JP2008216807A - Imaging lens, imaging unit and portable information terminal with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which restrains degradation of performance due to decentering misalignment and inclination of the lens while decreasing the number of lenses for which it is necessary to provide a lens holding mechanism. <P>SOLUTION: The imaging lens 1a is equipped with a lens group 16a arranged on a subject side and having positive refractive power, and a third lens 13a directly or indirectly formed on the subject-side surface of an imaging device 15 and having curved surface shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens used for a small camera such as a digital still camera, and more particularly to an imaging lens having a short overall lens length suitable for a small camera incorporated in a portable information terminal and a cellular phone.

  In recent years, digital still cameras using solid-state image sensors represented by CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) have been rapidly spread, and various digital still cameras have been developed. Miniaturization of digital still cameras is progressing year by year with the progress of technology in solid-state imaging devices. Among them, a camera mounted on a portable information terminal or a mobile phone is particularly required to be reduced in size and weight (hereinafter also referred to as “downsizing / lightening”) due to the size limitation of the housing.

  In recent years, the number of pixels of solid-state imaging devices represented by CCD and CMOS has been dramatically increased. As a result, the number of pixels exceeding 1 million pixels is increasing in cameras mounted on the above-described mobile phones and the like. Depending on the product, cameras with 3 to 5 million pixels are mounted. On the other hand, low-pixel cameras of 1 million pixels or less are still mounted on mobile phones that prioritize miniaturization and weight reduction. However, there is a strong demand for a camera with a high pixel size and weight reduction, and it is necessary to improve the performance of the camera without using many heavy and large lenses.

  Therefore, conventionally, attempts have been made to reduce the size and weight by using a small plastic lens and a higher-order aspheric lens.

  For example, in Patent Document 1, three lenses are used to optimize the refractive power of each lens, thereby reducing the size and improving the performance. In addition, the back focus is increased with respect to the entire length.

Moreover, in patent document 2, size reduction and cost reduction are aimed at using two plastic aspherical lenses.
Japanese Patent No. 3770493 (registered on February 17, 2006) JP 2001-183578 A (published July 6, 2001)

  As described above, in recent years, there has been a demand for an imaging lens (lens optical system) that is small and lightweight and has high resolution. Further, in order to realize a wide angle as a further improvement in the performance of the imaging lens, it is necessary to suppress deterioration of aberration of the light beam off the optical axis.

  However, the imaging lens described in Patent Document 1 uses a large number of lenses, and it is difficult to further reduce the size. In particular, the third lens G3 has a convex shape toward the subject side in order to have a positive refractive power, and requires a certain physical thickness at the center of the optical axis. In addition, the use of a large number of lenses complicates the mechanism of the lens holding portion (hereinafter also referred to as a lens holding mechanism), resulting in a problem of inferior mass productivity. In addition, since it is necessary to secure the back focus, the optical length becomes long.

  The imaging lens described in Patent Document 2 must correct aberrations of all light beams including light beams off the optical axis by using two lenses by reducing the number of lenses. A lens with a large number must be used. Therefore, there is a problem that the performance of the imaging lens is deteriorated due to the eccentricity and inclination of the lens.

  The present invention has been made in view of the above problems, and mainly provides an imaging lens that reduces the number of lenses that need to be provided with a lens holding mechanism and suppresses performance deterioration due to eccentricity and inclination of the lens. It is intended to provide.

  In order to solve the above-described problems, an imaging lens according to the present invention is an imaging lens that forms a subject image on an imaging element, and is a first lens having a positive refractive power and disposed on the subject side. A lens group; and a second lens group having a curved surface formed directly or indirectly on the surface of the imaging element on the subject side.

  According to said structure, the aberration which cannot be corrected in a 1st lens group can be favorably corrected in a 2nd lens group by making an imaging lens into 2 groups structure. More specifically, aberration correction and incident angle correction with respect to the image sensor can be performed on the light beam incident on the image sensor. That is, aberrations that cannot be corrected in the first lens group can be corrected favorably by the second lens group.

  As a result, it is not necessary to correct aberrations of all the light beams including the light beam off the optical axis only by the first lens group, and it is possible to avoid the heavy use of higher-order aspheric coefficients in the first lens group. An increase in the number of lenses constituting one lens group can be suppressed.

  Further, since the second lens group is formed directly or indirectly on the subject side surface of the image sensor, there is no need to provide a new lens holding mechanism in the lens barrel that holds the lens.

