JP7644580B2 - Lens units and camera modules - Google Patents

Description

The present invention relates to a lens unit and a camera module, and in particular to a lens unit and a camera module that can be installed in an on-board camera mounted on a vehicle such as an automobile.

In recent years, automobiles have been equipped with on-board cameras to assist with parking and prevent collisions through image recognition, and there are also attempts to apply this to autonomous driving. Camera modules such as on-board cameras generally include a lens unit that includes 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 that is placed between at least one of the lenses in the lens group (see, for example, Patent Document 1).

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, a lens group L consisting of a plurality of lenses arranged along an optical axis O is assembled and housed in the inner housing space S of the lens barrel 102, and an O-ring 104 is inserted between the first lens 100, which is positioned closest to the 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, a stepped reduced diameter portion 100b, the diameter of which is reduced at the image side portion of the lens 100, is provided on the outer peripheral side surface 100a of the first 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 the inner peripheral surface 102a of the lens barrel 102, thereby sealing the object side end of the lens barrel 102.

Also, as shown in FIG. 7, when the curvature of the back surface 100c facing the image side of the first lens 100 is larger than the curvature of the front surface 100d facing the object side, the anti-reflection film generally provided on the lens surface to increase light transmittance generally has a multi-layer 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 to this, a water-repellent film may be provided on the anti-reflection film on the surface 100d exposed to the outside.

JP 2013-231993 A

However, even if waterproofing is provided by 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 condensation occurs 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 occurs particularly on the back surface 100c of the first lens 100, making it easy for fogging to occur and making image evaluation difficult.

For this reason, it is possible to apply some kind of treatment to the back surface 100c to prevent fogging, but in that case, it is also necessary to take into account the incidence angle dependency, which is easily affected by the curvature of the back surface 100c and the layered state of the anti-reflection film, so as not to impair the anti-reflection properties of the anti-reflection film.

The present invention has been made in consideration of the above 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 further 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.

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 rear 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 rear surface;
An anti-reflection film provided on the rear surface of the lens;
The present invention is characterized by comprising:

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 via an electrode. In other words, the lens back surface is directly heated by a lens heating means having a transparent conductive film and an electrode. This effectively prevents fogging on the lens back surface, or quickly eliminates the deterioration of the visibility of the lens due to fogging on the lens back surface, and ensures the desired visibility 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 electrodes are simply electrically connected to the transparent conductive film, the increase in manufacturing costs associated with the installation of the lens heating means can be kept low, and since almost no new space is required to install the lens heating means, the size can be maintained almost the same as that of a conventional lens unit that does not have 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.

In the above configuration, the transparent conductive film may be, for example, indium tin oxide (ITO), but is not limited thereto. The transparent conductive film must be provided over at least the entire 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 the light ray passing through the position farthest from the optical axis among the light rays passing through the lens surface, and the range of the effective diameter of the lens corresponds specifically to the lens area through which the light incident on the image sensor (image sensor) of the lens unit passes, and is determined by the size of the image sensor. Metal electrodes such as silver and copper can be used as the electrodes. The resistance value of the transparent conductive film between the electrodes is preferably set to 50 to 200 Ω.

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 top of 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, in order to satisfy the spectral characteristics, the transparent conductive film must be made thin, and the distribution of heat generated by the lens heating means will not be uniform.

Specifically, as shown in Figure 4, the anti-reflection properties of the 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-layered anti-reflection film was provided on the lens surface, case C2 (AR coating + ITO film) in which a single-layered anti-reflection film was provided on top of that and an ITO film was provided as a transparent conductive film, and three cases C3, C4, and C5 (ITO film + AR coating (a); ITO film + AR coating (b); ITO film + AR coating (c)) in which three ITO films of different thicknesses were provided as transparent conductive films and a single-layered anti-reflection film was provided on each of them.

