JPS5917403B2 - Camera with automatic focus adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an automatic focus adjustment device for a camera that allows focus adjustment of a photographic lens to be performed with high precision.

The scanning mechanism of the photoelectric distance measuring device is operated once in the forward and reverse directions, and the maximum value or minimum value (this value is selected according to the circuit design) of the photoelectric signals detected in the forward direction scanning stage is determined. It is.

) is stored in the circuit, and when a photoelectric signal approximately equal to the maximum or minimum value stored in the forward scanning stage comes in the backward scanning stage, the detection signal causes the photographing lens in the moving state to adjust the focus. Cameras are known that have an automatic focusing device of the stop type. In such an automatic focusing device for a camera, the slower the scanning speed of the scanning mechanism of the photoelectric distance measuring device, the better the focusing accuracy is. because,
Normally, the photographing lens moves in conjunction with a scanning mechanism, etc., and its movement is stopped by the detection signal of the maximum value (or minimum 5 values) from the distance measuring device. Naturally, there is some time lag before the camera (for example, a magnet) works and stops the movement of the photographic lens, so if the scanning speed of the scanning mechanism is slow, the lens will stop moving.
This is because the moving speed of the photographing lens linked to this decreases, and the deviation of the stopping position of the photographing lens is reduced. Also,
When the main illumination light of the subject is a fluorescent lamp, the discharge cycle of the fluorescent lamp is superimposed on the output from the light receiving element, which shifts the position of the maximum value (or minimum value) and distorts the detection signal. This will cause an error in the transmission time. and,
When locking a photographic lens by inserting a claw-like member into a sawtooth-like stop, the photographic lens will be set at the same location no matter what part of the valley of one sawtooth the claw-like member enters. However, in a system where the stop position of the photographic lens is determined in stages, if the moving speed of the photographic lens is slowed down as in the present invention, the detection signal can be transmitted by the fluorescent light as described above. The time error is sufficiently small that it falls within the valley of one sawtooth;
In other words, it also has the effect of being able to lock the photographing lens at the position determined by the detection signal. Furthermore, since the photographic lens is quite heavy, no matter how it is actuated (spring, motor, etc.), a large amount of inertia is placed on the power source. As a result, the operation becomes unstable, and even when the photographic lens is stopped, the problem of photographic blur due to vibration etc. occurs. According to the present invention, since the moving speed of the photographic lens can be slowed down during the focus setting stage of the photographic lens, the above-mentioned drawbacks can be solved. As mentioned above, it can be said that the accuracy of focus adjustment increases as the scanning speed of the scanning mechanism of the photoelectric distance measuring device and the speed of the photographic lens linked to its operation are slower. This means that the shutter will be released.
There is naturally a limit to the time required for automatic focus adjustment.

It is considered from experience to be about 100 ms. In other words, an ordinary photographer can press the shirt release button and
The camera is held in the shooting state for about 00ms, but if any longer than that, the camera is considered to have finished shooting.
Of course, if focus adjustment requires more time than this, the shutter opportunity will be missed and the desired photograph will not be taken. Therefore, there is a limit that the scanning speed of the scanning mechanism of the photoelectric distance measuring device cannot be lowered below a certain level. The present invention aims to overcome the above-mentioned limitations and to provide an automatic focusing device with higher precision.For this purpose, the scanning speed in the reverse direction of the photoelectric distance measuring device is made slower than the scanning speed in the forward direction. This makes effective use of the time limit. The present invention will be explained below based on the drawings. FIG. 1 is a schematic diagram showing an example of a mechanism for forward and reverse scanning of a scanning optical path, FIG. 2 is an operating circuit diagram of an automatic focus adjustment device, and FIG. 3 is a characteristic diagram of a subject position detection signal.

