Lens units and camera modules

Abstract

To provide a lens unit capable of preventing fogging on a rear surface of a lens without impairing antireflection characteristics of an antireflection film and a camera module.SOLUTION: A lens unit 11 includes lens heating means 48 that has: a transparent conductive film 31 provided on a lens back surface 13a facing an image side of a lens 13 positioned on the most object side constituting a lens group L; and at least a pair of electrodes 32A, 32B electrically connected to the transparent conductive film 31, and generates Joule heat at the lens back surface 13a by applying a current to the transparent conductive film 31 by applying a voltage between the electrodes 32A and 32B. Also, an antireflection film 31 is provided on the lens back surface 13a in a laminated state with the transparent conductive film 31.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lens unit and a camera module, and more particularly to a lens unit and a camera module that can be provided in an on-board camera mounted on a vehicle such as an automobile. [Background technology]

[0002] In recent years, automobiles have been equipped with on-board cameras to support parking and prevent collisions through image recognition, and attempts are also being made to apply them to autonomous driving. In addition, camera modules such as such on-board cameras generally include a lens unit having a lens group consisting of multiple lenses arranged along an optical axis, a lens barrel that houses and holds the lens group, and an aperture member arranged between at least one of the lenses in the lens group (for example, see Patent Document 1).

[0003] In particular, in the case of a lens unit for an in-vehicle camera, when at least a part of the lens unit is installed outside the vehicle, as shown in Fig. 7, in a state where a lens group L consisting of a plurality of lenses arranged along an optical axis O is assembled and housed in an inner housing space S of a lens barrel 102, an O-ring 104 is interposed between a first lens 100 positioned on the most object side of the lens group L and the lens barrel 102 to prevent water and dust from entering the lens group L inside the lens barrel 102. In this case, an outer peripheral side surface 100a of the first lens 100 is provided with a stepped reduced diameter portion 100b having a reduced diameter at the image side portion of the lens 100, and an O-ring 104 is attached to this reduced diameter portion 100b, and the O-ring 104 is compressed in the radial direction between the outer peripheral side surface 100a of the first lens 100 and an inner peripheral surface 102a of the lens barrel 102, thereby sealing the object side end of the lens barrel 102.

[0004] 7, when the curvature of the back surface 100c facing the image side of the first lens 100 is larger than that of the front surface 100d facing the object side, the antireflection film generally provided on the lens surface to increase the light transmittance generally has a multilayer structure when provided on the front surface 100d and a single layer when provided on the back surface 100c, taking into consideration that the more layers there are and the greater the curvature, the higher the incidence angle dependency becomes. In addition, a water-repellent film may be provided on the antireflection film on the front surface 100d exposed to the outside. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-231993 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, even if waterproofing is implemented using the O-ring 104 as described above, moisture (water vapor) can enter the lens unit through various routes. Therefore, when the difference between the outside air temperature and the temperature inside the lens unit becomes large, the water vapor inside the lens unit condenses and condenses on the lens surface. In particular, in the inter-lens space S1 between the first lens 100 and the adjacent second lens 101, which is most affected by the temperature difference with the outside, condensation tends to occur, particularly on the back surface 100c of the first lens 100, causing fogging and making image evaluation difficult.

[0007] For this reason, it may be possible to apply some kind of treatment to the rear surface 100c to prevent fogging. In that case, however, it is also necessary to take into account factors such as the incidence angle dependency that is easily affected by the curvature of the rear surface 100c and the layered state of the antireflection film, so as not to impair the antireflection properties of the antireflection film.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a lens unit and a camera module that can effectively prevent fogging on the rear surface of the lens, and also aims to provide a lens unit and a camera module that can prevent fogging on the rear surface of the lens without compromising the anti-reflection properties of the anti-reflection film. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a lens unit including a lens group including a plurality of lenses arranged along an optical axis of the lenses, and a lens barrel in which the lens group is housed, a lens heating means having a transparent conductive film provided on a lens back surface facing the image side of the lens located closest to the object side that constitutes the lens group, and at least a pair of electrodes electrically connected to the transparent conductive film, and configured to apply a voltage between the electrodes to cause a current to flow through the transparent conductive film and generate Joule heat on the lens back surface; An anti-reflection film provided on the rear surface of the lens; The present invention is characterized by comprising:

