JP2014232283A - Camera protection cover and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-made spherical cover that protects an optical system of a camera such as an on-vehicle camera, a monitor camera or the like, has excellent environmental resistance performance, and suppresses an influence of aberrations with respect to the optical system, and to provide an imaging device capable of attaching the cover.SOLUTION: There is provided a protection cover that is formed into a spherical shape capable of being attached on a subject side of an imaging lens of an imaging device provided with the imaging lens and an image pickup element photoelectrically converting an object image formed via the imaging lens, and that satisfies a formula EPO<T<EPI, where, with a contact point between an object side surface of a lens on the most object side of the imaging lens and an optical axis defined as a reference and with an image pickup element side defined as a positive direction, EPO is a limit on an object side at an incident pupil position in a flux of total light incident to the image pickup element, EPI is a limit on the image pickup element side thereat, and T is a center position of a radius of curvature of a spherical-shape protection cover protecting a camera module; and an imaging device capable of attaching the protection cover.

Description

  The present invention relates to a resin protective cover used for protecting an imaging lens of an imaging device such as an in-vehicle camera and a surveillance camera, and an imaging device equipped with the protective cover.

  In recent years, with the increase in demand for in-vehicle camera modules, it has become necessary to take countermeasures on the assumption that they will be used in various environments. For example, the first lens arranged closest to the object side among the imaging lenses used in an in-vehicle camera mounted on the vehicle body is exposed to a severe environment, and therefore, when resin is used, it deteriorates due to scratches, ultraviolet rays, or the like. Therefore, glass is generally used for the first lens. Alternatively, as disclosed in Patent Document 1, it is necessary to protect the lens from dust and external force by providing a protective glass on the front surface of the lens.

  However, in a harsh environment such as a desert, it is difficult to maintain the quality for a long time even if it is glass, and it is costly and troublesome to replace the camera module each time. Therefore, it is preferable to periodically replace the camera module in a severe environment using a replaceable cover that protects the first lens of the camera module. As a material for the cover, glass is desirable in terms of performance, but resin is advantageous in terms of cost. However, although resin is widely used over glass in terms of light weight and economy, a plastic material having poor hardness and sufficient scratch resistance has not been put into practical use yet. Furthermore, since the protective cover has a function as a lens, aberration may occur and optical performance may be deteriorated.

JP 2010-271545 A

  The present invention provides a resin spherical cover that protects an optical system of a camera such as an in-vehicle camera or a surveillance camera, has excellent environmental resistance, and suppresses the influence of aberration on the optical system, and an imaging device that can be attached to the cover. To do.

  In order to solve the above problems, the protective cover of the present invention can be attached to the subject side of the imaging lens of an imaging device including an imaging lens and an imaging device that photoelectrically converts an object image formed through the imaging lens. An object at the entrance pupil position in all rays incident on the image sensor, with the contact point between the object side surface of the lens on the most object side of the image pickup lens and the optical axis as a reference 0 and the image sensor side as a positive direction When the side limit is EPO, the imaging element side limit is EPI, and the center position of the radius of curvature of the spherical protective cover protecting the camera module is T, EPO <T <EPI is satisfied.

Preferably, R> √ {(Y / 2) ² + EPO ² } is satisfied, where R is the radius of curvature of the sphere of the protective cover and Y is the effective ray diameter of the object side surface of the most object side lens. It is characterized by that.

  More preferably, a hard coat is formed on the object side surface of the protective cover.

  More preferably, the film thickness d of the hard coat satisfies 5 μm <d <15 μm.

  More preferably, the d-line reflectivity Rd of the hard coat satisfies Rd <5.0%, and the d-line absorption Kd at a thickness of 10 μm satisfies Kd <1.0%.

More preferably, the thermal expansion coefficient α of the hard coat at −30 ° C. to 70 ° C. satisfies 10 ⁻⁷ mm / ° C. <α <10 ⁻⁵ mm / ° C.

  More preferably, the protective cover is formed of a cycloolefin resin.

  More preferably, the hard coat is formed of a hybrid material having an organic material containing at least an acrylic material and an inorganic material containing silica-based reactive fine particles.

  In order to solve the above problems, the imaging apparatus of the present invention is characterized in that the protective cover can be attached.

  According to the present invention, a resin spherical cover that protects an optical system of a camera such as an in-vehicle camera or a surveillance camera, has excellent environmental resistance, and suppresses the influence of aberration on the optical system, and an image pickup apparatus that can be attached to the cover. Can be provided.

