JPS59162515A - Focus information detector - Google Patents

Abstract

PURPOSE:To obtain focus information accurately on the basis of the phase shift between light images formed on an image formation surface by light beams which are passed alternately at intervals of one screen through a couple of holes in a luminous flux control plate arranged near the exit pupil of a photographic lens. CONSTITUTION:The luminous flux control plate 23 is constituted of laminating a polarizer 41, light shield member 42, liquid-crystal layer 43, transparent layer 44, and analyzer 45. The couple of holes 24 and 25 are formed in the light shield member 42 and transparent electrodes 46 and 47 are fitted therein. Then, lead wires are led out from electrodes 46a and 47a for applying AC electric fields to the transparent electrodes 46 and 47. Further, the directions of polarization of the polarizer 41 and analyzer 45 cross each other at right angle. Then when AC electric fields are applied to the liquid-crystal layer 43 through the transparent electrodes 46 and 47, the rotations of incident light beams 48 and 49 in the liquid-crystal layer in their directions of polarization are minimized and transmitted light is minimized. When no AC electric field is applied, the plane of polarization is rotated by 90 deg. in the liquid-crystal layer 43 to maximize the transmitted light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus information detection device used in an imaging device that obtains a video signal by forming a subject image on a photoelectric conversion surface using an optical system including an imaging lens or the like.

Among conventional focus information detection devices of this type, there is one that uses a detection means based on one image shift. FIG. 1 shows the operating principle of one example.

In the figure, 1 is the subject, and the optical image of this subject 1 is the lens 2.
As a result, an image 3 is formed on a photoelectric conversion surface of an image sensor or an image pickup tube installed at the focus position FO. In this case, at the out-of-focus position F1 in front of the in-focus position, the light beam 5 that has passed through the upper half of the lens 2 and the light beam 5 that has passed through the lower half of the lens 2 each pass through the illustrated position. Therefore, at the above-mentioned out-of-focus position F1, 4 and 5
A deviation of a distance t occurs between the two. Further, at an out-of-focus position F2 located behind the in-focus position FO, the positional relationship between 4 and 5 is reversed, resulting in 6 and 7.

As shown in FIG. 1, as a means for obtaining information on the amount of deviation t, small lens groups 8a, 8b, .
Install multiple... And small lens groups 8a, 8b.
There are one pair of photoelectric conversion elements 9a with the center of each lens as a boundary.

10a, 9b, 10b... are installed, and the photoelectric conversion element 9
A, 9b, . . . allow the light flux that has passed through the lower region of the lens 2 to be incident thereon, and the photoelectric conversion elements 10a, 10b, . Then, the focus information detector 11 detects the photoelectric conversion elements 9&, 9b...
The photoelectric conversion outputs are read in the order of . to obtain the time-series image information of 4 or 6, and the photoelectric conversion elements 10a, 1
The photoelectric conversion outputs are read in the order of 0b... to obtain the time-series image information in 5 or 7 above, and the spatial shift amount of the obtained image information is subjected to signal processing to obtain focus information. is output from the output terminal 12.

In this way, the conventional focus information detection device requires a plurality of small lens groups, and each of these small lens groups requires a pair of charge conversion elements, so the configuration of the detection system is extremely complicated. Moreover, it took a lot of effort to align the small lens group and the photoelectric conversion element group. Therefore, there was a drawback that the cost was high.

The present invention was made based on these circumstances,
The purpose is to eliminate the need for small lens groups or photoelectric conversion element groups,
It is an object of the present invention to provide a focus information detection device whose detection system has a simple configuration and can be manufactured at low cost.

In order to achieve the above object, the present invention is characterized by having the following configuration. That is, the light flux from the subject is brought into a transparent state or a dim state near the exit pupil of the imaging lens in the imaging device. A light flux control plate with a pair of holes symmetrically arranged around the optical axis is arranged, and the light transmitted through the pair of holes and the glare are controlled.
The switching is performed alternately in synchronization with the screen cycle such as the field cycle or frame cycle of the video signal. The present invention is characterized in that focus information is obtained by detecting the phase shift of the optical images on the imaging plane that are obtained alternately by the switching operation.