[0010] In the present invention, a transparent conductive film having resistance is provided on the lens back surface facing the image side of the lens located closest to the object side, and Joule heat is generated on the lens back surface by passing a current through the transparent conductive film through an electrode, that is, the lens back surface is directly heated by a lens heating means having a transparent conductive film and an electrode, so that fogging on the lens back surface can be effectively prevented, or the deterioration of the visibility of the lens due to fogging on the lens back surface can be quickly eliminated, and the desired visibility can be ensured in a short time. In addition, since the conductive film is transparent, it does not affect the visibility of the lens unit. Furthermore, since the transparent conductive film is provided on the lens back surface and the electrode is electrically connected to the transparent conductive film, the increase in manufacturing cost associated with the installation of the lens heating means can be suppressed, and since almost no new space is required for installing the lens heating means, the size can be maintained almost the same as that of a conventional lens unit without a lens heating means (the entire lens unit does not become larger). The effect obtained in this way is particularly beneficial when the lens located closest to the object side is a glass lens with low thermal conductivity.

[0011] In the above configuration, the transparent conductive film may be, for example, indium tin oxide (ITO) as described above, but is not limited thereto. The transparent conductive film must be provided over at least the entire range of the effective diameter of the lens, and may be provided over almost the entire back surface of the lens. In contrast, the electrodes must be provided outside the effective diameter of the lens so as not to obstruct the field of view of the lens. Here, the effective diameter of the lens means the diameter of a circle whose radius is the distance from the optical axis of a ray passing through a position farthest from the optical axis among the rays passing through the lens surface, and the range of the effective diameter of the lens specifically corresponds to the lens area through which light incident on the imaging sensor (imaging element) of the lens unit passes, and is determined by the size of the imaging sensor. In addition, metal electrodes such as silver and copper can be used as the electrodes. In addition, the resistance value of the transparent conductive film between the electrodes is preferably set to 50 to 200 Ω.

[0012] In the above configuration, it is preferable that an anti-reflection film is provided on the transparent conductive film. In this regard, the present inventors have verified how the lamination position of the transparent conductive film with respect to the anti-reflection film affects the reflectance of the anti-reflection film when the transparent conductive film constituting the lens heating means is used together with the anti-reflection film, and have found that if the transparent conductive film is positioned on the anti-reflection film so as to cover the anti-reflection film, not only will the reflectance of the anti-reflection film be higher than the reflectance of the anti-reflection film alone that is not covered by the transparent conductive film (the anti-reflection characteristics will be reduced), but also the transparent conductive film will have to be made thin in order to satisfy the spectral characteristics, and the distribution of heat generated by the lens heating means will not be uniform.

[0013] Specifically, as shown in Figure 4, the anti-reflection properties of these film stack structures and the heat distribution state due to the ITO film were investigated for case C1 (AR coating only), in which only a single-layer anti-reflection film was provided on the lens surface; case C2 (AR coating + ITO coating), in which a single-layer anti-reflection film was provided and an ITO film was further provided on top of that as a transparent conductive film; and three cases C3, C4, and C5 (ITO coating + AR coating (a); ITO coating + AR coating (b); ITO coating + AR coating (c)), in which ITO films of three different thicknesses were provided as transparent conductive films and then a single-layer anti-reflection film was further provided on each of those.

