JPS5842444B2 - Focal plane detection device for optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focal plane detection device for an optical system, and particularly to a device for detecting a focal plane by relatively vibrating the focal plane of an optical system and the light receiving surface of a photoelectric element in the optical axis direction. .

It has already been proposed to vibrate a photoelectric element in the optical axis direction of an optical system and detect the focal plane position of the optical system based on the output of the photoelectric element at that time.

As shown in FIG. 1, when the photoelectric element matches the focal plane position at position C due to the above-mentioned vibration of the photoelectric element, the element output becomes maximum, and as the element shifts forward or backward from the focal plane position, the output gradually decreases.

The method described above compares the photoelectric element outputs A and B before and after the vibration center of the photoelectric element as shown in Fig. 1, and when the values are equal, the vibration center coincides with the focal plane position C, so the focal plane is It detects surfaces.

However, this method assumes that the element output curve is symmetrical with respect to the focal plane position C, as shown by the solid line in Figure 1, but in reality, in many optical systems, the focal plane position C is symmetrical, as shown by the dotted line. It is symmetrical only near the surface position, and becomes asymmetrical when moving away from there.

Therefore, in order to accurately detect the focal position, it is necessary to reduce the vibration amplitude of the photoelectric element so that the symmetry is maintained.

However, if this is done, the element output representing the deviation from the focal plane becomes small, and if the photoelectric element is far away from the focal plane, it becomes impossible to obtain an output with a small vibration amplitude. .

An object of the present invention is to provide an optical focal plane detection device having a wide range of focal plane detection and sufficient detection accuracy.

The present invention vibrates the light-receiving surface or the focal plane largely in the optical axis direction when the light-receiving surface of the photoelectric element is largely deviated from the focal plane of the optical system, and when the misalignment between the light-receiving surface and the focal plane becomes small, This reduces the vibration amplitude.

In FIG. 2, a photoelectric element 2 is supported by a vibrator 3 near the focal plane of an objective lens 1 so that it can vibrate in the optical axis direction and in a direction perpendicular to the optical axis.

The oscillator 5 generates a sinusoidal drive signal g having a frequency f1 as shown in FIG. 4g.

This drive signal g is applied to an automatic amplitude controller (Automa), which will be described later.
tic amplitude control) 6
The signal is sent to the driver 7 via the oscillator 7, which activates the vibrator 3 to vibrate the photoelectric element 2 in the optical axis direction at a frequency f1.

Further, the second oscillator 8 generates a second sine wave drive signal with a frequency f2 larger than the frequency f1, and based on this, the second driver 9 operates the vibrator 3 to move the photoelectric element 2 in a direction perpendicular to the optical axis. Then, rotate and vibrate at a frequency f2.

With such a configuration, when the photoelectric element 2 is vibrating with an amplitude l in the optical axis direction behind the focal plane position 10 of the objective lens 1 as shown in FIG. The alternating current output of the photoelectric element 2 due to rotational vibration in a plane perpendicular to the axis occurs when it is closest to the focal plane 10, that is, at position 2a.
It is maximum when .

This is shown in FIG. At the peak point on the (-1-) side of the sine waveform of the drive signal g, the photoelectric element 2 reaches the nearest position 2a.At the peak point on the → side, the photoelectric element 2 reaches the focal plane 1.
Since it reaches the farthest position 2b farthest from 0, Fig. 4 I
As shown in (a), the AC output of the photoelectric element 2 reaches its maximum amplitude at the time of this positive peak.

In FIG. 4I, a, it is assumed that when the photoelectric element 2 reaches the far right side from the position 2a, the optical image formed by the lens 1 becomes sufficiently blurred on the photoelectric element 2, and no AC output is generated.

In addition, when the photoelectric element 2 is vibrating to the left of the focal plane 10 as shown in FIG. At the peak of the photoelectric element 2
produces an AC output with maximum amplitude.

When the vibration center of the photoelectric element 2 coincides with the focal plane 10 as shown in FIG. 2 generates an AC output with maximum amplitude, as shown in (a) of FIG. 4.

The AC output of such a photoelectric element 2 is as shown in FIG.
The signal is amplified by a preamplifier 11 and an AC amplifier 12, detected by a detector 13, synchronously detected by a synchronous detector 14 using a reference signal of frequency f1 from 5, and smoothed by a low-pass filter 15.

The output waveforms of each circuit at this time are shown in FIGS.
The case of H will be explained separately with reference to FIG.

When the focal plane 10 is in front of the center of vibration of the photoelectric element 2, as shown in Fig. 3 (■), that is, in the case of front focus, the AC output of the photoelectric element 2 shown in a of Fig. 4 I is transmitted to the amplifier. The waveform is amplified by 11 and 12, becomes C, is detected, becomes d, is synchronously detected, and is smoothed to become output e of 15.

Similarly, in the case of rear focus in Figure 3 ■ and focusing in Figure 3 ■
The output a has the waveforms shown in Figures 1 and 2, c, d, and e, respectively.

As is clear from the above, the outputs of the low-pass filter 15 are positive, negative, and zero during front focus, rear focus, and in-focus, respectively, and have values that are approximately compared to the amount of deviation of the photoelectric element 2 with respect to the focal plane.

Therefore, by sending the output of the low-pass filter 15 to the display 16, the focal plane position, that is, front focus, rear focus, and focus can be displayed.

Next, the absolute value of the output of the low-pass filter 15 is taken by the absolute value circuit 17.

This is shown in Figure 4f.

Therefore, this absolute value output f has a value that is approximately proportional to the distance between the focal plane and the photoelectric element, regardless of front focus or rear focus.

The output f of the absolute value circuit 1T is input to the automatic amplitude controller 6 via an adder 18, which will be described later.

