JP2014219638A - Optical branch filter and imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical branch filter capable of changing a reflective index and transmittance of a visible range at high speed and high accuracy.SOLUTION: An optical branch filter includes: a transparent first substrate and a second substrate, arranged opposing to each other so that the opposing surfaces are arranged in parallel, and having a multilayer film on each of the opposing surfaces; and an actuator capable of adjusting a clearance between the first substrate and the second substrate to be a predetermined spacing of 5-300 nm. Incident light from a side of the first substrate is interfered through being reflected by the multilayer film of the second substrate and the multilayer film of the first substrate, and part of the incident light is reflected to the side of first substrate, and the rest of the incident light is transmitted to a side of the second substrate. By changing a clearance between the first substrate and the second substrate by the actuator, catoptric light amount in visible light can be changed within a range of 0-50%, and a transmitted light volume can be changed within a range of 50-100%.

Description

  The present invention relates to a light branching filter capable of changing the reflectance and transmittance of visible light, and a photographing apparatus using the light branching filter.

  A conventional single-lens reflex camera is equipped with a movable mirror, and the subject light is guided to the viewfinder optical system by the mirror when not shooting. However, when shooting, the mirror retracts out of the shooting optical path and exposes the film or image sensor. Then, immediately after the photographing is completed, the mirror returns to the photographing optical path to guide the subject light to the finder optical system. Due to such a mechanism, the image pickup apparatus becomes larger and heavier, and the finder image disappears during photographing, so that the subject at the moment of photographing cannot be seen. Especially when shooting while following fast-moving subjects such as sports, races, animals, etc., it is difficult to observe the subject while continuously shooting it, and so-called decisive momentary shooting may be missed. It was.

  On the other hand, a single-lens reflex camera having a function of branching a light beam by a fixed mirror has been proposed. In this type of single-lens reflex camera, for example, a light branching filter (also referred to as a pellicle mirror) is used as a fixed mirror that guides a light beam to a finder system. With this light branching filter, it is possible to always branch the photographing light in both directions of the viewfinder side and the film (imaging device) side, and always observe the state of the subject with the viewfinder during photographing.

  For example, Japanese Patent Laid-Open No. 3-109504 (Patent Document 1) divides photographic lens transmitted light, guides reflected light to a finder optical system, and guides transmitted light to an image sensor. ) Is disclosed. This light branching filter is designed so that the intensity of transmitted light (light toward the image sensor) and reflected light (light toward the viewfinder) is 50% each when installed at 45 degrees. When such a half mirror type light branching filter is used, the amount of light reaching the image sensor is reduced, which causes a problem that the exposure time becomes longer or the distance that the flash light reaches becomes shorter. In order to solve such a problem, for example, a complicated mechanism such as enabling the light branching filter to be moved as in the past is required at the time of shooting under low illumination conditions or flash shooting.

  In recent digital single-lens reflex cameras, an LCD (Liquid Crystal Display) panel is provided on the back of the main body, and an image received by the image sensor can be confirmed on the LCD panel. Therefore, for example, there has been proposed a digital single-lens reflex camera in which only this LCD panel is mounted without providing an optical viewfinder, and a photographer takes a picture while checking an LCD panel image. In such a configuration, it is possible to design such that the automatic focus detection device is installed on the upper part of the camera body and the light reflected by the light branching filter is guided to the automatic focus detection device.

  As a digital single-lens reflex camera that does not have a finder optical system and uses an optical branching filter for an automatic focus detection device, Japanese Patent Application Laid-Open No. 2010-282133 (Patent Document 2) has a wavelength of 400 to 650 nm. Discloses an imaging apparatus provided with a fixed optical branching filter having a reflectance of 25 to 35% and a reflectance of about 60% or more in the vicinity of a wavelength of 700 nm. This optical branching filter has a relatively high reflectivity with respect to auxiliary light for autofocus detection (infrared light near 700 nm) compared to visible light, so the amount of light introduced into the autofocus detector is increased and accuracy is increased. Automatic focus detection can be achieved. However, even when such a fixed light branching filter is used, it is impossible to completely reduce the reflectance of visible light to 0%. In this example, it is always 25 to 35%. Since visible light is reflected and guided to the automatic focus detection device side, there is a problem in that the amount of light on the image sensor side decreases and the captured image becomes dark.

