JP2758648B2 - Focus detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device, and more particularly, to a focus detection device based on a triangulation method, and more particularly to a focus detection device in which a distance measurement range on a close side is enlarged.

2. Description of the Related Art Conventionally, an autofocus camera that measures a subject distance based on the principle of triangulation and drives a photographing optical system to a focal point based on the measured distance data is known. The principle of such a passive type distance measuring device will be described with reference to FIG. Can be obtained by Here, f is the first and second lenses 61 and 62 from which the image of this lens is formed.
Are the lengths of the sensors 63 and 64, S is 1/2 of the base line length, and t is the image forming point formed on the first and second sensors 63 and 64 when the subject 65 is at ∞. With reference to the reference position, the amount of deviation of the current imaging position of the subject image from the reference position is shown. The deviation amount t can be obtained by performing a correlation operation between the data of the first sensor 63 and the data of the second sensor 64.

By the way, in order to make the shortest measurable distance in such a distance measuring device smaller than the conventional distance l _MIN , the following three methods can be considered as understood from the above equation (1).

In the first method, the base length S is reduced. That is, a first lens 61 and a second lens 62 indicated by dotted lines in FIG. 17, respectively.
In the directions of arrows A ₁ and A ₂ to indicate
If the second lenses 61a and 62a are used, the distance measurement range on the closest side is l
It becomes _MIN .

In the second method, as shown in FIG. 18, the first and second sensors 63 and 64 indicated by dotted lines are extended by arrows A ₃ to extend the measurement range of the image displacement amount t from the reference position. , A ₄
Assume that the sensors 63a and 64a have moved to the positions indicated by the solid lines.

The third method is to use first and second lenses as shown in FIG.
61, 62, the focal length f is shortened, and the first and second directions in the directions of arrows A ₅ and A ₆
The second lenses 61, 62 are moved closer to the first and second sensors 63, 64 to obtain lenses 61a, 62a indicated by solid lines.

However, the first method shown in FIG. 17 requires a mechanism for moving the lens with high accuracy, so that the distance measuring device becomes complicated and the cost increases. In the second method shown in FIG. 18, there is no need to change the mechanism, but the cost increases because the size of the sensor in the longitudinal direction increases. Furthermore, in the third method shown in FIG. 19, by shortening the focal length of the lens and moving the lens closer to the sensor, the amount of displacement t of the image with respect to the subject distance is compressed. Although the range is widened, if the measurement accuracy of the image shift amount t is poor, the distance measurement accuracy will be reduced. Therefore, the necessary distance measurement accuracy cannot be obtained depending on the photographing lens used.

Therefore, in the fourth method shown in FIG. 20, the first and second prisms 66 and 67 are inserted before the first and second lenses 61 and 62, and the deflection angle δ of the prisms 66 and 67 is used. An attempt is made to expand the distance measurement range on the closest side. These first and second prisms
The image formed on the sensor by the deflection angle δ of 66, 67 is
That is, the image is detected to be smaller by the correction value Δt of the image shift amount t. Therefore, the above equation (1) Becomes This means that the same effect as that obtained by increasing the sensor correction amount Δt in the second method is obtained. The difference between the fourth method and the second method is that the correction amount Δ
That is, the subject distance does not become Δ due to t.

The fourth method shown in FIG. 20 is disadvantageous in that the number of optical components increases as compared with the above-described first to third methods. However, since the positional accuracy of the prism is rougher than that of the lens, the prism moving mechanism is used. Easy to make. In addition, the second to increase the sensor
This method is more advantageous in terms of cost than the method of (1). A means for extending the distance measurement range by using a prism has already been disclosed in Japanese Patent Application Laid-Open No. 61-148434.

