JPS591961B2 - automatic focus detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic focus detection device, in particular, which includes an imaging optical system and a light receiving means, so that the imaging position of the subject by the optical system is on the optical axis, and is centered on the planned imaging position. If it is within the set predetermined range, a predetermined correlation output is obtained from the light receiving means according to the amount of difference (defocus amount) between the image forming position and the planned image forming position, and this output is used to determine the defocus amount and the object to be examined. This invention relates to a device that can calculate the distance to.

5 Conventionally, the head section of the distance detecting device is servo-controlled by the output of the distance detecting device so that the distance between the head section and the object to be measured becomes a predetermined value, and when the head section finally comes to rest, the distance between the head section and the object to be measured becomes a predetermined value. The amount of movement from the reference position is measured with a length measuring device such as an encoder, and the distance to the subject is measured based on the measured 10 value, that is, the amount of defocus.

According to this method, in order to maintain the distance between the head and the object to be crushed at a predetermined value, the head, which has a considerable mass, is servo-controlled, which requires advanced technology that takes into account the inertial force of the head. This requires 15 complex mechanisms. The head part is the first
As shown in the figure, when the head part is stationary at a position a certain distance away from the subject, it is stopped by a damping movement centered on the stationary position P due to servo control, so the head part remains completely stationary. The major drawback is that it takes time to measure the situation.

This is due to the fact that the imaging position must be driven to the expected imaging position. SUMMARY OF THE INVENTION An object of the present invention is to provide a novel automatic 25-dynamic focus detection device that solves the drawbacks of the conventional example.

In order to achieve such an object, in the present invention, if the imaging position of the subject by the imaging optical system is on the optical axis and within a predetermined range centered on the expected imaging position, Focusing on the fact that the amount of difference from the image position, that is, the differential 30 orcus amount, has a predetermined correlation, especially a linear relationship, with the output of the light receiving means, the image forming The method is characterized by calculating the amount of defocus from the expected imaging position. That is, the present invention is characterized in that the amount of defocus is determined without driving the image forming position 35 to the expected image forming position. Furthermore, the present invention is characterized in that when the image forming position is not within the predetermined range, the image forming position is moved within the predetermined range and the amount of movement thereof is also detected.

According to the present invention, if the imaging position of the subject by the imaging optical system is within the predetermined range, the imaging position is not finally driven to the expected imaging position as in the conventional case, but the imaging position is moved to that position. The amount of defocus can be determined from the correlation function between the direct output and the amount of defocus while the object remains stationary or the control is released during movement, and based on this, the distance to the object can be quickly detected.

Further, when the image forming position is not within the predetermined range, it is moved to an arbitrary position that is detected to be within the predetermined range by a known drive means (for example, a servo drive), the amount of movement at that time is detected, and at the same time Calculate the amount of defocus from the output value of the light receiving means at that time using a correlation function with the amount of defocus,
By combining both and detecting the distance to the subject based on this, it becomes possible to arbitrarily expand the distance detection range.

According to the present invention, the amount of deviation from the predetermined distance to the subject is calculated by adding it to the above-described amount of defocus or further to the amount of movement, and this is calculated as the distance to the predetermined subject. By adding this, it is possible to measure the absolute distance to the subject.

It is also possible to use the amount of defocus or a value added to the amount of movement as the amount of displacement of the focusing optical system to the in-focus position.

Hereinafter, an embodiment using servo drive as the drive means will be described in detail.

In this embodiment, a known variable focal length imaging optical system is used to discriminate the servo drive direction.

In Fig. 2, reference numeral 1 denotes the head part of the distance detection device, and inside the head part 1 there is an objective lens 2, and a focal length mirror whose focal length is centered at f and changes between f+Δf1 and f-ΔF2. 3. A pinhole plate 5 placed at a fixed position from the focal mirror and having a hole 4 at its center, and a light receiver 6 that receives the light beam passing through the hole 4 of the pinhole plate 5.
Contains.

The focal length mirror 3 changes its focal length in response to a signal from the oscillation circuit 101. The signal from the light-receiving element 6 is amplified by AC in an AC amplifier circuit 102 and sent to the oscillation circuit 1.
The signal is input to the synchronous rectifier circuit 103 together with the signal from 01 and synchronously rectified. When the distance between the subject 7 and the head section 1 is D, the output E from the synchronous rectifier circuit 103 is set to zero. Such electrical processing circuits (101, 102
, 103) is already a widely used method. In general, the present invention is applicable when the difference (defocus amount) d between the subject 7 and the head section 1 is smaller than the distance D,
Attention was paid to the fact that a correlation, especially a linear relationship as shown in FIG. 3, holds between the amount of defocus d and the output E from the synchronous rectifier circuit 103. In FIG. 3, the vertical axis represents the output E, and the horizontal axis represents the amount of defocus d. When the amount of defocus d is between -d1 and D2, the output E and the amount of defocus d have a linear relationship. When the defocus amount d is -d1, the output E becomes -E1, and when d is D2, the output E becomes E2. At this time, conversely, the value of output E is -E1
and E2, from this output E to the differential focus amount d
can lead to. Therefore, the output E from the synchronous rectifier circuit
If it is detected that E is between -E1 and E2, the amount of differential focus d can be determined from the value of the output E at that time, and the amount of movement of the head section 1 and the amount of differential focus d can be calculated by adding the amount of movement of the head section 1 and the amount of differential focus d to the value of D. The distance to the specimen is determined.