The automatic amplitude controller 6 adjusts the amplitude of the output g of the oscillator 5 to the adder 1.
Since the output of the automatic amplitude controller 6 is converted into an amplitude approximately proportional to the output of the automatic amplitude controller 6, the output of the automatic amplitude controller 6 is large when the front and back are in focus, and becomes small when in focus, as shown in the fourth diagram.

Therefore, the photoelectric element 2 is vibrated with an amplitude approximately proportional to the absolute value of the amount of deviation from the focal plane.

In this way, the photoelectric element 2 is vibrated with a large amplitude when it is largely deviated from the focal plane, and with a smaller amplitude as it approaches the focal plane.

Note that when the switch 21 for starting focal plane detection is closed, the one-jit multivibrator 20 supplies a large bias signal for a certain short time and then a very small bias signal to the adder 18.

This bias signal is passed to the absolute value circuit 17 by the adder 18.
The photoelectric element 2 is vibrated with a large amplitude at the start of focal plane detection.

Therefore, the detectable range of the focal plane is expanded, and even if the photoelectric element 2 is located far away from the focal plane at the time of starting detection, detection is possible.

Then, after the predetermined period of time has elapsed, a small bias signal is supplied, but this small bias signal is
Even if the output of 2 becomes zero, it works to vibrate 2 with a small amplitude.

Of course, automatic focusing can be achieved by inputting the output of 15 to the servo drive system 22 and thereby moving 1 in the optical axis direction.

Next, a second embodiment will be described with reference to FIG. 5, in which the oscillator 5 and automatic amplitude controller 6 of the first embodiment are replaced with voltage-controlled oscillators.

voltage controlled oscillator
ed oscillator) 24 is controlled by the output of the adder 18 related to the amount of deviation of the photoelectric element 2 from the focal plane, and when the amount of deviation is large and the output of the adder 18 increases, the voltage controlled oscillator 24 lowers the frequency. When the output becomes smaller, a higher frequency drive signal is generated.

Even if the vibrator 3, which is a mechanical system, is driven with a drive signal of the same amplitude, the amplitude decreases to an amplitude proportional to the square of the reciprocal of the frequency.

Therefore, when the amount of deviation is small, the photoelectric element 2 is driven at a higher frequency than when it is large, and its amplitude becomes smaller.

In the second embodiment, the vibration frequency of the photoelectric element increases as the vibration center approaches the focal plane, so the focal plane position can be detected in a shorter time than in the first embodiment. Can be executed.

In this example, the photoelectric element 2 was vibrated in the optical axis direction, but
Since the present invention is characterized by relatively vibrating the focal plane of the photoelectric element 2 and the objective lens 1 and making the vibration amplitude variable, the first step is to achieve this relative vibration. The configuration shown in FIG. 6 may also be used.

In FIG. 6, F is a film surface, 26 is a half mirror, and 128 is a lens.

30 is a holder for the lens 28, which is vibrated in the optical axis direction by a vibrator.

2 is a photoelectric element which is vibrated in a direction perpendicular to the optical axis by another vibrator.

With this configuration, when the holder 30 vibrates, the focal plane of the objective lens 1 vibrates in the optical axis direction with respect to the photoelectric element 2.

In the above explanation, it is assumed that the vibration amplitude of the photoelectric element 2 is approximately proportional to the amount of deviation of the photoelectric element with respect to the focal plane, but it does not necessarily have to be proportional, and as the amount of deviation increases,
The vibration amplitude may be increased.

In addition, in this embodiment, the vibration amplitude is continuously changed in response to changes in the amount of deviation, but the amount of deviation is divided into a plurality of ranges, and a certain amount of vibration is changed for the amount of deviation within a certain range. amplitude, and other vibration amplitudes for deviations within other ranges.
They may be made to correspond to each other.

[Brief explanation of drawings]

FIG. 1 is a characteristic curve diagram showing the photoelectric element output with respect to the photoelectric element position, FIG. 2 is a block diagram for explaining the first embodiment of the optical system focus detection device according to the present invention, and FIG. A diagram showing the positional relationship with the objective lens, FIG. 4 is a waveform diagram showing that the photoelectric element generates different photoelectric outputs depending on the position where it is placed, and FIG. 5 is for explaining the second embodiment of the present invention. FIG. 6 is a block diagram showing a specific configuration of the vibration amplitude means.

Claims (1)

[Scope of Claims] 1. A light-receiving surface of a photoelectric element disposed near a focal plane of an optical system and a focal plane of the optical system are relatively vibrated in the optical axis direction of the optical system, so that the focal plane and the light-receiving surface are A device for detecting a focal plane of an optical system based on the photoelectric element output related to a distance between surfaces, comprising: a vibration means for relatively vibrating the light receiving surface and the focal plane; a vibration amplitude of the vibration means is A focal point of an optical system characterized by comprising a control means for controlling the vibrating means based on the output of the photoelectric element so that the vibrating means is wide when the distance between the two surfaces is large (and is small when the distance is small) Surface detection device. 2. The focal plane detection device for an optical system according to claim 1, wherein the vibrating means further vibrates the photoelectric element in a direction perpendicular to the optical axis. 3. In the focal plane detection device for an optical system according to claim 2, the detection device further includes a detector for detecting the output of the photoelectric element and a synchronous detector, and the synchronous detector detects the output of the vibrating means. It is characterized in that the output of the detector is synchronously detected using a signal with a period equal to the vibration period in the optical axis direction as a reference signal. 4. The focal point of the optical system according to any one of claims 1 to 3. The surface detection device is characterized in that the control means includes a forcing means for forcibly increasing the vibration amplitude of the vibration means in the optical axis direction temporarily at the start of focal plane detection.