That is, the "autofocusing device having a near-joint focusing function" described in the above-mentioned Japanese Patent Application Laid-Open No. 61-148434 is a distance measuring means provided with a detecting unit for exceeding a short-range photographing limit of a photographing lens, and a distance measuring means. A distance setting means for the photographing lens for setting the distance of the photographing lens based on the distance signal, and a correction lens inserted into the photographing lens and a wedge inserted into at least the distance measuring optical system in accordance with a detection signal for exceeding the short distance photographing limit. Optical correction means of the optical system, and means for performing distance measurement again by the optical system corrected by the detection signal of the imaging limit excess,
When the subject is closer than the short-range shooting limit, a correction lens is inserted into the shooting lens based on the detection signal, and at least the incident optical path of the distance measurement optical system is corrected and distance measurement is performed again to set the distance of the shooting lens. An optical wedge mechanically inserted in the distance measuring optical system is equivalent to the prisms 66 and 67 shown in FIG. 20. Therefore, by inserting the optical wedge, the distance measurement range on the close side is extended.

In addition, instead of a prism, a flat plate that transmits light is provided between the light receiving lens and the light receiving element, and the tilt of the flat plate is changed in conjunction with the focus ring, thereby allowing the flat plate to operate in the same manner as the prism. Japanese Patent Application Laid-Open
It is disclosed in JP-A-63-75717.

That is, the "autofocusing device" described in Japanese Patent Application Laid-Open No. 63-75717 discloses an "autofocusing device" which is arranged between a light receiving element and a light receiving lens with respect to an axis orthogonal to a plane including 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 light emitted from the light emitting element to pass therethrough, and this flat plate is connected to a focus ring so as to rotate according to its movement, and the focus ring is driven by the output of the light receiving element Means for performing the operation. The flat plate is a prism shown in FIG.
In addition to the same action as 66 and 67, the light rotates as the focus ring moves, so the received light beam is polarized as the plane plate rotates, and the light receiving state at the light receiving element changes, and as a result, the light at the close side is changed. The ranging range is extended.

[Problems to be Solved by the Invention] However, the above-mentioned Japanese Patent Application Laid-Open No. 61-14 / 1986 inserts an optical wedge mechanically inserted into the distance measuring optical system into the distance measuring optical system.
The proposal described in JP 8434, and providing a plane plate through which subject light passes between the light receiving element and the light receiving lens, and interlocking this plane plate with the focus ring so that the received light beam is polarized as the plane plate rotates. In any of the proposals described in Japanese Patent Application Laid-Open No. 63-75717, a mechanical switching means is required in any case, which is not preferable because the apparatus becomes large and complicated. If possible, it is desirable to perform the same function by electrical means.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to use the optical wedge acting as a prism made of an optical material having an electrically variable refractive index to achieve the same effect as inserting a prism or using a parallel plate. Accordingly, an object of the present invention is to provide a focus detection device in which the distance range on the closest side that can be measured is extended.

[Means and Actions for Solving the Problems] A focus detection device according to the present invention is a focus detection device that detects the distance to a subject based on the principle of triangulation, and electrically changes the refractive index to perform measurement. A distance measuring optical system including an optical wedge capable of deflecting an optical axis for distance, a refractive index control means for controlling a refractive index of the optical wedge, and a subject distance according to subject light guided to the distance measuring optical system A data output unit that outputs data related to the object, a memory that stores a correction value for correcting the data related to the subject distance, and a refractive index of the optical wedge to a specific refractive index by the refractive index control unit. A correction unit configured to correct data related to the subject distance based on the correction value stored in the memory when the setting is performed. Rank Receiving the subject light from the subject and detecting the distance to the subject based on the amount of displacement between the two images, further comprising: Projecting light for use, receiving reflected light from the subject, and outputting the distance data based on the light receiving position, and wherein the focus detection device sets the refractive index of the optical wedge to an initial value. Outputting data related to the subject distance in a set state, changing the refractive index of the optical wedge when the focus state cannot be detected in this state, and outputting data related to the subject distance. Features.

Hereinafter, the present invention will be described with reference to the illustrated embodiments. First,
Prior to describing an embodiment of the present invention, FIG.
The outline of the embodiment will be described. As shown in FIG. 1, the focus detection device detects the distance to the subject 1a, 1b based on the principle of triangulation, and can electrically change the refractive index. A distance measuring optical system 10 including optical wedges 2a ₁ and 2b ₁ ;
a ₁ , 2b ₁ a refractive index control means 5 for controlling the refractive index; a signal output means for outputting an electric signal related to the subject distance in accordance with the subject light guided to the distance measuring optical system 10; It is characterized by comprising distance data output means 6 for outputting subject distance data from the refractive indexes of the chemical wedges 2a ₁ and 2b ₁ and the electric signal. FIG. 2 explains the basic principle of the present invention, and FIGS. 3 to 8 explain the operating principle of the optical wedge used in the present invention.

