JP5028163B2 - Optical equipment - Google Patents

Description

  The present invention relates to an optical apparatus such as a digital camera, and more particularly, to a surface of an optical member disposed in or near the focal plane, such as a solid-state imaging device, an optical filter, or a lens incorporated in the optical apparatus. The present invention relates to a structure that suppresses the adhesion of water.

  Conventionally, when a foreign substance such as dust adheres to the vicinity of the focal plane of a photographing lens of a lens interchangeable digital single-lens reflex camera, there is a problem that the shadow of the foreign substance is reflected on the solid-state imaging device. Such foreign matter is caused by dust entering from the outside when the lens is replaced, or fine wear powder such as resin, which is the structural member, is generated with the operation of the shutter and mirror inside the camera. It is considered. The foreign matter generated due to such a cause is an optical filter such as an infrared cut filter or an optical low-pass filter (hereinafter referred to as LPF) disposed on the entire surface of the cover glass for protecting the solid-state image sensor. May get in between. In such cases, the camera had to be disassembled to remove it. For this reason, it has been extremely effective to provide a sealed structure so that foreign matter does not enter between the cover glass of the solid-state imaging device and the optical filter.

However, when a foreign object adheres to the surface of the optical filter opposite to the side facing the solid-state image sensor, if the foreign object is in the vicinity of the focal plane, the foreign object is reflected in the solid-state image sensor. The problem remains.
JP 2003-005254 A (page 8, FIG. 1 and FIG. 9) JP 2000-029132 A (page 8, FIG. 2)

  Therefore, in order to solve the above problems, there is one that cleans the cover glass surface of the solid-state imaging device with a wiper (Patent Document 1). By configuring the camera in this way, it is possible to remove the foreign matter attached to the cover glass surface of the solid-state imaging device or the outermost surface of the dust-proof structure (for example, the optical filter surface) without removing the lens and without disassembling the camera. However, in the configuration of Patent Document 1, the cover glass surface of the solid-state imaging device and the outermost surface of the dustproof structure are rubbed with a wiper. For this reason, for example, when a hard foreign material such as a metal powder adheres, there is a possibility that the foreign material may damage the surface of the cover glass of the solid-state imaging device or the outermost surface of the dust-proof structure. In addition, since the foreign matter removed by the wiper floats in the camera, there is a problem that the removed foreign matter once again adheres to the cover glass surface of the solid-state imaging device and the outermost surface of the dust-proof structure.

  Therefore, as a solution to the former problem, a transparent electrode is formed on each of the cover glass surface of the solid-state image sensor and the surface of the optical filter in order to prevent foreign matter from adhering to the cover glass surface of the solid-state image sensor. (Patent Document 2). According to the technique described in Patent Document 2, by applying a potential to the transparent electrode provided on the cover glass surface of the solid-state image sensor and the surface of the optical filter, the cover glass surface of the solid-state image sensor and the surface of the optical filter are applied. Neutralizes generated static electricity. In this way, adhesion of dust to the cover glass surface of the solid-state image sensor and the surface of the optical filter is suppressed. However, since the transparent electrodes are provided on the cover glass surface and the optical filter surface, the transmittance of light to the image sensor is lowered. For this reason, an optical adverse effect occurs. Further, static electricity generated on the surface of the cover glass of the solid-state imaging device and the surface of the optical filter is not constant depending on the surrounding environment (temperature and humidity) and usage conditions. For this reason, there existed a malfunction that the control for neutralizing static electricity became difficult and the suppression effect became insufficient because static electricity was not neutralized.

  An object of the present invention is to solve the above-mentioned drawbacks of the prior art.

  A feature of the present invention is to provide an optical apparatus that has no adverse optical effect on an optical image picked up by an image pickup unit and suppresses the adhesion of dust to the optical element.

In order to achieve the above object, an optical apparatus according to one embodiment of the present invention includes the following arrangement. That is,
An optical device comprising an imaging means for converting an optical image of a subject into an electrical signal, and an optical element disposed on the subject side of the imaging means,
A first concavo-convex structure formed by arranging, on the object side surface of the optical element, first particles having a particle size of 200 nm or less on the object side surface of the optical element; and a surface of the first particle and a predetermined number attached to, the grain size than the first particle is provided a second concave-convex structure formed by the second particles are small, the object side surface of the optical element, attached to the surface The van der Waals force between dust and dust is reduced .

  ADVANTAGE OF THE INVENTION According to this invention, the optical bad influence with respect to the optical image imaged with an imaging means can be eliminated, and adhesion of dust to an optical element can be suppressed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

[Embodiment 1]
Hereinafter, an interchangeable-lens digital single-lens reflex camera (hereinafter abbreviated as D-SLR) according to Embodiment 1 of the present invention will be described with reference to FIGS.

  FIG. 1 is a side sectional view for explaining a schematic configuration of the imaging unit 10 and the focal plane shutter 50 of the D-SLR 100 according to Embodiment 1 of the present invention.

  In FIG. 1, an imaging unit 10 integrates an optical element 11 such as glass or a filter, a holding member 12 that holds the optical element 11, and the optical element 11 and the holding member 12 in contact with the surface of the optical element 11. A supporting plate 13 is provided. The solid-state imaging device 15 includes a cover member 15a for protecting the solid-state imaging element 15b. A sealing member 16 for sealing between the cover member 15a of the solid-state imaging device 15 and the optical element 11 and a connection terminal 15c of the solid-state imaging device 15 are connected to the substrate 17. Furthermore, the board 17 is mounted with electrical elements that constitute a control circuit that controls the operation of the D-SLR 100. The holding plate 18 is integrated with the solid-state imaging device 15 to fix the solid-state imaging device 15 to the chassis of the D-SLR 100 (not shown) with screws (not shown).