[0014] More specifically, in case C1, a SiO 2 anti-reflection coating material with a refractive index of 1.45 is applied to a glass lens (TAF1) with a refractive index of 1.77. 2 In case C2, a film laminate structure was adopted in which SiO, an anti-reflection film material with a refractive index of 1.45, was laminated on a glass lens (TAF1) with a refractive index of 1.77. 2 In case C2, a film laminate structure is adopted in which indium tin oxide (ITO) with a refractive index of 1.74 is laminated to a thickness of 25.00 nm on a glass lens (TAF1) with a refractive index of 1.77, and SiO 2 , an anti-reflection film material with a refractive index of 1.45, is laminated on the ITO with a thickness of 25.00 nm on the glass lens (TAF2) with a refractive index of 1.77. 2In case C4, indium tin oxide (ITO) with a refractive index of 1.74 is laminated to a thickness of 50.00 nm on a glass lens (TAF1) with a refractive index of 1.77, and SiO 2 In case C5, indium tin oxide (ITO) with a refractive index of 1.74 is laminated to a thickness of 100.00 nm on a glass lens (TAF1) with a refractive index of 1.77, and SiO 2 A film stack structure was adopted in which the film stack structure was laminated to a thickness of 97.00 nm, and the film stack structure was optimized by a predetermined simulation at a predetermined light incident angle, and the spectral characteristic curves L1 to L5 shown in the spectral characteristic diagrams of Figures 5 and 6 (spectral characteristic diagrams showing the relationship between the reflectance (%) of the anti-reflection film and the incident light wavelength (nm)) were obtained. Here, the spectral characteristic curves L1 to L5 correspond to cases C1 to C5, respectively.

[0015] As can be seen from the spectral characteristic diagram shown in Figure 5, in case C2 in which an ITO film is laminated on an anti-reflection film (AR coat), the reflectance is not completely within the specified incident wavelength range (450nm to 650nm) of 1.5 or less, as shown by the spectral characteristic curve L2, and the distribution of heat generated by the ITO film is not uniform with the thinness of the ITO film (15.00nm). It was also found that if the ITO film is made thicker to achieve a uniform heat distribution, it becomes even more difficult to achieve the desired optical characteristics (for example, anti-reflection characteristics with a reflectance of 1.5 or less within the specified incident wavelength range (450nm to 650nm)). In contrast, in case C3 where an anti-reflection film (AR coating) is laminated on the ITO film, as shown by the spectral characteristic curve L3, the reflectance is completely within the specified incident wavelength range (450 nm to 650 nm) and the desired spectral characteristics (anti-reflection characteristics) are obtained, and it was also found that the distribution of heat generated by the ITO film is uniform with the thickness of the ITO film (25.00 nm). And, above all, as can be seen from FIG. 5, the spectral characteristics of this case C3 (see the spectral characteristic curve L3) are not significantly different from the spectral characteristics of case C1 where no ITO film is provided (see the spectral characteristic curve L1). This means that even when an ITO film is provided in addition to an anti-reflection film, as long as an anti-reflection film is provided on the ITO film, it is possible to maintain almost the same spectral characteristics (anti-reflection characteristics) as in the case of only an anti-reflection film without an ITO film.

[0016] On the other hand, Fig. 6 compares the spectral characteristics of three cases C3, C4, and C5 with different ITO film thicknesses, and shows the spectral characteristic curves L3 to L5 of a film stack structure in which an anti-reflection film is provided on an ITO film. As can be seen from this figure, in a film stack structure in which an anti-reflection film is provided on an ITO film, even if the thickness of the ITO film increases to a certain extent, the reflectance remains at or below 1.5 within the specified incident wavelength range (450 nm to 650 nm), and the desired spectral characteristics (anti-reflection characteristics) are obtained, and the spectral characteristics (anti-reflection characteristics) do not change significantly with an increase in thickness within the specified incident wavelength range. In relation to this, the present inventors conducted various repeated experiments and found that, particularly when the ITO film is 40 nm to 100 nm thick, good heat distribution uniformity can be obtained while maintaining the desired spectral characteristics (anti-reflection characteristics).

[0017] Based on the above, the inventors have concluded that by adopting a film lamination configuration in which an anti-reflective film is provided on a transparent conductive film, it is possible to prevent fogging on the back surface of the lens due to heat generated by the transparent conductive film without compromising the anti-reflective properties of the anti-reflective film (while making use of the anti-reflective properties of the anti-reflective film), and to achieve good heat distribution uniformity while maintaining the desired anti-reflective properties within a specified film thickness range of the transparent conductive film.

