JPH0311313A - Focus detector - Google Patents

Abstract

PURPOSE:To obtain a focus detector whose measurable distance range on the close side is extended by using an optical wedge, which is made of optical materials having an electrically variable refractive index and functions as a prism, to obtain the same effect that a prism is inserted to a parallel flat plates are used. CONSTITUTION:Distances up to objects 1a and 1b are detected based on the principle of trigonometry. For the purpose of detecting them, a range finding optical system 10 including optical wedges 2a1 and 2b2 whose refractive indexes are electrically changed, a refractive index control means 5 which controls refractive indexes of optical wedges 2a1 and 2b2, and a signal output means which outputs an electric signal related to the object distance in accordance with the object light led to the range finding optical system 10 are provided. A distance data output means 6 is provided which outputs object distance data based on the refractive indexes of optical wedges 2a1 and 2b2 and the electric signal. Thus, the measurable distance range of the focus detector is quickly extended without using mechanism members, and a range finder is miniaturized.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a focus detection device, specifically a δ-1 distance device based on the triangular 71N distance method, and particularly a focus detection device with an expanded distance measurement range on the close side. Regarding.

[Prior Art] Conventionally, an autofocus camera is known in which all object distances are determined based on the principle of triangulation and the photographing optical system is driven to a focused point based on this 11) I short data.

This passive type ΔPI range cover system is the first
To explain with reference to FIG. 6, the distance g to the subject can be found as -8 g-□ (1). Here, f is the length from the first and second lenses 61 and 62 to the first and second sensors 6B and 64 where images of these lenses are formed, and S is the base line length 1.
/2, and t is the distance from the reference position of the current imaging position of the subject image, with the imaging points formed on the first and second sensors 63 and 64 when the subject 65 is in the rice field as the reference position. The amounts of deviation are shown respectively. The deviation it can be determined by performing a correlation calculation between the data of the first sensor 63 and the data of the second sensor 64.

By the way, in order to make the closest distance that can be achieved by aPJ distance in such a distance measuring device to MIN, which is smaller than before,
As can be seen from the above equation (1), the following three methods can be considered.

The first method is to reduce the baseline length S. That is, the 17th T
I! The first lens 61 and the second lens 62, respectively indicated by dotted lines in J, are moved in the directions of arrows A and A, respectively, to the first lens 61 and second lens 62, respectively indicated by solid lines. Second lens 61,g
, 62a, the Δl distance range on the closest side is 'MIN.

In the second method, in order to widen the ap1 constant range of the image deviation Qt from the reference position, as shown in FIG. The second sensors 63, 64 are indicated by arrow A3. A4
The sensor 63 has been expanded in the direction of and moved to the position indicated by the solid line.
a, 64a.

The third method is the first method as shown in FIG. The focal length fif of the second lens 61, 62 is shortened, and the arrow A5.
1st in direction A6. Move the second lens 61°62 to the first lens. Lenses 61a and 62a are brought close to the second sensors 63 and 64 and shown by solid lines.

However, since the first method shown in FIG. 17 requires a mechanism for moving the lens with high precision, the distance measuring device becomes complicated and the cost increases.

Further, in the second method shown in FIG. 18, there is no need to change the mechanism at all, but the cost increases due to the increase in the longitudinal dimension of the sensor. Furthermore, in the third method shown in FIG. 19, the focal length of the lens is shortened and the lens is moved closer to the sensor, thereby compressing the image shift Ht with respect to the subject distance. Although the range is widened, if the 311 constant accuracy of the image shift Qt is poor, the distance measurement accuracy will be reduced. Therefore, depending on the photographic lens used, the necessary distance measurement accuracy may not be obtained.

Therefore, in the fourth method shown in FIG. 20, the first lens 61. Second prism 66.6
7 is inserted, and the n1 distance range on the near side is expanded by the deflection angle δ of the prisms 66 and 67. The image formed on the sensor by this ml and the deflection angle δ of the second prism 66,67 is the correction value Δt of the image deviation Qi.
will be detected as small. Therefore, the above (1)
The formula is: This means that the same effect as that obtained by increasing the sensor correction by Δt in the second method described above can be obtained. The fourth method differs from the second method in that even if the detected image shift N t ' is O, the correction amount Δt prevents the object distance from becoming a hot pot.