FIG. 2 is a block diagram for explaining the basic principle of the focus detection device of the present invention. In the figure, subject 1
The objects from a and 1b are optical wedges formed by a liquid crystal prism.
The light is projected onto a distance measuring optical system 10 including lenses 3a and 3b and sensors 4a and 4b via 2a ₁ and 2b ₁ . An output signal from the distance measuring optical system 10 is supplied to a judging means 8 so that the output of the judging means 8 is supplied to a correcting means 9 and a distance measuring range switching means 7 comprising an AC power supply 7b and a switch 7a. Has become.

In such a configuration, the subject light from the subject 1b located further on the closer side than the distance measurement limit on the closer side is transmitted to the optical wedge 2a.
₁ , 2b ₁ , respectively, pass through the lenses 3a, 3b and become dashed lines la, lb and head toward the sensors 4a, 4b. Cannot image. Therefore, determination unit 8 sends a signal to the distance measurement range switching means 7 detects this, it switches 7a of the switching means 7 is turned on by the AC voltage is wedge 2a ₁ from an AC power source 7b, 2b It will be applied to ₁ . Then, since the refractive index of the optical wedges 2a ₁ and 2b ₁ is increased, the subject light from the subject 1b further closer than the closest distance measurement limit is:
The light is refracted inward by the optical wedges 2a ₁ and 2b ₁ so that an image is formed on the sensors 4a and 4b. The output signals from the sensors 4a and 4b obtained in this way are corrected by the correction means 9 so that a correct distance measurement value can be obtained.

That is, according to the present invention, an electrically variable refractive index optical wedge is arranged in front of the light receiving lens, and a voltage applied to the optical wedge is
By controlling according to the subject distance, a focus detection device in which the distance measurement range on the close side is enlarged is configured.

Next, the operation principle of the optical wedge will be described. The optical wedge used in the present invention is an optical prism (hereinafter, referred to as a liquid crystal) filled with a liquid crystal utilizing the property that the refractive index changes when the voltage applied to the liquid crystal is changed. (Referred to as a prism).

 FIGS. 3A and 3B are longitudinal sectional views of a liquid crystal prism.
It is DD 'sectional drawing. As shown in the figure, the liquid crystal prism
The basic configuration of 15 consists of two transparent optical members 12 and 13 and a spacer 1
Liquid crystal 14 is sealed in the space formed by 8, 19
I have. On the side of the two transparent optical members 12 and 13 that touch the liquid crystal 14
Has a transparent conductive layer formed thereon, and the liquid crystal 14 has a variable resistor 16
AC voltage can be applied from the AC power supply 17 through the
ing. FIGS. 3A and 3B show that P
Liquid crystal (ε > Ε_⊥) Is homogeneous when the applied voltage is 0V
The state of arrangement is shown.

In general, 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 vertex angle of the prism.

δ = (n−1) α (3) From equation (3), it can be seen that changing the refractive index n or the apex angle α changes the deflection angle δ of the prism.

The liquid crystal prism 15 has a refractive index n using its birefringence.
Is changed. In a liquid crystal (nematic phase), liquid crystal molecules are fluctuating microscopically, and not all molecules are arranged in the same direction. Is defined.