  Japanese Patent Application Laid-Open No. 2010-282172 (Patent Document 3) discloses an optically isotropic light-transmitting film (light branching filter) for separating subject light that has passed through a photographing optical system into transmitted light and reflected light. An image pickup apparatus including the above is disclosed, and the ratio of the amount of transmitted light to reflected light can be adjusted by an inorganic material layer formed on the light transmissive film. However, the light branching filter described in Patent Document 3 also has a problem that the amount of light on the image sensor side decreases and the captured image becomes dark.

  Japanese Patent Application Laid-Open No. 2000-199818 (Patent Document 4) discloses a color image reading apparatus provided with an etalon type optical filter in which two transparent substrates provided with a reflective film on one side are arranged so that the surfaces provided with the reflective film face each other. It discloses that the transmission wavelength can be shifted by changing the distance between two transparent substrates of the filter, and information of different colors (blue, green, red, etc.) can be read. In the present invention, a transparent substrate is driven using a piezoelectric element (piezo transducer) that expands and contracts by an applied voltage, and the substrate interval is controlled at high speed (about μsec) and with high accuracy (about nm). However, this variable optical filter can be used as a wavelength band filter for shifting the transmission wavelength, but does not control the light quantity ratio between the reflected light and the transmitted light, so it does not function as a light branching filter. .

JP-A-3-109504 JP 2010-282133 A JP 2010-282172 A JP 2000-199818

  Accordingly, an object of the present invention is to provide a light branching filter that can change the reflectance and transmittance in the visible range at high speed and with high accuracy, and to use the light branching filter as a fixed light branching filter of an imaging apparatus. This makes it possible to quickly switch between the light on the finder side (automatic focus detection device side) and the light on the image sensor without using a movable mirror, and the fixed image is darkened during shooting. It is to solve the essential problem of the mirror.

  As a result of diligent research in view of the above object, the present inventors alternately laminated a high refractive index film having a refractive index of 1.9 to 2.7 and a low refractive index film having a refractive index of 1.35 to 1.5 on one surface of two transparent substrates. These two transparent substrates are arranged in parallel with the surfaces of the multilayer films facing each other, and by changing the distance between them, visible light (wavelength 400 to 700 nm) is formed. The inventors have found that the amount of reflected light can be switched in the range of 0% to 50% (the amount of transmitted light is 100% to 50%), and have arrived at the present invention.

That is, the light branching filter of the present invention is
A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance of 5 to 300 nm;
Incident light from the first substrate side is reflected by the multilayer film of the second substrate and the multilayer film of the first substrate to cause interference, and a part of the incident light is reflected by the first film. A filter that reflects the first substrate side and transmits the remaining light to the second substrate side,
By changing the distance between the first substrate and the second substrate with the actuator, the amount of reflected light to the first substrate side in visible light (wavelength 400 to 700 nm) is 0 to 50%. And the amount of light transmitted to the second substrate side can be changed in a range of 50 to 100%.

  When the distance between the first substrate and the second substrate is increased, the amount of reflected light toward the first substrate increases and the amount of transmitted light toward the second substrate decreases. When the distance between the first substrate and the second substrate is reduced, the amount of reflected light toward the first substrate decreases and the amount of transmitted light toward the second substrate increases. Is preferred.

  The first substrate and the second substrate are preferably made of optical glass, transparent ceramics, or transparent plastic.

  The multilayer film formed on the opposing surfaces of the first substrate and the second substrate includes a high refractive index film having a refractive index of 1.9 to 2.7 at a wavelength of 587.56 nm and a low refractive index having a refractive index of 1.35 to 1.5 at a wavelength of 587.56 nm. A multilayer film in which a total of two or more layers are alternately laminated is preferable.

  It is preferable that the actuator is a piezoelectric element that expands and contracts according to an applied voltage.

  It is preferable that an antireflection film for visible light (wavelength 400 to 700 nm) is formed on the incident side of the first substrate and the emission side of the second substrate.

The photographing apparatus of the present invention
A light branching filter that separates the subject light passing through the photographing optical system into reflected light and transmitted light;
A focus detector on which the reflected light of the light branching filter is incident;
An image sensor on which light transmitted through the light branching filter is incident;
The light branching filter is:
A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance;
The ratio between the reflected light amount and the transmitted light amount can be changed by changing the distance between the first substrate and the second substrate by the actuator.

  It is preferable that the light branching filter is disposed between the photographing optical system and the image sensor.