  Note that an uneven structure 11 a is provided on the surface of the optical element 11 facing the focal plane shutter 50. As shown in FIG. 4B, the concavo-convex structure 11a is provided in a substantially V-shaped concave shape (first concavo-convex structure) arranged at a pitch (first period) P1 and the concave shape. A concave shape 11c (second concavo-convex structure) having a pitch (second period) P2 is formed. Hereinafter, this structure is called a fractal structure. In both cases, the depth and pitch are at least smaller than the wavelength range of visible light (380 nm to 770 nm) so as not to adversely affect the optical image formed on the image sensor 15b.

  4A to 4C are views for explaining the action of the concavo-convex structure 11 a on the dust 30 attached to the surface of the optical element 11. FIG. 4 will be described in detail later.

  The concavo-convex structure 11a, which is a fractal structure, presses a mold (stamper) having a nano-order fine shape against a layer of a resin such as acrylic or polycarbonate or a fluorine resin provided on the surface of the optical element 11, for example. Is formed. That is, since it can be formed by a manufacturing method such as nanoimprint in which the fine shape of the mold is transferred to the resin layer, it can be easily formed without selecting the material of the optical element 11.

  In addition, as a manufacturing method of this fractal structure, it can form also by the wet process currently disclosed by Unexamined-Japanese-Patent No. 2000-144116 or Unexamined-Japanese-Patent No. 2000-1787, for example. However, it is not productive because it takes a long time to form a film and it is difficult to control the film thickness. Therefore, as described above, it is desirable to form the concavo-convex structure 11a by a dry process such as a nanoimprint method.

  Next, the focal plane shutter 50 will be described. The front curtain 21 includes a plurality of shutter blades 21a to 21d. The rear curtain 22 is also composed of a plurality of shutter blades. The intermediate plate 23 divides the drive space of the front curtain 21 and the rear curtain 22 in the focal plane shutter 50. The presser plate 24 is a presser plate for the rear curtain 22, and at the same time, an opening 24a is provided at a substantially central portion for imaging. Further, the cover plate 25 is a pressing plate for the front curtain 21 and at the same time, an opening 25a is provided at a substantially central portion for imaging. Reference numeral 29 denotes a stopper rubber having a stopper portion that is positioned when the shutter blades 21a to 21d of the front curtain 21 are opened.

  The D-SLR 100 is a single-plate digital color camera using an image sensor 15b such as a CCD or CMOS sensor, and an image signal representing a moving image or a still image by driving the image sensor 15b continuously or once. Get. Here, the imaging element 15b is an area sensor of a type that converts the exposed light into an electrical signal for each pixel, accumulates charges according to the amount of received light, and reads the accumulated charges.

  FIG. 2 is a schematic diagram showing the configuration of the camera system of D-SLR 100 according to the first embodiment, and the same parts as those in FIG. The camera system includes a camera body (imaging device) and a lens device that is detachably attached to the camera body.

  In FIG. 2, reference numeral 101 denotes a mount mechanism that connects a removable lens device 102 to the D-SLR 100, and the lens device 102 is electrically and mechanically connected to the D-SLR 100 via the mount mechanism 101. . Then, by attaching the lens device 102 having different focal lengths to the D-SLR 100, it is possible to obtain shooting screens having various angles of view. An optical element 11 is provided in the optical axis L 1 from the photographing optical system 103 provided in the lens device 102 to the solid-state imaging device 15. The optical element 11 limits the cutoff frequency of the photographing optical system 103 so that a spatial frequency component higher than necessary for the object image (optical image) is not transmitted onto the solid-state imaging device 15.

  A signal read from the solid-state imaging device 15 is subjected to predetermined processing as will be described later, and then displayed on the display unit 107 as image data. The display unit 107 is attached to the back surface of the D-SLR 100 so that the user can directly observe the display on the display unit 107. Note that if the display unit 107 is composed of an organic EL spatial modulation element, a liquid crystal spatial modulation element, a spatial modulation element using microparticle electrophoresis, power consumption can be reduced, and the display unit 107 can be made thin. be able to. Thereby, power saving and size reduction of D-SLR100 can be achieved.

  Specifically, the solid-state imaging device 15 is a CMOS process compatible sensor (hereinafter referred to as a CMOS sensor) which is one of amplification type solid-state imaging devices. By adopting this CMOS sensor, the peripheral transistors such as the MOS transistor of the area sensor unit and the imaging device drive circuit, AD conversion circuit, and image processing circuit can be formed in the same process, so the number of masks and the process process are compared with the CCD. It can be greatly reduced. In addition, since random access to an arbitrary pixel is possible, reading that is thinned out for displaying an image becomes easy. Thereby, the display unit 107 can display in real time at a high display rate. The solid-state imaging device 15 utilizes the above-described features, and performs an image output operation for display (reading out a part of the light-receiving area of the solid-state imaging device 15) and a high-definition image output operation (total light reception). Read out in the area).

  The movable half mirror 111 reflects a part of the light flux from the photographing optical system 103 and transmits the rest. The half mirror 111 has a refractive index of about 1.5 and a thickness of 0.5 mm. Reference numeral 105 denotes a focusing screen disposed on a predetermined imaging plane of an object image formed by the photographing optical system, and 112 denotes a pentaprism. The finder lens 109 is a lens for observing an object image formed on the focusing screen 105, and is composed of one or a plurality of finder lenses (not shown). The focusing screen 105, the pentaprism 112, and the finder lens 109 constitute a finder optical system.

  A movable sub-mirror 122 is provided behind the half mirror 111 (on the image plane side), and the light beam that has passed through the half mirror 111 is reflected near the optical axis L 1 and guided to the focus detection unit 121. . The sub mirror 122 rotates around a rotation shaft provided on a holding member of the half mirror 111 (not shown) and moves in conjunction with the movement of the half mirror 111. The focus detection unit 121 receives the light beam from the sub mirror 122 and performs focus detection by the phase difference detection method.

