performed in a short time in this type of camera, there is a problem in that taking the depth of field into consideration, it takes longer than necessary to perform highly accurate distance measurement.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjustment device that makes it possible to quickly perform necessary and sufficient focus adjustment by utilizing the hyperfocal distance of a photographic lens.

The gist of the present invention for achieving the above-mentioned object is to provide a means for roughly detecting the position of a subject using reflected light of projected light when the subject is extremely far away and the lens position is far away, and a photographing lens. means for detecting the current position of the
A means for determining a hyperfocal distance based on focal length information and aperture information of a photographic lens, a means for detecting a current lens position of the photographic lens, and a comparison between the hyperfocal distance and the lens position of the photographic lens. and means for focusing the photographing lens to a hyperfocal distance.

First, each component of the circuit configuration shown in FIG. 1 will be explained in order of reference numerals.

1: An electric motor that adjusts the focus of the photographic lens on the subject by moving the photographic lens (not shown) along the optical axis direction.

2: A lens position detection circuit composed of a brush and a resistor that are linked to the movement of the photographic lens in the optical axis direction. This detection circuit 2 is set so that the output voltage increases as the photographing lens moves from the close side to the infinity side.

3: A light-receiving lens for guiding the reflected light from the subject to a light-receiving element 8.9, which will be described later. This light-receiving lens 3 is linked to the movement of the photographic lens in the optical axis direction, and when the photographic lens is in focus on the subject, the projection light reflected by the subject is incident on the boundary between the light-receiving elements 8 and 9. is set to.

4: Clock pulse generation circuit that generates clock pulses.

5: Amplifier.

6: A light emitting element that repeatedly blinks when the clock pulse amplified by the amplifier 5 is input.

7: A projection lens for projecting the near-infrared light obtained from the light emitting element 6 toward the subject.

8 and 9: Light receiving element whose output changes depending on the amount of incident light. When the photographic lens is in focus due to the action of the light-receiving lens 3, the outputs of the light-receiving elements 8.9 are approximately equal.

10・11: By inputting the clock pulse from the clock pulse signal generation circuit 4, only the output of the light receiving element 8.9 when the light emitting element 6 is lit is connected to the capacitor 1.
2. Synchronous circuit that integrates each of 13.

12@13: Capacitor.

14: A differential amplifier that outputs the difference between the integral value of capacitor 12 and the integral value of capacitor 13.

15: A variable gain amplifier that can amplify the output of the differential amplifier 14 and change the gain at that time. This output voltage becomes the focus detection information 4 of the front focus φ of the photographing lens and the back focus. That is, the output of the variable gain amplifier 15 is positive when the front is in focus, approximately zero when the focus is on, and
In the case of rear focus, it is negative.

16: A latch circuit that latches the output of the differential amplifier 14 at a timing described later.

17: Adder.

18: Analog switch that is turned on when the output of the inverter 66 is at a high level (hereinafter referred to as H level).

19: Amplifier. The output voltage of the amplifier 19 controls the forward rotation, reverse rotation, stop, and driving speed of the electric motor I. That is, when this output is positive, the electric motor 1 rotates in the normal direction and moves the photographing lens toward infinity. When it is negative, the electric motor 1 reverses and moves the photographing lens to the close side. If the value is substantially zero, the electric motor 1 is stopped. Further, the driving speed of the electric motor 1 changes depending on the magnitude of the output voltage of this amplifier 19,
The photographic lens is moved faster as the blur becomes larger.

20: Summing amplifier that adds the integral values of capacitors 12 and 13.

21a to 21c: voltage dividing resistors for setting reference levels of comparators 22 and 23, which will be described later. These resistors 21
The connection point of a and 21b is the inverting input of the comparator 23,
The connection point between the resistors 21b and 21c, which has a voltage 'lower than the voltage at the connection point between the resistors 21a and 21b, is connected to the non-inverting input of the comparator 22.

22/23: Comparator. The output of the summing amplifier 20 is connected to the non-inverting input of the comparator 23. Therefore, the outputs of comparators 22 and 23 are sent to summing amplifier 20.
When the output of is higher than the voltage level at the connection point of the voltage dividing resistors 21a and 21b, the comparator 23 becomes H level and the comparator 22 becomes low level (hereinafter referred to as L level),
When the output of the summing amplifier 20 is between the voltage levels at the connection point of the resistors 21a and 21b, both comparators 22 and 23 are at L level, and the output of the summing amplifier 20 is between the voltage levels at the connection point of the resistors 21a and 21b.
comparator 23 when the voltage level is lower than the voltage level at the connection point of
is at L level, and comparator 22 is at H level.