  It is preferable that the facing surface of the light branching filter is disposed with an inclination of 10 to 30 ° with respect to the optical axis of the photographing optical system.

  The distance between the first substrate and the second substrate of the light branching filter is switched at least at two points, a first distance and a second distance that is larger than the first distance, The ratio between the reflected light amount and the transmitted light amount when set to the first distance (reflected light amount / transmitted light amount) is the ratio between the reflected light amount and the transmitted light amount when set to the second distance (reflected light amount / transmitted light amount). Is preferably smaller than.

  It is preferable that the first distance is set when a still image is captured, and the second distance is set when the still image is not captured.

  It is preferable to set the first distance or the distance between the first distance and the second distance when continuously capturing still images.

  It is preferable to set the first distance or the distance between the first distance and the second distance when shooting a moving image.

  The optical branching filter of the present invention has been adopted in conventional single-lens reflex cameras because the ratio of the amount of reflected light / the amount of transmitted light can be easily adjusted by controlling the distance between two substrates with high accuracy. Even if a movable mirror is not used, visible light can be switched between the viewfinder side and the imaging element side, and the structure of the imaging apparatus can be simplified and reduced in weight. Furthermore, since the amount of transmitted light can be adjusted, it is possible to design an imaging apparatus without causing a reduction in the amount of light to the image sensor, which becomes a problem when a fixed optical branching filter is used.

It is a schematic diagram which shows an example of the optical branching filter of this invention. It is a schematic cross section which shows an example of the board | substrate with which the multilayer film was provided. It is a graph which shows the spectral reflection characteristic of the board | substrate with which the 4 layer film | membrane was provided. It is a schematic cross section which shows an example of the filter which makes two board | substrates with which the multilayer film was provided oppose. It is a graph which shows the spectral reflection characteristic of the filter which makes two board | substrates with which 4 layer films | membranes were made to oppose. It is a graph which shows the spectral reflection characteristic of the filter which makes two board | substrates with which 4 layer films | membranes were made to oppose. It is a schematic diagram which shows an example of the imaging device of this invention. 2 is a graph showing spectral reflection characteristics of an antireflection film produced in Example 1. FIG. 4 is a graph showing the spectral transmission characteristics of the light branching filter of Example 1. 4 is a graph showing the spectral transmission characteristics of the light branching filter of Example 1. 6 is a graph showing the spectral reflection characteristics of the multilayer film produced in Example 2. 4 is a graph showing spectral reflection characteristics of an antireflection film produced in Example 2. 6 is a graph showing the spectral transmission characteristics of the light branching filter of Example 2. 6 is a graph showing the spectral transmission characteristics of the light branching filter of Example 2. It is a schematic diagram which shows an example of a piezoelectric element.

[1] Optical branching filter The optical branching filter of the present invention is
A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance of 5 to 300 nm;
Incident light from the first substrate side is reflected by the multilayer film of the second substrate and the multilayer film of the first substrate to interfere with each other, and a part of the incident light is first reflected. A filter that reflects to the substrate side and transmits the remaining light to the second substrate side,
By changing the distance between the first substrate and the second substrate with the actuator, the amount of reflected light to the first substrate side in visible light (wavelength 400 to 700 nm) is 0 to 50%. And the amount of light transmitted to the second substrate side can be changed in a range of 50 to 100%.

The multilayer film provided on the opposing surfaces of the first substrate and the second substrate comprises a high refractive index film having a refractive index of 1.9 to 2.7 and a low refractive index film having a refractive index of 1.35 to 1.5 at a wavelength of 587.56 nm. It is preferable to laminate them alternately. Furthermore, the multilayer film is preferably 2 to 10 layers, and more preferably 3 to 6 layers. The optical film thickness of each layer is preferably 1 nm to 250 nm, and more preferably 5 nm to 225 nm. The material of the high refractive index _{film, TiO 2, Nb 2 O 5} , Ta 2 O 5, ZrO 2, HfO 2, CeO 2, SnO 2, In 2 O 3, ZnO, Sn -doped In ₂ O _3, Al Doped ZnO, Ga-doped ZnO, La ₂ O ₃ , Sb ₂ O _{3 and the} like are mentioned. Examples of the material of the low refractive index film include MgF ₂ , SiO ₂ , a mixture of SiO ₂ and Al ₂ O ₃ , and the like. . These high-refractive index films and low-refractive index films can be formed by physical vapor deposition methods such as vacuum vapor deposition, sputtering, and ion plating, chemical vapor deposition such as thermal CVD, plasma CVD, and photo-CVD. However, the vacuum evaporation method is preferable. Furthermore, it is a single layer made of an organic fluorine compound (Canon Optron Co., Ltd .: OF-CK, Merck Co., Ltd .: Substance WR4, Tokyo Product Development Laboratory Co., Ltd .: Parack Coat, etc.) as an anti-sticking layer on the outermost layer on the air side A molecular layer (optical film thickness of 1 nm to 10 nm) may be applied.