  The optical path splitting system composed of the half mirror 111 and the sub mirror 122 can take a first optical path splitting state for guiding light to the finder optical system. Further, a second optical path split state (positions indicated by broken lines in FIG. 2: 111 ′ and 122 ′) withdrawn from the photographing optical path to directly guide the light beam from the imaging lens to the solid-state imaging device 15 can be taken. I can do it. The movable flash light emitting unit 114 is movable between a storage position stored in the D-SLR 100 and a light emission position protruding from the D-SLR 100. The focal plane shutter 50 adjusts the amount of light incident on the image plane. Reference numeral 119 denotes a main switch for starting up the D-SLR 100. The release button 120 that is pressed in two stages starts a shooting preparation operation (photometry operation, focus adjustment operation, etc.) by a half-press operation (SW1 is ON), and a shooting operation (solid state) by a full-press operation (SW2 is ON). Recording of the image data read from the imaging device 15 to the recording medium is started. The information display unit 180 in the optical finder is a display unit that displays specific information on the focusing screen 105. Reference numeral 104 denotes an aperture.

  FIG. 3 is a block diagram for explaining the electrical configuration of the camera system of the D-SLR 100 according to the first embodiment, and the same parts as those in FIGS. 1 and 2 described above are indicated by the same symbols.

  This camera system has an imaging system, an image processing system, a recording / reproducing system, and a control system. The imaging system has an imaging unit 10 that includes a photographic optical system 103 and a solid-state imaging device 15. The image processing system includes an A / D converter 130, an RGB image processing circuit 131, and a YC processing circuit 132. The recording / reproducing system includes a recording processing circuit 133 and a reproducing processing circuit 134, and the control system includes a camera system control circuit (control means) 135, an operation detection circuit 136, and a driving circuit 137. The connection terminal 138 is a terminal that is connected to an external computer or the like and is standardized to transmit and receive data. The above-described circuit is driven by receiving power from a small fuel cell (not shown).

  The imaging system is an optical processing unit that forms an image of light from an object (subject side) on the imaging surface of the solid-state imaging device 15 via the imaging optical system 103. The driving of the diaphragm 104 provided in the photographing optical system 103 is controlled, and the focal plane shutter 50 is driven through the shutter control circuit 145 as necessary, so that an appropriate amount of light is emitted from the solid-state imaging device 15. Can receive light. The solid-state imaging device 15 according to the first embodiment uses an imaging element 15b in which 3700 square pixels are arranged in the long side direction and 2800 in the short side direction, and the total number of pixels is about 10 million. Yes. In addition, R (red), G (green), and B (blue) color filters are alternately arranged in each pixel to form a so-called Bayer array in which four pixels form a set. In this Bayer arrangement, the overall image performance is improved by arranging more G pixels that are easily felt when an observer views an image than R and B pixels. In general, in image processing using this type of image sensor, a luminance signal is generated mainly from G, and a color signal is generated from R, G, and B.

  A signal read from the solid-state imaging device 15 is supplied to the above-described image processing system via the A / D converter 130, and image data is generated by image processing in this image processing system. The A / D converter 130 is a signal conversion circuit that converts, for example, an output signal of the image sensor 15b into a 10-bit digital signal according to the amplitude of the signal read from each pixel of the image sensor 15b. . Image processing after this A / D conversion processing is executed by digital processing. The image processing system is a signal processing circuit that obtains an image signal of a desired format from R, G, and B digital signals. The R, G, and B color signals are converted into a luminance signal Y and a color difference signal (R−Y), ( B-Y) and the like are converted into a YC signal. The RGB image processing circuit 131 is a signal processing circuit that processes the output signal of the A / D converter 130, and includes a white balance circuit, a gamma correction circuit, and an interpolation calculation circuit that performs high resolution by interpolation calculation. The YC processing circuit 132 is a signal processing circuit that generates a luminance signal Y and color difference signals RY and BY. The YC processing circuit 132 generates a high-frequency luminance signal generation circuit that generates a high-frequency luminance signal YH, a low-frequency luminance signal generation circuit that generates a low-frequency luminance signal YL, and color difference signals RY and BY. It has a color difference signal generation circuit. The luminance signal Y is formed by combining the high frequency luminance signal YH and the low frequency luminance signal YL.

  The recording / reproducing system is a processing system that outputs an image signal to a memory (such as a memory card) (not shown) and outputs an image signal to the display unit 107. The recording processing circuit 133 performs image signal writing processing and reading processing on the memory, and the reproduction processing circuit 134 reproduces the image signal read from the memory and outputs it to the display unit 107. The recording processing circuit 133 includes a compression / expansion circuit for compressing the YC signal representing still image data and moving image data in a predetermined compression format and expanding the compressed data. This compression / decompression circuit has a frame memory for signal processing and the like, stores YC signals from the image processing system for each frame in this frame memory, and signals stored from each block among a plurality of blocks. Is compressed and encoded. This compression coding is performed, for example, by performing two-dimensional orthogonal transformation, normalization, and Huffman coding on the image signal for each block. The reproduction processing circuit 134 is a circuit that converts the luminance signal Y and the color difference signals RY and BY into a matrix signal, for example, an RGB signal. The signal converted by the reproduction processing circuit 134 is output to the display unit 107 and displayed (reproduced) as a visible image. The reproduction processing circuit 134 and the display unit 107 may be connected via wireless communication such as Bluetooth (registered trademark). By connecting wirelessly in this way, an image captured by this camera can be monitored from a distance.