 FIGS. 4A and 4B show a P-type liquid crystal (n_e> N₀) Lord
Molecular structure of cyanobiphenyl series as an example of the component and its
Are shown, respectively. And liquid
Crystalline molecules have their dielectric anisotropy, or ε ≠ ε_⊥For the first
5 Applied voltage as shown in FIGS. (A), (B) and (C)
Follow V. In other words, the vibration
When the linearly polarized light 20 enters the liquid crystal cell, the apparent liquid crystal
Refractive index n_θVaries according to the rotation angle θ according to the following equation (4).
Become

That is, the applied voltage V is applied voltage from a state exhibiting a refractive index n _e for extraordinary light, as shown in FIG. 5 (A) When the 0V V
When the applied voltage V is high, the refractive index for ordinary light changes to n ₀ , as shown in FIG. 5 (C), and a state when the applied voltage V shown in FIG. ing. Therefore, the refractive index of MiKakeue n _theta is a function of the applied voltage V as shown in the following equation (5).

n _θ = n (V) (5) As a result, the deflection angle δ _LC of the prism-shaped liquid crystal is
In accordance with the applied voltage V, the refractive power for the extraordinary light changes continuously from the refractive power for the ordinary light. Therefore,
The above equation (3) becomes the following equation (6), and the refractive power can be adjusted by the voltage.

δ _LC (V) = (n (V) −1) α (6) That is, by applying a voltage, the deflection angle δ becomes the third angle.
Will vary in the direction of arrow A ₉ shown in FIG. (A). Usually, the response time τ in the electro-optic phenomenon of a nematic liquid crystal
_r and the recovery time τ _d are expressed by the following equations (7) and (8).
It is known that it is proportional to the square of the liquid crystal thickness d.

 τ_r= Ηd^Two/ (Ε₀ΔεV^Two−Kπ²) …… (7) τ_d= Ηd^Two/ Kπ²) (8) where η is the viscosity, K is the elastic modulus, V is the applied voltage, Δε
(= | Ε −ε_⊥|) Represents the dielectric anisotropy, respectively.
I have.

Therefore, in the application of the liquid crystal prism, if it is desired to increase the response speed, the shape shown in FIG. 6A is transformed into the shape shown in FIG. 6B to effectively reduce the thickness of the liquid crystal. Alternatively, the shape shown in FIG. 7A may be changed to a shape obtained by laminating thin prisms shown in FIG. 7B.

Since the liquid crystal prism is an optical element utilizing birefringence of liquid crystal, it is not shown in FIG. 3, but it is necessary to provide a polarizing plate and allow only linearly polarized light to enter. Otherwise, two deflection angles δ will occur. Alternatively, there is a method of solving this problem by superposing two liquid crystal prisms such that the liquid crystal alignment directions are orthogonal to each other. When the light transmittance of the prism becomes a problem, the structure becomes complicated. However, it is better to use the latter method in which two liquid crystal prisms are overlapped so that the liquid crystal alignment directions are orthogonal to each other.

FIG. 8 shows a block diagram of a drive circuit for the liquid crystal prism 2a. A general liquid crystal display element is a binary drive of ON / OFF such as an output of a flip-flop circuit 21Q, for example. However, in the present invention, the voltage adjustment is 0 to about 10V, so the voltage adjustment circuit 22 is required. . In general, the liquid crystal element is driven by AC in order to prevent the deterioration of the liquid crystal material, and the driving frequency is output by the oscillation circuit 23 at a driving frequency of 30 to 1 KHz except for two-frequency driving. However, in the liquid crystal optical element as in the present invention, higher accuracy and stability may be required more than a normal liquid crystal display element. In such a case, if slight fluctuation caused by AC driving becomes a problem, a series of DC driving including DC driving is performed when performing distance measurement operation and then AC refresh driving from the viewpoint of LCD protection. The driving method is preferred.

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

FIG. 9 is a block diagram showing the configuration of a focus detection apparatus according to a first embodiment of the present invention. In the figure, the liquid crystal prism
2a and 2b are arranged in front of the distance measuring optical system 10a, and bend the luminous flux from the subject 1a by the voltage applied from the liquid crystal drive circuit 27 to change the distance measurement range of the focus detection device.
The distance measuring optical system 10a including the lenses 3a and 3b, the mirrors 36a and 36b, and the right-angle prism 37 forms an image on the line sensor 4 according to the subject distance. The line sensor 4 is a group A sensor 4a, B
The image of the subject formed on each of the group sensors 4b is photoelectrically converted and output to the interface circuit 24. The interface circuit 24 controls the charge accumulation time of the line sensor 4 according to a command from the microcomputer 25, and A / D converts data obtained from the sensor 4 and outputs the data to the microcomputer 25. In addition, distance measuring optical system 10a
The output of the temperature sensor 26 for monitoring the temperatures of 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 a command from the microcomputer 25 to the liquid crystal molecules of the liquid crystal prisms 2a and 2b. The description of the driving circuit 27 will be described later.