The incident side surface of the first substrate and the emission side surface of the second substrate, that is, the surface of the first substrate and the second substrate on which the multilayer film is not formed, An antireflection film for visible light is preferably formed. As an antireflection film, a low-refractive index film material such as SiO ₂ or MgF ₂ with an optical film thickness of 90 nm to 190 nm and a high refractive index film material such as ZrO ₂ or Ta ₂ O ₅ are used. Two-layer antireflection film formed with optical film thickness of 180 nm to 380 nm and low refractive index film material SiO ₂ or MgF ₂ with optical film thickness of 90 nm to 190 nm, or high refractive index film material TiO ₂ Ordinarily used antireflection films such as a six-layer antireflection film in which Nb ₂ O ₅ and low refractive index film materials SiO ₂ and MgF ₂ are laminated in an optical film thickness of 5 nm to 190 nm can be used.

  As the actuator, it is preferable to use a piezoelectric element that expands and contracts by an applied voltage from an actuator control unit.

  The substrate is preferably made of optical glass, transparent ceramics, or transparent plastic.

(1) Embodiments Hereinafter, the optical branching filter of the present invention will be described in more detail with reference to specific embodiments, but the present invention is not limited thereto.

(a) Overall Configuration As shown in FIG. 1, the optical branching filter 10 of the present invention is provided with a transparent first substrate 1a provided with a multilayer film 2a and a multilayer film 2a of the first substrate 1a. A transparent second substrate 1b which is arranged in parallel with a certain gap 3 so as to face the opposite surface, and is provided with a multilayer film 2b on the opposite surface, and the first substrate 1a and the second substrate 1b The piezoelectric element 51 that connects one end of the first substrate 1a through the distance adjusting plates 41a and 41b and the other end of the first substrate 1a and the second substrate 1b through the distance adjusting plates 42a and 42b. And the piezoelectric element 52. The piezoelectric element 51 and the piezoelectric element 52 are expanded and contracted by a voltage applied from a drive circuit in accordance with a signal from a control device, and both end portions of the first substrate 1a and the second substrate 1b (in FIG. By driving the interval adjusting plates 41a and 41b and the interval adjusting plates 42a and 42b provided at the lower end portion, the distance of the gap 3 between the first substrate 1a and the second substrate 1b is set to the opposing surface. Can be changed while maintaining the parallelism.

  The interval adjusting plates 41a and 42a and the interval adjusting plates 41b and 42b are respectively bonded to the surfaces of the first substrate 1a and the second substrate 1b opposite to the surfaces on which the multilayer films 2a and 2b are provided. It is preferable to provide them. The spacing adjustment plates 41a and 41b and the spacing adjustment plates 42a and 42b are connected by the piezoelectric elements 51 and 52, and the spacing adjustment is performed so that the spacing between the substrate 1a and the substrate 1b can be changed smoothly. It is preferable to provide a guide (not shown) between the plates 41a and 41b and between the interval adjusting plates 42a and 42b to connect them movably.

  The first substrate 1a and the second substrate 1b are provided on the surface opposite to the surface on which the multilayer films 2a and 2b are provided, respectively, and an antireflection film 6a and an antireflection film for visible light (wavelength 400 to 700 nm), respectively. Preferably it has 6b.

(b) Filter comprising the first substrate and the second substrate On the optical glass substrate 1 having a refractive index of 1.516 (for example, S-BSL7 (nd = 1.516) manufactured by OHARA INC.), for example, as shown in Table 1. Two layers of MgF ₂ (nd = 1.388) and TiO ₂ (nd = 2.308) are alternately provided from the substrate 1 side to form a multilayer film 2 having a four-layer structure as shown in FIG. The 5 ° incident spectral reflectance of the substrate provided with the multilayer film 2 is shown in FIG.

