JP4645286B2 - Focus detection system and photographing apparatus - Google Patents

Description

  The present invention relates to a focus detection system and an imaging device including the focus detection system.

  As a focus detection device that detects the focus adjustment state using part of the subject light that has passed through the photographic lens, the light in the near-infrared wavelength range included in the subject light is reflected and separated by the infrared dichroic mirror, and the light Is used for phase difference focus detection (see, for example, Patent Document 1).

JP 2003-322791 A

  However, the above-described focus detection apparatus has a problem that phase difference focus detection cannot be performed when the subject light does not include light in a wavelength region near the infrared region.

The focus detection system according to the first aspect of the present invention is disposed in the optical path of the subject light that has passed through the photographing optical system, and separates and emits infrared light from incident light and transmits light other than the infrared light. An infrared optical element, a light amount detection unit for detecting the amount of light in the infrared region separated by the infrared optical element, and a light having a specific wavelength in the visible region from the incident light are disposed in the optical path of the subject light. A diffractive optical element capable of selectively switching between a first state that diffracts and exits and transmits light other than light of a specific wavelength and a second state that transmits incident light; and an infrared optical element or wherein by receiving more light emitted in the diffractive optical element, focus detection unit that detects a focus adjustment state of the photographic optical system, the diffraction when the detected amount of light at a light quantity detecting unit is equal to or less than a predetermined reference value optics Is controlled to the first state, and the light quantity detector The issued amount of light in the case larger than the predetermined reference value, characterized in that it comprises a control unit for controlling the diffractive optical element in the second state.
The invention according to claim 2 is the focus detection system according to claim 1, wherein the diffractive optical element is a hologram provided on the photographing optical system side of the infrared optical element.
According to a third aspect of the present invention, in the focus detection system according to the second aspect, the diffractive optical element is provided corresponding to a region in which the focus adjustment state is detected in the focus detection unit.
According to a fourth aspect of the present invention, in the focus detection system according to any one of the first to third aspects, the focus adjustment state detected based on the light emitted from the infrared optical element is emitted from the diffractive optical element. The correction is made so as to correspond to the focus adjustment state detected based on the light.
According to a fifth aspect of the present invention, there is provided a photographing apparatus that receives the light transmitted through the focus detection system according to any one of the first to fourth aspects and the infrared optical element and the diffractive optical element and captures a subject image as a photographed image. And an autofocus control means for performing a focus adjustment operation of the photographing optical system based on a detection result of the focus detection unit.
According to a sixth aspect of the present invention, in the photographing apparatus according to the fifth aspect , a photoelectric conversion type image pickup element that receives light transmitted through the infrared optical element and the diffractive optical element and picks up a subject image, and a photoelectric conversion type image pickup element And an evaluation value calculation unit that calculates a focus evaluation value based on the imaging signal of the image pickup signal, and the autofocus control means is configured to focus the imaging optical system based on the detection result of the focus detection unit and / or the calculation result of the evaluation value calculation unit. The adjustment operation is performed.
According to a seventh aspect of the present invention, in the photographing apparatus according to the sixth aspect , the photoelectric conversion type imaging element has a filter composed of filter elements having different spectral transmission characteristics, and the diffractive optical element is a transmission element of each filter element. The light in the wavelength region excluding the wavelength region near the rate peak is diffracted as light of a specific wavelength.
According to an eighth aspect of the present invention, in the photographing apparatus according to the sixth or seventh aspect , the photoelectric conversion type imaging element also serves as an imaging unit.

  According to the present invention, when the amount of light in the infrared region detected by the light amount detector is equal to or less than a predetermined reference value, focus detection can be performed with light having a specific wavelength in the visible region diffracted by the diffractive optical element. it can.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an embodiment of a focus detection system according to the present invention, and shows a schematic configuration when the focus detection system is applied to a digital camera 1. Reference numeral 2 denotes a photographing lens. A subject image formed by the photographing lens 2 is picked up by an image pickup element 3 which is a photoelectric conversion element. As the image sensor 3, an image sensor such as a CCD type or a CMOS type is used.