Therefore, when using this detection circuit, there is no need to wait until the head section driven by the servo mechanism comes to rest. An electrical processing circuit using the principle of the present invention described above is shown in 1 in FIG.
04 to 109, and a flowchart of this circuit is shown in FIG. Hereinafter, the circuits 104 to 109 described above will be explained with reference to FIG.

Reference numeral 104 denotes a control completion detection circuit which detects whether the output E from the synchronous rectification circuit 103 is within a region -E, ≦E≦E2, which has a linear relationship with the above-mentioned defocus amount d.

This region -E1≦E≦E2 indicates a value specific to the detection system, and the value of ElFE2 must be determined by examining the relationship between the end synchronous rectifier circuit E and the amount of defocus d.

When the control detection circuit 104 determines that the value of E is not between -E1 and E2, the output E is input to the servo/drive circuit 105.

In the servo drive circuit 105, depending on whether the input value E is positive or negative, the servo drive device drives the head unit 1 so as to move it closer to the subject 7, or vice versa. Drive away from the vehicle. By repeating such servo driving, when the value of E enters a region having a linear relationship with the amount of defocus d, the signal from the control detection circuit is transmitted to the distance conversion circuit 106 and the length measuring device 107.
to go into. The distance conversion circuit 106 is E, which is E, ≦E≦E2.
This circuit calculates the defocus amount d from the value of . On the other hand, the length measuring device 107 detects the head 1 by the signal from the control detection circuit.
An encoder or the like is used in a device that measures the amount of deviation δ from the standard position from the subject, that is, the distance D between the subject 7 and the head portion 1. Defocus amount d from the distance conversion circuit 106 and length measuring device 107
The amount of deviation δ is input to the addition circuit 108, and is added to the above-described constant distance D between the subject 7 and the head section 1. The signal from the adder circuit 108 is input to a display circuit 109, and the distance between the subject and the head section 1 is displayed. In the above embodiment, an automatic distance measuring method using a focusable optical system has been described, but as is clear from the above points, the present invention can be applied to an automatic distance measuring method using any optical system.

That is, when the output from the synchronous rectifier circuit is E1 and the defocus amount is d, there is a relationship of E-φ(d) between -d1≦d≦D2, and φ(-d1)=-E1, φ(D2 )E2(E
1<E2), then E in the range of d - D, , D2 - d
It can be used in distance detection circuits designed to be E1, E2 and E2. As described above, according to the present invention, it is possible to detect the amount of differential focus at a position before the final imaging position of the object by the imaging optical system without driving it to the expected imaging position, and when using servo control as the movement mechanism. In addition, it becomes possible to free or stop control near the planned imaging position, simplifying the apparatus and shortening the detection time. Furthermore, according to the present invention, even if the image formation position is not within a predetermined range centered on the expected image formation position, distance detection is performed by first moving it within the predetermined range using an encoder or the like and adding the amount of movement. This also has the effect of arbitrarily expanding the distance detection range, that is, the dynamic range.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing characteristics of a servo control device, FIG. 2 is a diagram showing an embodiment of the present invention, and FIGS. 3 and 4 are diagrams for explaining the present invention. DESCRIPTION OF SYMBOLS 1... Head part, 3... Focal mirror, 7... Subject, 101... Oscillation circuit, 102... AC amplifier circuit, 103... Synchronous rectifier circuit, 104... Control Completion detection circuit, 105... Servo drive circuit, 106...
Distance conversion circuit, 107... Length measuring device, 108... Addition circuit, 109... Display circuit.

Claims (1)

[Claims] 1. an imaging optical system, a light receiving means that outputs a signal according to the imaging state of the subject by the imaging optical system, and a position where the imaging position of the subject by the imaging optical system is on the optical axis, and the planned imaging a determining means for determining whether or not the position is within a predetermined range from a predetermined imaging plane using a signal output from the light receiving means; a calculation means for calculating the amount of defocus between the imaging position and the planned imaging plane when it is determined that the imaging position of the subject by the imaging optical system is within the range; an automatic focus detection device comprising: a drive means for driving at least a part of the imaging optical system when it is determined that the imaging optical system is not within a predetermined range.