  Two substrates 1 (the first substrate 1a and the second substrate 1b) provided with the multilayer film 2 are prepared, and the surface on the side where the multilayer films 2a and 2b are provided as shown in FIG. Make them face each other at an interval of 17.6 nm. Thus, the two substrates 1a and 1b provided with the multilayer films 2a and 2b are opposed to each other so that the gap 3 between the multilayer films 2a and 2b has an optical film thickness of 17.6 nm made of air (refractive index 1.0). Think of it as a layer. That is, by making the first substrate 1a and the second substrate 1b face each other, as shown in Table 2, the multilayer film 2a provided on the first substrate 1a, the air layer (gap 3), the second Thus, a filter having a multilayer film of 9 layers composed of the multilayer film 2b provided on the substrate 1b is obtained. As shown in FIG. 5, the filter having the multilayer film of 9 layers between the substrates 1a and 1b has an interference effect between the first multilayer film 2a, the air layer (gap 3) and the second multilayer film 2b. It has a spectral reflection characteristic in which almost no reflection is observed in visible light (wavelength 400 to 700 nm).

  The interval between the substrates 1a and 1b provided with the multilayer films 2a and 2b is changed to 173.0 nm, and the structure shown in Table 3 is obtained. As shown in FIG. 6, the filter having the multilayer film of 9 layers between the substrates 1a and 1b has a reflectivity of about 50% (that is, a transmittance of about 50%) with respect to the light in the visible range, and light splitting. Can be used as filter 10.

  That is, in the optical branching filter 10 configured such that the substrates 1a and 1b having the multilayer films 2a and 2b are opposed to each other, the interval between the two substrates 1a and 1b is changed from 17.6 nm to 173.0 nm (at least The reflectance for visible light can be changed from 0 to 50% (that is, the transmittance is 100 to 50%) only by moving one substrate by 155.4 nm.

(c) Piezoelectric Element For controlling the distance between the substrates 1a and 1b of the optical branching filter 10, it is preferable to use a piezoelectric element capable of controlling expansion and contraction at a high speed of, for example, μsec and with a high accuracy of nm. As shown in FIG. 15, the piezoelectric element 200 has a structure in which piezoelectric ceramics 201 are laminated via an internal electrode 202, and by applying a voltage to the external electrode 203 to which the internal electrode 202 is connected, Displacement occurs in the stacking direction. For example, when the voltage is applied to the piezoelectric element 200 having a size of L1 = L2 = 0.9 mm and H = 1.6 mm, the amount of displacement in the stacking direction is as shown in Table 4, and the first substrate and the second substrate The interval between and can be changed.

  By controlling the substrate interval of the optical branching filter using a piezoelectric element, the reflectance (transmittance) can be switched between 0% and 50% in a very short time. Therefore, by using this optical branching filter in place of the movable mirror in the photographing apparatus, it is possible to quickly switch the optical path to the automatic focus detector and the image sensor.

[2] Shooting device The shooting device of the present invention includes a light branching filter that separates subject light that has passed through a shooting optical system into reflected light and transmitted light;
A focus detector on which the reflected light of the light branching filter is incident;
An imaging device comprising an imaging device on which light transmitted through the light branching filter is incident,
The light branching filter is:
A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance;
The ratio between the reflected light amount and the transmitted light amount can be changed by changing the distance between the first substrate and the second substrate by the actuator.

  The imaging apparatus 100 of the present invention is preferably configured using the optical branching filter 10 of the present invention. As shown in FIG. 7, the imaging apparatus barrel 102 to which the imaging optical system 101 is attached, and the imaging element 103, an automatic focus detector 104, and an imaging apparatus including a light branching filter 10 for branching light (subject light) incident through the imaging optical system 101 to the imaging element 103 and the automatic focus detector 104 The photographic optical system 101 includes an interchangeable photographic lens, a diaphragm, and the like. The photographic lens is driven by a signal from the automatic focus detector 104 and can perform an autofocus operation.

  The image sensor 103 is a sensor such as a CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), etc., and an image signal extracted from the image sensor 103 is transmitted to the image signal processor 107, and a signal obtained by compressing the image signal is transmitted. It is stored in a recording medium such as a flash memory. A current subject image (a video signal obtained by processing the image pickup signal of the image sensor 103) is displayed on the image display unit 108 provided on the back surface of the photographing apparatus main body 105. As the image display unit 108, a flat display such as an LCD or an organic EL (Electroluminescence) is used.