It is a figure which shows the imaging lens structure of the imaging device of this embodiment. FIG. 6 is an aberration characteristic diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to the present embodiment. It is a figure which shows the relationship between the imaging lens in this embodiment, and an entrance pupil. It is a figure which shows the protective cover to which this invention in this embodiment is applied. It is a figure which shows the entrance pupil position of all the light rays of the imaging lens in this embodiment. It is an aberration characteristic figure in the state where a protective cover was applied to the imaging lens in this embodiment. It is the figure which attached the protective cover to the imaging device of this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of the imaging lens of the embodiment in an optical section. In these embodiments, as shown by 100 in FIG. 1, in order from the object side, a first lens 110, a second lens 120, a third lens 130, an aperture stop 140, a fourth lens 150, an IRCF or a cover glass 160, The imaging lens 100 is a four-lens configuration in which an imaging element 170 such as a CCD (Charge Coupled Device) or a CMOS (Complementary Mental-Oxide Semiconductor device) is disposed.

  The first lens 110 is a meniscus concave lens having a negative refracting power with its convex surface facing the object side and having an aspheric surface on the imaging side, and the second lens 120 has a negative refracting power and has an imaging surface. The third lens 130 is a bi-aspherical convex lens having a positive refractive power with the convex surface facing the object side surface, and the fourth lens 150 is a convex surface on the imaging side surface. Is a convex lens having positive refractive power and aspherical surfaces.

  The first lens, the second lens, and the third lens are made of a resin material. As described above, by using a resin material, weight reduction and cost reduction can be realized, and an aspherical shape can be easily manufactured. In particular, by configuring the third lens 130 with a high dispersion material, it is possible to satisfactorily correct lateral chromatic aberration.

  1, the light incident from the object side includes the object side R1 surface 1, the imaging surface side R2 surface 2 of the first lens 110, the object side R3 surface 3 of the second lens 120, and the imaging surface. Side R4 surface 4, object side R5 surface 5 of the third lens 130, imaging surface side R6 surface 6, surface 7 of the aperture stop 140, object side R7 surface 8 of the fourth lens 150, imaging surface side R8 surface 9, cover glass The light passes through the object side R9 surface 10 and the imaging surface side R10 surface 11 of 160 in order and is condensed on the imaging surface 12 of the imaging element 170.

  The entrance pupil in the imaging lens 100 is positioned as shown in FIG. The entrance pupil position is a point that extends the part of the object side space of the principal ray passing through the center of the stop and intersects with the optical axis. When considering all rays incident on the image sensor 170, it is located closest to the object side. Assume that the entrance pupil position is EPO and the entrance pupil position closest to the image sensor is EPI.

  Not only light rays parallel to the optical axis but also light rays from various angles enter the imaging lens 100 and contribute to image formation. In particular, in-vehicle cameras and surveillance cameras need to capture a wide range, so a wide-angle lens is often used, and in some cases, a fish-eye lens having an angle of view close to 180 ° may be used. When the protective cover 180 is provided on the object side of the imaging lens 100, it is important to consider so that the optical performance is not deteriorated with respect to light rays incident from various angles.

  In order not to generate an aberration or the like that deteriorates the optical performance with respect to the incident light, it can be avoided by preventing the protective cover 180 from functioning as a lens. The shape of the protective cover 180 and the attachment position to the imaging lens 100 will be described with reference to FIG.

  As shown in FIG. 4, the protective cover 180 is formed in a spherical shape, and is arranged so that the center of curvature radius of the sphere is the position of the entrance pupil. By doing so, light rays from various angles that contribute to the image formation of the imaging lens 100 are incident on the spherical surface of the protective cover 180 from the normal direction, so that the light rays are refracted by the protective cover 180. Therefore, it is possible to avoid working as a lens, and it is possible to suppress deterioration of optical performance such as aberration.

  However, the position of the entrance pupil of the optical system varies depending on each angle of view as shown in FIG. The vertical axis in FIG. 5 indicates the distance from the optical axis center on the imaging plane of the imaging lens 100, and the horizontal axis indicates the position of the entrance pupil with the imaging element side as the positive direction with respect to the surface vertex of the object side surface of the first lens. Indicates. It can be seen from FIG. 5 that, in the imaging lens 100, the entrance pupil position changes from the imaging element side to the object side surface as the distance from the optical axis center increases.