[0018] In the above configuration, it is preferable that the anti-reflection film contains a metal. If the anti-reflection film contains a metal, even if the anti-reflection film is provided on the transparent conductive film so as to cover it, the Joule heat generated by the transparent conductive film can be transmitted to the outer surface through the anti-reflection film, thereby realizing the desired anti-fogging effect. In addition, the anti-reflection film is preferably made of SiO , which has low incidence angle dependency, particularly when the curvature of the rear surface of the lens is large (the radius of curvature is small). 2 or MgF 2 It is preferably formed from and preferably in the form of a single layer.

[0019] In the above-mentioned configuration of the present invention, it is preferable that a protective film is provided on the anti-reflection film. By providing such a protective film, damage to the anti-reflection film, which is weak in strength, can be prevented, and corrosion of the electrodes below the anti-reflection film can be prevented, thereby avoiding deterioration of the electrodes. Furthermore, a water-repellent film may be provided as such a protective film. This makes it possible to realize a lens that has both anti-reflection and water-repellent properties in addition to a lens heating function. In this case, it is preferable that the water-repellent film is provided over the entire lens surface to enhance the water-repellent performance.

[0020] In the above configuration, it is preferable that a recess is provided in a region outside the effective diameter of the adjacent lens on the image side of the lens located closest to the object on the surface facing the object side, and an electrode is disposed in this recess. By arranging the electrode in this manner within the recess, it is possible to prevent the lenses joined together with the electrode sandwiched between them from rattling when the electrode is not provided along the entire circumference of the lens.

[0021] In the above configuration, it is preferable that a light-shielding treatment is applied to the peripheral area of ​​the rear surface of the lens facing the recess in which the electrode is disposed. This makes it possible to make the electrodes invisible from the outside by a light-shielding treatment such as blackening, thereby realizing a good appearance and allowing the area outside the effective diameter of the lens to be used compactly, which can also contribute to miniaturization of the unit.

[0022] In addition, in the above configuration, when the radius of curvature of the lens back surface is 5 mm or less, it is preferable that the antireflection film has a single-layer structure. Considering that the incidence angle dependency increases as the antireflection film becomes multi-layered and as the curvature of the lens back surface increases (the radius of curvature decreases), it is important to make the antireflection film in a single layer form when the radius of curvature of the lens back surface is 5 mm or less, thereby reducing the incidence angle dependency and making it possible to easily achieve the desired antireflection characteristics (without adversely affecting the antireflection characteristics). Note that, when the radius of curvature of the lens back surface exceeds 5 mm, the antireflection film may have a multilayer structure within a range that does not adversely affect the antireflection characteristics.

[0023] In the above configuration, the thickness of the transparent conductive film (the dimension of the film along the optical axis) is preferably 40 to 100 nm. If the thickness of the transparent conductive film is thinner than 40 nm, the distribution of heat generated by the transparent conductive film due to current flow is not uniform. If the thickness of the transparent conductive film is thinned to such a thickness, when the transparent conductive film is formed by vapor deposition, depending on the film formation method, the thickness of the outer peripheral edge of the transparent conductive film may become even thinner (vapor deposition may be uneven) due to the curvature of the back surface of the lens, and in that case, the desired anti-fogging effect may not be obtained due to the uneven heat distribution. On the other hand, if the thickness of the transparent conductive film exceeds 100 nm, the deposition surface may become rough (surface roughness becomes uneven), especially when the transparent conductive film is formed by vapor deposition, and there is a risk of light diffusion.