  The auto-focus detector 104 is an image sensor (area sensor) that receives the reflected light from the optical branching filter 10, a signal processor that processes the output signal of the image sensor, and a drive that controls the position of the auto-focus lens of the imaging optical system. Part. In the signal processing unit, an automatic focus evaluation value is generated using an imaging signal of a specified area of the captured image or the entire area of the captured image, and the automatic operation of the imaging optical system 101 is performed so that the automatic focus evaluation value is maximized. The position of the focus lens is controlled. As the autofocus method, any one of a phase difference type autofocus and a contrast detection type autofocus, or a method using both of them can be used.

  The optical branching filter 10 is configured so that the opposing surfaces of the first substrate and the second substrate are at a fixed angle with respect to the optical axis of the imaging optical system 101 so that the reflected light is guided to the autofocus detector 104. Inclined and disposed between the imaging optical system 101 and the image sensor 103. The inclination angle of the light branching filter 10 is appropriately determined depending on the position where the automatic focus detector 104 is installed, but is preferably 10 to 30 °. That is, the light branching filter 10 is preferably a fixed light branching filter 10 disposed so that the incident angle of light with respect to the opposing surface is 10 to 30 °.

  The distance between the first substrate and the second substrate of the optical branching filter 10 is set to a predetermined value of, for example, 5 to 300 nm by driving a piezoelectric element (see FIG. 1) by a voltage applied from the actuator control unit 106. Can be adjusted to distance. Usually, switching can be performed at at least two points, ie, a first distance and a second distance that is larger than the first distance, and when the first distance is set (when the substrate interval is narrow). The ratio of the reflected light amount to the transmitted light amount when the ratio between the reflected light amount and the transmitted light amount (reflected light amount / transmitted light amount) is set to the second distance (when the substrate interval is wide) (reflected light amount / transmitted light amount). Smaller than. That is, when the substrate interval is narrowed, the amount of transmitted light increases and the amount of reflected light decreases. Conversely, when the substrate interval is widened, the amount of transmitted light decreases and the amount of reflected light increases.

  For example, a filter formed by opposing two substrates [configuration of Table 1] provided with a multi-layer film, the distance between the two substrates is 17.6 nm (first distance) [configuration of Table 2] and 173.0 nm (first The distance between the reflected light amount and the transmitted light amount can be changed by setting so that the distances can be switched to each other. By switching the substrate interval to 17.6 nm (first distance) at the time of still image shooting (exposure), the optical branching filter generates almost 100% visible light (wavelength 400 to 700 nm). Therefore, high sensitivity can be secured. In addition, when non-photographing is performed, by switching the substrate interval to 173.0 nm (second distance), the optical branching filter guides 50% of visible light to the image sensor 103 and reflects 50% of visible light to automatically detect the focus. Therefore, the autofocus operation can be performed while checking the current subject image.

  Also, during continuous shooting of still images or moving images, it is preferable to set the first distance and increase the ratio of the amount of transmitted light to the image sensor, as in the case of single-frame shooting of still images. When there is a request for performing an autofocus operation during shooting (during exposure), such as when shooting a subject that moves rapidly, the distance between the first distance and the second distance By setting the distance between the substrates, it is possible to perform an autofocus operation while ensuring a certain degree of sensitivity.

  The photographing apparatus 100 of the present invention does not require an optical viewfinder because the image display unit 101 has a function as an electronic viewfinder. Therefore, in the configuration shown in FIG. 7, an optical viewfinder is not provided, and the light reflected upward by the light branching filter 10 is guided to the autofocus detector 104 and used only for driving the autofocus lens. Yes. By omitting the optical viewfinder, optical components such as a focus plate, a pentaprism, and an eyepiece can be omitted.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
A multilayer film shown in Table 1 is formed on one side of a 1 mm thick S-BSL7 parallel flat substrate (Ohhara Co., Ltd., nd = 1.516) by the vacuum evaporation method, and the antireflection film shown in Table 5 is formed on the opposite side. Was formed by vacuum evaporation. A substrate in which only the antireflection film shown in Table 5 alone was provided on one side of the S-BSL7 parallel flat substrate was prepared, and the 5 ° incident spectral reflectance was measured using a visible spectral altimeter U4000 manufactured by Hitachi. The results are shown in FIG.