The clock signal of the oscillation circuit 28 is
It is used not only as a source for 25, but also for generating an alternating voltage for driving a liquid crystal.

The microcomputer 25 includes an interface circuit 24
The distance to the subject is calculated based on the data input from. Then, the extension amount of the photographing lens 33 is calculated from the calculation data. The microcomputer 35 controls the photographing lens 33 so that the output of the position detection circuit 29 matches the extension amount.
A control signal is sent to the motor drive circuit 30 in order to extend the photographing lens through the motor 34 and the rack mechanism 34a.
The object light forms an image on the film surface 35 by sliding the object 33 in the optical axis direction.

E ² PROM (Electrically Erasable Programmable Read O
In the nly Memory), data for various corrections necessary at the time of distance measurement is written. The display circuit 32 displays various information based on the distance measurement result.

Next, the configuration of the liquid crystal drive circuit 27 will be described with reference to FIG. In the figure, a DC / DC converter 41 is for boosting the voltage of a battery 42 to a voltage value required to change the refractive index of the liquid crystal. The frequency divider 43 is for dividing the frequency of the clock signal output from the oscillation circuit 28 (see FIG. 9) to a frequency required for driving the liquid crystal. Divided clock signal in the frequency divider 43, the transistors Q ₀ and the resistor R _0, R
₁ , the amplitude of the clock signal is amplified to the voltage boosted by the converter 41, and the D-type flip-flop circuit 44
Enter The output Q of the flip-flop circuit 44 is
The transistors Q ₁ and Q ₂ are turned on and off alternately via the resistors R ₂ and R ₃ .

By this operation, the voltage generated at the resistors R ₄ and R ₅ is changed to the arrows A ₁₁ and A ₁₂
Thus, the alternating voltage is applied to the liquid crystal prism 2a in the same manner as described above. Then, to control the amplitude of the alternating voltage, the emitter voltages of the transistors Q ₁ and Q ₂ may be changed.
Then, 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 to be applied to the emitters of the transistors Q ₁ and Q ₂ . Is being applied.

The operation of the present embodiment thus configured will be described below with reference to the flowchart shown in FIG. 11, focusing on the operation of "AF" by the microcomputer 25. First, "set a macro flag" in step S100. Normally, immediately after the "AF" routine is called, the voltage applied to the liquid crystal prisms 2a and 2b is 0V. Therefore, as described above, the refractive index of the liquid crystal is in a high refractive index state, and the deflection angle δ of the prism is also large. Therefore, the distance measurement range is closer to the close side, that is, biased toward the macro.

In steps S101 to S103, the microcomputer
Numeral 25 integrates the line sensor 4 through the interface circuit 24 to obtain the outputs of the group A sensor 4a and the group B sensor 4b as digital values. In step S104, the microcomputer 25 takes in the measurement data output from the temperature sensor 26 through the interface circuit 24. This sensor 26 is for measuring the temperatures of the distance measuring optical system 10a and the liquid crystal prisms 2a and 2b. In step S105, the interval t (16th image) of the image formed on each sensor 4a, 4b is obtained from the sensor data obtained by the group A sensor 4a and the group B sensor 4b.
Is calculated by “correlation calculation”. Next, the process proceeds to step S106, where it is determined whether or not the distance has been measured based on the result of the correlation operation. If the distance has been measured, the process branches to step S200.

In this step S200, it is determined whether or not the "macro flag" is set ("1"). If the "macro flag" is reset ("0"), the voltage is applied to the liquid crystal prism 45, so that it is obtained. There is no need to correct for the image spacing t. Accordingly, the flow branches to step S203 to calculate the subject distance and the extension amount of the photographing lens 33 shown in FIG.
Next, in step S204, based on the calculation result, the microcomputer 25 controls the motor 34 to drive the photographing lens 33 to a predetermined position. In step S205,
Ends AF and “displays” the subject distance. Then, the process proceeds to step S206 to reset the flag and the liquid crystal driving circuit.
The output of 27 (see FIG. 9) is returned to 0 V, "initialized", and the routine returns.

