JPH0534648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in automatic focus control devices for cameras and the like.

Conventionally, many automatic focus control devices of this type have been proposed and put into practical use. However, when considering photography under conditions where the imaging magnification is close to 1:1, the direction of movement of the lens and the direction of movement of the imaging position are the same at less than 1:1 magnification, but at higher magnifications, they are different. It will be in the opposite direction. That is, the direction of movement of the lens and the direction of movement of the imaging position are reversed from the point where the photographing magnification becomes equal to the same magnification. Therefore,
Conventional automatic focus control devices change the direction of the detected focusing error using positive and negative signals and move the lens using the positive and negative signals.In conventional automatic focus control devices, automatic focus control is performed only when the imaging magnification is less than 1x. Therefore, even if an automatic focus control device is used when photographing at life-size or higher magnification, the lens moves in a direction that further increases the focusing error.

In order to improve this drawback, an automatic focus control device may be considered which is provided with a means for manually reversing the moving direction of the lens, such as a reversing switch. However, with these methods, it is easy to select the direction of lens movement only when the photographing magnification is clearly less than or greater than 1:1, and when the photographing distance is approximately appropriate; When photographing nearby, it is difficult to make effective selections. Furthermore, when photographing is performed by varying the distance to the subject while experimenting with framing and subject composition, as in very general photography, the operation is cumbersome and the effectiveness is low.

An object of the present invention is to solve the above-mentioned problems, and to enable correct automatic focus control operation regardless of whether the photographing magnification is less than 1x or more than 1x, without requiring manual switching operations. An object of the present invention is to provide an automatic focus control device that can perform the following steps.

In order to achieve this object, the present invention provides a focus detection circuit that repeatedly performs focus detection operations and outputs a focus detection signal representing the amount and direction of focus deviation with respect to the in-focus state for each focus detection operation; When the detection signal indicates front focus, the photographic lens is
and, when the focus detection signal indicates rear focus, drive the photographing lens in a second direction opposite to the first direction by an amount corresponding to the shift amount. In an automatic focus control device equipped with a drive circuit, the focus detection signal output from the focus detection circuit is latched until the next focus detection signal is input, and the latch contents are updated every time the focus detection signal is input. The latch circuit compares the focus detection signal of the latch circuit with the focus detection signal that is input next to the latch circuit, and determines that the deviation amount and direction of both signals are the same, and that the deviation of the focus detection signal of the latch circuit is A comparator circuit that generates an output when the shift amount of the focus detection signal input to the next latch circuit is greater than the shift amount of the focus detection signal input to the next latch circuit, and a comparator circuit that generates an output while the focus detection operation is performed multiple times. a determination circuit that generates an output when the camera is in focus; and a determination circuit that generates an output when the camera is in focus; The present invention is characterized in that it is provided with a switching circuit that switches the photographing lens to a state in which the photographing lens is driven in the first direction when the rear focus is indicated.

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

The drawings illustrate an embodiment of the invention. Reference numeral 1 denotes a focus detection device, which is a known device that is provided at or near the planned focal plane and outputs a positive or negative signal depending on the deviation of the focal point from the planned focal plane, that is, a focusing error. In this focusing error signal, for example, a positive signal represents a front focus signal, and a negative signal represents a rear focus signal. Reference numeral 2 denotes a lens drive motor that drives the photographic lens in either direction in response to a focus error signal from the focus detection device 1 to eliminate a focus error. A clock generator 3 outputs clock pulses of a predetermined period to sample and hold circuits 4 and 5 and a counter 6. The sample and hold circuit 4 outputs a focusing error signal for each clock pulse output from the clock generator 3 to a line 7, and at the same time, the sample and hold circuit 5 outputs a focusing error signal at the time of the previous clock pulse generation to a line 8. do. The T flip-flop 9 is a non-inverting amplifier 10.
and the inverting amplifier 11. When the T flip-flop 9 is on the set side, that is, when the output of the terminal Q is high level and the output of the terminal is low level, the non-inverting amplifier 10 is selected.
A signal having the same sign as that output on line 7 is input to lens drive motor 2. On the other hand, when the T flip-flop 9 is on the reset side, the inverting amplifier 11 is selected, and a signal obtained by inverting the sign of the signal output to the line 7 is input to the lens drive motor 2.