  On the other hand, the operation detection circuit 136 in the control system detects the operation of the main switch 119 and the release button 120 shown in FIG. 2 (other switches are not shown) and outputs the detection result to the camera system control circuit 135. . The camera system control circuit 135 receives the detection signal from the operation detection circuit 136 and performs an operation according to the detection result. In addition, the camera system control circuit 135 generates a timing signal for performing an imaging operation and outputs the timing signal to the drive circuit 137 of the imaging apparatus. The drive circuit 137 receives the control signal from the camera system control circuit 135 and generates a drive signal for driving the solid-state imaging device 15. The information display circuit 142 receives a control signal from the camera system control circuit 135 and controls driving of the information display unit 180 (FIG. 2) in the optical viewfinder.

  The control system controls driving in the imaging system, image processing system, and recording / reproducing system in accordance with the operation of various switches provided in the D-SLR 100. For example, when SW2 is turned ON by operating the release button 120, the control system (camera system control circuit 135) drives the solid-state imaging device 15, operates the RGB image processing circuit 131, compresses the recording processing circuit 133, and the like. To control. Further, the control system changes the display (the state of the display segment) in the optical finder by controlling the driving of the information display unit 180 in the optical finder via the information display circuit 142.

  Next, the focus adjustment operation of the photographic optical system 103 will be described.

  The camera system control circuit 135 is connected to the AF control circuit 140. Further, by mounting the lens device 102 to the D-SLR 100 by the mount mechanism 101, the camera system control circuit 135 is connected to the lens system control circuit 141 in the lens device 102 via the mount contacts 101a and 102a. The AF control circuit 140, the lens system control circuit 141, and the camera system control circuit 135 communicate data necessary for specific processing with each other.

  The focus detection unit 121 (focus detection sensor 167) outputs a detection signal in a focus detection area provided at a predetermined position in the shooting screen to the AF control circuit 140. The AF control circuit 140 generates a focus detection signal based on the output signal from the focus detection unit 121 (FIG. 2), and detects the focus adjustment state (defocus amount) of the photographing optical system 103. Then, the AF control circuit 140 converts the detected defocus amount into a drive amount of a focus lens that is a part of the photographing optical system 103. Then, the converted information regarding the driving amount of the focus lens is transmitted to the lens system control circuit 141 via the camera system control circuit 135. Here, when the focus adjustment is performed on the moving object, the AF control circuit 140 takes into account the time lag from when the release button 120 is fully pressed until the actual imaging control is started. Predict an appropriate stop position. Then, information regarding the driving amount of the focus lens to the predicted stop position is transmitted to the lens system control circuit 141.

  On the other hand, when the camera system control circuit 135 determines that the luminance of the subject is low and sufficient focus detection accuracy cannot be obtained based on the signal from the image sensor 15b, the camera system control circuit 135 is provided in the flash light emitting unit 114 or the D-SLR 100. A white LED or fluorescent tube (not shown) is driven. This illuminates the object. The lens system control circuit 141 receives information on the driving amount of the focus lens from the camera system control circuit 135. Based on this information, the driving of the AF motor 147 disposed in the lens device 102 is controlled, and the focus lens is moved in the direction of the optical axis L1 by the driving amount through a driving mechanism (not shown). As a result, the photographing optical system 103 is brought into focus. As described above, when the focus lens is composed of a liquid lens or the like, the interface shape is changed. When the lens system control circuit 141 receives information about the exposure value (aperture value) from the camera system control circuit 135, the lens system control circuit 141 controls the driving of the aperture drive source (actuator) 143 in the lens device 102. Accordingly, the diaphragm 104 is operated so as to have a diaphragm aperture diameter corresponding to the diaphragm value.

  The shutter control circuit 145 controls the front curtain drive source 35, the charge source 36, and the rear curtain drive source 37. The front curtain drive source 35 is composed of an electromagnetic actuator composed of a known coil or yoke, a drive lever, and the like. The charge source 36 is composed of a drive lever, a spring, and the like for performing the closing operation in order to bring the front curtain 21 that has performed the opening operation into the closed state shown in FIG. 1 again. Further, the rear-curtain drive source 37 is configured by an electromagnetic actuator and a drive lever that are configured by known coils and yokes for opening and closing the rear curtain 22. When the information about the shutter speed from the camera system control circuit 135 is received, the front curtain drive source 35, the rear curtain drive source 37, and the charge source 36, which are the drive sources of the front curtain 21 and the rear curtain 22 of the focal plane shutter 50. Control the drive. Thereby, the front curtain 21 and the rear curtain 22 are operated so as to achieve the shutter speed. By the operation of the focal plane shutter 50 and the diaphragm 104, an appropriate amount of object light can be directed to the image plane side. When the AF control circuit 140 detects that the subject is in focus, this information is transmitted to the camera system control circuit 135. At this time, if SW2 is turned on by a full press operation of the release button 120, the photographing operation is performed by the imaging system, the image processing system, and the recording / reproducing system as described above.

  Next, with reference to FIGS. 4 to 6, the effect of the concavo-convex structure 11 a provided on the surface of the optical element 11 according to the present embodiment will be described.

  FIGS. 4A to 4C are enlarged views of a portion A in FIG. 1 and show a state in which dust adheres to the surface of the optical element 11. In the figure, 30 is dust. Further, as described later, a liquid bridge is formed between the dust 30 and the surface of the optical element 11. In the present embodiment, the liquid bridge (solid line in FIG. 4C) formed when the surface of the optical element 11 has the uneven structure 11a is 70, and the surface of the optical element 11 has no uneven structure 11a. The liquid bridge formed (broken line (C) in FIG. 4) is shown as 70 '.

  When the dust 30 is now attached to the surface of the optical element 11, water molecules (not shown) contained in the air aggregate between the dust 30 and the surface of the optical element 11 to form the liquid bridge 70. By this liquid bridge 70, an adhesion force FL expressed by the equation (1) acts between the dust 30 and the surface of the optical element 11, which is a liquid bridge force.

FL = 2πσD cos θ (N) (1)
In this equation (1), σ is the surface tension (N / m) of water, D is the diameter (m) of the dust 30, and θ is the contact angle (degree) of the water with respect to the surface of the optical element 11.