The fourth method shown in FIG. 20 has the disadvantage that the number of optical parts increases compared to the first to third methods described above, but since the positional accuracy of the prism is rough compared to that of a lens, the prism movement mechanism Good quality. In addition, the second
This method is cost-effective compared to the above method. Such a means for extending the distance measurement range using a prism has already been disclosed in Japanese Patent Application Laid-Open No. 148434/1983.

That is, the "automatic focus device having a close focusing function" described in the above-mentioned Japanese Patent Application Laid-Open No. 61-148434 has a distance measuring means equipped with a detecting section for detecting an excess of the close-range photographing limit of the photographing lens, and a distance measuring means having a Δp1 A distance setting means for the photographing lens that sets the distance of the photographing lens based on a distance signal; and a distance setting means for inserting a correction lens into the photographic lens and an optical wedge in at least the 71F1 distance optical system according to a detection signal of exceeding the short distance photographing limit. It is equipped with an optical correction means for the optical system, and a means for re-doing all distance using the optical system corrected based on the detection signal of exceeding the photographing limit, and when the subject approaches the close-range photographing limit, the photographing is performed based on the detection signal. It has a close focusing function characterized by inserting a correction lens into the lens, correcting at least the incident optical path of the distance measuring optical system, performing distance measurement again, and setting the distance of the photographing lens. , an optical T-wedge mechanically disposed in the +111 distance optical system so as to be freely inserted into the prism 66.6 shown in FIG.
7, the distance measurement range on the close side is expanded by inserting this optical wedge.

In addition, instead of a prism, a flat plate that passes light is placed between the light-receiving lens and the light-receiving element, and the inclination of this flat plate is changed in conjunction with the focus ring, allowing the flat plate to have the same effect as a prism. The technical means that made it possible to
It is disclosed in Japanese Patent No. 3-75717.

That is, the "automatic focusing device" described in Japanese Patent Application Laid-Open No. 63-75717 has an optical focus between a light receiving element and a light receiving lens with respect to an axis perpendicular to a plane containing the optical axis of the light receiving lens and the optical axis of the projection lens. A flat plate is provided that is rotatable and allows the light beam projected from the light emitting element to pass through, and this flat plate is connected to a focus ring so that it rotates according to the movement of the focus ring, and the focus ring is driven by the output of the light receiving element. This means that there is a means to do so. This plane plate has the same effect as the prisms 66 and 67 shown in FIG. The light receiving condition changes,
This expands the AI distance range on the close side.

[Problem to be solved by the invention]

However, the optical wedge mechanically inserted into the 1iIP1 distance optical system is A? The proposal described in the above-mentioned Japanese Patent Application Laid-Open No. 148434/1988 for inserting it into the J-range optical system, or by providing a flat plate that passes the object light between the light receiving element and the light receiving lens and interlocking this flat plate with the focus ring. In the proposal described in the above-mentioned Japanese Patent Application Laid-Open No. 83-75717, in which the received light beam is polarized as the plane plate rotates, a mechanical switching means is required, which increases the size of the device.
This is not desirable because it complicates the process. If possible, it is desirable to perform similar actions by electrical means.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and achieve the same effect as inserting a prism or using a parallel plate by using an optical wedge that acts as a prism and is made of an electrically variable refractive index optical material. Thus, it is an object of the present invention to provide a focus detection device that expands the measurable distance range on the close side.

[Means and effects for solving the problem] As the concept of the focus detection device is shown in FIG. A distance measuring optical system 1 which is a detection device and includes optical wedges 2 a and 2 b l that can electrically change the refractive index.
0, the refractive index control means 5 for controlling the refractive index of the optical wedge 2 a 2 b i, and the electric power related to the object distance according to the object light guided to the distance measuring optical system 10. The apparatus is characterized by comprising a signal output means for outputting a signal, and a distance data output means 6 for outputting object distance data from the refractive index of the optical wedge 2a12br and the electric signal. .

〔Example] The present invention will be explained below with reference to illustrated embodiments.