  That is, in the imaging lens according to the present invention, the number of lenses that need to be provided with a lens holding mechanism can be reduced, and the imaging lens can be reduced in size and weight.

  Further, according to the above configuration, the back focus can be reduced to zero or very small, so that an effect of reducing the size of the imaging lens (optical system) is achieved.

  According to the above configuration, since the second lens group and the image sensor can be handled as a unit, the effect of the inclination of the second lens group relative to the image sensor and the eccentricity deviation can be suppressed. .

  In the imaging lens according to the present invention, it is preferable that the second lens group is formed on a flat plate formed on the surface on the subject side.

  According to said structure, when a plane board is used as the positioning part with respect to the optical axis of an imaging lens, there exists an effect which can suppress the influence of the inclination of a 2nd lens group, and eccentric deviation.

  Further, according to the above configuration, since the second lens group is formed in contact with the flat plate, the thickness of the second lens can be reduced. That is, by forming the second lens group on the plane plate by 2P (Photoreplication Process) molding or the like, a thin second lens group that cannot be held alone can be formed on the plane plate. For example, the lens shape can be such that the center thickness is 0 and the thickness is only on the outside of the shaft. As a result, the optical length can be minimized and the optical characteristics can be improved.

  According to said structure, it can also be set as the lens shape which has a very thin thickness outside a shaft and has thickness only in a center part. As a result, the optical length can be minimized and the optical characteristics can be improved.

  In the imaging lens according to the present invention, it is preferable that the second lens group is directly formed on the subject side surface.

  By setting it as the said structure, there exists an effect which can use the 2nd lens group as a cover for preventing damage to an image pick-up element.

  Further, according to the above configuration, since the second lens group is formed directly on the image sensor, the thickness of the second lens can be reduced. That is, by forming the second lens group on the image sensor by 2P (Photoreplication Process) molding or the like, a thin second lens group that cannot be held alone can be formed on the image sensor. For example, the lens shape can be such that the center thickness is 0 and the thickness is only on the outside of the shaft. As a result, the optical length can be minimized and the optical characteristics can be improved.

  According to said structure, it can also be set as the lens shape which has a very thin thickness outside a shaft and has thickness only in a center part. As a result, the effect of minimizing the elongation of the optical length and improving the optical characteristics is also achieved.

  In the imaging lens according to the present invention, it is preferable that the surface of the second lens group on the imaging element side has a planar shape.

  According to the above configuration, it can be used as an assembly reference surface when the imaging lens system is assembled, and the assembly can be simplified and the mass production efficiency can be improved.

  Further, according to the above configuration, since various optical coating films can be easily formed on the second lens group, other optical elements or parts (for example, an aperture, a shutter, various filters, an optical film, a prism, etc.) can be easily formed. The effect which can be attached to is produced.

  Moreover, according to said structure, the center thickness of a 2nd lens group can be made small, and there exists an effect which can contribute to size reduction of a lens system.

  According to said structure, the thickness outside a shaft can also be made thin and the effect which can contribute to size reduction of an imaging lens is also show | played together.

  In the imaging lens according to the present invention, it is preferable that the imaging lens is further configured to satisfy the following conditional expression (1).

d / f <1.5 (1)
However,
d: Distance from the surface closest to the subject to the image plane (optical length)
f: Total focal length of the entire lens system By satisfying the conditional expression (1), the total lens length can be shortened. As a result, there is an effect that an imaging lens that is further reduced in size and weight can be realized.

  In the imaging lens according to the present invention, it is preferable that the imaging lens is further configured to satisfy the following conditional expression (2).

-2.0 <f1 / f2 <0.5 (2)
However,
f1: Synthetic focal length of the first lens group f2: Synthetic focal length of the second lens group By satisfying the conditional expression (2), various aberrations such as spherical aberration, astigmatism, and distortion are further improved. There is an effect that it is possible to realize an imaging lens that can be corrected to a high level.

  In the imaging lens according to the present invention, it is further preferable that the curved shape on the subject side of the second lens group is an aspherical shape having a positive refractive power in the peripheral portion.

  According to said structure, the aberration of the light beam outside an optical axis can be correct | amended favorably. As a result, there is an effect that it is possible to further suppress the deterioration of the aberration of the light beam outside the optical axis.