  Here, when considering the liquid bridging force for the same dust 30, the surface tension (surface energy) of water is constant. Therefore, the contact angle θ is different between the case where the concavo-convex structure 11 a is present on the surface of the optical element 11 and the case where there is no concavo-convex structure 11 a as described later. Here, the respective contact angles θ are assumed to be θ1 and θ2 (θ1 <θ2, see FIG. 4C).

  Here, the contact angle θ is the ratio of the surface energy of each of water and the concavo-convex structure 11a (or the surface of the optical element 11). Here, attention is paid to the portion where the dust 30 and the concavo-convex structure 11a are in contact. (See FIG. 5).

  FIG. 5 is an enlarged view of a portion where dust and the uneven structure are in contact with each other.

  As shown in FIG. 5, when the concavo-convex structure 11 a is present, the dust 30 is in contact with at least one of the single concavo-convex structures 11 b constituting the concavo-convex structure 11 a, and the liquid bridge is formed between the single concavo-convex structure 11 b and the dust 30. 70a is formed. Actually, since the dust 30 and the concavo-convex structure 11a are in contact with the plurality of single concavo-convex structures 11b, a plurality of liquid bridges 70a are formed. Therefore, it can be said that the aggregate of the liquid bridge 70a is the liquid bridge 70 shown in FIG.

  Regardless of the magnitude relationship between the surface energy of the single concavo-convex structure 11b and the surface energy of the optical element 11 without the concavo-convex structure 11a, the contact area when the concavo-convex structure 11a and the dust 30 are in contact with each other, The contact area when the surface and the dust 30 are in contact is compared. In this case, since the contact area when the concavo-convex structure 11a and the dust 30 are in contact with each other is smaller, the contact angle apparently changes depending on the presence or absence of the concavo-convex structure 11a. As a result, the contact angle when the concavo-convex structure 11a and the dust 30 are in contact with each other increases, so that θ1 <θ2.

  Here, the size of the liquid bridge 70 formed between the dust 30 and the surface of the concavo-convex structure 11 a is compared with the size of the liquid bridge 70 ′ formed between the dust 30 and the surface of the optical element 11. Compared with the liquid bridge 70 ′ without the uneven structure 11a (S2 in FIG. 4C), the liquid bridge 70 with the uneven structure 11a is smaller (S1 in FIG. 4C).

  In the formula (1), only the contact angle θ is different depending on the presence or absence of the concavo-convex structure 11a. For this reason, when the contact angle θ increases, the adhesion force FL decreases (0 degree ≦ θ ≦ 90 degrees). That is, when the adhesion force FL1 when the concavo-convex structure 11a is present and the adhesion force FL2 when there is no concavo-convex structure 11a are compared, FL1 <FL2.

  That is, the uneven structure 11a reduces the adhesion force of the dust 30 to the uneven structure 11a (optical element 11). For this reason, even if the dust 30 tries to adhere to the optical element 11, if there is the concavo-convex structure 11 a, the adhesion force becomes small. As a result, due to the influence of gravity applied to the dust 30, the dust 30 easily falls from the surface of the optical element 11, and is difficult to adhere to the surface of the optical element 11.

  Apart from this, when the dust 30 adheres to the surface of the optical element 11 or the concavo-convex structure 11 a, van der Waals force that is an interaction force acts between the dust 30 and the surface of the optical element 11. This van der Waals force is an adhesion force Fv expressed by equation (2).

Fv = HD / (square of 12 × Z) (N) Equation (2)
In this formula (2), H is the Hamarker constant (J) of the dust 30, D is the diameter (m) of the dust 30, and Z is the separation distance between the dust 30 and the surface of the concavo-convex structure 11 a (or the optical element 11). .4 nm.

  Here, when the van der Waals force with respect to the same dust 30 is considered, since the diameter D and the Hammer constant H of the dust 30 are constant, the case where there is a concavo-convex structure 11 a on the surface of the optical element 11, The separation distance Z will be different.

  FIG. 6 is a diagram for explaining Van der Waals forces.

  In the first place, Van der Waals force is an interaction force acting between two objects. This interaction force can be obtained by taking the sum (integration) of the energy between all atoms in one object and all atoms in another object. (Reference: Intermolecular force and surface force, written by JN, Israel Ativiri, Asakura Shoten, P.172). Therefore, as shown in FIG. 6, the van der Waals force acting between the dust 30 and the optical element 11 can be obtained in the same manner.

  By the way, when the concavo-convex structure 11a is provided on the surface of the optical element 11, the total of van der Waals forces acting between the dust 30 and the single concavo-convex structure 11b forming the concavo-convex structure 11a is Van der Waals force acting during Of course, it is conceivable that van der Waals force is generated between the dust 30 and the surface of the optical element 11 under the uneven structure 11a. Here, the separation distance Z increases by the distance of the uneven structure 11a, that is, the depth of the single uneven structure 11b. Compared to Z = 0.4 nm in the above formula (2), Z is 500 times when the depth of the single relief structure 11b is 200 nm. Therefore, since the van der Waals force is reduced by the square of Z, the van der Waals force acting between the dust 30 and the surface of the optical element 11 is a negligible value.

  As described above, since the contact area between the dust 30 and the concavo-convex structure 11a is smaller than the contact area between the dust 30 and the surface of the optical element 11, the separation distance from the dust 30 is increased by the difference in the contact area. This range exists in the concavo-convex structure 11a. That is, in the formula (2), the van der Waals force Fv ′ acting between the concavo-convex structure 11a and the dust 30 can be expressed by the following formula (3). Now, the separation distance for the area in contact with the dust 30 is Z1, and the separation distance for the area that is no longer in contact with the dust 30 by providing the concavo-convex structure 11a is Z2.