First, before explaining the present invention in detail, the basic principle of the present invention will be explained with reference to FIG. 2, and the operating principle of the optical wedge used in the present invention will be explained with reference to FIGS. 3 to 8.

FIG. 2 is a block system diagram for explaining the basic principle of the focus detection device of the present invention. In the figure, subject 1a
, lb is projected onto a distance measuring optical system 10 consisting of lenses 3a, 3b, and sensors 4a, 4b via optical wedges 2g, 2b1 formed of liquid crystal prisms. The output signal from the ranging optical system 10 is supplied to the determining means 8, and the output of the determining means 8 is supplied to the correcting means 9 and the ranging range switching means 7 consisting of the AC type 197b and the switch 7a. It looks like this.

In such a configuration, the object light from the object 1b located closer than the All distance limit on the near side is transmitted through the optical wedges 2a, 2b1, and lenses 3a, 3b1.

are transmitted through the dashed lines 11a and job, respectively, and head toward the sensors 4a and 4b, but since the subject 1b is closer than the distance measurement limit on the close side, it is the sensor 4a.

4b cannot be imaged. Therefore, the determining means 8
detects this and sends a signal to the ranging range switching means 7,
As a result, the switch 7a of the switching means 7 is turned on, and the AC voltage from the AC power supply 7b is applied to the optical wedge 2a 2b.
1 will be applied.

l' Then, the refractive index of the optical wedge 2 a 2 b 1 increases l', so that the object 1b on the closer side than the distance measurement limit on the close side
The object light from the lens is refracted inward in the figure by the optical wedges 2a1 and 2bl, thereby forming an image on the sensors 4a and 4b. Sensor 4a obtained in this way
, 4b is corrected by the correcting means so that a correct measured distance value can be obtained.

In other words, in the present invention, an electrically variable refractive index optical wedge is placed in front of the light receiving lens, and the 7u pressure applied to this optical wedge is
Close-up AF is controlled according to the subject distance.
This is a focus detection device with an expanded J distance range.

Next, to explain the operating principle of the optical wedge, the optical wedge used in the present invention can be operated by changing the voltage applied to the liquid crystal.
It is formed of an optical prism filled with liquid crystal (hereinafter referred to as a liquid crystal prism) that utilizes the property of changing its refractive index.

Figures 3 (A) and (B) are longitudinal cross-sectional views of the liquid crystal prism and D
-D' sectional view. As shown in the figure, liquid crystal prism 1
The basic structure of No. 5 is such that a liquid crystal 14 is sealed in a space formed by two transparent optical members 12 and 13 and a spacer 18 and 19. A transparent conductive layer is formed on the sides of the two transparent optical members 12 and 13 that are in contact with the liquid crystal 14, so that an alternating voltage can be applied to the liquid crystal 14 from an AC power source 17 via a resistor 16. . And this third
Figures (^) and (B) show a state in which P-type liquid crystals (E, >8.) are homogeneously aligned when the applied voltage Ov.

Generally, the deflection angle δ of a prism is expressed as follows, where n is the refractive index of the material constituting the prism, and α is the m-angle of the prism.

δ−(n −1)α ・・・・・・・・・(3) This (
From formula 3), when the refractive index n or the apex angle α is changed,
It can be seen that the deflection angle δ of the prism changes.

The liquid crystal prism 15 uses its birefringence to adjust the refractive index n.
It is classified as a method that changes the In liquid crystal (nematic phase), microscopically the liquid crystal molecules are swaying, and although not all molecules are aligned in the same direction, optically it is considered to be a uniaxial crystal, and it has a refractive index ellipsoid. is defined.

FIGS. 4(A) and 4(B) respectively show the molecular structure of a cyanobiphenyl system as an example of the main component of a P-type liquid crystal (n8>no) and its refractive index ellipsoid. and,
Due to its dielectric anisotropy, that is, ε# to ε, the liquid crystal molecules tilt according to the applied voltage V, as shown in FIGS. In other words, when direct film light 20 vibrating in the direction in the plane of the drawing is made perpendicularly incident on the liquid crystal cell, the apparent refractive index nB of the liquid crystal changes according to the rotation angle θ according to the following equation (4), that is, the applied voltage V is OV
When , the refractive index n for extraordinary light is shown as shown in FIG. 5(A), and when the applied voltage is high, the refractive index n for ordinary light is shown as shown in FIG. 5(C). In between, there is a state in which the applied voltage ■ shown in FIG. 5(B) is at an intermediate value. Therefore, the apparent refractive index n. is a function of the applied voltage V as shown in equation (5) below.