  In the imaging lens according to the present invention, the lens closest to the image plane of the first lens group has a convex shape on the image plane side, and the lens closest to the subject of the second lens group. However, it is preferable that the subject has a concave shape.

  Alternatively, in the imaging lens according to the present invention, the lens closest to the image plane of the first lens group has a concave shape on the image plane side, and is closest to the subject side of the second lens group. This lens preferably has a convex shape on the subject side.

  According to said structure, a 1st lens group and a 2nd lens group can be made into a nested structure, and there exists an effect which can shorten optical length.

  In the imaging lens according to the present invention, it is preferable that the flat plate is made of glass having an optical coating film.

  According to said structure, the said flat plate has an effect as a cover glass which protects an image pick-up element.

  In the imaging lens according to the present invention, it is preferable that the second lens group is made of a resin material.

  According to said structure, a 2nd lens group can be easily formed on a plane plate or an image pick-up element. As a result, there is an effect that the flat plate or the image sensor can be prevented from being damaged when the second lens group is formed.

  In the imaging lens according to the present invention, it is further preferable that the maximum value of the thickness of the second lens group satisfies the following conditional expression.

0 <d <d1 (3)
However,
d: Maximum value of thickness of second lens group d1: Thickness of plane plate Damage to plane plate due to formation of thick second lens group on plane plate by satisfying conditional expression (3) above The effect which can suppress etc. is produced. In addition, there is an effect that the extension of the optical length due to the increase in the thickness of the second lens group can be suppressed.

  In addition, an imaging device including an electrical conversion unit that converts a light beam that has passed through the imaging lens into an electrical signal, an imaging lens of the present invention that forms a subject image on the electrical conversion unit of the imaging device, and a subject side An imaging unit including an opening for entering light and a housing made of a light-shielding member, and a portable information terminal including the imaging unit are also included in the present invention. include.

  As a result, it is possible to realize an imaging unit that can reduce the number of lenses that need to be provided with a lens holding mechanism and suppress deterioration in performance due to eccentricity and inclination of the lens, and a portable information terminal equipped with the imaging unit. .

  As described above, the imaging lens according to the present invention includes the second lens group having a curved surface formed directly or indirectly on the subject-side surface of the imaging element. .

  According to the above configuration, aberrations and the like that cannot be corrected by the first lens group can be favorably corrected by the second lens group formed directly or indirectly on the surface on the subject side. That is, the second lens group formed on the flat plate or the image sensor can effectively correct the aberration of the light beam outside the optical axis.

  Therefore, since the imaging lens can be configured without using many lenses having higher-order aspheric coefficients in the first lens group, it is possible to suppress performance degradation of the imaging lens due to the eccentricity and inclination of the lens.

  Further, according to the above configuration, the second lens group is formed on the flat plate or the image pickup device, so that it is not necessary to provide a new holding mechanism in the lens barrel that holds the lens. The number of lenses that need to be provided can be reduced. Therefore, the imaging lens can be reduced in size and weight.

  As a result, it is possible to reduce the number of lenses that need to be provided with a lens holding mechanism and to suppress performance deterioration due to decentering and tilting of the lens.

Embodiment 1
An embodiment according to an imaging lens of the present invention will be described below with reference to FIG.

(Configuration of imaging lens 1a)
The configuration of the imaging lens 1a will be described below with reference to FIG. FIG. 1 is a cross-sectional view of the imaging lens 1a.

  As shown in FIG. 1, the imaging lens 1a includes a lens group 16a (first lens group), a third lens 13a (second lens group), and a plane plate in order from the subject side (left hand side in FIG. 1). 14. Below, the 3rd lens 13, the plane plate 14, and the lens group 16a are explained in full detail.

  The image sensor 15 is not a component constituting the imaging lens 1a, but is illustrated in FIG. 1 for the sake of convenience in order to clarify the positional relationship of the components constituting the imaging lens 1a. The image sensor 15 will be described in detail in the third embodiment.

(Third lens 13a)
The third lens 13 a is a lens having a curved surface formed so as to be in contact with the subject side surface portion of the flat plate 14. Since the third lens 13a is formed on the subject side surface of the flat plate 14, there is no need to provide a lens holding mechanism for holding the third lens 13a. Therefore, the number of lenses that need to be provided with a lens holding mechanism can be reduced.

  The shape of the third lens 13a is not particularly limited as long as it is a curved surface shape, but it is preferably an aspherical shape, and more preferably an aspherical shape having a concave optical axis center. . Moreover, it is preferable that it is aspherical shape which has positive refractive power in a peripheral part.