Hereinafter, details of the present invention will be clarified by examples shown in the drawings. FIGS. 2 and 3 are diagrams showing a schematic configuration of an optical system in an embodiment of the present invention. In FIG. 2, light from a subject 21 passes through a pair of holes 24 and 25 of a light flux control plate 23 provided near the exit pupil of this lens 22, and reaches a photoelectric conversion surface of an image sensor 26.
The image is formed on 27. The pair of holes 24 and 25 are provided at symmetrical positions across the center O of the light flux control plate 23.

Note that the portions other than the pair of holes described above are formed of an optical material. Thus, the -NLD holes 24 and 25 form images on the photoelectric conversion surface 27 by the light beams that have passed through the upper region 22a and lower region 22b of the lens 22, respectively.

According to the above results, the image formed on the photoelectric conversion surface 27 does not shift when in focus, but when it is out of focus, it causes an image shift in the vertical direction as shown by reference numerals 31 and 32 in Fig. 3. .

FIG. 4 specifically shows the structure of the light flux control plate 23. In FIG. 4, 41 is a polarizer (+), 42 is a light member, 43 is a liquid crystal layer, 44 is a transparent electrode, and 45 is an analyzer, which are stacked. The pair of holes 24.25 described above are provided in the luminous member 42, into which the transparent electrodes 46.4'l are fitted. 46a.

Reference numerals 47a are electrodes for applying an alternating current electric field to the transparent electrodes 46 and 47, respectively, and are led out to the outside via lead wires or thin film patterns. Note that the polarizer 41 and analyzer 45 have orthogonal polarization angles.

Thus, when a suitable alternating current electric field is applied to the liquid crystal layer 43 through the transparent electrodes 46 and 47, the rotation of the polarization direction of the incident light 48, 49 within the liquid crystal layer is minimized, and the amount of transmitted light is minimized.

When no alternating electric field is applied, the deflection plane rotates 90' within the liquid crystal layer 43, and the transmitted light becomes maximum. FIG. 5 is a plot diagram showing the electrical configuration of the control system. In FIG. 5, a signal outputted from the photoelectric conversion surface 27 of the image sensor 26 is supplied to a video processor 51, and becomes, for example, an NTSC video signal as shown in FIG. 6A, and is sent out from an output terminal 52. This video signal is also supplied to a vertical synchronization separator 53, and a vertical synchronization signal as shown in FIG. 6B contained in the video signal is separated and extracted. The separated and extracted vertical synchronizing signal is sent to a flip-flop circuit 54. A signal output from the flip-flop circuit 54 as shown in FIG. becomes the input. And gate 5 yen'.

A square wave pulse train is applied from a terminal 58 to the other input of each of the input terminals 57 . Thus, square wave pulse trains as shown in FIG. 6E and F are sent out from the AND gates 55 and 57, respectively. The outputs of the AND gates 55 and 57 are applied to the transparent electrodes 46 and 4fi fitted into the pair of holes 24.25 of the light flux control plate 23, respectively, and switch the holes 24.25 into a transparent state or a dim light state. do. In this embodiment, the pair of holes 24 and 25 generate a ray of light when the square wave pulse train from the AND gates 55 and 57 is applied to the transparent electrodes 46 and 47, that is, when an alternating current electric field is applied to the liquid crystal layer 43. When the square wave pulse train from the AND gates 55 and 57 is not applied to the transparent electrodes 46, 47, that is, when no alternating current electric field is applied to the liquid crystal layer 4.3, the liquid crystal layer 4.3 enters a transparent state.