  A light branching filter as shown in FIG. 1 was produced by making two of these substrates face each other on which the multilayer films were formed. As shown in FIG. 15, the used piezoelectric element had a size of L1 = L2 = 0.9 mm and H = 1.6 mm. The light branching filter is set so that a light beam is incident at an incident angle of 20 °, and the voltage applied to the piezoelectric element from the actuator driving circuit is set to 0.0 V, 0.2 V, 0.4 V, 3.5 V, 3.7 V and 3.9. Spectral transmittance was measured while changing V. Table 6 shows the distance between the substrate gaps corresponding to these applied voltages. The measurement results of the spectral characteristics at this time are shown overwritten in FIGS.

  From these results, this optical branching filter has a transmittance by switching the applied voltage of the actuator drive circuit between 3.7 V and 0.2 V and switching the distance of the substrate gap between 201.5 nm and 17.5 nm. It can be seen that can be instantaneously switched between about 50% and about 100%. Therefore, when this optical branching filter 10 is used in the photographing apparatus 100 as shown in FIG. 7, when the applied voltage of the actuator driving circuit is 3.7 V, 50% of the incident light is reflected. While directing to the autofocus detector 104 and performing autofocus detection, 50% of the incident light is transmitted to the image sensor 103 to observe the subject image, and the applied voltage is applied at the moment of shooting (exposure) Switch to 0.2 V, let the incident light pass through 100% and expose with the image sensor 103. Immediately return the applied voltage to 3.7 V and perform autofocus detection with reflected light of 50% of the incident light. The subject image can be observed with 50% of the transmitted light.

Example 2
A multilayer film shown in Table 7 was formed on one side of a Zeonex 480R parallel plane substrate (Zeon Corporation, nd = 1.525) with a thickness of 1 mm, and its 5 ° incident spectral reflectance was measured with the Hitachi Spectrophotometer U4000. It was measured. The results are shown in FIG. An antireflection film shown in Table 8 was formed on the opposite surface of the substrate provided with the multilayer film by vacuum deposition. A substrate in which only the antireflection film shown in Table 8 was provided on one side of the Zeonex 480R parallel flat substrate was prepared, and the 5 ° incident spectral reflectance was measured with a visible spectral altimeter U4000 manufactured by Hitachi. The results are shown in FIG.

  A light branching filter as shown in FIG. 1 was produced by making two of these substrates face each other on which the multilayer films were formed. As shown in FIG. 15, the used piezoelectric element had a size of L1 = L2 = 0.9 mm and H = 1.6 mm. The light branching filter is set so that light is incident at an incident angle of 20 °, and the voltage applied from the actuator drive circuit to the piezoelectric element is 0.5 V, 0.7 V, 0.9 V, 4.1 V, 4.3 V, and 4.5. Spectral transmittance was measured while changing V. Table 9 shows the distance between the substrate gaps corresponding to these applied voltages. The measurement results of the spectral characteristics at this time are shown overlaid on FIGS.

  From these results, this optical branching filter can change the transmission voltage by switching the applied voltage of the actuator drive circuit between 4.3 V and 0.7 V and switching the substrate gap distance between 232.5 nm and 43.4 nm. It can be seen that can be instantaneously switched between about 70% and about 100%. Therefore, when this optical branching filter 10 is used in a photographing apparatus 100 as shown in FIG. 7, when the applied voltage of the actuator driving circuit is 4.3 V, 30% of the incident light is reflected. While directing to the autofocus detector 104 and performing autofocus detection, 70% of the incident light is transmitted and guided to the image sensor 103 to observe the subject image, and the applied voltage is applied at the moment of shooting (exposure) Switch to 0.7 V, transmit 100% of incident light and expose with image sensor 103. Immediately return the applied voltage to 4.3 V and detect auto focus with 30% of the incident light. The subject image can be observed with 70% of the transmitted light.

  The light branching filter of the present invention has a transmittance of 0% to 50% (reflectance of 100% to 0%) even if the distance for changing the distance between the two substrates facing each other is as small as 5 to 300 nm. Therefore, it is possible to use a piezoelectric element that can be driven at high speed. Therefore, it is suitable as a light branching filter that guides the incident light to the imaging device to the autofocus detector and the image sensor, performs autofocus detection while checking the subject, and momentarily blocks the light to autofocus detection during shooting As a result, 100% light is guided to the image sensor, and automatic focus detection can be performed immediately after exposure. Therefore, it is possible to solve both the problem of subject tracking when using a conventional movable mirror and the problem that a captured image at the time of photographing using a fixed optical branching filter becomes dark.