If the macro flag is set ("1") in step S200, the process proceeds to step S102. And E ²
The correction value Δt of the image interval t is read from the PROM 31. As shown in FIG. 12, the correction value Δt is such that the light flux l ₁ from the subject 1a passing through the liquid crystal prisms 2a and 2b having the refractive index n ₀ is
When based on the position of the image formed on the sensor 4 via 3b, shows a displacement of the image formed on the sensor 4 by the light beam l ₂ when the refractive index n _e. As already explained, _ne >
a n _0, n _e by increasing the applied voltage is changed to n _0. Since the refractive index n _e have a dependency on temperature, the correction amount Δt varies with temperature. Further, even when the temperature is constant, the correction value Δt changes according to the incident angle θ of the light beam from the subject to the liquid crystal prism.

The incident angle θ can be obtained from the image interval 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, the correction value Δt calculated in advance or obtained by actual measurement is written in the E ² PROM 31 and the microcomputer 25 calculates the correction value from the temperature data and the interval t between the images. May be read out. By adding the read correction value Δt to the image interval t in step S202, correct image interval data can be obtained. In this embodiment, although at macro ranging has a voltage applied to the liquid crystal to 0V, and so as not to cause a temperature change of the refractive index n _e with temperature, voltage may be applied at macro ranging. In this case, if the value of the D / A converter corresponding to the temperature is input in advance to the E ² PROM, the voltage control of the microcomputer 25 is simplified. In this case, the correction value Δt of the potential amount may be determined only by a change in the incident angle of the liquid crystal prisms 2a and 2b.

Returning to FIG. 11, if it is determined in step S106 that the correlation cannot be established, the process proceeds to step S107. By the way, when the temperature of the liquid crystal rises and becomes higher than a certain temperature, the liquid crystal becomes an isotropic liquid and does not show the refractive index anisotropy. In this state, it is not possible to control the deflection angle of the liquid crystal prism 2a, 2b by the voltage, temperature in step S107, the liquid crystal prism is determined whether the temperature T ₀ can be controlled. If the temperature is not possible, the process branches to step S300 to "display" that the AF is impossible by the display circuit.

If the temperature can be controlled, the process branches to step S208. In step S108, if the macro flag is reset ("φ"), it indicates that the second distance measurement in which the voltage was applied and the distance measurement range was changed to the 電 圧 side was impossible.
If it is set ("1"), the process branches to step S109 because it is necessary to apply the voltage and measure the distance again. And
The voltage data to the refractive index n ₀ D / A converter 46 (10
(See the figure). Then, it waits for the “timer” in step S110 until the change in the refractive index of the liquid crystal is completed.

Since the response of the change in the refractive index of the liquid crystal depends on the temperature and the applied voltage, the value of the timer is changed based on the temperature data read in step S104 and the data set in the D / A converter 46. After the end of the refractive index change, the macro flag is reset in step S111, and the process returns to step S101 to measure the distance on the long distance side again.

FIG. 13 is a block diagram of a focus detection device showing a second embodiment of the present invention. The second embodiment differs greatly from the first embodiment in that an active system is used instead of the passive system. Except for this point, since the configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

The block diagram shown in FIG. 13 is a light projection system in which a light beam is projected from the light emitting element 52 toward the subject 1a, and the reflected light from the subject 1a is received by a PSD (Position Sensitive Device) 51 to measure the distance. An example in which a liquid crystal prism is applied to a distance measuring device of the formula is shown, and the position t of the light beam of the light emitting element 52 incident on the PSD 51, which changes according to the subject distance, is shown.
_{By obtaining r} , the subject distance can be calculated. Position t _r of the object reflected light beam is determined from the ratio of the current I _1, I ₂ to be output from the PSD51, since equivalent and spacing t of the image in the first embodiment, the position of the reflected light beam
If t _r is obtained, it can be treated in the same manner as the first embodiment. In the case of the light projection type, the distance cannot be measured if the light beam reflected back from the subject is weak, so that a measure to improve the transmittance of the liquid crystal prism 2a is required.