As a result, there are 24.25 holes per field period of the video signal.
The translucent state and binding and light state can be switched. That is, as shown in FIG. 6, during the odd field period TA, for example, the hole 24 is in a light-transmitting state, and the hole 25 is in a light-blocking state. In the even field period TB, on the contrary, the hole 2 is in the light state, and the hole 25 is in the light-transmitting state. Photoelectric conversion surface 2
As mentioned above, the image formed on the lens 7 causes an image shift in the vertical direction when it is out of focus, but in this device, during the odd field period TA, the image formed on the light beam passing through the upper half of the lens 22 is focused. , during the even field period TB, an image is formed by the light beam passing through the lower half region of the lens 22. As a result, no phase shift occurs between the video signal in the odd field period TA and the video signal in the even field period TB when in focus, but a phase shift occurs when out of focus.

In addition, the focal point position is in the front direction (
The direction of the phase shift is opposite when moving toward the lens (lens side) and when moving toward the rear.

The video signal outputted from the video processor 51 is envelope-detected by an envelope detector 59 as shown in FIG. 6G, and then sent to an LPF 60 to remove high frequency components as shown in FIG. 6H. The reason for providing the above LPF6.0 is that when the difference output of the video signal is obtained as described later, if the video signal contains a high frequency component, the polarity of the difference output will fluctuate. This is to prevent it from becoming impossible to determine whether the focus has shifted. The output of the LPF 60 becomes one input of the difference circuit 61, and is sent to the lv delay circuit 62 for l vertical synchronizing signal period (/
After being delayed by 60 sec), it becomes the other input of the difference circuit 61°. Also, the output of the LPF 60 is sent to the slope detector 62.
', and either the positive slope region or the negative slope region of the signal is detected. The output of this slope detector 62' is given to an analog gate 63 as a control signal.

Therefore, the difference circuit 61 added to the analog gate 63
Only one of the positive slope and negative slope regions will pass through the differential output. analog gate 63
The signal that has passed through is supplied to a lens drive motor 65 as focus information via an envelope detector 64.

FIGS. 7(a) and 7(b) are waveform diagrams showing the effect when obtaining the above focus information, 71 is a waveform showing an example of a video signal, and 72 is a signal waveform delayed by the 1V delay circuit 62. be. As is well known, there is a strong correlation between each field of a video signal, and there will not be a large difference in signal waveforms between adjacent fields except for extremely fast-moving subjects. Therefore, at the time of focusing, the phases of the video signals 71 and 22 match, and when the focal position is in front of the photoelectric conversion surface 27 area, the phase of 7 is relative to 72 as shown in the figure (&). lags behind, and conversely, when the focal position is in the rear direction, 71 will lead in phase with respect to 72, as shown in FIG. 7(b). 1
3a, 73b and 74&, 74b are difference signals obtained by subtracting signal 71 from signal 72 in difference circuit 61. Now, when the positive polarity gradient region of the video signal (the region in the arrow direction in FIG. 7) is gated by the control signal from the gradient detector 62',
The difference signal becomes 73a or 73b □ depending on the defocus direction. The magnitude of the difference signal 73h or 73b becomes the amount of focus shift. A signal obtained by envelope detection of this difference signal 73a or 73b becomes focus information.

Although this device has an extremely simple configuration, it uses the correlation between the video signal of a field at a certain time and the video signal of the previous field to detect a phase shift state and obtain focus information. As a result, the detection system can be simplified.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above embodiment, a single liquid crystal layer 43 is used, but for example, one hole may be made to correspond to a plurality of divided liquid crystals, and each liquid crystal is provided with a voltage corresponding to the intensity of the subject light. The same effect as conventional iris control may be obtained by applying .

Furthermore, by controlling the magnitude of the voltage applied to the liquid crystal, the transition between the transparent state and the light state can be made gradual, thereby achieving the same effect as conventional iris control. .