  By making the shape of the third lens 13a an aspherical shape in which the central portion of the optical axis has a concave shape, the thickness of the central portion of the optical axis can be reduced and the thickness outside the optical axis can be increased. As a result, it is possible to effectively correct the light beam outside the optical axis without increasing the optical length. In the shape of the third lens 13a, the thickness at the center of the optical axis may be zero. This is because there is almost no need to correct aberration at the center of the optical axis.

  Hereinafter, the case where the third lens 13a has an aspherical shape in which the central portion of the optical axis has a concave shape will be described as an example.

  As described above, when the third lens 13a has an aspherical shape in which the center of the optical axis has a concave shape, it is preferable that the following conditional expression (3) is satisfied.

0 <d <d1 (3)
However,
d: Maximum thickness of the third lens 13a d1: Thickness of the flat plate 14 By satisfying the conditional expression (3), the influence on the optical length is minimized and the third lens 13a is formed. The damage to the flat plate 14 at the time can be suppressed. When the above conditional expression (3) is not satisfied, that is, when the thickness of the third lens 13a is thick, the absolute value of the shape change due to shrinkage during molding becomes large. Furthermore, when the material of the third lens 13a is resin, the difference in expansion coefficient from the cover glass is large, so that distortion is likely to occur. In addition, when the thickness of the third lens 13a is increased, birefringence is likely to occur, and the optical characteristics of the imaging lens 1a are hardly stabilized.

  The material of the 3rd lens 13a will not be specifically limited if the 3rd lens 13a can be formed so that it may have the curved surface shape mentioned above. Specifically, the material of the third lens 13a is preferably resin or glass, and more preferably resin. It is also possible to use liquid or liquid crystal as a lens. Furthermore, since the present invention is not limited to the visible region, a semiconductor such as silicon can be used as the material of the third lens 13a.

  By using resin as the material of the third lens 13a, the third lens 13a can be easily formed on the flat plate 14, and the flat plate 14 is prevented from being damaged when the third lens 13a is formed. Can do.

  In addition, as a formation method for forming the third lens 13a on the flat plate 14, a conventionally known method can be used. Specifically, when the third lens 13a is made of resin, molding using a 2P (Photoreplication Process) method can be exemplified.

(Flat plate 14)
In this embodiment, the flat plate 14 is provided to prevent the image sensor 15 from being damaged, and a third lens 13a is formed on the side surface of the subject side.

  The material of the flat plate 14 is not particularly limited, but is preferably made of glass having an optical coating film. That is, a cover glass for protecting the image sensor 15 is preferable.

  Note that the flat plate 14 itself has no influence on the light rays incident on the imaging lens 1a. That is, in the present embodiment, the flat plate 14 serves as a cover for the image sensor 15.

(Configuration of lens group 16a)
The configuration of the lens group 16a will be described below with reference to FIG. The lens group 16a has a positive refractive power with respect to a light beam incident from the subject side, and is configured by a first lens 11a, an aperture stop 10 and a second lens 12a in order from the subject side. The number of lenses constituting the first lens group 16a is not particularly limited as long as it is at least one. However, from the viewpoint of reducing the size and weight of the imaging lens 1a and correcting various aberrations such as spherical aberration, astigmatism and distortion, it is preferable that the number is about two.

(First lens 11a, second lens 12a)
The first lens 11a is a lens having a convex shape on the subject side, a concave shape on the image side, a spherical shape on the subject side surface, and a low-order aspheric shape on the image side surface.

  The material of the first lens 11a is not particularly limited. Specifically, plastic, glass, semiconductor, liquid crystal, liquid, etc. can be used as the material of the first lens 11a. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  The shape of the second lens 12a is a lens having a concave shape on the subject side, a convex shape on the image side, and an aspheric shape on both the subject side surface and the image side surface. Specifically, as the material of the second lens 12a, plastic, glass, semiconductor, liquid crystal, liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  As a method for forming the first lens 11a and the second lens 12a, a conventionally known method can be used. For example, when the first lens 11a and the second lens 12a are made of plastic, they are preferably formed by injection molding.