When photographing is continued under conditions where the photographing magnification is less than or greater than 100%, the direction of movement of the imaging position according to the driving direction of the lens does not always change. Therefore, the automatic focus control operation in this case is performed as follows. For example, when a positive signal is input to the lens drive motor 2, the lens is moved in the retracting direction, and when a negative signal is input, the lens is moved in the retracting direction. It is assumed that the signal is the front focus signal and the negative signal is the rear focus signal. When the photographing magnification is less than 1x, the moving direction of the lens and the moving direction of the imaging position are the same, so the T flip-flop 9 is held on the set side, the non-inverting amplifier 10 is selected, and the lens drive motor 2 is A signal having the same sign as the signal output from the focus detection device 1 is input to the . That is, when the focus detection device 1 outputs a positive signal that is a front focus signal, the lens drive motor 2 receives the positive signal and moves the lens in the retracting direction to perform a focusing operation, and performs focus detection. When the device 1 outputs a negative signal that is a rear focus signal, the lens drive motor 2 receives the negative signal and moves the lens in the extending direction to perform a focusing operation. Conversely, when the imaging magnification exceeds 1x, the direction of movement of the lens and the direction of movement of the imaging position are opposite, so the T flip-flop 9 is held on the reset side and the inverting amplifier 11 is selected.
A signal whose sign is inverted from the signal output from the focus detection device 1 is input to the lens drive motor 2 . That is, when the focus detection device 1 outputs a positive signal that is a front focus signal, the lens drive motor 2 receives a negative signal and moves the lens in the extending direction to perform a focusing operation, and the focus detection device When the lens drive motor 2 outputs a negative signal which is a rear focus signal, the lens drive motor 2 receives a positive signal and moves the lens in the focusing direction to perform a focusing operation.

Next, the operation when the photographing magnification changes from less than the same magnification to more than the same magnification, or from more than the same magnification to less than the same magnification will be described. The former case will be explained below as an example. In this case, the T flip-flop 9 initially holds the set side, and when the photographing magnification exceeds 1x in this state, for example, when the focus detection device 1 outputs a positive signal that is a front focus signal, the lens drive motor A positive signal is input to 2 to move the lens in the retraction direction. As a result, the imaging position moves to the front, which further increases the focusing error. At this time, a signal representing the focusing error at the previous clock pulse from the clock generator 3 is input to the non-inverting input terminal of the comparator 12.
3 and 14, it is detected that this signal is a positive and significant value, and a high level signal is output to the AND gate 15. Furthermore, the comparator 16 receives a signal representing the current focusing error from the sample and hold circuit 4 at its non-inverting input terminal, and a signal representing the previous focusing error from the sample and hold circuit 5 at its inverting input terminal. Therefore, the comparator 16 detects that the current focusing error has become larger in the positive direction than the previous focusing error, and outputs a high level signal to the AND gate 15. Therefore, the output of AND gate 15 becomes high level, and the output of NOR gate 17 becomes low level. As a result, the counter 6 is released from reset and starts counting the clock pulses input from the clock generator 3. When the counter 6 counts a predetermined number of clock pulses, that is, when the focus condition is not improved even after performing the lens driving operation a predetermined number of times, the counter 6 outputs a cancel signal to the T flip-flop 9. As a result, the T flip-flop, which has been on the set side, is switched to the reset side, and the moving direction of the lens corresponding to the positive and negative signals output from the focus detection device 1 is reversed. That is, the automatic focus control operation is changed from one corresponding to a photographing magnification less than 1x to one corresponding to a photographing magnification exceeding 100%, and the automatic focus control operation is performed correctly.

The same goes for the case where the focus detection device 1 outputs a negative signal that is the back focus signal. is a significant value, and the comparator 21 detects that the current focusing error has become larger in the negative direction than the previous focusing error, so the AND gate 22
The output of NOR gate 17 becomes high level, and the output of NOR gate 17 becomes low level. The following is exactly the same as when the focus detection device 1 outputs a positive signal.