no-n (V) ・・・・・・・・・(5) As a result, the deflection angle δLC of the prism-shaped liquid crystal changes from the refractive power for extraordinary light to the refractive power for ordinary light depending on the applied voltage V. It will change continuously. Therefore, the above (
Equation 3) becomes as shown in Equation (6) below, and it becomes possible to adjust the refractive power by voltage for one week.

δt, c (V) = (n (V) -1) α---
--- (6) That is, by applying a voltage, the deflection angle δ changes in the direction of arrow A9 shown in FIG. 3 (^). Normally, the response time τ 1 recovery time τ in the electro-optical phenomenon of nematic liquid crystal is expressed as follows (7), (
8), and is known to be proportional to the square of the liquid crystal thickness d.

2 2 2 τ −ηd / (π to ε0ΔεV −) ``・・・・・・・・・(7) τ −ηd2/to π2) ・・・・・・・・・(8)
Here, η is the viscosity modulus, is the elastic modulus, ■ is the applied voltage, and Δε
(-1ε and -εE1) respectively represent dielectric anisotropy.

Therefore, in the application of liquid crystal prisms, if you want to make the response faster, change the shape shown in Figure 6 (^) to Figure 6 (B
) to effectively reduce the thickness of the liquid crystal, or change the shape shown in Figure 7(^) to the shape shown in Figure 7(B) where thin prisms are laminated. Become.

Since the liquid crystal prism is an optical element that utilizes the birefringence of liquid crystal, it is equipped with a polarizing plate, although it is not shown in Figure 3.
Only linearly polarized light needs to be incident. Otherwise, 2
Two deflection angles δ will occur. Alternatively, there is a method of overlapping two liquid crystal prisms such that their liquid crystal orientation directions are perpendicular to each other to solve this problem. If the light transmittance of the prism is a problem, it is better to use the latter method in which two liquid crystal prisms are stacked so that the liquid crystal alignment directions are perpendicular to each other, although the structure becomes complicated.

FIG. 8 shows a block diagram of the drive circuit for the liquid crystal prism 2a. General liquid crystal display elements include, for example, the Q, ?? of the flip-flop circuit 21. ) The voltage adjustment circuit 22 is required because the voltage adjustment is from 0 to about 10V in the present invention. Generally, liquid crystal elements are driven by AC to prevent deterioration of the liquid crystal material.
Excluding dual frequency drive etc., the drive frequency is 30~IKH
The oscillation circuit 23 outputs the signal at z. However, in a liquid crystal optical element such as the present invention, higher precision and stability may be required than in a normal liquid crystal display element.

In such a case, what if the severe fluctuation caused by AC drive becomes a problem? It is preferable to use a series of driving methods including DC driving, such as DC driving during IN distance operation, and then AC refresh driving from the viewpoint of liquid crystal maintenance.

The above is the operating principle of a liquid crystal prism. An embodiment of the present invention in which the distance measurement range on the close side is expanded using such a liquid crystal prism will be described below.

FIG. 9 is a structural block diagram of a focus detection device showing a first embodiment of the present invention. In the figure, liquid crystal prism 2
a and 2b are arranged in front of the 11-1 distance optical system 10a, and bend the light flux from the subject 1a by the voltage applied from the liquid crystal drive circuit 27, and adjust the distance aPj of the focus detection device.
Change the fixed range. Lenses 3a, 3b, mirror 36a
, 36b, and a distance measuring optical system 10a consisting of a right angle prism 37.
forms an image on the line sensor 4 according to the subject distance. The line sensor 4 includes A group sensors 4 a and B
j! The subject images formed on the respective sensors of one sensor 4b are outputted to the interface circuit 24 after the light weight is exchanged. The interface circuit 24 controls the charge accumulation time of the line sensor 4 according to instructions from the microcomputer 25, and also converts the data obtained from the sensor 4 into an A/D converter.
It is converted and output to the microcomputer 25. Also,
The output of a temperature sensor 26 that monitors the temperatures of the distance measuring optical system 10a and the liquid crystal prisms 2a and 2b is A/D converted and output to the microcomputer 25.

