JPS597911A - Focusing detector - Google Patents

Abstract

PURPOSE:To detect focusing precisely with simple constitution by allowing a photoelectric converting element consisting of a light position detector to receive an object image formed of pieces of lumnous flux passed through different paths of an optical system, and detecting the relative position relation of the image. CONSTITUTION:The light position detector consists of a high-resistance Si substrate 10, P type resistance laye 11, n<-1> layer 12, and electrodes 13, 14 and 15, and when light L is incident to the P type resistance layer 11, currents IA and IB corresponding to the incidence position are obtained at the electrodes 14 and 15 by lateral photo effect to find the center of gravity of the image. An iris splitter 35 makes light transmission parts 35a, 35b, 35c and 35d transparent successively and a two-dimensional light position detector 37 detects a vertical and a horizontal direction through electrodes 38 and 39, and 40 and 41. Noises are removed through a filter of which a center frequency is equal to the operating frequency of the iris splitter 35 to obtain a composite output, i.e. the sum of absolute values or squares of respective components.

Description

[Detailed description of the invention]

0 Generally, when the pupil of an optical system is divided into seven parts, when the pupil is out of focus, each divided light beam moves in a different direction 'i'''
This principle is explained in detail in Figure 1. In Figure 1 (a), 1 is an imaging lens, and 2 is a lens located in front of the imaging lens 1 near the pupil. The light shielding plate 3 has an aperture 2a with a diameter of
is imaged, but when it is out of focus, it corresponds to the front bin and rear bin (
1, 2 images Q1 and 1 are placed at positions shifted in opposite directions in the direction perpendicular to the light 111O. Q2 is formed on the image plane 3. FIG. 1(b) shows the case where the aperture 2a of the light shielding plate 2 is moved to the opposite side with respect to the optical axis O, and when focusing, the image plane 3
An image Q' is formed above, but when out of focus, the front bin and
flA' (J+, Q'2) corresponding to the rear bin
is formed on the image plane 3. Therefore, if the aperture of the light plate 2 is moved, for example, from the position shown in FIG. 1(a) to the position shown in FIG. In the case of the front bin, the image moves from Ql to the position of Q(