[0024] A camera module according to the present invention includes the lens unit. With this configuration, the effects of the lens unit described above can be obtained with the camera module. Effect of the Invention

[0025] According to the present invention, a transparent conductive film having resistance is provided on the rear surface of the lens facing the image side of the lens located closest to the object, and Joule heat is generated on the rear surface of the lens by passing a current through this transparent conductive film via an electrode. This makes it possible to effectively prevent fogging on the rear surface of the lens, or to quickly eliminate the deterioration in lens visibility associated with fogging on the rear surface of the lens, thereby ensuring the desired visibility in a short period of time. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic cross-sectional view of a lens unit according to an embodiment of the present invention, in which an anti-reflection film is provided on a transparent conductive film on the rear surface of a lens located closest to the object side. [Diagram 2] 2 is an enlarged cross-sectional view of a portion A of the lens unit of FIG. 1. [Diagram 3]2 is a schematic cross-sectional view of a camera module including the lens unit of FIG. 1. [Figure 4] FIG. 13 is a table showing detailed stacking data of each film stacking structure to be compared. [Diagram 5] FIG. 5 is a diagram showing the spectral characteristics of a part of the film stack structure shown in FIG. [Figure 6] FIG. 5 is a spectral characteristic diagram of another part of the film stack structure shown in FIG. [Figure 7] FIG. 1 is a schematic cross-sectional view of a conventional lens unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The lens unit of this embodiment is particularly intended for use as a camera module for an in-vehicle camera, and is fixedly installed on the outer surface of a vehicle, with wiring leading into the vehicle and connected to a display or other device. Hatching is omitted for multiple lenses in Figures 1, 2, 3, and 7.

[0028] 1 shows a lens unit 11 according to an embodiment of the present invention. As shown in the figure, the lens unit 11 of this embodiment includes a cylindrical lens barrel 12 made of, for example, resin (or metal), a plurality of lenses arranged in a stepped inner storage space S of the lens barrel 12, for example, five lenses consisting of a first lens 13, a second lens 14, a third lens 15, a fourth lens 16, and a fifth lens 17 from the object side, and two diaphragm members 22a and 22b. In this embodiment, the diaphragm members 22a and 22b are interposed between the second lens 14 and the third lens 15 and between the third lens 15 and the fourth lens 16, and are "aperture diaphragms" that limit the amount of transmitted light and determine the F-number, which is an index of brightness, or "light blocking diaphragms" that block light rays that cause ghosts and light rays that cause aberrations. An in-vehicle camera equipped with such a lens unit 11 includes the lens unit 11, a board having an image sensor (not shown), and an installation member (not shown) for installing the board on a vehicle such as an automobile.

[0029] The multiple lenses 13, 14, 15, 16, and 17 assembled and held in the inner storage space S of the lens barrel 12 are stacked and arranged with their optical axes aligned, and the lenses 13, 14, 15, 16, and 17 are arranged along a single optical axis O to form a group of lenses L used for imaging. In this case, the first lens 13 that is positioned closest to the object and that constitutes the lens group L is a spherical glass lens that has a convex surface on the object side and a concave surface on the image side with a curvature larger than the curvature of the convex surface, and the other lenses 14, 15, 16, and 17 are resin lenses, but are not limited to this (for example, the first lens 13 may be a resin lens). In addition, the surfaces of these lenses 13, 14, 15, 16, and 17 are provided with an anti-reflection film, a hydrophilic film, a water-repellent film, etc., as necessary, but in particular, in this embodiment, the lens back surface 13a facing the image side of the first lens 13 as a glass lens is provided with a transparent conductive film 31, at least a pair of electrodes 32A, 32B electrically connected to the transparent conductive film 31, and an anti-reflection film 30, as described below. Although not shown, the lens surface 13b facing the object side of the first lens 13 is also provided with an anti-reflection film 30.

[0030] In this embodiment, the two lenses, the fourth and fifth lenses 16 and 17, located on the image side, form a cemented lens (composite lens) 40. The fourth and fifth lenses 16 and 17 constituting such cemented lens 40 are assembled by fitting an annular convex portion 16a on a surface facing the image side of the fourth lens 16 located on the object side into a corresponding annular concave portion 17a on a surface facing the object side of the fifth lens 17 located on the image side, as shown in the figure, and are fixed by an adhesive or the like.