Fv ′ = {HD / (12 × Z1 squared)} + {HD / (12 × Z2 squared) (N) (3)
Here, the second term of the formula (3) (Van der Waals force acting on the area that is no longer in contact with the dust 30) is smaller than the first term because the separation distance Z2 is larger than Z. Further, the separation distance between the dust 30 and the surface of the optical element 11 when there is no concavo-convex structure 11a is Z.

Z = Z1 ... Formula (4)
Even in the case of formula (4), as described above, the area where the concavo-convex structure 11a is in contact with the dust 30 is smaller than the contact area of the optical element 11 when there is no concavo-convex structure 11a. Therefore, the first term of the expression (3) is smaller than the van der Waals force that acts on the optical element 11 when the concavo-convex structure 11a is not obtained, which is obtained by the expression (2). That is, when the adhesion force Fv1 when the concavo-convex structure 11a represented by the expression (3) is present and the adhesion force Fv2 when there is no concavo-convex structure 11a are compared, Fv1 <Fv2.

  Therefore, the uneven structure 11 a reduces the adhesion force of the dust 30 to the uneven structure 11 a (optical element 11), so that the adhesion force that the dust 30 tends to adhere to the optical element 11 decreases. Therefore, it becomes easy to fall from the surface of the optical element 11 due to the influence of gravity applied to the dust 30, and it becomes difficult to adhere to the surface of the optical element 11.

  Next, FIG. 7 is a figure explaining the effect of the uneven structure 11a.

  FIG. 7A is a diagram showing a state where glass beads (true spheres) having an average particle diameter of 60 μm are dispersed on the surface of a solid Si substrate. FIG. 7B shows a state where the substrate is turned upside down from the state of FIG. 7A and then returned to the state of FIG. 7A again. FIG. 7C shows a Si substrate in which a periodic concavo-convex structure 11a is provided by a femtosecond laser on a solid Si substrate surface as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-211203 (FIGS. 15 and 16). Indicates. FIG. 7C shows a state in which glass beads (true spheres) having an average particle diameter of 60 μm are dispersed on the substrate surface. FIG. 7D shows a state where the substrate is turned upside down from the state of FIG. 7C and then returned to the state of FIG. 7C again.

  As is clear from FIGS. 7A to 7D, as shown in FIGS. 7A and 7B, in the Si substrate having no uneven structure 11a on the substrate surface, the glass beads spread on the surface are turned upside down. But almost no fall. However, as shown in FIGS. 7C and 7D, in the Si substrate having the concavo-convex structure 11a on the substrate surface, it can be seen that most of the scattered glass beads are dropped by turning the substrate upside down. That is, it was confirmed that the adhesion between the glass beads and the Si substrate surface was reduced by providing the concavo-convex structure 11a on the surface.

  According to the above configuration, it is possible to provide an optical device that reduces the adhesion of dust to the surface of the optical element without adversely affecting the optical characteristics.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the structure similar to the above-mentioned Embodiment 1, and the description is abbreviate | omitted.

  FIG. 8 is a side sectional view for explaining a schematic configuration of the imaging unit 10 and the focal plane shutter 50 of the camera 100 according to the second embodiment.

  FIG. 9A is an enlarged view of a portion B in FIG. 8 and shows a state in which dust 30 adheres to the surface of the optical element 11.

  8 and 9A, reference numeral 40 denotes a concavo-convex structure formed of at least one kind of particles on the surface of the optical element 11 facing the focal plane shutter 50 side. As shown in FIG. 9B, here small particles (second particles) 40b (second uneven structure) are predetermined around large particles (first particles) 40a (first uneven structure). The number is attached. These are arranged on the surface of the optical element 11 at a predetermined pitch (first period) or randomly. The large particles 40a and the small particles 40b constituting the concavo-convex structure 40 are made of a low refractive index material such as MgF2 or SiO2, or are hollow to have a low refractive index. For example, the large particle 40a has a particle size of 200 nm. In addition, since there is concern about adverse effects such as optical scattering when the particle diameter is in the visible light wavelength range (about 350 nm to 700 nm) or larger, it is desirable that the large particles 40a have a particle diameter of 200 nm or less. .

  Moreover, the coupling | bonding of the large particle 40a and the small particle 40b is the method currently disclosed by Unexamined-Japanese-Patent No. 2005-28356, for example, and the small particle 40b has couple | bonded with the surface of the large particle 40a. Further, the uneven structure 40 may be arranged on the surface of the optical element 11 by an LB (Langmuir-Blodgett) method or the like.

  Next, with reference to FIG. 10, the effect of the concavo-convex structure 40 provided on the surface of the optical element 11 according to the second embodiment will be described.

  FIG. 10 is an enlarged view focusing on the portion where the dust 30 and the concavo-convex structure 40 are in contact with each other in FIG. 9. Again, as in the first embodiment, a liquid bridge is formed between the dust 30 and the surface of the optical element 11. In the second embodiment, the liquid bridge (solid line in FIG. 10) formed when the surface of the optical element 11 has the concavo-convex structure 40 is formed 70, and is formed when the surface of the optical element 11 does not have the concavo-convex structure 40. A liquid bridge (broken line in FIG. 10) is indicated by 70 '.

  When the dust 30 adheres to the surface of the optical element 11, water molecules (not shown) contained in the air aggregate between the dust 30 and the surface of the optical element 11 to form the liquid bridge 70. As in the first embodiment, the liquid bridge 70 causes an adhesion force FL, which is a liquid bridge force, expressed by the equation (1) between the dust 30 and the surface of the optical element 11.

  Here, since the surface tension (surface energy) of water is constant when the liquid bridging force with respect to the same dust 30 is considered, it will be described later with and without the uneven structure 40 on the surface of the optical element 11. Thus, the contact angle θ is different. Let them be θ1 and θ2, respectively (θ1 <θ2, see FIG. 9A).