  Although not shown, the photographing lens 2 is provided with a focus adjustment lens, and the focus adjustment lens 4 is moved in the optical axis direction by a focus adjustment unit 4 including a lens driving actuator. Make adjustments. A half mirror 5 that reflects light in the infrared region (hereinafter referred to as infrared light) and transmits light having a wavelength other than the infrared region is disposed on the optical axis between the photographing lens 2 and the image sensor 3. It is installed.

  A liquid crystal hologram 8 which is a diffractive optical element capable of turning on and off the diffraction function is provided on the surface of the half mirror 5 on the photographing lens side. The liquid crystal hologram 8 can turn on and off the hologram function (diffraction function) by controlling the applied voltage. On / off of the hologram function of the liquid crystal hologram 8 is performed by the drive unit 9. Although details of the on / off control operation will be described later, the hologram function of the liquid crystal hologram 8 is normally in an off state, and the liquid crystal hologram 8 is in a state of transmitting subject light.

  Infrared light included in the subject light transmitted through the liquid crystal hologram 8 is reflected by the half mirror 5 and guided to the first focus detection unit 6 that detects the focus adjustment state of the photographing lens 2. In the present embodiment, the first focus detector 6 detects the focus adjustment state by a known phase difference detection method, but may detect the focus adjustment state by another method. On the other hand, the light transmitted through the half mirror 5 enters the image sensor 3.

  The second focus detection unit 7 detects the contrast state of the captured subject image based on the imaging data of the imaging device 3. That is, the focus evaluation value is calculated by a known contrast detection method using the imaging data of the area corresponding to the focus detection area in the imaging area of the imaging device 3. When the focus evaluation value reaches a peak, a focused subject image is obtained. The control unit 10 controls the focus adjustment of the photographing lens 2 by the focus adjustment unit 4 based on the detection results of the first and second focus detection units 6 and 7, and also controls the liquid crystal hologram 8 via the drive unit 9. On / off control of the hologram function is performed.

  The liquid crystal hologram 8 is obtained by sandwiching a polymer dispersed liquid crystal in which liquid crystal particles are dispersed in an isotropic polymer polymer between a pair of transparent substrates. This polymer-dispersed liquid crystal has a periodic layered structure in which layers with high density of liquid crystal particles and layers with low density of liquid crystal particles appear alternately. This periodic layered structure has the same periodic structure as the interference fringe pattern to be stored as a hologram in the polymer dispersed liquid crystal. Each transparent substrate is provided with an electrode made of a transparent conductive film, and the applied voltage is controlled by the drive unit 9 to turn on / off the hologram function of the liquid crystal hologram 8.

  Note that the liquid crystal hologram 8 of FIG. 1 has the above-described layered structure only for the region corresponding to the focus detection area, and only this region can exhibit the hologram function. In other areas not corresponding to the focus detection area, the liquid crystal particles are almost uniformly dispersed. The electrode formed on the transparent substrate of the liquid crystal hologram 8 is divided into a region corresponding to the focus detection area and other regions, and a voltage can be applied independently. Further, although the liquid crystal hologram 8 is disposed on the photographing lens side of the half mirror 5, it may be disposed on the surface on the imaging element side.

[Description of On / Off State of Liquid Crystal Hologram 8]
2A and 2B are diagrams for explaining an on / off control operation of the liquid crystal hologram 8. FIG. 2A shows a case where the hologram function is turned off, and FIG. 2B shows a case where the hologram function is turned on.

  The state shown in FIG. 2A can be formed by turning on the applied voltages of both the electrode in the region corresponding to the focus detection area and the electrode in the other region. When a predetermined voltage is applied to the electrodes, the liquid crystal molecules in the liquid crystal particles are aligned by an electric field. However, in the liquid crystal hologram 8, the effective refractive index of the liquid crystal particles at that time is set to be substantially equal to the refractive index of the polymer. ing.