(Aperture stop 10)
The aperture stop 10 is a device for adjusting the amount of light passing through the imaging lens 1a. The position where the aperture stop 10 is provided is not particularly limited. Although FIG. 1 shows a case where it is provided between the first lens 11a and the second lens 12a, it may be provided closer to the subject than the first lens 11a. You may be provided in the 3rd lens 13a side rather than the lens 12a.

(Construction conditions of the imaging lens 1a)
Next, the configuration conditions of the imaging lens 1a will be described. The imaging lens 1a is preferably configured to satisfy the following conditional expressions (1) and (2).

d / f <1.5 (1)
-2.0 <f1 / f2 <0.5 (2)
However,
d: Distance from the surface closest to the subject to the image plane (optical length)
f: the combined focal length of the lens group 16a and the third lens 13a (the combined focal length of the entire lens system)
f1: Composite focal length of the lens group 16a f2: Composite focal length of the third lens 13a and the flat plate 14 The conditional expression (1) is an expression for defining the maximum optical length in the imaging lens 1a. By satisfying the conditional expression (1), the total lens length of the imaging lens 1a can be shortened, and the imaging lens 1a can be further reduced in size and weight.

  The conditional expression (2) is an expression for defining the Petzval sum of the optical system. When the power relationship between the lens group 16a, the third lens 13a, and the flat plate 14 satisfies the conditional expression (2), each aberration can be corrected more satisfactorily.

  Further, even when f1 / f2 becomes positive, the aberration is prevented from becoming large by being within the range of the conditional expression (2).

(Additional notes)
Although the case where the third lens 13a is formed on the flat plate 14 has been described in the present embodiment, the third lens 13a may be formed directly on the image sensor 15.

[Embodiment 2]
Another embodiment of the imaging lens according to the present invention will be described below with reference to FIG. FIG. 2 is a cross-sectional view of the imaging lens 1b.

  In addition, about the member similar to Embodiment 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted. Therefore, in the present embodiment, only the lens group 16b (lens having a positive refractive power) will be described below.

  Also in FIG. 2, as in FIG. 1, for the sake of convenience, the image sensor 15 is illustrated in FIG. 2 in order to clarify the positional relationship of the components constituting the imaging lens 1 b.

(Configuration of lens group 16b)
The configuration of the lens group 16b will be described below with reference to FIG. The lens group 16b is composed of an aperture stop 10, a first lens 11b, and a second lens 12b in order from the subject side (left hand side in FIG. 2). The number of lenses constituting the lens group 16b is not particularly limited as long as it is at least one lens. However, from the viewpoint that the imaging lens 1b can be reduced in size and weight and that various aberrations such as spherical aberration, astigmatism, and distortion can be corrected satisfactorily, the number is preferably about two.

(First lens 11b, second lens 12b)
The first lens 11b is a lens having a convex shape on the subject side, a concave shape on the image side, a spherical shape on the side surface of the subject, and a low-order aspheric shape on the side surface of the image surface.

  The material of the first lens 11b is not particularly limited. Specifically, as the material of the first lens 11b, plastic, glass, semiconductor, liquid crystal, liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  The second lens 12b has a concave shape on the subject side and a convex shape on the image side. Both the subject side surface and the image side surface are aspherical lenses. Specifically, as the material of the second lens 12a, plastic, glass, semiconductor, liquid crystal, liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  As a method for forming the first lens 11b and the second lens 12b, a conventionally known method can be used. For example, when the first lens 11b and the second lens 12b are made of plastic, they are preferably formed by injection molding.

(Aperture stop 10)
Since the aperture stop 10 is described in detail in the first embodiment, the description thereof is omitted in the present embodiment. In FIG. 2, the case where it is provided closer to the subject than the first lens 11b and between the first lens 11b and the second lens 12b is taken as an example.

(Conditions for imaging lens 1b)
Next, the configuration conditions of the imaging lens 1b will be described. The imaging lens 1b is also preferably configured to satisfy the following conditional expressions (1) and (2).

d / f <1.5 (1)
-1.4 <f1 / f2 <0.5 (2)
However,
d: Distance from the surface closest to the subject to the image plane (optical length)
f: Combined focal length of the lens group 16b and the third lens 13a f1: Combined focal length of the lens group 16b f2: Combined focal length of the third lens 13a and the flat plate 14 The conditional expression (1) is the imaging lens 1b. Is an expression for defining the maximum optical length in. By satisfying the conditional expression (1), the total lens length of the image pickup lens 1b can be shortened, and the image pickup lens 1b can be realized further than being reduced in size and weight.