[0031] In this embodiment, an O-ring 26 serving as a seal member is interposed between the first lens 13, which is located closest to the object side, and the lens barrel 12 to prevent water and dust from entering the lens group L inside the lens barrel 12. In this case, a stepped reduced diameter portion 13d having a smaller diameter at the image side portion of the lens 13 is provided on the outer circumferential side surface 13c of the first lens 13, and an O-ring 26 is attached to this reduced diameter portion 13d, and the O-ring 26 is compressed in the radial direction between the outer circumferential side surface 13c of the first lens 13 and the inner circumferential surface 12c of the lens barrel 12, thereby sealing the object side end of the lens barrel 12.

[0032] Inside the lens barrel 12, a cylindrical inner wall 12b is provided on the object side, and a groove is formed between the inner wall 12b and the outer wall 12a. An annular body 27 is provided in the groove, and an O-ring 26 is in close contact with the annular body 27. The reason for forming a groove between the inner wall 12b and the outer wall 12a is that if there is no groove and the inner wall 12b and the outer wall 12a are integrated, the wall thickness will be thick, and this is to prevent a large sink mark from occurring when molding and cooling the resin lens barrel 12, causing a loss of dimensional accuracy. The annular body 27 is made of a relatively soft elastic material, such as Teflon (registered trademark). The annular body 27 has the function of supporting the O-ring 26 in the optical axis direction. Since the annular body 27 is a separate member from the lens barrel 12, it is possible to change the annular body 27 to one with a different height depending on the size of the O-ring 26, ensuring that the O-ring 26 seals with an appropriate elastic force.

[0033] Furthermore, with lens group L assembled and housed in inner housing space S of lens barrel 12, crimping portion 23 at its object side end (upper end in FIG. 1) is crimped radially inward, thereby fixing first lens 13, which is positioned closest to the object side of lens group L, to the object side end of lens barrel 12 by crimping portion 23. Note that the fixing of first lens 13 is not limited to crimping portion 23, and may be performed by a fixing portion that is attached to the object side end of lens barrel 12 after lenses 13, 14, 15, 16, and 17 are housed in lens barrel 12.

[0034] Furthermore, an inner flange portion 24 having an opening with a diameter smaller than that of fifth lens 17 is provided at the end (the lower end in FIG. 1) of lens barrel 12 on the image side. By this inner flange portion 24 and crimped portion 23, multiple lenses 13, 14, 15, 16, and 17 and diaphragm members 22a and 22b constituting lens group L within lens barrel 12 are held and fixed in the optical axis direction.

[0035] 3 is a schematic cross-sectional view of a camera module 300 of the present embodiment having the lens unit 11 configured as described above. As shown in the figure, the camera module 300 includes the lens unit 11 of FIG. 1 to which the filter 100 is attached.

[0036] The camera module 300 includes an upper case (camera case) 301, which is an exterior component, and a mount (base) 302 that holds the lens unit 11. The camera module 300 also includes a seal member 303 and a package sensor (imaging element) 304.

[0037] Upper case 301 is a member that engages with flange portion 25 that is provided like a brim on outer wall 12a of lens barrel 12, and that exposes the object side end of lens unit 11 and covers the other portions. Mount 302 is disposed inside upper case 301, and has female threads 302a that screw into male threads 11a of lens unit 11. Seal member 303 is a member that is interposed between the inner surface of upper case 301 and outer peripheral surface 12a of lens barrel 12 of lens unit 11, and is a member that maintains airtightness inside upper case 301.

[0038] Package sensor 304 is disposed inside mount 302, and is disposed at a position where it receives an image of an object formed by lens unit 11. Package sensor 304 has a transparent cover on the outside and is equipped with a CCD, CMOS, etc. inside, and converts light that is collected through lens unit 11 and reaches it into an electrical signal. The converted electrical signal is converted into analog data or digital data, which is a component of image data captured by the camera.