24: Two-man power or gate.

25@27: When the output of the OR gate 24 is inverted from L level to H level, its Q output temporarily becomes H level.
A monostable multibibreak.

26: 3-man power or gate. The single power is connected to the Q output of the monostable multivibrator 25.

28/29 An analog switch that is turned on when the output of the NOR gate 26 becomes H level. By turning on these switches 28.29, capacitor 12.1
3 is reset and stops the integration of the output of the synchronization circuit 10.11 30: Set-reset flip-flop. Its S input is connected to the Q output of the monostable multivibrator 33, and its R input is connected to the output of the OR gate 26. Furthermore, the flip-flop 30 is set by the output of a power-up clear circuit (not shown) at the start of power supply to the entire circuit.

31/32: Frequency dividing circuit. The frequency dividing circuit 31 changes the frequency dividing ratio according to the output of the A/D converter 39. Frequency divider circuit 3
1.32 are each reset when the output of the OR gate 26 becomes H level. The frequency dividing circuit 32 further divides the frequency of the output of the frequency dividing circuit 31, and the output becomes H level at each predetermined time.

33: OK-) When the output of 26 is inverted from H level to L level, the Q output becomes H level ≠ 4 times, a monostable multi-vibration break.

34: Two-man power AND gate that inputs the clock pulse from the clock pulse generation circuit 35 to the frequency dividing circuit 31 when the Q output of the monostable multivibrator 30 is at H level.

35: Clock pulse generation circuit.

36φ37=variable voltage divider. The variable voltage divider 36 outputs a higher level depending on the focal length of the photographing lens at longer focal lengths, and the variable voltage divider 37 outputs a higher level as the aperture value signal at the time of photographing approaches the aperture value.

38: A summing amplifier RPa that adds the outputs of the variable voltage dividers 36 and 37 and outputs 1/2 of the hyperfocal distance signal. 39: Converts the analog output of the summing amplifier 38 into a digital signal.

40: An inverting amplifier that converts the signal of the summing amplifier 20 to a higher level as the signal becomes lower.

41: A differential amplifier in which the output of the inverting amplifier 40 is connected to a non-inverting input, and the output of the lens position detection circuit 2 is connected to an inverting input.

42: A variable gain amplifier that changes the gain depending on the output of the summing amplifier 38 and amplifies the output of the inverting amplifier 41.

43.46: Comparator.

44a*44b*45a-45b: voltage dividing resistor.

49: Two-man power or gate. The outputs of comparators 43 and 46 are connected. Its output is connected to an AND gate 56 via an AND gate 50 and an inverter 55.

50-56: 2 man power and gate. The input power is connected to the output of the frequency divider circuit 31.

51: Monostable multipibrator whose Q output is once inverted to H level and Q output to L level when the output of AND gate 50 is inverted from L level to H level. Its Q output is connected to the output of the OR gate 26 and also to the clear terminal of the monostable multi/stable 27.

52: D latch circuit in which the output of the comparator 46 is connected to the 01 human power, and the output of the comparator 43 is connected to the 02 human power. This D latch circuit 52 latches each input of D1 and D2 when the Q output of the monostable multivibrator 51 becomes H level, and is reset when the Q output becomes H level.

In addition, the 01 and Q2 outputs are sent to the amplifier 53 and the inverting amplifier 5.
The signal is outputted to the adder 17 via 4.

53: Amplifier.

54: Inverting amplifier.

55: Inverter.

57: Set-reset flip-flop. Its R input is the output of the comparator 23, and its S input is the AND gate 56.
connected to the output of Further, this free flip-flop 57 is reset by the output of a power-up clear circuit (not shown) at the start of power supply to the entire circuit.

58: 2 input AND gate. The Q output of the set-reset flip-flop 57.27 is connected to the input terminal, and its output is connected to the output of the OR gate 26.

59: Comparator for comparing the output of the lens position detection circuit 2 and the output of the summing amplifier 38. The output of the position detection circuit 2 is connected to the non-inverting input, and the output of the summing amplifier 38 is connected to the inverting input.