FIG. 14 is a block diagram of a focus detection device showing a third embodiment of the present invention. In the first and second embodiments, the distance measurement range is set to two sides of the ∞ side and the close side by using a liquid crystal prism.
In the third embodiment, the voltage applied to the liquid crystal is not two but is further increased, and the distance measurement range is divided into a plurality. By increasing the number of divisions, it is possible to cover a wide ranging range even if the size of the sensor is small. The conventional method of mechanically inserting a prism requires a plurality of prisms and is difficult to realize.However, it can be realized only by using a liquid crystal prism having an electrically variable refractive index as in the present invention. This is an example. In the third embodiment, the basic configuration is the same as that of the first embodiment except for the point that the distance measurement area is divided into an area, an area, and an area.
The same components as those used in the first and second embodiments are denoted by the same reference numerals, and the description of the configuration will be omitted.
Only the operation will be described below.

FIG. 15 is a flowchart for explaining the "AF" operation of the microcomputer 25 in the third embodiment.
In FIG. 15, the same routines as those in FIG. 11 showing the flow of the first embodiment are denoted by the same step numbers, and the description thereof will be omitted.
A description will be given below with the 00s attached.

In FIG. 15, "3" corresponding to the number of distance measurement areas is set in a counter in step S401. The value of the counter indicates the position of the distance measurement range now. In this case, the distance in the area of FIG. 14 can be measured without applying a voltage to the liquid crystal prism. Steps S101 to S105 are omitted, and the process proceeds to step S106. If it is determined that the distance can be measured based on “correlation OK”, that is, the result of the correlation operation, step S411 is performed.
Branch to

In steps S411 and S412, the value of the counter is determined. If the counter is "1", the refractive index of the liquid crystal is not a voltage is applied so that the n _0, since the distance measurement range is in the region, the first embodiment similarly to the refractive index of n ₀ Correction shall be performed based on the time. Therefore, if the counter is "1", the flow branches to step S203. If the counter is "2" or "3", the process proceeds to steps S413 and S414, and the corresponding correction amount is set to the E ² PROM 31 according to the temperature data and the correlation value.
(See FIG. 9). Then, the process proceeds to step S202 and subsequent steps, but steps S202 to S206 are the same as the operations in the flowchart in the first embodiment, and will not be described.

If it is determined in step S106 that the correlation is not "OK", that is, that the distance cannot be measured, the process proceeds to step S402, and the value of the counter is decremented by one. In step S403, it is determined whether or not the value of the counter is “0”. If the content of the counter is "0", ranging has been performed in all of the areas 1 to 4, but since ranging data has not been obtained, the flow branches to step S300 and subsequent steps. The processing of steps S300 and S301 is the same as the operation of the flowchart of FIG.

If the content of the counter is not 0 in step S403,
Proceeding to step S404, it is checked whether the content of the counter is equal to 2. That is, it is necessary to change the distance measurement range by changing the voltage applied to the liquid crystal prism according to the distance measurement area. Therefore, in steps S404 to S406, the microcomputer 25 controls the liquid crystal driving circuit so that the range or the range is set in the region according to the value of the counter.
Data is supplied to 27 D / A converters 46 (see FIG. 10). Then, when the change of the refractive index of the liquid crystal prism ends after the time specified by the “timer” in step S110 elapses,
The process returns to step S101 to measure the distance again.

If the voltage applied to the liquid crystal prism is finely controlled, the area for distance measurement can be divided in any manner, and the line sensor 4 can be reduced accordingly. However, since the number of times of integration of the sensor increases, if the number of divisions is increased, the time required for distance measurement will increase accordingly. Therefore, the number of divisions of the ranging area and the miniaturization of the line sensor are commensurate with each other. In the third embodiment, the number of divisions of the ranging area is set to three.