More specifically, in case C1, a film laminate structure is adopted in which SiO ₂ , an anti-reflection film material having a refractive index of 1.45, is laminated to a thickness of 93.00 nm on a glass lens (TAF1) having a refractive index of 1.77. In case C2, a film laminate structure is adopted in which SiO ₂ , an anti-reflection film material having a refractive index of 1.45, is laminated to a thickness of 65.00 nm on a glass lens (TAF1) having a refractive index of 1.77, and indium tin oxide (ITO) having a refractive index of 1.74 is laminated to a thickness of 15.00 nm on the SiO 2. In case C3, a film laminate structure is adopted in which indium tin oxide (ITO) having a refractive index of 1.74 is laminated to a thickness of 25.00 nm on a glass lens (TAF1) having a refractive index of 1.77, and indium tin oxide (ITO) having a refractive index of 1.45 is laminated to a thickness of 25.00 nm on the ITO. In case C1, 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 50.00 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 to a thickness of 90.00 nm on the glass lens (TAF1). 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 50.00 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 to a thickness of 90.00 nm on the glass lens (TAF1). In case C3, 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 100.00 nm on a glass lens (TAF1) with a refractive index of 1.77, and SiO A film stack structure was adopted in which _{2 and 3} were stacked to a thickness of 97.00 nm, and the film stack structure was optimized by a predetermined simulation at a predetermined light incidence angle, resulting in 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 wavelength (nm) of incident light). Here, the spectral characteristic curves L1 to L5 correspond to cases C1 to C5, respectively.

As can be seen from the spectral characteristics diagram shown in Figure 5, in case C2, in which an ITO film is laminated on an anti-reflection film (AR coat), the reflectance does not completely fall below 1.5 within the specified incident wavelength range (450 nm to 650 nm) as shown by the spectral characteristics curve L2, and the thinness of the ITO film (15.00 nm) did not result in a uniform distribution of heat generated by the ITO film. It was also found that if the ITO film were made thicker to achieve a uniform heat distribution, it would become even more difficult to achieve the desired optical characteristics (for example, anti-reflection characteristics that result in a reflectance of 1.5 or less within the specified incident wavelength range (450 nm to 650 nm)). In contrast, in case C3, in which an anti-reflection film (AR coat) 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 is 1.5 or less, and the desired spectral characteristics (anti-reflection characteristics) are obtained. 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 without an ITO film (see the spectral characteristic curve L1). This means that even if 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, the spectral characteristics (anti-reflection characteristics) can be maintained almost the same as in the case of only an anti-reflection film without an ITO film.

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 is increased 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 increasing thickness within the specified incident wavelength range. In relation to this, the inventor 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).

Based on the above, the inventors have concluded that by adopting a film stacking configuration in which an anti-reflective film is provided on a transparent conductive film, it is possible to prevent fogging on the rear surface of the lens due to heat generated by the transparent conductive film without impairing 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.

In the above-mentioned configuration, it is preferable that the anti-reflection film contains metal. If the anti-reflection film contains 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 transferred to the outer surface through the anti-reflection film, and the desired anti-fogging effect can be realized. In addition, the anti-reflection film is preferably made of _SiO2 or _MgF2 , which has low incidence angle dependency, and is preferably formed in a single layer form, especially when the curvature of the lens back surface is large (the curvature radius is small).

In the above 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 has low strength, can be prevented, and corrosion of the electrodes below the anti-reflection film can be prevented, thereby avoiding deterioration of the electrodes. A water-repellent film may be provided as such a protective film. This makes it possible to realize a lens that has 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 water-repellent performance.

In the above configuration, it is preferable that a recess is provided in the surface facing the object side of the adjacent lens adjacent on the image side to the lens located closest to the object side in an area outside the range of the effective diameter of the adjacent lens, and an electrode is disposed within this recess. By arranging the electrode within the recess in this way, it is possible to avoid a situation in which the lenses joined to each other across the electrode become loose when the electrode is not provided around the entire circumference of the lens.

In addition, in the above configuration, it is preferable that a light-shielding treatment is applied to the peripheral area of the back 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 applying a light-shielding treatment such as ink painting, 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 the miniaturization of the unit.