The liquid crystal drive circuit 27 applies a voltage based on instructions from the microcomputer 25 to the liquid crystal prism 2a.

2b is applied to the liquid crystal molecules. A description of the drive circuit 27 will be given later.

The clock signal of the oscillation circuit 28 is used as a source oscillation for the microcomputer 25, and is also used to generate the lightning pressure for driving the liquid crystal.

The microcomputer 25 is the interface circuit 2
The distance to the subject is calculated based on the data manually generated from step 4. Then, the amount of extension of the photographing lens 33 is calculated from this p output data. The microcomputer 25 sends a control signal to the motor drive circuit 30 in order to extend the photographing lens 33 so that the output of the position detection circuit 29 matches the amount of extension, thereby causing the motor 34. Rack mechanism 34a
By sliding the photographing lens 33 in the optical axis direction through the lens 33, the object light is imaged on the film surface 35.

E2PROM (Electrically Era
sablc Progra*able Read
0nly Memory) is written with various correction data necessary for distance measurement.

What about the display circuit 32? Various information based on the ip+distance result is displayed.

Next, the configuration of the liquid crystal drive circuit 27 will be explained with reference to FIG. In the figure, the DC/DC converter 41 is connected to the battery 4
This is for boosting the voltage No. 2 to a voltage value necessary for changing the refractive index of the liquid crystal. The frequency divider 43 converts the clock signal output from the oscillation circuit 28 (see FIG. 9) into J? This is for dividing the frequency up to one wave number. The clock signal frequency-divided by the frequency divider 43 is amplified by the transistor Q and the resistors Ra and R1 to the voltage boosted by the converter 41, and is input to the D-type flip-flop circuit 44. . Outputs Q and O of the flip-flop circuit 44 alternately turn on and off transistors Q and Q2 via resistors R2 and R3.

Due to this operation, the voltage generated across resistors R4 and R5 is indicated by the arrow Ai
The voltage is applied to the liquid crystal prism 2a alternately like t''12, which is the same as applying an alternating voltage to the liquid crystal prism 2a.In order to control the amplitude of this alternating voltage, the transistors QI, It is sufficient to change the emitter voltage of Q2.

Therefore, the digital data from the microcomputer 25 (see FIG. 9) is converted into a voltage value as analog data by the D/A converter 46, and then the impedance is converted by the buffer circuit 47 and the transistor Q.
It is applied to the emitter of Q2.

The operation of this embodiment configured as described above will be explained below with reference to the flowchart shown in FIG. 11, focusing on the "AF" operation by the microcomputer 25. First, in step 5100, "set macro flag"
do. Normally, immediately after calling the "AF" routine, the voltage applied to the liquid crystal prisms 2a and 2b is 0.
■It is. Therefore, as described above, the refractive index of the liquid crystal is high, and the deflection angle δ of the prism is also large. Therefore, the ApJ distance range is biased toward the close side, that is, toward the macro.

In steps 8101 to 8103, the microcomputer 25 integrates the line sensor 4 through the interface circuit 24, and obtains the outputs of the A group sensor 4a and the 8 group sensor 4b as digital values. Step 510
4, the microcomputer 25 takes in the lPj constant data output from the temperature sensor 26 through the interface circuit 24. This sensor 26 measures the temperature of the distance measuring optical system 10a and the liquid crystal prisms 2a, 2b.
This is for determining the I. In step 5105, the interval t (see FIG. 16) between the images formed on each sensor 4a, 4b is calculated by a "correlation calculation" from the sensor data obtained by the A group sensor 4a and the 8 group sensor 4b.

Next, the process proceeds to step 5106, and it is determined based on the result of the correlation calculation whether or not the distance can be measured. If the distance can be measured, the process branches to step 5200.

In this step 5200, it is determined whether the "macro flag is set ("1") or not, and it is reset ("
O"), the voltage is applied to the liquid crystal prism 45, so there is no need to correct the distance t between the obtained images. Therefore, the process branches to step 8203 and the subject distance and the above-mentioned FIG. The amount of extension of the photographic lens 33 shown is calculated.