[0039] As described above in relation to Figure 1, the first lens 13 as a glass lens provided at the object side end of the lens barrel 12 has a lens front surface 13b facing the object side and a lens back surface 13a facing the image side, and in particular, in this embodiment, in a longitudinal section along the optical axis, lens front surface 13b, which is the object side surface, is convex, and lens back surface 13a, which is the image side, is formed to be concave with a curvature larger than that of lens front surface 13b (having a radius of curvature smaller than the radius of curvature of lens front surface 13b (set to 5 mm or less in this embodiment)).

[0040] As clearly shown in an enlarged view in FIG. 2 (an enlarged view of part A in FIG. 1), a transparent conductive film 31 made of, for example, indium tin oxide (ITO) is provided on the lens back surface 13a of the first lens 13 at least over the entire effective diameter range of the first lens 13, particularly beyond the effective diameter range of the lens in this embodiment, by deposition or the like, with a thickness of, for example, 40 to 100 nm. If the thickness of the transparent conductive film 31 is thinner than 40 nm, the distribution of heat generated by the transparent conductive film 31 when current is applied becomes non-uniform. On the other hand, if the thickness of the transparent conductive film 31 exceeds 100 nm, when the transparent conductive film 31 is formed by deposition as in this embodiment, the deposition surface becomes rough (surface roughness becomes non-uniform), and there is a risk of light diffusion. As described above, such transparent conductive film 31 needs to be provided over at least the entire range of the effective diameter of first lens 13, and therefore in this embodiment, as an example, it is provided over the entire spherical concave region F1 of lens back surface 13a and a part of the aspherical outer peripheral region (the entire outer peripheral flat bonding region F2 that bonds with surface 14a facing the object side of second lens 14). Here, the range of the effective diameter of the lens corresponds to the region of lens 13 through which light incident on package sensor 304 passes, and is determined by the size of package sensor 304 (as described above).

[0041] Moreover, at least a pair of electrodes 32A, 32B are electrically connected to such a transparent conductive film 31. In particular, in this embodiment, a pair of arc-shaped electrodes 32A, 32B are provided facing each other on the outer periphery of the transparent conductive film 31 outside the range of the effective diameter of the first lens 13 and the second lens 14, which is an adjacent lens adjacent to the first lens 13 on the image side (see Figs. 1 and 3). Of course, the number of electrode pairs can be set arbitrarily, and the arrangement position and shape of the electrodes can also be set arbitrarily, but in this embodiment, the electrodes 32A, 32B are provided in an arc shape outside the range of the effective diameter of the lenses 13, 14 as described above so as not to obstruct the field of view of the lenses. In this case, each electrode 32A, 32B is accommodated in a recess 14c provided on the surface 14a facing the object side of the second lens 14, specifically, on the surface 14a facing the object side of the outer periphery flange portion 14b formed on the radial outer side of the second lens 14, so as not to protrude in the optical axis direction. A transparent conductive film 31 extending over the outer circumferential flat bonding region F2 of the first lens 13 via the bottom surface of the recess 14c is electrically connected to these electrodes 32A and 32B.

[0042] Although not shown, electrical wiring extending from a power source (not shown) is electrically connected to the pair of electrodes 32A, 32B, thereby forming a lens heating means 48 that generates Joule heat on the lens rear surface 13a by applying a voltage between the electrodes 32A, 32B to pass a current through the transparent conductive film 31. Metal electrodes such as silver, copper, and nickel can be used as the electrodes.

[0043] In addition, in the lens unit 11 of the present embodiment, a light-shielding treatment is applied to the peripheral flat bonding region F2 of the lens back surface 13a of the first lens 13 facing the recess 14c. In particular, in the present embodiment, the entire lens back surface 13a of the first lens 13 except for the spherical recessed region F1 is blackened as a light-shielding treatment (the blackened portion is indicated by reference numeral 50 in FIG. 2).

[0044] In addition, an anti-reflection film 30 for suppressing reflection of incident light is provided on the transparent conductive film 31. In particular, in the present embodiment in which the lens rear surface 13a has a large curvature (a radius of curvature of 5 mm or less), a SiO 2 or MgF 2 An anti-reflection film 30 made of (preferably containing a metal) is provided in a single layer structure by deposition or the like on the transparent conductive film 31 over the entire recessed region F1 of the lens back surface 13a. The anti-reflection film 30 is thus provided above the transparent conductive film 31, not below it. Furthermore, a protective film (e.g., a water-repellent film) may be further provided on the anti-reflection film 30.