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

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 when current is applied 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 edge of the transparent conductive film may become even thinner (vapor deposition may occur unevenly) due to the curvature of the back surface of the lens. In that case, the desired anti-fogging effect may not be obtained due to 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 may become uneven), especially when the transparent conductive film is formed by vapor deposition, and there is a risk of light diffusion.

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

According to 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, and Joule heat is generated on the lens back surface by passing a current through this transparent conductive film via an electrode. This effectively prevents fogging on the lens back surface, or quickly eliminates the deterioration of the lens visibility caused by fogging on the lens back surface, ensuring the desired visibility in a short time.

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. FIG. 2 is an enlarged cross-sectional view of a portion A of the lens unit of FIG. 1 . 2 is a schematic cross-sectional view of a camera module including the lens unit of FIG. 1. FIG. 13 is a table showing detailed stacking data of each film stacking structure to be compared. FIG. 5 is a diagram showing spectral characteristics of a part of the film stack structure shown in FIG. 4 . FIG. 5 is a spectral characteristic diagram of another part of the film stack structure shown in FIG. 4 . FIG. 1 is a schematic cross-sectional view of a conventional lens unit.

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

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 the 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 substrate having an image sensor (not shown), and an installation member (not shown) for installing the substrate on a vehicle such as an automobile.

The lenses 13, 14, 15, 16, and 17 are assembled and held in the inner storage space S of the lens barrel 12, and 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, which is positioned closest to the object side of the lens group L, is a spherical glass lens having 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 anti-reflection films, hydrophilic films, water-repellent films, 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.

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

In this embodiment, an O-ring 26 is inserted between the first lens 13, which is located closest to the object, and the lens barrel 12 as a seal member 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, the diameter of which is reduced at the image side portion of the lens 13, is provided on the outer peripheral 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 peripheral side surface 13c of the first lens 13 and the inner peripheral surface 12c of the lens barrel 12, sealing the object side end of the lens barrel 12.

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 to prevent a large sink mark from occurring when molding and cooling the resin lens barrel 12, which would cause a loss of dimensional accuracy, since the wall thickness would be thick if the inner wall 12b and the outer wall 12a were integrated without a groove. 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 a different height depending on the size of the O-ring 26, ensuring that the O-ring 26 seals with an appropriate elastic force.

In addition, when the lens group L is assembled and housed in the inner housing space S of the lens barrel 12, the crimping portion 23 at the object side end (upper end in FIG. 1) is crimped radially inward, so that the first lens 13, which is located closest to the object side of the lens group L, is fixed to the object side end of the lens barrel 12 by this crimping portion 23. Note that the fixing of the first lens 13 is not limited to the crimping portion 23, and may be performed by a fixing portion that is attached to the object side end of the lens barrel 12 after the lenses 13, 14, 15, 16, and 17 are housed in the lens barrel 12.

The end of the lens barrel 12 on the image side (the lower end in FIG. 1) is provided with an inner flange portion 24 having an opening with a smaller diameter than the fifth lens 17. The inner flange portion 24 and the crimped portion 23 hold and fix the lenses 13, 14, 15, 16, and 17 and the aperture members 22a and 22b that make up the lens group L inside the lens barrel 12 in the optical axis direction.

Figure 3 is a schematic cross-sectional view of a camera module 300 of this embodiment having a lens unit 11 configured as described above. As shown in the figure, this camera module 300 is configured to include the lens unit 11 of Figure 1 to which a filter 100 is attached.

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 sealing member 303 and a package sensor (imaging element) 304.

The upper case 301 is a member that engages with the flange portion 25 that is provided in a brim-like shape on the outer wall 12a of the lens barrel 12, and that exposes the object side end of the lens unit 11 and covers the other parts. The mount 302 is disposed inside the upper case 301, and has a female thread 302a that screws into the male thread 11a of the lens unit 11. The seal member 303 is a member that is interposed between the inner surface of the upper case 301 and the outer peripheral surface 12a of the lens barrel 12 of the lens unit 11, and is a member that maintains airtightness inside the upper case 301.