In the figure, 1 is a rotating mirror, 2 is a fixed mirror 3 is a mirror prism, 4 and 5 are lenses, and 6 and 7 are light receiving elements each consisting of a photodiode array. The optical path guided from the rotating mirror 1 to the light receiving element 6 via the mirror prism 3 and the lens 4 is a scanning optical path.
Reciprocating scanning in the forward and reverse directions is performed by the left and right reciprocating rotations of the . Mirror prism 3 and lens 5 from fixed mirror 2
The optical path guided to the light-receiving element 7 via is a fixed optical path. Although the illustrated embodiment shows a distance measuring device using a scanning optical path and a fixed optical path, the present invention can also be carried out even if both optical paths are scanning optical paths, and the scanning mechanism may include a prism or lens instead of using a mirror. You can also use A specific example of the means for rotating the rotating mirror 1 left and right is as shown in FIG.
By pressing a release button (not shown), the control member 8 is unlocked and moved to the left by the spring 9, causing the rotating mirror 1 to be rotated left and right by the cam 8a via the cam link 10. Cam 8a rotates with rotating mirror 1 on the first steeply sloped cam surface.
is rapidly rotated to the right, and then the rotating mirror 1 is slowly rotated to the left by a cam surface with a gentle slope during return. On the other hand, the control member 8 is provided with a lens drive section 8b, and a driven pin 11a implanted in the lens barrel 11 is engaged with the drive section 8b, so that when the control member 8 moves to the left, , while the rotating mirror 1 is being rapidly rotated clockwise, the lens drive section 8b does not act on the driven pin 11a, and when the rotating mirror 1 is rotated back, it engages with the driven pin 11a, and from that point on, the lens drive section 8b does not act on the driven pin 11a. 11b is moved in correspondence with the scanning rotation of the rotating mirror 1. Here, the movement of the lens 11b is caused by the driven pin 11a being engaged with the lens drive section 8b of the control member 8, and the lens 11b being moved accordingly. 1111111 moves, and the cam pin 11c installed in the lens barrel slides in the cam groove of the cam sleeve 12 fixedly provided to the camera body. The control member 8 also includes an enable switch 1.
3, the switching cam 8c closes the enable switch 13 when the control member 8 returns and rotates the rotating mirror 1, and continues to maintain the closed state. keep it. Furthermore, the control member 8
is provided with a stopper 8d, and when the rotary mirror 1 enters return rotation and the enable switch 13 is closed, the outputs from the light received by the light receiving elements 6 and 7 are the most coincident, that is, the distance measuring device When the object position is grasped again while scanning in the reverse direction of the scanning optical path, a solenoid stop signal is sent to the solenoid 14, the locking pawl 15 engages with the stop portion 8d, and the control member 8
Therefore, both the rotary mirror 1 and the lens 11b are stopped with the subject position known. Thereupon, a known means (not shown) is activated to release the shutter and photograph with accurate distance setting.
FIG. 2 shows an example of an operating circuit in which the distance measuring device grasps the position of the object and activates the solenoid while scanning the scanning optical path in the reverse direction. As mentioned above, the enable switch 13 is open while the rotary mirror 1 is rapidly rotating forward, that is, while the scanning optical path is scanning in the forward direction, and therefore the light receiving elements 6 and 7 between them are open. The outputs of are compared and passed through an adder SA, a maximum value detection circuit PD, an amplifier AMPl, and a differentiation circuit to provide a focus position detection signal VD, which signal VD is cut off by a switch 13 to operate a solenoid 14. There isn't. The light-receiving elements 6 and 7 are each composed of a photodiode array, and the optical images of the subject on the light-receiving elements 6 and 7 are calculated as photoelectric comparison signals by an adder SA, and the outputs of the light-receiving elements 6 and 7 are Correlation signals V showing voltages so high that they match overall. It is output as O from the adder SA. The maximum value detection circuit PD is a circuit that extracts the maximum value signals V and D from this correlation signal VcO, and passes its own output signal through a rectifier D to detect the detection voltage VDT obtained by charging the comedy/length C1 and the correlation signal VcO. When the voltages are compared and the voltage of CO is higher than VDT, the voltage of VcO is output, and the voltage of VcO is equal to VD.
When the voltage is lower than the voltage of T, the maximum value signal PD is output by outputting a low level voltage. amplifier AMP
l waveform-shapes the maximum value signal VpO to form an automatic focus detection signal VAF.