  The conditional expression (2) is an expression for defining the Petzval sum of the optical system. When the power relationship between the lens group 16b, the third lens 13a, and the flat plate 14 satisfies the conditional expression (2), various aberrations can be corrected more satisfactorily.

(Additional notes)
Although the case where the third lens 13b is formed on the flat plate 14 has been described in the present embodiment, the third lens 13b may be formed directly on the imaging element 15.

[Embodiment 3]
Another embodiment of the imaging lens according to the present invention will be described below with reference to FIG. FIG. 3 is a cross-sectional view of the imaging lens 1c.

  Note that members similar to those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

  Also in FIG. 3, as in FIG. 1, for the sake of convenience, the image sensor 15 is illustrated in FIG. 3 in order to clarify the positional relationship of the components constituting the imaging lens 1 c.

(Configuration of lens group 16c)
The configuration of the lens group 16c will be described below with reference to FIG. The lens group 16c includes an aperture stop 10, a first lens 11c, and a second lens 12c in order from the subject side (left hand side in FIG. 3). The number of lenses constituting the lens group 16c is not particularly limited as long as it is at least one lens. However, from the viewpoint that the imaging lens 1b can be reduced in size and weight and that various aberrations such as spherical aberration, astigmatism, and distortion can be corrected satisfactorily, the number is preferably about two.

(First lens 11c, second lens 12c)
The shape of the first lens 11c is a lens having a convex shape on the subject side, a concave shape on the image plane side, and an aspheric shape on both the subject side surface and the image side surface.

  The material of the first lens 11c is not particularly limited. Specifically, as the material of the first lens 11c, plastic, glass, semiconductor, liquid crystal, liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  The shape of the second lens 12c is a lens having a convex shape on the subject side, a concave shape on the image side, and an aspheric shape on both the subject side surface and the image side surface. Specifically, as the material of the second lens 12c, plastic, glass, semiconductor, liquid crystal, liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  As a method for forming the first lens 11c and the second lens 12c, a conventionally known method can be used. For example, when the first lens 11c and the second lens 12c are made of plastic, they are preferably formed by injection molding.

(Third lens 13b)
In the present embodiment, the third lens 13b is a curved lens having a spherical shape with a convex shape on the subject side. However, as long as the following conditional expressions (2) and (3) are satisfied, the shape of the third lens 13b may have an aspherical shape.

-2.0 <f1 / f2 <0.5 (2)
0 <d <d1 (3)
However,
f1: Combined focal length of the lens group 16c f2: Combined focal length of the third lens 13b and the flat plate d: Maximum thickness of the third lens 13b d1: Thickness of the flat plate 14 (Additional Notes)
Although the case where the third lens 13c is formed on the flat plate 14 has been described in the present embodiment, the third lens 13c may be formed directly on the image sensor 15.

[Embodiment 4]
An imaging unit including the imaging lens according to Embodiments 1 to 3 will be described below as Embodiment 3. In addition, about the member similar to Embodiment 1-3, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

(Configuration of the imaging unit 100)
The configuration of the imaging unit 100 will be described below with reference to FIG. FIG. 4 is a cross-sectional view of the imaging unit 100. In FIG. 4, for convenience, the imaging lens is the imaging lens 1 a, but is not limited to this, and can be changed as appropriate within the scope of the present invention.

  As illustrated in FIG. 4, the imaging unit 100 includes an imaging lens 1 a, an imaging element 15, a housing 21, a support substrate 22, a flexible printed board 23, an infrared light cut filter 24, and a lens holding unit 25.

(Image sensor 15)
The imaging element 15 is an electronic component that includes an electrical conversion unit that converts a light beam that has passed through the imaging lens 1a into an electrical signal. In general, the image sensor 15 is formed with an electrical conversion unit in which pixels are two-dimensionally arranged at the center of the light receiving side surface, and a signal processing circuit is formed around the electrical conversion unit. The signal processing circuit sequentially drives each pixel to obtain a signal charge, an A / D converter that converts each signal charge into a digital signal, and a signal processing that forms an image signal output using the digital signal. It consists of parts.

  In addition, a large number of pads (not shown) are provided in the vicinity of the outer edge of the light receiving side surface of the image sensor 15 in the present embodiment, and are connected to the support substrate 22 via bonding wires W.

  Note that the type of the image sensor 15 is not particularly limited. Specifically, a CCD, a CMOS, or the like can be used.