[Effects of the Invention] As described above, according to the present invention, focus is quickly achieved by using an optical wedge of a liquid crystal prism formed of a liquid crystal whose refractive index can be changed electrically without using a mechanism member. The range that can be measured by the detection device can be extended,
Further, a remarkable effect that the distance measuring device can be reduced in size because a mechanism member is not required is exhibited.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the focus detection device of the present invention, FIG. 2 is a block diagram illustrating the basic principle of the focus detection device of the present invention, and FIG. 3 (B) is a vertical sectional view of a liquid crystal prism used for the wedge, FIG. 3 (B) is a sectional view taken along the line DD ′ in FIG. 3 (A), and FIGS. FIGS. 5A, 5B, and 5C are diagrams showing a cyanobiphenyl-based molecular structure as an example of a P-type liquid crystal used in the liquid crystal prism shown in FIG. FIG. 4 (A),
FIG. 5B is an explanatory diagram showing the dielectric anisotropy of the liquid crystal molecules, that is, the arrangement of the liquid crystal molecules and the polarization direction with respect to the applied voltage. FIG. 5A shows the case where the applied voltage is 0 V. ) Shows the case where the applied voltage is an intermediate value, FIG. 5 (C) shows the case where the applied voltage is high, and FIGS. 6 (A) and (B) and FIGS. 7 (A) and 7 (B) ,
FIG. 6 (B) shows the liquid crystal prism having a sectional shape shown in FIG. 6 (A) and FIG.
Alternatively, a longitudinal sectional view for explaining the sectional shape shown in FIG. 7 (B), FIG. 8 is a block diagram showing an example of a driving circuit of the liquid crystal prism, and FIG. 9 is a first embodiment of the present invention. FIG. 10 is a block diagram showing an example of a configuration of a liquid crystal drive circuit in FIG. 9; FIG. 11 is a block diagram showing a configuration of a liquid crystal drive circuit in FIG. 9; FIG. 12 is a flowchart of the AF operation of the computer. FIG. 12 is an optical arrangement diagram of a distance measuring optical system for explaining the correction value Δt of the image interval t in steps S201 and S202 in FIG. 11, and FIG. FIG. 14 is a block diagram of a focus detection device according to a second embodiment of the present invention, FIG. 14 is a block diagram of a focus detection device according to a third embodiment of the present invention, and FIG. Flow of AF operation of microcomputer in embodiment FIG. 16 is an optical layout diagram of a passive type distance measuring device in a conventional focus detection device, and FIGS. 17 to 20 show conventional means for expanding the distance measuring range on the close side in FIG. In the optical layout diagram to be explained,
17 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 and bringing the sensor closer to the light receiving lens.
FIG. 20 is an optical arrangement diagram for explaining a method of disposing a prism in front of a light receiving lens. 1a, 1b subject 2a, 2b liquid crystal prism (optical wedge) 2a ₁ , 2b ₁ 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) 26 Temperature sensor (signal output means)

Claims (4)

(57) [Claims] 1. A focus detection device for detecting a distance to a subject based on the principle of triangulation, comprising an optical wedge capable of electrically changing a refractive index and deflecting an optical axis for distance measurement. A distance measuring optical system, a refractive index control unit that controls a refractive index of the optical wedge, and a data output unit that outputs data related to a subject distance in accordance with subject light guided to the range measuring optical system. A memory that stores a correction value for correcting data related to the subject distance; and a memory that stores the correction value when the refractive index of the optical wedge is set to a specific refractive index by the refractive index control unit. And a correction unit configured to correct data related to the subject distance based on the correction value. 2. The apparatus according to claim 1, wherein the focus detection device receives the subject light from the subject at different positions, and detects a distance to the subject based on the amount of displacement between the two images. Item 2. The focus detection device according to Item 1. 3. The focus detecting device according to claim 2, wherein the focus detecting device projects distance measuring light toward the subject, receives reflected light from the subject, and outputs the distance data based on a light receiving position. Item 2. The focus detection device according to Item 1. 4. The focus detection device outputs data related to the subject distance in a state where the refractive index of the optical wedge is set to an initial value. If the focus state cannot be detected in this state, the focus detection device outputs the data. 4. The focus detection apparatus according to claim 1, wherein a refractive index of the optical wedge is changed, and data related to the subject distance is output.