Next, in step 5204, based on this calculation result, the microcomputer 25 controls the motor 34 to drive the photographing lens 33 to a predetermined position. Step 520
In step 5, AF is completed and the subject distance is "displayed". Then, the process proceeds to step 5206, where the flag is reset and the output of the liquid crystal drive circuit 27 (see FIG. 9) is set to OV.
Return to "Initial" (then return.

If the macro flag is set (“1”) in step 5200, the process advances to step 5201. Then, the correction value Δt for the image interval t is read out from the E2PROM 31. This correction value Δt is, as shown in FIG.
Refractive index n. Subject 1 passing through the liquid crystal prisms 2a and 2b
When the light flux g1 from a is based on the position of the image formed on the sensor 4 via the lenses 3a and 3b, the refractive index n
It shows the amount of displacement of the image formed on the sensor 4 due to the luminous flux 12 at the time. As already explained, n8>no, and by increasing the applied voltage n. is n. Changes to Since the refractive index n8 is dependent on temperature, the correction amount Δt changes depending on the temperature. In addition, even if the temperature is constant, the angle of incidence θ of the light ray from the subject to the liquid crystal prism will compensate for the I
The E value Δt changes.

The incident angle θ can be determined by the image spacing t.

Therefore, the correction value Δt needs to be determined based on the temperature data and the image interval t. Since it is difficult to calculate Δt with a microcomputer, it is necessary to calculate it in advance or calculate the actual ΔP1.
The correction value Δt obtained by
The microcomputer 25 may read out the necessary correction value Δt from the temperature data and the image interval t.

The read correction value Δt is adjusted to 1 of the image in step 5202.
By adding this to the 81 interval t, correct image interval data can be obtained. In this embodiment, the voltage applied to the liquid crystal is set to OV during macro distance measurement, but a voltage may be applied during macro distance measurement to prevent temperature changes in the refractive index n. In this case, voltage control by the microcomputer 25 can be simplified by manually inputting D/A converter values according to the temperature into the E2FROM in advance. In this case, the correction value Δt of the displacement amount may be determined only by the change in the angle of incidence of the liquid crystal prisms 2a and 2b.

Returning to FIG. 11, if it is determined in step 5106 that correlation cannot be established, the process advances to step 5107. By the way, when the temperature of liquid crystal increases to a certain temperature or higher, it becomes an isotropic liquid and no longer exhibits refractive index anisotropy. In this state, the deflection angle of the liquid crystal prisms 2a and 2b is set to ff by the voltage.
i+Jg! Since it is not possible to J, step 510
In step 7, it is determined whether the humidity is at a humidity To that can be controlled by the liquid crystal prism. If the temperature is impossible,
The process branches to step 5300, and the display circuit displays that AF is not possible.

If the temperature is controllable, the process branches to step 5108. In step 5108, if the macro flag is reset (“φ”), this indicates that the second distance of 1111, in which the voltage was applied and the distance measurement range was changed to the ω side, was impossible. If it is set (“1°”), it is necessary to apply a voltage and set the INl distance again, so step 510
Branch to 9. And the refractive index is n. The voltage data to be set is set in the D/A converter 46 (see FIG. 10). Then, the "timer" in step 5110 waits until the change in the refractive index of the liquid crystal ends.

Since the responsiveness of the refractive index change of the liquid crystal depends on the temperature and applied voltage, this timer chain is changed based on the temperature data read in step 5104 and the data set in the D/A converter 46. After the refractive index change is completed, the macro flag is reset in step 5111, and the process returns to step 5101 in order to extend the range on the long distance side to 11P+distance again.

FIG. 13 is a block system diagram of a focus detection device showing a second embodiment of the present invention. The major difference between this second embodiment and the first embodiment is that an active method is used instead of a passive method.

Except for this point, the structure is the same as that of the first embodiment, so the same constituent members are given the same reference numerals and the explanation thereof will be omitted.