  Accordingly, the radius of curvature of the protective cover 180 is not determined at a single point, and it is not strictly spherical that the normal relationship is established with respect to the total luminous flux. In principle, if the protective cover 180 is formed with an aspherical shape, it can be established, but the cost becomes high. Therefore, by arranging the radius of curvature center of the spherical protective cover 180 between the object side limit EPO and the image sensor side limit EPI of the entrance pupil position of the total luminous flux contributing to the imaging of the imaging lens 100, the influence of the aberration can be reduced. The protective cover 180 suppressed as much as possible can be realized in a spherical shape at a low cost.

In the imaging lens 100 of the present embodiment, 2 mm from the surface vertex of the object side surface of the first lens located between the object side limit EPO of the entrance pupil position and the image sensor side limit EPI based on the characteristics as shown in FIG. As shown in FIG. 4, the center of curvature radius of the protective cover 180 is arranged at the position
Further, in order to protect the imaging lens 100, the protective cover 180 needs to cover at least the first lens. Therefore, if the radius of curvature of the sphere of the protective cover 180 is R and the effective ray diameter of the object side surface of the first lens is Y, the protective cover 180 satisfies R> √ {(Y / 2) ² + EPO ² }. The radius of curvature R of the sphere is determined.

  In the imaging lens 100 of the present embodiment, based on the characteristics shown in FIG. 5, a position 2 mm from the surface vertex of the object side surface of the first lens between the object side limit EPO and the image sensor side limit EPI of the entrance pupil position. A protective cover 180 having an inner diameter of 6 mm and an outer diameter of 7 mm is arranged as shown in FIG.

  Furthermore, regarding the environment resistance, glass is used for the first lens in conventional surveillance cameras and in-vehicle cameras. This is because, among the environmental resistance performances, the resin cannot satisfy the requirements for scratch resistance, chemical resistance, and weather resistance. Therefore, the above three environmental performances are improved by applying a hard coat to the resin.

  Moreover, according to the protective cover 180 of this embodiment, since the film thickness d of the hard coat 19 is larger than 5 μm, the hard coat can have sufficient strength. Further, according to the imaging optical system of the present embodiment, since the hard coat film thickness d is smaller than 15 μm, it is possible to suppress the occurrence of cracks due to the difference in thermal expansion coefficient α with the material of the protective cover 180.

  Further, according to the protective cover 180 of the present embodiment, the d-line reflectivity Rd of the hard coat is less than 5.0%, and the d-line absorption Kd at a thickness of 10 μm is less than 1.0%. The transmittance of the protective cover 180 with hard coat is preferably high because low transmittance causes stray light and insufficient light quantity, and it is desired to suppress deterioration of the light quantity in the hard coat. In order to suppress the deterioration of the light amount, it is required to reduce the reflectance Rd and the absorptance Kd of the hard coat. The reflectivity Rd of the hard coat 19 can be adjusted by the refractive index nd and the surface roughness of the hard coat 19, and the reflectivity is high when the refractive index Kd becomes too high, or when the surface roughness is rough and light is irregularly reflected. Become. By satisfying the above-described reflectance Rd, it is possible to suppress the deterioration of the light amount from the reflectance side. Further, the absorption rate Kd of the hard coat 19 can be adjusted by the amount of the ultraviolet absorber added for improving the environmental resistance performance of the hard coat 19, and sufficient ultraviolet resistance can be obtained by satisfying the above-described absorption rate. Thus, it is possible to suppress the deterioration of the light amount from the absorptivity side.

  Further, according to the protective cover 180 of the present embodiment, the thermal expansion coefficient α at −30 ° C. to 70 ° C. is 10−7 mm / ° C. <α <10 −5 mm / ° C. A large difference in the thermal expansion coefficient α between the hard coat and the protective cover 180 may cause a stress when the temperature changes and cause cracks in the hard coat. In order to suppress the occurrence of cracks, the thermal expansion coefficient α of the hard coat is required to be included in the range of 1/10 to 10 times the thermal expansion coefficient α of the material of the protective cover 180. The material used to form the protective cover 180 is generally x × 10 −6 mm / ° C. (x is a positive integer less than 10) at −30 ° C. to 70 ° C., which is a temperature environment assumed to be used. is there. Therefore, the occurrence of cracks in the hard coat can be suppressed when the hard coat has the above-described thermal expansion characteristics.

  Further, according to the protective cover 180 of the present embodiment, since the cycloolefin resin is used as the material of the protective cover 180, it is possible to provide the above-described refractive power, color dispersion characteristics, and absorption characteristics.