  As shown in FIG. 10, when the uneven structure 40 is present, the dust 30 is in contact with at least one of the large particles 40 a or the small particles 40 b constituting the uneven structure 40, and the large particles 40 a or the small particles 40 b and the dust 30 Between these, a liquid bridge 70a is formed.

  Actually, since the dust 30 and the concavo-convex structure 40 are in contact with the plurality of large particles 40a or the small particles 40b, a plurality of liquid bridges 70a are formed, and the aggregate of the liquid bridges 70a is shown in FIG. It can be said that this is the liquid crosslinking 70 shown.

  Regardless of the magnitude relationship between the surface energy of the large particles 40a and the small particles 40b and the surface energy of the optical element 11 when there is no concavo-convex structure 40, the contact area when the concavo-convex structure 40 and the dust 30 are in contact, and the optical element 11 The contact area when the surface 30 and the dust 30 are in contact with each other is compared. In this case, since the contact area where the concavo-convex structure 40 and the dust 30 are in contact with each other is smaller, the contact angle apparently changes depending on the presence or absence of the concavo-convex structure 40. As a result, the contact angle when the concavo-convex structure 40 and the dust 30 are in contact with each other is increased to satisfy θ1 <θ2.

  In this way, the size of the liquid bridge 70 formed between the dust 30 and the surface of the concavo-convex structure 40 is compared with the size of the liquid bridge 70 ′ formed between the dust 30 and the surface of the optical element 11. In this case, the liquid bridge 70 with the concavo-convex structure 40 is smaller than the liquid bridge 70 ′ without the concavo-convex structure 40 (S2 in FIG. 9A) (S1 in FIG. 9A). ).

  Further, in the above formula (1), only the contact angle θ differs depending on the presence or absence of the concavo-convex structure 40, so that the adhesive force decreases as the contact angle θ increases (0 ° ≦ θ ≦ 90 °). That is, when the adhesion force FL1 when the uneven structure 40 is present and the adhesion force FL2 when there is no uneven structure 40 are compared, FL1 <FL2. That is, the uneven structure 40 weakens the adhesion force of the dust 30 to the uneven structure 40 (optical element 11). As a result, even if the dust 30 tries to adhere to the optical element 11, if the uneven structure 40 is present, the adhesion force is reduced, and the dust 30 is easily dropped from the surface of the optical element 11 due to the influence of gravity applied to the dust 30. As a result, it becomes difficult for the dust 30 to adhere to the surface of the optical element 11.

  Apart from this, when the dust 30 adheres to the surface of the optical element 11 or the concavo-convex structure 40, as in the first embodiment, the van der Waals force (interaction force (2)) The applied force Fv) acts between the dust 30 and the surface of the optical element 11.

  Here, the van der Waals force for the same dust 30 is considered. Since the diameter D and the Hamarker constant H of the dust 30 are constant, the separation distance Z differs between when the uneven structure 40 is present on the surface of the optical element 11 and when it is not present. That is, when the concavo-convex structure 40 is provided on the surface of the optical element 11, the sum of van der Waals forces acting between the dust 30 and the large particles 40a and the small particles 40b forming the concavo-convex structure 40 is It becomes van der Waals force acting between 40. Of course, van der Waals force may be generated between the dust 30 and the surface of the optical element 11 under the concavo-convex structure 40, but the distance of the concavo-convex structure 40, that is, the particle size of the large particles 40 a (for example, 200 nm). ), The separation distance Z increases. Here, compared with Z = 0.4 nm in the formula (2), when the particle size of the large particle 40a is 200 nm, Z is 500 times, so the van der Waals force is reduced by the square of Z. The van der Waals force acting between 30 and the surface of the optical element 11 may be ignored.

  Here, as described above, the contact area between the dust 30 and the uneven structure 40 is smaller than the contact area between the dust 30 and the surface of the optical element 11. Therefore, the uneven structure 40 increases the separation distance from the dust 30 by the difference in the contact area. That is, in the formula (2), the van der Waals force acting between the concavo-convex structure 40 and the dust 30 can be expressed as the following formula (5). Here, the separation distance corresponding to the area that is in contact with the dust 30 is Z1, and the separation distance corresponding to the area that is no longer in contact with the dust 30 by providing the uneven structure 40 is Z2.

Fv ′ = {HD / (12 × Z1 squared)} + {HD / (12 × Z2 squared) (N) (5)
Here, the second term (Van der Waals force acting on the area that is no longer in contact with the dust 30) in the equation (5) is smaller than the first term because the separation distance Z2 is larger than Z1. Further, the separation distance Z between the dust 30 and the surface of the optical element 11 when there is no uneven structure 40,
Z = Z1 (6)
And Even in this case, as described above, the area where the uneven structure 40 is in contact with the dust 30 is smaller than the contact area of the optical element 11 when the uneven structure 40 is not provided. As a result, the first term of the formula (5) is smaller than the van der Waals force acting on the optical element 11 in the absence of the concavo-convex structure 40, which is obtained by the formula (2). That is, when the adhesion force Fv1 in the case where the concavo-convex structure 40 represented by the formula (5) is present and the adhesion force Fv2 in the case where there is no concavo-convex structure 40 are compared, Fv1 <Fv2.

  Therefore, it can be seen that such an uneven structure 40 reduces the adhesion of the dust 30 to the uneven structure 40 (optical element 11). As a result, even if the dust 30 tries to adhere to the optical element 11, the adhesion force is reduced when the uneven structure 40 is present. For this reason, it becomes easy to fall from the surface of the optical element 11 due to the influence of gravity applied to the dust 30. As a result, the dust 30 is less likely to adhere to the surface of the optical element 11.

  As described above, according to the second embodiment, the concavo-convex structure 40 can reduce the liquid crosslinking force as well as the van der Waals force without adversely affecting the optical characteristics. Thereby, the optical apparatus which suppressed adhesion of dust to the surface of an optical element can be provided.