[7 Also, in the case of the rear bin, the image moves from Qi> to the position Q5. For example, there is a device that uses this principle to detect the entire focus, such as the one disclosed in Japanese Patent Publication No. 56-1 3929. Direction VC1ga1. For example, in the case of an image with intensity changes only in the vertical direction (・C), it was only possible to detect the focused sound. This is because a one-dimensional solid-state image sensor is used as a photodetector to output dust information k4<?y.Therefore, a two-dimensional solid-state image sensor is used and two It is possible to detect the phase shift of a two-dimensional image by performing pupil classification in two dimensions, but the amount of calculation in the two-dimensional case is larger than that in the one-dimensional case (because the amount of calculation increases by the square of the ), and the actual situation is difficult.Furthermore, even in the case of − dimensions, analog or digital calculations such as correlation are indispensable in order to know the relative position of the image. It was necessary to make corrections because the difference in light weight caused by factors such as The purpose of this VA is to provide a complete focus detection device with a simple configuration and high accuracy that enables full elliptical focusing by simply controlling the focusing mechanism so that the output of the detector is reduced. The optical position detector will be explained with reference to Fig. 2. Fig. 2 shows the lateral φ photo effect (Lateral φ photo effect) on the semiconductor surface.
Photo. The basic structure of an optical position detector using f8ffect)i is shown, in which 10 is a high-resistance Si substrate, 1] is a p-type paper antilayer, 12 is an n+ layer, 13 is a common electrode, and 14.15 is an electrode. The surface layer has a photoelectric effect due to the p-n junction. Therefore, when light is incident on the p-type paper layer as shown in the figure, output currents IA and xB are obtained from the electric bodies 14 and 15, respectively, depending on the position of the light incident. Here electrode】4 and】
Distance between 5 and 1 resistance? rRe, and the distance from the electrode [4] to the light incident position kx + its partial resistance is TLx
, and if the photocurrent generated by the incident light is '(5I), then if the resistive layer is uniform, the following equation can be obtained.
By performing the calculation IA + I13 11 from IB, the incident position of the light, that is, the distance X, can be determined regardless of the incident energy, that is, the entrance angle. ... (4) Required from. Although the above explanation is not about the operation of a -dimensional optical position detector, the principle is the same even in the case of a two-dimensional optical position detector. When an image with a photoelectric distribution similar to that shown in Fig. 3 is formed, the light intensity distribution iI. (x), the output type K IA (x) at the electrode 14', ]5 due to the light incident at the position X. Intx) IA (xi = r I□ (x), IB (x)
-, I From Equation (8), the center of gravity of the image formed on the optical position detector can be determined as follows.Next VC1 This invention using the optical position detector described above e The focus detection device is shown in FIGS. 4 and 5, 1F.
The light transmitting portion 2]a and 21b'i are controlled to be alternately visible by a pupil divider using a liquid crystal or an electrochromic device corresponding to the above. 22 is an imaging lens, and 23 is the aforementioned one-dimensional optical position detection element disposed at the focal position of the imaging lens 22. The light beams entering through the transparent parts 2]a and 21b'4 of the pupil splitter 21 are imaged on the optical position detector 23 via the imaging lens 22. Also, FIG. 5 shows a block diagram of an electric circuit that processes the output signal from the optical position detector 23 [2, 2, 24, 24' are the two electric circuits 1 of the optical position detector 23]. J
- an amplifier for amplifying the output currents IA and IB' from the
25 is a subtracter that performs all calculations (white A-IB), 26 is (I, +
IB) Adder that performs all calculations; 27 is a divider that performs the calculation of equation (8); 28 is a transparent part of the pupil divider 21 that alternately
A drive circuit 29 is a divider 27 for controlling the
This control circuit removes the DC bias component from the output signal of the controller, and its circuit configuration is, for example, as shown in FIG. Here, 31 is a rectifier circuit, 32 is a t/i differentiator circuit, 33 is a connominator, and 34 is a zero level detector. A power converter 33 makes a positive/negative determination to determine whether the signal is decreasing or increasing, and if it is increasing, the lens driving device 3o is reversed. Focusing can be detected when the zero level detector 34 detects that the signal has become 1 zero. Further, the lens driving device 30 is configured to move the imaging lens 22 in a predetermined direction at the same time as the start of the focus detection operation, and as the imaging lens 22 moves in the predetermined direction, the optical position detector Since the relative positions of the centers of gravity of the two images on 23 change, the amplitude of the AC component of the output signal of the divider 27 also changes. That is, this amplitude gradually decreases when the imaging lens 22 moves closer to the in-focus position, and increases gradually when the imaging lens 22 moves away from the in-focus position. Therefore, Figure 6 (including smoothing circuit)
The output of the rectifier circuit 3 also gradually decreases when the imaging lens 22 moves closer to the in-focus position, and gradually increases when the source lens 22 moves away from the in-focus position. Thus, the output of the differentiating circuit 32 becomes negative when approaching the in-focus position, and becomes positive when moving away from the in-focus position. Furthermore, the output of the converter ξ regulator 33 is
When the output of the differential circuit 32 is negative, rLJ is stable, and when the output of the differentiating circuit 32 is positive, it is at the "H" level. Also, the zero level detector 34 outputs a signal only when the output of the rectifier circuit 3 is zero. My heart is getting better at output. The outputs of the connominator 33 and the zero level detector 34 are supplied to a lens drive circuit 30, and the lens drive circuit 30
When the output is at rLJ level, it continues to operate as it is, but when it is at l-'HJ level, it reverses the driving direction and stops its operation when a signal is supplied from zero level detector 34. According to the embodiment configured as follows, the imaging lens is driven by the lens drive circuit 30 at the start of operation. 22 is moved in a predetermined direction, and at this time, the controller 33 of the control circuit 29 determines whether the imaging lens 22 is approaching the in-focus position or moving away from the in-focus position. has a lens drive device 30
, the driving direction is reversed, and the rectifier circuit 31 of the control circuit 29