In the block system diagram shown in FIG. 13, a light beam is projected from a light emitting element 52 toward a subject 1a, and the reflected light from the subject 1a is converted into a PSD (Position Sensi).
An example is shown in which a liquid crystal prism is applied to a light projection type distance measuring device that measures distance by receiving light from a PSD 51. By determining t, the object distance can be calculated. The position t of this object reflected light beam is PS
Current output from D51 11. It is determined from the ratio of I2,
Since this is equivalent to the image interval t in the first embodiment, once the position t of the reflected light beam is determined, the same processing as in the first embodiment can be performed. In the case of a light projection type,
If the light beam reflected by the object and returned is weak, distance measurement will not be possible, so it is necessary to devise ways to improve the transmittance of the liquid crystal prism 2a.

FIG. 14 is a block system diagram of a focus detection device showing a third embodiment of the present invention. Above 1. In the second embodiment, an example was shown in which the 11-1 distance range was divided into two, the ■ side and the close side, using a liquid crystal prism. In this third embodiment, the ranging range is divided into a plurality of parts. If the number of divisions is increased, a wider distance measurement range can be covered even if the size of the sensor is smaller. The conventional method of mechanically inserting prisms requires multiple prisms,
Although this method is difficult to implement, this embodiment can only be realized by using a liquid crystal prism whose refractive index is electrically variable as in the present invention.

In this third embodiment, the 8-1 distance areas are defined as area ■, area ■,
The basic configuration is the same as that of the first embodiment except for the fact that it is divided into three areas (3). Components that are the same as those used in the second embodiment are given the same reference numerals, and explanations of the configurations thereof will be omitted and only the operations will be described below.

FIG. 15 is a flow chart explaining the "AF" operation of the microcomputer 25 in this third embodiment. In this FIG. 15, routines that are the same as those in FIG. 11 showing the flow of the first embodiment are given the same step numbers and their explanations are omitted, and only the different routines are given step numbers of 54 QO series. Explain.

In FIG. 15, in step 5401, the counter 71
111 Set "3°" corresponding to the number of distance regions.

The value of the counter indicates the current position of the range measurement range, and in this case, the range (2) in FIG. 14 can be measured without applying voltage to the liquid crystal prism. Steps 8101 to 5105 are omitted and the process proceeds to step 5106.
If it is determined that the p1 distance can be achieved, the process branches to step 5411.

In step 5411.412 the chain of counters is determined. If the counter is “1”, the refractive index of the liquid crystal is n
Since the voltage is applied so that the distance is 0, and the range of distance measurement is the area 3, the refractive index is n as in the first embodiment. The correction shall be made based on the time of . Therefore, if the counter is "1", the process branches to step 8203. If the counter is “2” and “3”, step 8413
and 5414, the corresponding correction ports are set in the E2FROM 31 (Fig. 9 2) according to the temperature data and the correlation value.
(see). The process then proceeds to step 5202 and subsequent steps, but steps 8202 to 5206 are omitted because they are the same as the operations in the flowchart in the first embodiment.

If it is determined in step 5106 that the correlation is not OK, that is, distance measurement is not possible, the process proceeds to step 5402, where the counter chain is decremented by 1. In step 5403, it is determined whether the value of the counter is "0". If the content of the counter is "0", it means that distance measurement was carried out in all of the areas (2) to (2), but no distance measurement data was obtained, so the process branches to step 8300 and subsequent steps. This step 53
The processing of 00°5301 is the 11th process in the first embodiment above.
The operation is the same as that shown in the flowchart in the figure, so the explanation will be omitted.

If the content of the counter is not 0 in step 5403, the process proceeds to step 5404, where it is checked whether the content of the counter is equal to 2 or not. In other words, it is necessary to change the /1Ilj distance range by changing the voltage applied to the liquid crystal prism depending on the distance measurement area. Therefore, steps 8404~
In 5406, the microcomputer 25 provides data to the D/A converter 46 (see 101ci!J) of the liquid crystal drive circuit 27 so that the &FI distance range is set in the ■ area or ■ area according to the value of the counter. . Then, when the time specified by the "timer" in step 5110 has elapsed and the change in the refractive index of the liquid crystal prism ends, the process returns to step 5101 to perform the Δ-j distance again.