  In the second embodiment, the large particles 40 a forming the concavo-convex structure 40 are arranged on the surface of the optical element 11. However, the present invention is not limited to this. For example, the surface of the large particles 40a and the small particles 40b is provided with a water-repellent coating to impart water repellency to the large particles 40a and the small particles 40b. 40 may be provided with water repellency. Thereby, compared with the above-mentioned embodiment, the contact angle with the dust 30 can be further increased, and the liquid bridging force can be further reduced. Thereby, the optical apparatus which suppressed adhesion of dust to the surface of an optical element further can be provided.

  The present invention is not limited to this. For example, the large particles 40a and the small particles 40b that form the uneven structure 40 may be formed of a conductive material. Alternatively, the surfaces of the large particles 40a and the small particles 40b may be provided with a conductive coating to impart conductivity to the large particles 40a and the small particles 40b. Thereby, conductivity can be imparted to the concavo-convex structure 40 as well. That is, by adding various functions to the large particles 40a and the small particles 40b that form the uneven structure 40, the uneven structure 40 can function more effectively. Thus, it is possible to provide an optical device which has a function such as conductivity and which suppresses the adhesion of dust to the surface of the optical element.

  In the present embodiment, the concavo-convex structure 40 is provided directly on the surface of the optical element 11, but the present invention is not limited to this. For example, a dielectric multilayer film is often provided on the surface of the optical element 11 in order to reduce the surface reflectivity and cut infrared light.

  FIG. 11 is a diagram showing a modification of the concavo-convex structure 40 according to Embodiment 2 of the present invention.

  Here, the uneven structure 40 is provided on the outermost surface of the dielectric multilayer film 60. Thereby, the desired optical performance (spectral transmittance, etc.) is maintained by the dielectric multilayer film 60 below the concavo-convex structure 40, and the adhesion of the dust 30 to the surface of the optical element 11 is suppressed by the concavo-convex structure 40. can do. Of course, it goes without saying that the dielectric multilayer film 60 is designed in consideration of the optical characteristics (refractive index, etc.) of the concavo-convex structure 40.

  When the dielectric multilayer film 60 is provided on the concavo-convex structure 40 to obtain a desired optical performance, the dielectric multilayer film 60 fills the fine shape on the surface of the optical element 11 provided in the concavo-convex structure 40. And become flat. Therefore, in order to reduce the adhesion of the dust 30, it is necessary to dispose the uneven structure 40 on the outermost surface of the dielectric multilayer film 60 as described above.

  By the way, in the above-described embodiment, the uneven structure 40 is provided on the surface of the optical element 11. However, when the optical element 11 is not provided between the focal plane shutter 50 and the solid-state imaging device 15, that is, when the focal plane shutter 50 and the solid-state imaging device 15 face each other, Dust 30 adhering to the surface becomes a problem.

  FIG. 12 is a side view for explaining a schematic configuration of the imaging unit 10 and the focal plane shutter 50 of the D-SLR 100 when the optical element 11 is not provided between the focal plane shutter 50 and the solid-state imaging device 15. It is sectional drawing.

  In this case, the fine particle single layer 80 is provided on the surface of the cover member 15 a of the solid-state imaging device 15. As a result, the same effects as those described in the above-described embodiments can be obtained, and the adhesion of dust to the surface of the solid-state imaging device 15 can be suppressed.

  Further, when a multilayer film such as an antireflection film is formed on the surface of the cover member 15a of the solid-state imaging device 15, as described above, the first embodiment or the second embodiment is formed on the outermost surface of the multilayer film. Any of the concavo-convex structure 80 described in the above may be provided. Thereby, the adhesive force of the dust 30 can be reduced while obtaining desired optical performance. In this way, it is possible to suppress dust from adhering to the surface of the solid-state imaging device 15.

It is a sectional side view for demonstrating schematic structure of the imaging part and focal plane shutter of D-SLR which concern on Embodiment 1 of this invention. It is the schematic which shows the structure of the camera system of D-SLR which concerns on this Embodiment 1. FIG. It is a block diagram explaining the electrical structure of the camera system of D-SLR which concerns on this Embodiment 1. FIG. In this Embodiment, it is a figure explaining the effect | action of the uneven structure with respect to the dust adhering to the surface of the optical element. It is an enlarged view of the location where dust and an uneven structure contact. It is a figure explaining Van der Waals force. It is a figure explaining the effect of the uneven structure concerning this embodiment. It is a sectional side view for demonstrating schematic structure of the imaging part of D-SLR which concerns on this Embodiment 2, and a focal plane shutter. It is an enlarged view of the B section of FIG. FIG. 10 is an enlarged view focusing on a portion where dust and the concavo-convex structure are in contact with each other in FIG. 9. It is a figure which shows the modification of the uneven structure which concerns on Embodiment 2 of this invention. Side section for explaining schematic configurations of D-SLR imaging unit and focal plane shutter when optical element according to other embodiment is not provided between focal plane shutter and solid-state imaging device FIG.

Claims (4)

An optical device comprising an imaging means for converting an optical image of a subject into an electrical signal, and an optical element disposed on the subject side of the imaging means,
A first concavo-convex structure formed by arranging, on the object side surface of the optical element, first particles having a particle size of 200 nm or less on the object side surface of the optical element; and a surface of the first particle and a predetermined number attached to, the grain size than the first particle is provided a second concave-convex structure formed by the second particles are small, the object side surface of the optical element, attached to the surface An optical apparatus characterized by reducing van der Waals force between dust and dirt . The first particles and the second particles, optical apparatus according to claim 1, characterized in that the water repellency is imparted. The optical apparatus according to claim 1 , wherein the first particles and the second particles have conductivity. 4. The optical apparatus according to claim 1, wherein the first and second particles are made of a low refractive index material or are hollow.