[0045] As described above, according to this embodiment, the transparent conductive film 31 having resistance is provided on the lens back surface 13a facing the image side of the first lens 13 located closest to the object side, and Joule heat is generated on the lens back surface 13a by passing a current through the transparent conductive film 31 via the electrodes 32A and 32B. In other words, the lens back surface 13a is directly heated by the lens heating means 48 having the transparent conductive film 31 and the electrodes 32A and 32B. This makes it possible to effectively prevent fogging on the lens back surface 13a, or to quickly eliminate deterioration in the visibility of the lens due to fogging on the lens back surface 13a, and ensure the desired visibility in a short time. In particular, this embodiment employs a film stacking form in which the antireflection film 30 is provided on the transparent conductive film 31, so that fogging on the lens back surface 13a can be effectively prevented by the uniform heat generated by the transparent conductive film 31 without impairing the antireflection properties of the antireflection film 30.

[0046] The present invention is not limited to the above-described embodiment, and can be modified in various ways without departing from the gist of the present invention. For example, in the present invention, the shapes of the lens, the lens barrel, and the like, and the formation forms of the anti-reflection film and the transparent conductive film are not limited to the above-described embodiment. In addition, the material of the film, the film thickness, the material and the arrangement form of the electrodes and the lenses can be set arbitrarily. In addition, the electrodes do not have to be arc-shaped, and they do not have to be provided on the outer periphery of the lens. In addition, the transparent conductive film is not limited to ITO. In addition, in the above-described embodiment, the anti-reflection film is provided on the transparent conductive film, but the anti-fogging effect by heating can be obtained even if the transparent conductive film is provided on the anti-reflection film. [Explanation of symbols]

[0047] 11 Lens unit 12 Telescope tube 13 The First Lens 13a Lens back 14 Second lens (adjacent lens) 14a surface 14c Recess 30 Anti-reflection coating 31 Transparent conductive film 32A,32B electrode 48 Lens heating means 50 Blackened area (light blocking treatment) 300 Camera Module L lens group O optical axis

Claims

1. A lens unit including a lens group including a plurality of lenses arranged along an optical axis of the lenses, and a lens barrel in which the lens group is housed, a lens heating means having a transparent conductive film provided on a lens back surface facing the image side of the lens located closest to the object side that constitutes the lens group, and at least a pair of electrodes electrically connected to the transparent conductive film, and configured to apply a voltage between the electrodes to cause a current to flow through the transparent conductive film and generate Joule heat on the lens back surface; An anti-reflection film provided on the rear surface of the lens; Equipped with a concave portion is provided on a surface of the adjacent lens adjacent on the image side to the lens located closest to the object side, the surface facing the object side, the surface being in contact with the back surface of the lens, and the electrode is disposed within the concave portion so as not to protrude in the optical axis direction; the transparent conductive film extends over the entirety of the spherical concave region of the lens back surface and the entirety of the peripheral flat joint region of the lens back surface that contacts the surface of the adjacent lens facing the object side; The lens unit is characterized in that the transparent conductive film extending over the outer circumferential flat bonding region via the bottom surface of the recess is electrically connected to the electrode.

2. The lens unit according to claim 1 , wherein the anti-reflection film is provided on the transparent conductive film.

3. The lens unit according to claim 1 , wherein a light-shielding treatment is applied to an outer peripheral area of ​​the rear surface of the lens, the outer peripheral area facing the recess.

4. 4. The lens unit according to claim 1, wherein the radius of curvature of the rear surface of the lens is 5 mm or less, and the anti-reflection film has a single-layer structure.

5. 5. The lens unit according to claim 1, wherein the transparent conductive film has a thickness of 40 to 100 nm.

6. A camera module comprising the lens unit according to claim 1 .

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