10 ... Optical branching filter
1 ... Board
1a: first substrate
1b ... second substrate
2 ... Multilayer film
2a, 2b ... Multilayer film
3 ... Gap
41a, 41b ... spacing adjustment plate
42a, 42b ... spacing adjustment plate
51, 52 ... Piezoelectric element
100 ... Photographing device
101 ... Shooting optics
102 ... Telescope barrel
103 ... Image sensor
104 ... Auto focus detector
105 ... Shooting device
106 ・ ・ ・ Actuator controller
107 ... Imaging signal processor
108 ・ ・ ・ Image display
200 ・ ・ ・ Piezoelectric element
201 ・ ・ ・ Piezoelectric ceramics
202 ... Internal electrode
203 ... External electrode

Claims (13)

A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance of 5 to 300 nm;
Incident light from the first substrate side is reflected by the multilayer film of the second substrate and the multilayer film of the first substrate to cause interference, and a part of the incident light is reflected by the first film. A filter that reflects the first substrate side and transmits the remaining light to the second substrate side,
By changing the distance between the first substrate and the second substrate with the actuator, the amount of reflected light to the first substrate side in visible light (wavelength 400 to 700 nm) is 0 to 50%. The light branching filter is characterized in that the amount of light transmitted to the second substrate side can be changed within a range of 50 to 100%.   2. The optical branching filter according to claim 1, wherein when the distance between the first substrate and the second substrate is increased, the amount of reflected light toward the first substrate increases, and the second When the amount of light transmitted to the substrate side decreases and the distance between the first substrate and the second substrate decreases, the amount of reflected light toward the first substrate decreases and the second The light branching filter is characterized in that the amount of light transmitted to the substrate increases.   3. The light branching filter according to claim 1, wherein the first substrate and the second substrate are made of optical glass, transparent ceramics, or transparent plastic.   4. The optical branching filter according to claim 1, wherein the multilayer film formed on the opposing surfaces of the first substrate and the second substrate has a high refractive index of 1.9 to 2.7 at a wavelength of 587.56 nm. An optical filter comprising a multi-layer film in which a refractive index film and a low refractive index film having a refractive index of 1.35 to 1.5 at a wavelength of 587.56 nm are alternately laminated.   5. The light branching filter according to claim 1, wherein the actuator is a piezoelectric element that expands and contracts according to an applied voltage.   6. The optical branching filter according to claim 1, wherein an antireflection film for visible light (wavelength: 400 to 700 nm) is formed on the incident side of the first substrate and the emission side of the second substrate. An optical branching filter characterized by being made. A light branching filter that separates the subject light passing through the photographing optical system into reflected light and transmitted light;
A focus detector on which the reflected light of the light branching filter is incident;
An imaging device comprising an imaging device on which light transmitted through the light branching filter is incident,
The light branching filter is:
A transparent first substrate and a second substrate, which are arranged to face each other so that the opposing surfaces are parallel, and each of the opposing surfaces is provided with a predetermined multilayer film;
An actuator capable of adjusting a distance between the first substrate and the second substrate to a predetermined distance;
An imaging apparatus, wherein a ratio between a reflected light amount and a transmitted light amount can be changed by changing an interval between the first substrate and the second substrate by the actuator.   8. The photographing apparatus according to claim 7, wherein the optical branching filter is disposed between the photographing optical system and the imaging element.   9. The photographing apparatus according to claim 7, wherein a facing surface of the light branching filter is disposed so as to be inclined by 10 to 30 degrees with respect to an optical axis of the photographing optical system.   10. The imaging device according to claim 7, wherein an interval between the first substrate and the second substrate of the optical branching filter is larger than a first distance and the first distance. When switching between at least two points with the second distance and setting the first distance, the ratio of the reflected light amount to the transmitted light amount (reflected light amount / transmitted light amount) is set to the second distance. An imaging device characterized by being smaller than the ratio of the reflected light amount to the transmitted light amount (reflected light amount / transmitted light amount).   11. The photographing apparatus according to claim 10, wherein the first distance is set when a still image is photographed, and the second distance is set when a still image is not photographed.   12. The photographing apparatus according to claim 11, wherein the first distance or a distance between the first distance and the second distance is set when still images are continuously photographed. apparatus.   12. The photographing apparatus according to claim 11, wherein when photographing a moving image, the photographing distance is set to the first distance or a distance between the first distance and the second distance.

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