60: A comparator that compares the output of the adder 17 with the voltage level determined by the voltage dividing resistors 61a and 61b. The output of the adder 17 is connected to the non-inverting input, and the voltage dividing resistors 61a, 61
The connection point b is connected to the inverting input.

61a and 61b = voltage dividing resistor.

63: 2 input AND gate. Its input is connected to the output of comparator 59.60.

64: 2-input OR gate. When the output of the AND gate 63 or the monostable multi-occurrence circuit 70 becomes H level, the output becomes H level and turns on the analog switch 65. Also, when the output is at L level, the inverter 66
The analog switch 18 is turned on via the .

65: Analog switch.

66: Inverter.

67: A differential amplifier in which the output of the lens position detection circuit 2, which is halved by the voltage dividing resistors 68a and 68b, is connected to the inverting input, and the output of the summing amplifier 38 is connected to the non-inverting input, and its output is connected to the analog switch 65. via amplifier 19
connected to.

68a/68b: Voltage dividing resistor.

69: 2 input AND gate.

70: The outputs of the comparator 22 and frequency divider circuit 32 are both H
A monostable multivibrator whose Q output temporarily becomes H level when the output of AND gate 69 changes from L level to H level.

Roughly speaking, the circuit operation in FIG. 1 is based on the interlocking relationship between the motor 1, the lens position detection circuit 2, and the light receiving lens 4, so that the light emitting element 6 emits light via the amplifier 5 based on the output of the pulse generation circuit 4. Light is projected onto the subject through the light projecting lens 7, and the reflected light is transmitted through the light receiving lens 3 to the light receiving elements 8.9.
It receives light and performs automatic focusing operation based on predetermined calculation processing.

That is, the photoelectric outputs of the light receiving elements 8 and 9 are respectively transmitted to the synchronous circuit 1.
0 and ll, only the reflected light synchronized with the projected light flux is integrated by the capacitors 12 and 13, the output difference is amplified by the differential amplifier 14 and the variable gain amplifier 15, and the latch circuit 16 is configured to latch the output. through the adder 17 and the analog switch 18, and the motor 1 by the adder 19.
drive. In this way, the output of the light receiving element 8.9 is balanced via the light receiving lens 3 which is linked to the photographing lens, thereby performing automatic focus adjustment.

Now, to explain the circuit operation of FIG. 1 in more detail, it can be divided into the following eight modes depending on the subject position and the photographing lens position. Note that the figure numbers indicate timing charts to which each mode corresponds.

Operation Subject position Lens position mode l Very far Far side Fig. 2 Mode 2 Very far Close Fig. 3 Mode 3 Far Far side Fig. 4 Mode 4 Far Close Fig. 3 Mode 5 Near Far side Fig. 3 Mode 6 Near Close-up side Fig. 5 Mode 7 Close-up Far side Fig. 6 Mode 8 Close-up, Close-up side Fig. 6 In mode 1, focus the photographing lens to the hyperfocal distance, and in mode 2, mode 4-mode 5. In mode 3, the photographing lens is roughly driven, and in mode 3, an alternating drive method is used in which control of the electric motor l and distance measuring operation are alternately performed.
In the case of mode 6, fist mode 7, and mode 8, a parallel drive system is used in which control of the electric motor 1 and distance measuring operation are performed concurrently.

(1) In Mode 1 When power is input, the light emitting element 6 starts blinking due to the operation of the clock pulse generation circuit 4. Also, the set-reset flip-flop 30 is set, and its Q output is the second
As shown in the figure, it becomes H level at time t1, turns on the gate of the AND gate 34, and clock pulse generation circuit 3
5 is counted by a frequency dividing circuit 31. When the count value of the frequency dividing circuit 31 reaches this value, its output becomes H level as shown in FIG. 2 and is output to the AND gates 50 and 56.

In this mode 1, since the lens position is on the far side, the output of the lens position detection circuit 2 is large. In addition, since the subject position is extremely far away, the amount of light incident on the light receiving element 8.9 is small, the output of the summing amplifier 2o is small, the output of the inverting amplifier 40 is large, and the two inputs to the differential amplifier 41 are There is no large difference, therefore, the output of the differential amplifier 41 is small, the outputs of the comparators 43 and 46 are at L level, the OR gate 49 is at L level, and the output of inverter 55 is at H level.
level. The output of the AND gate 56 becomes H level, and at the timing when the frequency divider circuit 31 becomes H level, the set/reset flip-flop 57 is set as shown in FIG.
Set.