The area with a distance of Δ11 can be divided into any number of areas by finely controlling the voltage applied to the liquid crystal prism, and the line sensor 4 can be made smaller accordingly. However, since the number of integrations performed by the sensor increases, unnecessarily increasing the number of divisions increases the time required for distance measurement. Therefore, there is a trade-off between the number of divisions of the Δ11 distance region and the miniaturization of the line sensor, and in this third embodiment, the number of divisions of the Ili distance region is set to three.

[Effects of the Invention] As described above, according to the present invention, the optical wedge of the liquid crystal prism made of liquid crystal whose refractive index can be electrically changed can be used to quickly focus without using mechanical members. The distance range that can be measured by the detection device can be expanded, and since no mechanical members are required, the 1111 range device can be miniaturized, which is a remarkable effect.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the focus detection device of the present invention, and FIG.
A block system diagram illustrating the basic principle of the focus detection device of the present invention. Figure 3 (^) is a vertical cross-sectional view of the liquid crystal prism used in the optical wedge in Figure 1, and Figure 3 (B) is Figure 3 (
The DD' cross-sectional view in A), Figure 4, and (B) show the molecular structure of cyanobiphenyl as an example of the P-type liquid crystal used in the liquid crystal prism shown in Figure 3 above, Diagrams showing the refractive index ellipsoid, Figures 5(A), (B), and (C) show the dielectric anisotropy of the liquid crystal molecules shown in Figures 4(A) and (I3) above,
In other words, it is an explanatory diagram showing the arrangement of liquid crystal molecules and the polarization direction with respect to the applied voltage. Fig. 5 (A) is when the applied voltage is Ov, Fig. 5 (B) is when the applied voltage is an intermediate value. (C)
6 (A), (B) and 7 (^), (
B) is a liquid crystal prism having a cross-sectional shape shown in FIG. 6(A) and FIG.
A vertical cross-sectional view illustrating the formation of the cross-sectional shape shown in FIG. 13 or FIG. FIG. 10 is a block diagram showing the configuration of the liquid crystal drive circuit in FIG. 9, and FIG. 11 is a block diagram showing the configuration of the liquid crystal drive circuit in FIG. FIG. 12 is a flowchart of the AF operation of the microcomputer in the embodiment. Steps 5201.
FIG. 13 is an optical layout diagram of the distance measuring optical system for explaining the correction value Δt of the image interval t in 5202. FIG. 13 is a block system diagram of the focus detection device showing the second embodiment of the present invention. , a block system diagram of a focus detection device showing a third embodiment of the present invention, FIG. 15 is a flowchart of the AF operation of the microcomputer in the third embodiment shown in FIG. 14, and FIG. 16 is a conventional focus detection system. FIGS. 17 to 20, which are optical layout diagrams of the passive type Apj distance device in the device, are optical layout diagrams illustrating conventional means for expanding the A#j distance range on the close side in FIG. Figure 17 is
Fig. 18 shows a method of reducing the base line length S, Fig. 18 shows a method of increasing the length of the sensor, and Fig. 19 shows a method of shortening the focal length of the light receiving lens to bring the sensor closer to the light receiving lens.
Figure 0 shows how to place a prism in front of the light receiving lens.
FIG. 4 is an optical layout diagram for explaining each. la, lb......Subjects 2a, 2b
・・・・・・・・・・・・Liquid crystal prism (optical wedge) 2a
, 2bt...Optical wedge■ 4.4a, 4b...Sensor (signal output means) 5
・・・・・・・・・・・・・・・・・・・・・Refractive index control means 6・・・・・・・・・・・・・・・・・・
...Distance data output means 10.10a...
... Distance measuring optical system 24 ......
......Interface circuit (signal output means) 25...................................................................Microcomputer (signal output means)

Claims (1)

[Claims] (1) A focus detection device that detects the distance to a subject based on the principle of triangulation, which includes a distance-measuring optical system including an optical wedge whose refractive index can be changed electrically; a refractive index control means for controlling a refractive index; a signal output means for outputting an electrical signal related to a subject distance according to the subject light guided to the distance measuring optical system; and a refractive index of the optical wedge and the electrical signal. A focus detection device comprising: distance data output means for outputting object distance data.