  Further, according to the protective cover 180 of this embodiment, the hard coat is formed of a hybrid material having at least an organic material including an acrylic material and an inorganic material including a silica-based reactive fine particle. Organic materials including acrylic materials can be cured by ultraviolet rays. For example, compared with thermosetting organic materials such as silicon, the curing speed is faster, less energy is used, and the process can be continued. Since no solvent is required and the resin can be cured at a low temperature, the resin protective cover 180 can be applied. On the other hand, since the organic material containing an acrylic material contains a large amount of a polyfunctional oligomer component having a high viscosity, the blending workability and coating workability of the coating liquid are lowered. In addition, since the shrinkage rate in curing of an organic material including an acrylic material is relatively large as a material of a hard coat, it can be a cause of warping and internal stress during curing. An inorganic material containing silica-based reactive fine particles has an effect of suppressing an increase in the viscosity of the coating liquid and an effect of reducing the shrinkage rate of an organic material containing an acrylic material. Therefore, in this embodiment, by forming a hard coat using the above-described hybrid material, the above-described effects due to the use of the acrylic organic material are obtained, and the blending workability and coating workability of the coating liquid are reduced. And the shrinkage rate can be reduced. Further, an inorganic material containing silica-based reactive fine particles has higher scratch resistance than an organic material, and the overall scratch resistance can be improved. Furthermore, since an inorganic material containing silica-based reactive fine particles has a lower crosslinking density than an organic material containing an acrylic material, the residual stress due to curing is low. Therefore, by using an inorganic material containing silica-based reactive fine particles, the difference between the surface layer and the inside affected by changes in the environment is smaller than that of an organic material containing acrylic, and the overall weather resistance is improved. Is possible.

  Moreover, since it is assumed that the protective cover 180 of this embodiment is often installed outside, the protective cover 180 may be exposed to high-humidity outside air or liquid may adhere to it. Although the protective cover 180 is covered with the hard coat, moisture slightly permeates through the hard coat, so that the protective cover 180 absorbs moisture and the refractive index may change, or the shape may change due to expansion. Therefore, it is preferable to use a material having a low water absorption rate for the protective cover 180. Specifically, it is desirable to suppress changes in refractive index and shape with a water absorption rate of less than 0.1%.

  1, the distance between the R1 surface 1 and the R2 surface 2 that is the thickness of the first lens 110 is D1, and the distance between the R2 surface 2 of the first lens 110 and the R3 surface 3 of the second lens 120 is as shown in FIG. D2, the distance between the R3 surface 3 and the R4 surface 4 that is the thickness of the second lens 120, D3, the distance between the R4 surface 4 of the second lens 120 and the R5 surface 5 of the third lens 130, D4, The distance between the R5 surface 5 and the R6 surface 6 having a thickness of 130 is D5, the distance between the R6 surface 6 of the third lens 130 and the surface 7 of the aperture stop 140 is D6, the surface 7 of the aperture stop 140 and the fourth lens 150. The distance between the R7 surface 8 is D7, the distance between the R7 surface 8 and the R8 surface 9 that is the thickness of the fourth lens 150 is D8, and the distance between the R8 surface 9 of the fourth lens 150 and the object side R9 surface 10 of the cover glass 160 The distance of D9, the thickness of the cover glass 160 R9 surface 1 When the distance between the R10 surface 11 D10, the distance between the R10 surface 11 of the cover glass 160 and the image plane 12 and D11.

  In addition, the aspherical shape of the lens described in the following numerical examples is expressed by the following equation. The direction from the object side to the image plane side is positive, k is a conic coefficient, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is When a 10th-order aspheric coefficient is used, it is expressed by the following equation. h represents the height of the light beam, c represents the reciprocal of the central radius of curvature, and Z represents the depth from the tangent plane with respect to the surface vertex.

  Hereinafter, specific numerical values of the imaging lens 100 will be described. In the numerical values of the examples, the focal length, F number, horizontal field angle, vertical field angle, image height, total lens length, and back focus (BF) are as shown in Table 1 below.

  The basic configuration of the imaging lens 100 according to Embodiment 1 is shown in FIG. 1, each numerical data (setting value) is shown in Table 2, and spherical aberration and aberration diagrams showing astigmatism are shown in FIG. In FIG. 2, in the example, the left shows spherical aberration, the center shows astigmatism, and the right shows distortion. The vertical axis of the spherical aberration diagram is normalized with the pupil diameter set to 1, the vertical axis of the astigmatism diagram represents the image height, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. Each is shown. In the distortion diagram, the vertical axis indicates the image height, and the horizontal axis indicates the distortion. As can be seen from FIG. 2, according to the embodiment, the spherical and astigmatism aberrations are satisfactorily corrected, and the imaging lens 100 having excellent imaging performance can be obtained. As shown in FIG. 1, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a concave shape on both sides, the third lens 130 has a biconvex shape, and is arranged on the image side of the aperture stop 140. The fourth lens 150 has a biconvex shape with convex surfaces facing both sides. Each resin lens has an aspherical surface.