The package sensor 304 is disposed inside the mount 302, and is positioned to receive the image of the object formed by the lens unit 11. The package sensor 304 also has a transparent cover on the outside and is equipped with a CCD, CMOS, etc. inside, and converts the light that is collected and reaches it through the lens unit 11 into an electrical signal. The converted electrical signal is then converted into analog data or digital data, which is a component of the image data captured by the camera.

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

As clearly shown in the enlarged view of FIG. 2 (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 lens diameter range 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 will not be 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 will become rough (surface roughness will not be uniform), and there is a risk of light diffusion. As described above, such a transparent conductive film 31 must be provided over at least the entire range of the effective diameter of the first lens 13, and therefore, in this embodiment, as an example, it is provided over the entire spherical concave area F1 of the lens back surface 13a and a part of the aspherical outer peripheral area (the entire outer peripheral flat joint area F2 that joins with the surface 14a facing the object side of the second lens 14). Here, the range of the effective diameter of the lens corresponds to the area of the lens 13 through which the light incident on the package sensor 304 passes, and is determined by the size of the package sensor 304 (as described above).

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 Figures 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. These electrodes 32A and 32B are electrically connected to a transparent conductive film 31 that extends over the bottom surface of the recess 14c and onto the outer circumferential flat bonding region F2 of the first lens 13.

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 back surface 13a by applying a voltage between the electrodes 32A, 32B and passing a current through the transparent conductive film 31. Metal electrodes such as silver, copper, and nickel can be used as the electrodes.

In addition, in the lens unit 11 of this embodiment, a light-shielding treatment is applied to the peripheral flat joint area F2 of the lens back surface 13a of the first lens 13, which faces the recessed area 14c. In particular, in this embodiment, the entire lens back surface 13a of the first lens 13, except for the spherical recessed area F1, is blackened as a light-shielding treatment (the blackened area is indicated by reference number 50 in FIG. 2).

In addition, an anti-reflection film 30 for suppressing reflection of incident light is provided on the transparent conductive film 31. In particular, in this embodiment in which the lens rear surface 13a has a large curvature (a radius of curvature of 5 mm or less), the anti-reflection film 30 made of SiO ₂ or MgF ₂ (preferably containing a metal) that has low incidence angle dependency 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 rear surface 13a. The anti-reflection film 30 is thus provided on the transparent conductive film 31, not on the lower layer, and a protective film (e.g., a water-repellent film) may be further provided on the anti-reflection film 30.

As described above, according to this embodiment, a 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 the deterioration of the visibility of the lens due to fogging on the lens back surface 13a, and to ensure the desired visibility in a short time. In particular, in this embodiment, a film stacking form in which the anti-reflection film 30 is provided on the transparent conductive film 31 is adopted, 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 anti-reflection properties of the anti-reflection film 30.

The present invention is not limited to the above-described embodiment, and can be modified in various ways without departing from the spirit of the present invention. For example, in the present invention, the shapes of the lenses, lens barrels, etc., and the formation forms of the anti-reflection film and transparent conductive film are not limited to the above-described embodiment. In addition, the material of the film, the film thickness, the material and arrangement form of the electrodes and lenses, etc. 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 a transparent conductive film is provided on the anti-reflection film.

REFERENCE SIGNS LIST 11 Lens unit 12 Lens barrel 13 First lens 13a Lens back surface 14 Second lens (adjacent lens)
14a: surface; 14c: recess; 30: anti-reflection film; 31: transparent conductive film; 32A, 32B: electrodes; 48: lens heating means; 50: blackened portion (light shielding treatment)
300 Camera module L Lens group O Optical axis

Claims (6)

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 rear 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 rear 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 to the lens located closest to the object side on the image side, the surface facing the object side, 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 . The lens unit according to claim 1, characterized in that the anti-reflection film is provided on the transparent conductive film. 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. 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. The lens unit according to claim 1 , wherein the transparent conductive film has a thickness of 40 to 100 nm. A camera module comprising the lens unit according to claim 1 .

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