Furthermore, only when the focus is out of focus, that is, when you want to adjust the focus, focus information is obtained by alternately switching to the blocking state or the transparent state in synchronization with the field cycle or frame cycle, and the above switching is stopped after focusing. Both holes 24 and 25 may be transparent. By doing this, the flicker-like image quality deterioration caused by the switching will not occur after focusing.In addition, the light flux control plate 23 is used only when adjusting the focus, and during image capture, the light flux is transmitted to the motor etc. The control plate 23 may be moved out of the optical path to make effective use of the luminous flux.

Furthermore, as shown in FIG. 8, the light shielding member part of the light flux control plate is replaced with transparent electrodes 81 and 82, and when focusing, the hole 2
By making not only the transparent first male electrode 46 and the second electrode 47 fitted in the transparent electrode 4.25 transparent, but also the transparent electrodes 81 and 82, the luminous flux can be used effectively).
In Fig. 8, 83 and 84 are insulators such as glass;
5 is an electrode for transparent electrodes 81 and 82.

Furthermore, as shown in FIG. 9, when adjusting the focus, a system of the nof mirror 92 and mirror 93 in the quick return mirror 91, the mirror 94, the field lens 95, the light flux control plate 23, the imaging lens 96, and the image pickup device 26 is used to adjust the focus. Information may be detected, and at the time of imaging after focusing, the quick return mirror 91 may be flipped up to allow the light beam to enter the imaging element 97 to perform imaging.

Further, a means for detecting the focus information by displaying the focus information on the monitor of the TV camera and observing the shift state of the image on the monitor may be provided.

As explained above, according to the present invention, the phase of the optical image obtained on the imaging plane by the light that passes alternately every frame period from the pair of holes in the light flux control plate arranged near the exit bell of the imaging lens. Since focus information is obtained based on the shift,
It is possible to provide a focus information detection device that does not require a small lens group or a photoelectric conversion element group as in the past, has a simple configuration, can be manufactured at low cost, and can accurately obtain focus information.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional focus information detection means, FIGS. 2 to 7 are diagrams showing an embodiment of the present invention, FIG. 2 is a diagram showing a schematic configuration of an optical system, and FIG. is a diagram showing the state of image shift obtained by the optical system VX, FIG. 4 is a diagram showing the structure of the light flux control plate, FIG. 5 is a block diagram showing the electrical configuration of the control system, and FIG. 6 is an explanation of the operation. Fig. 7(a) is a diagram showing the main parts in the embodiment. 21... Subject, 22... Lens, 23... Light flux control plate, 24. 25... Pair of holes, 26... Image sensor, 27... Photoelectric conversion surface, 41... Polarization Child, 42.
...Bright light member, 43...Liquid crystal layer, 44...Transparent electrode, 45...Analyzer, 46.47...Transparent electrode. Applicant's Representative Patent Attorney Takehiko Suzue Figure 4 Figure 6 j I 7 Procedure Amendment 1980 1. Kazuo Wakasugi, Commissioner of the Japan Patent Office 1, Case Indication Patent Application No. 158-36897 2 Name of the invention Focus information detection device: (Relationship with the famous case to be amended Patent applicant (037) Optical Industry Co., Ltd. 11, Agent

Claims (2)

[Claims] (1) In an imaging device in which a subject image is formed on a photoelectric conversion surface by an optical system consisting of an imaging lens or the like to obtain a video signal, a light beam from the subject image is transmitted through the imaging lens located near the exit pupil of the imaging device. A light flux control plate has a pair of holes arranged symmetrically about the optical axis to form a light state or a low light state, and a field period or frame period of the video signal, etc. to determine the light transmission state or low light state of the pair of holes. and a means for detecting the phase shift of the light image on the imaging plane alternately obtained by the switching by this means and using it as focus information. A focus information detection device characterized by: (2) The focus information detecting device according to claim (1), wherein the pair of holes that transmit the light flux into a transparent state or a dim light state are formed of a liquid crystal material.