Table 2 shows the diaphragm corresponding to each surface number of the imaging lens 100 in the embodiment, the radius of curvature R, the interval D, the refractive index Nd, and the Abbe number νd of each lens. Table 3 shows the aspheric coefficient of the predetermined surface.
<Numerical examples>

  FIG. 6 is an aberration characteristic diagram of the imaging lens 100 with the protective cover 180 attached. The left side shows spherical aberration, the center shows astigmatism, and the right shows distortion. The vertical axis of the spherical aberration diagram is normalized with the pupil diameter set to 1, the vertical axis of the astigmatism diagram represents the image height, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. Each is shown. In the distortion diagram, the vertical axis indicates the image height, and the horizontal axis indicates the distortion. As can be seen from FIG. 6, even when the protective cover 180 is attached, the spherical and astigmatic aberrations are good with no significant difference compared to the various characteristics when the protective cover 180 shown in FIG. 2 is not attached. The optical characteristics of the imaging lens 100 with excellent imaging performance are maintained.

  FIG. 7 shows a cross-sectional view of an embodiment in which a protective cover 180 is attached to the imaging apparatus 200 according to the present invention. The imaging lens 100 defines and holds a positional relationship by the housing 190. Screws or protrusions or grooves 181 for mounting on the housing side are formed on the inner periphery closest to the image sensor when the protective cover 180 is mounted, and screws correspondingly screwed on the outer periphery on the housing side. Alternatively, a fitting groove or a protrusion 191 is provided. When the protective cover 180 is attached to the imaging apparatus 200, the positions shown in FIG. 4 can be obtained together with the fixing of the protective cover 180 to the imaging apparatus 200 by screwing these screws or fitting the protrusions and the grooves. It is possible to realize the imaging apparatus 200 that is prescribed and has excellent environmental performance and suppresses the influence of aberration and has excellent imaging performance.

  Although the present invention has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various changes and modifications based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 100,100A ... Imaging lens 110 ... 1st lens 120 ... 2nd lens 130 ... 3rd lens 140 ... Aperture stop 150 ... 4th lens 160 ... Cover glass (or IRCF)
170... Imaging element (or imaging plane / imaging plane)
180 ... protective cover 190 ... casing 200 ... imaging device

Claims (9)

A spherical protective cover that can be attached to the subject side of the imaging lens of an imaging device including an imaging lens and an imaging device that photoelectrically converts an object image formed through the imaging lens,
The contact point between the object side surface of the lens closest to the object side of the image pickup lens and the optical axis is set as a reference 0, the image pickup element side is set as a positive direction, and the object side limit of the entrance pupil position for all rays incident on the image pickup element is EPO, EPO <T <EPI is satisfied, where the imaging element side limit is EPI, and the center of curvature radius of the spherical protective cover for protecting the camera module is T. R> √ {(Y / 2) ² + EPO ² } is satisfied, where R is a curvature radius of the sphere of the protective cover and Y is an effective ray diameter of the object side surface of the lens on the most object side. The protective cover according to claim 1.   The protective cover according to claim 1, wherein a hard coat is formed on the object side surface of the protective cover.   The protective cover according to claim 3, wherein a film thickness d of the hard coat satisfies 5 μm <d <15 μm.   5. The protection according to claim 3, wherein the d-line reflectivity Rd of the hard coat satisfies Rd <5.0% and the d-line absorption Kd at a thickness of 10 μm satisfies Kd <1.0%. cover. 6. The protective cover according to claim 3, wherein a thermal expansion coefficient α of the hard coat at −30 ° C. to 70 ° C. satisfies 10 ⁻⁷ mm / ° C. <α <10 ⁻⁵ mm / ° C. 6.   The protective cover according to claim 3, wherein the protective cover is formed of a cycloolefin resin.   The protective cover according to claim 3, wherein the hard coat is formed of a hybrid material having at least an organic material containing an acrylic material and an inorganic material containing a silica-based reactive fine particle.   An imaging apparatus to which the protective cover according to claim 1 can be attached.

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