Furthermore, in the comparator 22, the output from the summing amplifier 20 is small and lower than the voltage level at the connection point between the resistors 21b and 21c, so the output becomes H level. On the other hand, after the output of the frequency divider circuit 31 becomes H level, the output of the frequency divider circuit 32 becomes H level after some time, so that the output of the AND gate 69 becomes H level, and the monostable multivibrator 70 As shown in FIG. 2, the output remains at H level for a certain period of time until time t2. The output of the multivibrator 70 causes the output of the OR gate 64 to go to H level, turning on the analog switch 65 and turning on the inverter 66 to turn off the analog switch 18. At this time, since the signal of 1/2 of the hyperfocal distance from the summing amplifier 38 by the variable voltage divider 36 and 37 and the 1/2 signal of the lens position detection circuit 2 are input to the differential amplifier 67, The output drives the motor 1 via an amplifier 19. And, in the photographic lens, a differential amplifier 67
In other words, the photographic lens is moved so that the output of the lens position detection circuit 2 becomes zero, so that the output of the lens position detection circuit 2 matches the output of the summing amplifier 38, and the photographic lens is positioned at the hyperfocal distance.

(2) Mode 2 - Mode 4/Mode 5 For example, in mode 2, the lens position is close, so the output of the lens position detection circuit 2 is small, the output of the differential amplifier 41 is large, and the OR gate 49 is It becomes H level. and,
The AND gate 50 is turned on, and as shown in FIG. 3, the Q output of the monostable multivibrator 51 is at the H level for a certain period of time, and the Q output is at the L level for a certain period of time. Due to this Q output, D
The latch circuit 52 is latched, and the output of the comparator 43 outputting an H level is the output Q2 of the latch circuit 52.
, the motor 1 is controlled via the amplifier 53 and the adder 17.

In the case of Mode 2, Mode 4, and Mode 5, since the subject position and the lens position are extremely far apart, accurate focusing operation via the differential amplifier 14 is not performed.
Rough driving is performed by the output of the summing amplifier 20.

(3) Mode 3 In this case, both the subject position and the lens position are far away, so the output of the differential amplifier 41 is small, the output of the OR gate 49 is at L level, the output of AND gate 56 is at H level, and the output of the AND gate 56 is at H level. As shown in FIG. 4, the 2-lip flop 57 is set and its Q output becomes H level. When the subject position is far away, the output of the summing amplifier 20 is connected to the resistor 21.
The potential is between the potential at the connection point between a and 21b and the potential at the connection point between the resistors 21b and 21c, and the outputs of the comparators 22 and 23 are both at L level. In this state, as shown in FIG. 4, when the output of the frequency dividing circuit 32 becomes H level, the output of the output circuit 24 becomes H level, and the output of the monostable multivibrator 27 becomes H level. At the same time, the output of the multivibrator 25 also becomes H level, but as shown in FIG. 4, the multivibrator 27 maintains the H level for a longer time than the multivibrator 25. This multi/hay break 2
The latch circuit 16 is latched by the output of the variable gain amplifier 15. The motor 1 is driven by the output, that is, the focus error signal. Further, while the output of the OR gate 26 is at H level via the AND gate 58 and the output of the multivibrator 27 is at H level,
Analog switches 28 and 29 are turned on and capacitor 12.
13 is discharged. Therefore, an alternating drive system is adopted in which the focusing operation and distance measuring operation by the electric motor 1 are performed alternately.

(4) Mode 6/Mode 7φMode 8 In the case of mode 6, the output of the summing amplifier 20 is small until the output of the frequency dividing circuit 31 reaches the H level, and the comparator 23 is at the H level.
level is not reached. However, the output of the comparator 23 becomes H level before the output of the frequency dividing circuit 32 becomes H level. Here, since the subject position is close and the lens position is very close, when the outputs of both frequency dividing circuits 31 become H level, the output of the OR gate 49 becomes L level, and is passed through the inverter 55 and the AND gate 56 to the flip-flop. 5
7 is set. Then, when the output of the comparator 23 becomes H level just before time t3, the flip-flop 57 is reset and the AND gate 58 is turned off.

Then, the H level output of the comparator 23 makes the multivibrator 27 go to H level through the OR gate 24 and latches the latch circuit 16, so that the variable gain amplifier 1
The electric motor 1 is driven by the output of 5.