A differentiating circuit including a capacitor C2 and a resistor R3 converts this automatic focus detection signal VAF into a focus position detection signal VD indicating a pulsed focus position. FIG. 3 shows the state of each signal corresponding to the position being scanned by the rotating mirror 1, and the range of the forward scanning time t1 is the state during the rapid forward rotation of the rotating mirror 1, and the state during the reverse scanning time. T2 range is rotating mirror 1
It is in a state where it is slowly rotating back and forth. As shown in the figure, the maximum value of the correlation signal VcO often appears, and one-way scanning tends to generate an erroneous lens stop signal. Therefore, a forward and reverse scanning method is used.
When the rotating mirror 1 enters slow backward rotation after husking paddy, the rotary switch 13 is closed, and the outputs of the light receiving elements 6 and 7 are compared and a correlation signal is output from the adder SA. VcO is compared with the maximum voltage that charged the capacitor C1 during the previous forward rotation of the rotating mirror in the maximum value detection circuit PD, and the voltage is the same as that of the correlation signal only while the voltage of the correlation signal VcO is equal to or higher than the maximum voltage. It is converted into maximum value signals V and O that take the following values. The reason why the correlation signal voltage VcO exceeds the maximum voltage during the forward rotation of the rotary mirror is because the attenuation of the charge in the capacitor C1 is extremely small, so the correlation signal voltage VcO does not exceed the maximum voltage when the distance measuring device grasps the subject position. Therefore, the maximum value signal VPD indicates when the distance measuring device has accurately determined the subject position. Then, the maximum value signal VPD is shaped by the amplifier AMP1 to become an automatic focus detection signal VAF, which is further converted into a focus position detection signal D by a differentiation circuit, and is inputted to the amplifier AMP2 through the enable switch 13. Amplifier AMP2 receives focus position detection signal V. is converted into a step signal in which only the rising edge of the pulse in the positive direction is used, and the step signal is input to the solenoid 14 as a solenoid stop signal to control the lens barrel directly as shown in Figure 2 or as shown in Figure 1. It is stopped indirectly via a member. In addition, S in the figure is the film surface,
R1 to R3 in FIG. 2 are resistors. As described above, the present invention provides that the accuracy of the focus detection signal used by the distance measuring device to grasp the subject position by scanning in the forward and reverse directions of the scanning optical path is determined by the time distribution of the forward and reverse scans, that is, the speed ratio of the forward and reverse directions. Since this effect is almost unaffected, the reverse scanning speed and the corresponding lens movement speed are slowed down to ensure that the lens is accurately stopped at the focal position based on a highly accurate focus detection signal. It is something.

Therefore, according to the present invention, accurate automatic focus adjustment can be performed without increasing the total forward and reverse scanning time of the range finder, that is, without losing the shutter chance. In the present invention, the distance measuring device may scan from an infinite distance to the closest distance and return to an infinite distance, or vice versa. A circuit configuration in which a single configuration is used instead of multiple combined elements as in the embodiment, or a focus position detection signal is determined by minimum value detection and a solenoid is activated using the fall of the signal. may be changed.
Furthermore, the scanning mechanism of the photoelectric distance measuring device does not need to have its optical system separate from the photographing lens, and the present invention can be easily applied to a single-lens reflex camera by using a TTL type scanning mechanism and changing the moving speed of the photographing lens. It can also be applied to

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a mechanism for forward and reverse scanning of a scanning optical path, FIG. 2 is an operating circuit diagram of an automatic focusing device, and FIG. 3 is a characteristic diagram of a subject position detection signal. 1: rotating mirror, 2: fixed mirror, 3: mirror prism, 4, 5: lens, 6, 7: light receiving element, 8: control member,
8a: Cam, 8b: Lens drive section, 8c: Switching cam, 8d: Stopping section, 10: Cam link, 11: Lens lock 11a: Driven pin, 11b: Lens, 12: Cam sleeve, 13: Enable switch , 14: Solenoid, 15: Locking claw, SA: Addition unit, PD: Maximum value detection circuit, AMPl, AMP2: Amplifier, Cl, C2: Capacitor 1, R1 to R3: Resistor, S: Film surface, T, :
Forward scanning time, T2: Reverse scanning time, VcO: Correlation signal, VDT: Detection voltage, VPD: Maximum value signal, VA
F: automatic focus detection signal, VD: focus position detection signal.

Claims (1)

[Claims] 1 Using a photoelectric distance measuring device having a pair of optical systems, first scan in the forward direction over the distance measurement range, store the signal value when the images of the pair of optical systems match, and then scan in the reverse direction. In a camera having an automatic focus adjustment device that stops a photographing lens in a moving state for focus adjustment using a detection signal when a signal value generated in a step reaches the stored signal value, A camera having an automatic focus adjustment device, characterized in that the scanning speed is slower than the scanning speed in the forward direction.