When the output signal becomes zero, the operation of the lens driving device 30 is stopped by detecting this by the zero level detector 34. In this way, the in-focus position is obtained. Since this device does not need to operate synchronously with the drive circuit 28 of the pupil divider 21, it has a very simple configuration and can also provide real-time performance. 7 and 8 show another embodiment in which a two-dimensional optical position detector is used to detect focus in two directions perpendicular to each other. 35 is a pupil divider similar to the pupil divider 21 in FIG. 4, and is a transparent portion 35a that is controlled to become transparent one by one. 35b, 35c, and 35d are all equipped. 36 is the fourth
An imaging lens 37 is the same as the imaging lens 22 in the figure, and 37 is a two-dimensional optical position detector disposed at the focal position of the imaging lens 36, with electrodes 38 and 39 for vertical detection and horizontal detection. The electrodes 40 and 41 are provided. FIG. 8 is a block diagram of an electric circuit that processes the output signal from the optical position detector 37. Components that are the same as those in FIG. Nonondono ξ
pupil divider 35, whose center frequency is the pupil divider 35.
This corresponds to the frequency of the light shielding operation. That is, for example, when the transparent parts 35a, 35b, 35c, and 35d enter the passing state in this order, the time required for the period corresponds to the period corresponding to the center frequency of the bandpass filter. Therefore, when the pupil splitter 35 operates as described above, the output signal indicating the gravity center position itk of the image obtained in the vertical and horizontal directions of the two-dimensional optical position detector 37 has a frequency f except in the focused state. Since this is an oscillating alternating current signal, selecting the center frequency of the noise filter 42 to be f is effective in removing noise other than the necessary signals (which generally have different frequencies). In addition, noise is often high frequency, so a pantone filter is in order!
It is also possible to use a low-pass filter with a cutoff frequency of sof for ll. 43 is a synthesizer for synthesizing the output signals of the divider 27 in the vertical and horizontal directions, and the synthesis is performed in the form of, for example, the sum of absolute values of each component, the sum of squares, etc. so that each component is not lost. . 28'
are the transparent parts 35 a , 35 b , 35 of the pupil divider 35
This is a drive circuit that performs control to sequentially make c +35d transparent. According to this second embodiment, focus detection can be performed in the vertical and horizontal directions in the same manner as in the first embodiment, and in addition to obtaining the same effects as the first embodiment, additional advantages such as Focusing can be easily detected even for objects that are monotonous in one direction. FIG. 9 shows a third embodiment according to the present invention, 44
is an imaging lens; 45 is a mirror for dividing the pupil into half; 46 and 47 are output terminals 48°-19 and 50.
51' is a one-dimensional optical position detector, and the output signals from each output terminal are processed in the same manner as in the case of FIG. 8 (see FIG. 10). By subtracting the output signal from each divider 27 to another subtracter 52, a DC signal indicating the phase difference of the images is obtained, which is further processed by the control circuit 29 to detect focus. It is done. As described above, according to the present invention, focusing is performed using an optical position detector to reduce its output signal, and there is no need to operate the pupil splitter in synchronization with the drive of the pupil splitter. Unlike storage-type solid-state image sensors, there is no need for storage time or scanning time. Therefore, with a very simple configuration, focus can be detected continuously in real time, and the position of the center of gravity of an image can be measured. As is clear from equation (8), since it is unrelated to the amount of incident light, the difference in brightness of each detection image resulting from non-uniform distribution of light amount in the pupil due to eccentricity of the pupil, etc. does not affect the position detection accuracy. When configured to detect two-dimensional focus, it is possible to detect focus even for objects that are monotonous in one direction, which would be impossible or difficult to detect in the case of -dimensions. In this case, if a two-dimensional optical position detector is used, the detection signal can be processed by a circuit with about twice as many components as in the -dimensional case.The present invention has the above-mentioned effects, and can automatically By applying it to a focusing device, a simple and highly accurate automatic focusing device can be obtained.The light-transmitting part of the pupil divider can be opened and closed mechanically, for example, by rotating a disc with an eccentric aperture. However, it goes without saying that when automatic focusing is performed in an optical instrument such as a microscope that has a movable stage, the control circuit drives and adjusts the stage rather than the imaging lens.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the principle of focus detection of the present invention, Fig. 2 is a schematic sectional view showing an example of an optical position detector used in the present invention, and Fig. 3 is an image incident on the optical position detector. FIG. 4 is a perspective view showing the optical system of the one-dimensional focus detection device according to the present invention, FIG. 5 is a block diagram of the focus detection device shown in FIG. 4, and FIG. FIG. 7 is a block diagram showing an example of the circuit configuration of the control circuit; FIG. 7 is a perspective view showing the optical system of the two-dimensional focus detection device according to the present invention; FIG. 8 is a block diagram of the focus detection device of FIG. 9 is a perspective view showing an optical system of a phase difference focus detection device according to the present invention, and FIG. 10 is a block diagram of the focus detection device of FIG. 9. 1122.36144...Imaging lens, 2...Lighting plate, 3...Image surface, ]0...High resistance Si substrate, 1
1-p sub-resistance layer, ]2... single layer, 13... common electrode, ]4°15... electrode, 2], 35... pupil divider,
23.37°46.47... optical position detector, 24,
24'...Amplifier. 25... Subtractor, 26... Adder, 27...° divider, 28, 28'... Drive circuit, 29... Control circuit, 308. . Lens 1 drive circuit, 31... Rectifier circuit, 32... Differentiator circuit, 33... Connomitor, 34... Zero level detector, 42... Pantone ξ frame, 43
...Threat device, 45...Mirror, 52...Subtractor. Agent Ken Tsukasa Shinohara

Claims (1)

[Claims] Object images formed by the light beams passing through different paths of the imaging system are received by a photoelectric conversion element disposed on a regular imaging plane, and the relative positional relationship of the object images is adjusted. A focus detection device configured to detect a focus includes an optical position detector as a photoelectric conversion element, and further has a correlation with the amount of each object image based on the output signal of the optical position detector. A focus detection device 0 characterized in that it includes a control device for controlling a single focus adjustment mechanism to reduce a signal.