  As a result, both the region corresponding to the focus detection area and other regions are in a transmission state, and the hologram function is turned off in the region corresponding to the focus detection area. That is, the subject light L passes through the liquid crystal hologram 8, and the infrared light Lir contained in the subject light L is reflected by the half mirror 5 and enters the first focus detection unit 6. On the other hand, L1 transmitted through the half mirror 5 enters the image sensor 3. That is, the relationship is L = L1 + Lir.

  The state of FIG. 2B in which the hologram function is turned on is formed by turning off the voltage applied to the electrodes in the region corresponding to the focus detection area and turning on the voltage applied to the electrodes in the other regions. Can do. As a result, the hologram function of the region corresponding to the focus detection area of the liquid crystal hologram 8 is turned on, and the other regions are transmitted.

  When the subject light L enters the region corresponding to the focus detection area in which the hologram function is turned on, the light L2 having a specific wavelength in the visible range included in the subject light L is diffracted by the liquid crystal hologram 8 to detect the first focus. It enters the part 6. On the other hand, the infrared light component Lir of the light transmitted through the liquid crystal hologram 8 is reflected by the half mirror 5 and guided to the first focus detection unit 6, and the remaining light L3 transmitted through the half mirror 5 is the image sensor. 3 is incident. That is, the relationship is L = L2 + Lir + L3.

  On the other hand, since the other areas of the liquid crystal hologram 8 are in the transmission state when the applied voltage is on, the infrared light Lir contained in the subject light L is reflected by the half mirror 5 and the light L1 transmitted through the half mirror 5 is reflected. Incident on the image sensor 3. As light of a specific wavelength diffracted by the liquid crystal hologram 8, it is preferable to use light in a wavelength region as indicated by reference numerals 22 to 24 in FIG.

  Curves R, G, and B in FIG. 3 show an example of transmission characteristics of the RGB color filter provided in the image sensor 3, and the wavelength band used by the image sensor 3 for imaging is around 400 nm to 700 nm. I understand. That is, by diffracting the light in the wavelength regions 22 to 24 excluding the wavelength region in the vicinity of each transmittance peak of each filter with the liquid crystal hologram 8, the influence on the light beam used for imaging can be suppressed to a small level.

  As described above, the digital camera 1 shown in FIG. 1 has focus detection information detected by the first focus detection unit 6 based on the phase difference detection method and focus evaluation based on the contrast detection method detected by the second focus detection unit 7. This is a hybrid digital camera that performs focus adjustment based on value information. As an AF operation example in a hybrid type digital camera, for example, after performing a focusing operation using focus detection information by a phase difference detection method, focusing with higher accuracy using focus evaluation value information by a contrast detection method There is a method to perform the operation.

  By the way, when the light amount of the infrared light Lir included in the subject light L corresponding to the focus detection area is too small, focus detection by the phase difference detection method of the first focus detection unit 6 cannot be performed. Therefore, in the present embodiment, the reference amount of the infrared light Lir that makes it impossible to detect the focus is set in advance and stored in the control unit 10. The control unit 10 compares the light amount of the infrared light Lir detected by the first focus detection unit 6 with the set light amount reference value. When the amount of infrared light Lir detected by the first focus detection unit 6 is equal to or less than the reference value, the liquid crystal hologram 8 is set to the state shown in FIG. Focus detection by the phase difference detection method is performed using the diffracted light L2.

  On the other hand, when the amount of the infrared light Lir detected by the first focus detection unit 6 is larger than the reference value, the liquid crystal hologram 8 is turned off and reflected by the half mirror 5 as shown in FIG. Focus detection is performed using the infrared light Lir. In the state shown in FIG. 2B, not only the diffracted light L2 but also the infrared light Lir is detected by the first focus detection unit 6. However, since the light amount of the infrared light Lir is less than the reference value, the diffracted light. It is very small compared to L2, and its influence on focus detection can be ignored. Further, since the defocus amount calculated by the phase difference detection method is different between infrared light and visible light, the control unit 10 defocuses the infrared light when performing focus adjustment using infrared light. Is corrected to the one corresponding to visible light, and the focus is adjusted using the corrected one.