The above explanation describes the operation when the shooting magnification changes from less than 1x to more than 1x, but conversely, the same applies when the magnification changes from more than 1x to less than 1x. in this case,
Initially, the non-inverting amplifier 11 was selected, but it was detected that the focus condition was not improved even after performing lens driving operations a predetermined number of times, and the inverting amplifier 10 was selected. A control action is performed.

Although the embodiment shown in the drawings is based on an analog circuit, the present invention can be similarly applied to an automatic focus control device using a well-known digital circuit. Furthermore, in this embodiment, it is assumed that the focus state is not improved even after performing the lens driving operation a predetermined number of times, but for example, if the interval at which the lens driving operation is performed changes depending on the brightness, , it is also possible to detect that the focal state is not improved even if the lens driving operation is performed for a predetermined period of time, regardless of the changing interval.

In the illustrated embodiment, the lens drive motor 2, the non-inverting amplifier 10, and the inverting amplifier 11 correspond to the drive circuit of the present invention, the sample and hold circuit 5 corresponds to a latch circuit, the comparators 16 and 21 correspond to a comparison circuit, and the counter 6 corresponds to a determination circuit, and T flip-flop 9 corresponds to a switching circuit.

As explained above, according to the present invention, the latch latches the focus detection signal output from the focus detection circuit until the next focus detection signal is input, and updates the latch contents each time the focus detection signal is input. The circuit compares the focus detection signal of the latch circuit with the focus detection signal that is then input to the latch circuit, and determines that the amount and direction of deviation of both signals are the same, and the amount of deviation of the focus detection signal of the latch circuit. A comparator circuit that generates an output when the shift amount of the focus detection signal that is input next to the latch circuit is greater than a determination circuit that generates an output when the
In response to the output of the determination circuit, the drive circuit's response to the focus detection signal is such that when the focus detection signal indicates front focus, the photographing lens is driven in a second direction opposite to the previous direction, while rear focus is Since we have provided a switching circuit that switches the photographic lens to the first direction, which is the opposite of the previous direction, when the photographic magnification is less than 100%, there is no need for manual switching operations. Correct automatic focus control operation can be performed in any case of double or more.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Focus detection device, 2... Lens drive motor, 3... Clock generator, 4, 5... Sample hold circuit, 6... Counter, 9... T flip-flop, 10... Non-inverting amplifier, 11... ...Inverting amplifier, 12, 16, 18, 21... Comparator, 13, 14, 19, 20... Resistor, 15,
22...And Gate, 17...Noah Gate.

Claims (1)

[Scope of Claims] 1. A focus detection circuit that repeatedly performs focus detection operations and outputs a focus detection signal representing the amount and direction of focus deviation with respect to the in-focus state for each focus detection operation, When the focus detection signal indicates rear focus, the photographing lens is driven in a first direction by an amount corresponding to the shift amount, and when the focus detection signal indicates rear focus, the photographing lens is moved in a second direction opposite to the first direction. In an automatic focus control device comprising a drive circuit that drives an amount corresponding to the amount of deviation, the focus detection signal output from the focus detection circuit is latched until the next focus detection signal is input, and the focus detection signal is A latch circuit that updates the latch contents each time the latch circuit is input, compares the focus detection signal of the latch circuit with the focus detection signal that will be input next to the latch circuit, and determines that the deviation amount and direction of both signals are the same, and a comparator circuit that generates an output when the shift amount of the focus detection signal input next to the latch circuit is greater than the shift amount of the focus detection signal of the latch circuit, and the output of the comparison circuit is a determination circuit that generates an output when a focus detection operation is being performed, and a response to a focus detection signal of the drive circuit in response to the output of the determination circuit, when the focus detection signal indicates front focus. 1. An automatic focus control device comprising: a switching circuit for driving the photographic lens in the second direction when the camera is in focus, and driving the photographic lens in the first direction when indicating rear focus;