Also, the output of the OR gate 24 is connected to the multivibrator 25.
, the output of the multivibrator 25 becomes H level for a short time, and the analog switch 28.29 turns on via the OR gate 26, causing the capacitor 12.1 to turn on.
3 is instantaneously discharged. The capacitors 12 and 13 immediately start storing power, that is, start distance measuring operation. That is, a parallel drive system is employed in which the focusing operation of the motor l via the latch circuit 16 and the distance measuring operation are performed simultaneously.

In addition, in the case of mode 7 and mode 8, since the subject position is close, the rise of the output of the summing amplifier 20 is large as shown in FIG. 6, and the time t4 of one cycle is shorter than the similar time t3 in FIG. It's also small. In this case as well, the operation is almost the same as in the case of FIG. 5, and a parallel driving method is employed.

The present invention is particularly limited to Mode I among the above-mentioned modes, and when the subject position is extremely far away and the lens position is far away, distance measurement at a distance greater than the hyperfocal distance based on the required accuracy is prohibited. Since it is not necessary and requires less movement of the lens position, focusing is performed at the hyperfocal distance using the depth of field of the photographing lens, and the current lens position signal of the photographing lens and the zoom position and The hyperfocal distance, which is a required accuracy signal based on the aperture value, is compared, and if the focus is at a distance equal to or more than half the hyperfocal distance, the photographing lens is focused to the hyperfocal distance.

In other words, the hyperfocal distance is the closest distance from infinity to the depth of field, and is determined by the focal length and aperture of the photographic lens. If you focus on the hyperfocal distance, the depth of field will range from half the hyperfocal distance to infinity.

In this embodiment, the summing amplifier 38 outputs a signal corresponding to distance information that is half the hyperfocal distance. for example,
If the calculated hyperfocal distance is 10 m, half of it is 5.
Information corresponding to m is output from the summing amplifier 38, and the negative input terminal of the comparator 59 and the differential amplifier 67
Information about 5m is input to the plus input terminal of. Furthermore, if the current lens position information output from the lens position detection section 2 corresponds to 7 m, for example, the information corresponding to 7 m is sent to the plus input terminal of the comparator 59 and also to the minus terminal of the differential amplifier 67. However, the input to the negative terminal of the differential amplifier 67 is set to 1/2 potential by the voltage dividing resistor 68, 69, that is, it is input as information of 3.5 m. Therefore, the input at the positive input terminal of the comparator 59 is large, and an H level is output, turning the switch 65 on and the switch 18 off. The differential amplifier 67 outputs the difference between 5 m and 3.5 m, and the lens position detection section An electric motor 1 is driven via an amplifier 19 so that the output of 2 has a hyperfocal distance of 10 m.

In addition, although most of the processing in the example was performed using analog methods,
It goes without saying that A/D conversion may be implemented by software using a microprocessor or the like.

As explained above, the automatic focus adjustment device according to the present invention has
Utilizing the depth of field provided by the photographic lens, when the subject is extremely far away and the lens position is far away, by focusing at the hyperfocal distance, you can quickly eliminate unnecessary distance measurement operations. There is an advantage that focus adjustment can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an automatic focusing device according to the present invention, and FIGS. 2 to 6 are time charts of driving methods according to each mode. 1 is a motor, 2 is a lens position detection unit, 3 is a light receiving lens, 18.65 is a switch, 36.37 is a variable voltage divider,
38 is a summing amplifier, 59 is a comparator, 67 is a differential amplifier, and 68.69 is a voltage dividing resistor. Patent applicant: Canon Co., Ltd. Figure 2 Figure 3 tl t'2 Figure 4 tl t2 Figure 5 Figure 6

Claims (1)

[Claims] 1. When the subject is extremely far away and the lens position is far away, means for roughly detecting the subject position by reflected light of projected light and detecting the current position of the photographing lens. means for determining the hyperfocal distance based on focal length information and aperture information of the photographic lens; means for detecting the current lens position of the photographic lens; and means for determining the hyperfocal distance and the lens position of the photographic lens. and means for focusing the photographic lens to a hyperfocal distance. 2. The automatic focus adjustment device according to claim 1, wherein the means for roughly detecting the object distance is based on the magnitude of the output of a light receiving element that receives reflected light of the projected light.