  As described above, in the present embodiment, when the amount of infrared light detected by the first focus detection unit 6 is equal to or less than a predetermined reference value and focus detection by the phase difference detection method cannot be performed, the liquid crystal hologram The hologram function No. 8 is turned on, and the visible light L2 included in the subject light L is guided to the first focus detection unit 6 for focus detection. Therefore, it is possible to prevent a situation in which the infrared light contained in the subject light is small and focus detection cannot be performed as in the conventional case.

  In the above-described embodiment, the digital camera has been described as an example. However, the present invention can be applied to any imaging device that performs focus detection using infrared light. Furthermore, the present invention is not limited to the hybrid system, and can be applied to an imaging apparatus including only the first focus detection unit 6 that performs focus detection using infrared light. Further, not only a liquid crystal hologram but also a diffractive optical element that can turn on / off the diffraction function can be used as an optical element that guides light of a specific wavelength to the first focus detection unit 6. Note that the above description is merely an example, and the invention is not limited or constrained by the description of the embodiment.

It is a figure explaining one Embodiment of the focus detection system by this invention. It is a figure explaining the ON / OFF control operation | movement of the liquid crystal hologram 8, (a) shows the case where a hologram function is made into an OFF state, (b) shows the case where a hologram function is turned on. 6 is a diagram illustrating an example of transmission characteristics of an RGB color filter provided in the image sensor 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Camera 2: Shooting lens 3: Image pick-up element 4: Focus adjustment part 5: Half mirror 6: 1st focus detection part 7: 2nd focus detection part 8: Liquid crystal hologram 10: Control part

Claims (8)

An infrared optical element that is disposed in the optical path of the subject light that has passed through the photographing optical system, separates and emits infrared light from incident light, and transmits light other than the infrared light;
A light amount detector for detecting the amount of light in the infrared region separated by the infrared optical element;
A first state that is disposed in the optical path of the subject light, diffracts and emits light having a specific wavelength in the visible region from the incident light, and transmits light other than the light having the specific wavelength; A diffractive optical element capable of selectively switching between a second state of transmission;
By receiving more light emitted in the infrared optical element or the diffractive optical element, focus detection unit for detecting the focusing state of the photographing optical system,
When the amount of light detected by the light amount detector is less than or equal to a predetermined reference value, the diffractive optical element is controlled to the first state, and when the amount of light detected by the light amount detector is greater than a predetermined reference value And a control unit that controls the diffractive optical element to the second state. The focus detection system according to claim 1.
  The focus detection system, wherein the diffractive optical element is a hologram provided on the photographing optical system side of the infrared optical element. The focus detection system according to claim 2.
The diffractive optical element is provided corresponding to a region in which the focus adjustment state is detected in the focus detection unit. In the focus detection system according to any one of claims 1 to 3,
The focus detection unit corresponds to the focus adjustment state detected based on the light emitted from the diffractive optical element, the focus adjustment state detected based on the light emitted from the infrared optical element. A focus detection system characterized by correcting. The focus detection system according to any one of claims 1 to 4 ,
Imaging means for receiving light transmitted through the infrared optical element and the diffractive optical element and capturing a subject image as a captured image;
An imaging apparatus, comprising: an autofocus control unit that performs a focus adjustment operation of the imaging optical system based on a detection result of the focus detection unit. In the imaging device according to claim 5 ,
A photoelectric conversion type image pickup device that picks up a subject image by receiving light transmitted through the infrared optical element and the diffractive optical element;
An evaluation value calculation unit that calculates a focus evaluation value based on an imaging signal of the photoelectric conversion type imaging device;
The photographing apparatus according to claim 1, wherein the autofocus control means performs a focus adjustment operation of the photographing optical system based on a detection result of the focus detection unit and / or a calculation result of the evaluation value calculation unit. In the imaging device according to claim 6 ,
The photoelectric conversion type imaging device has a filter composed of filter elements having different spectral transmission characteristics,
The diffractive optical element diffracts light in a wavelength region excluding a wavelength region near each transmittance peak of the filter element as light of the specific wavelength. In the imaging device according to claim 6 or 7 ,
The photoelectric conversion type image pickup device also serves as the image pickup unit.

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