(Supporting substrate 22)
The support substrate 22 is a hard substrate that supports the imaging element 15 and the housing 21 on one surface thereof. The other surface of the support substrate 22 (the surface opposite to the surface on which the image sensor 15 is supported) is provided with a flexible printed circuit board 23 having one end connected thereto. The support substrate 22 is provided with a large number of signal transmission pads on both the front and back surfaces, and is connected to the image pickup device 15 via a bonding wire W on one surface and connected to the flexible printed circuit board 23 on the other surface. Yes.

(Flexible printed circuit board 23)
The flexible printed circuit board 23 is supplied with a voltage and a clock signal for driving the image pickup device 15 from an external circuit (for example, a control circuit included in an apparatus in which the image pickup unit 100 is mounted), and receives a digital YUV signal from the outside. It is a substrate that makes it possible to output to.

  Y is a luminance signal, U is a color difference signal between red and the luminance signal, and V is a color difference signal between blue and the luminance signal.

(Case 21 and lens holding part 25)
The housing 21 is light-shielding and is fixedly disposed so as to cover the image sensor 15 on the surface of the support substrate 22 on the image sensor 15 side. Specifically, the housing 21 is wide open so as to surround the image sensor 15 on the image sensor 15 side and is in contact with the support substrate 22, and a flanged cylinder having a small opening on the other end side. It is formed in a shape.

  The housing 21 includes a lens holding unit 25 therein. The lens holding unit 25 is a member for holding the first lens 11 a, the second lens 12 a, and the aperture stop 10.

  In addition, an infrared light cut filter 24 is fixedly disposed on the upper portion of the housing 21. The infrared light cut filter 24 may be fixedly disposed between the imaging lens 1a and the imaging element 15. Note that an infrared light cut function may be added to the cover glass.

[Embodiment 5]
A portable information terminal equipped with an imaging unit according to the fourth embodiment will be described below as a fifth embodiment. In addition, about the member similar to Embodiment 1-4, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

(Configuration of portable information terminal 200)
The configuration of a portable information terminal equipped with the imaging unit 100 will be described below with reference to FIGS. 5A to 5C are external views showing the external appearance of the portable information terminal 200, in particular, FIG. 5A is a front view, FIG. 5B is a rear view, and FIG. FIG.

  5A to 5C, the portable information terminal 200 includes an imaging unit 100, a speaker unit 101, a microphone unit 102, an input unit 103, a monitor unit 104, a light unit 106, and a shutter button 108. It is configured. The speaker unit 101 and the microphone unit 102 are used for inputting and outputting audio information. The monitor unit 104 is used to output video information. In the present embodiment, the monitor unit 104 is also used to display information obtained from the imaging unit. The light unit 106 is used as a light for illuminating the subject. In the present embodiment, the imaging unit 100 is disposed on the back surface of the monitor unit 104, but the arrangement method and the orientation of the imaging unit 100 are not limited to this.

  By operating the shutter button 108 or the input unit 103, it is possible to perform imaging by the imaging unit 100. The captured image is signal-processed in the portable information terminal 200 and displayed on the monitor unit 104. The captured image can be stored as electronic data in the portable information terminal 200 or stored in an external recording device.

  In the present embodiment, a so-called foldable portable information terminal in which the upper casing and the lower casing are connected via a hinge is taken as an example. Of course, portable information terminals that can be installed are not limited to folding types.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  Next, specific numerical examples of the imaging lens according to Embodiments 1 to 3 described above will be described.

(Example 1)
In Example 1, a numerical example of the imaging lens 1a described in Embodiment 1 will be described. Tables 1 and 2 show specific lens data for the configuration of the imaging lens 1a shown in FIG. Table 1 shows basic data portions of the imaging lens 1a, and Table 2 shows data related to the aspherical shape among the lens data of Table 1.

  Here, the “aspheric shape” in this specification and the like will be described. The aspherical shape in this specification and the like can be expressed by using the following aspherical expression (Equation 1) when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis.

  Where K is the conic constant, R is the radius of curvature, A, B, C and D are the 4th, 6th, 8th and 10th aspherical coefficients, respectively, and Z is the height Y from the optical axis. The length of a perpendicular line drawn from a point on the aspheric surface at the position to the tangent plane (plane perpendicular to the optical axis) of the apex of the aspheric surface is shown.

  “F” shown in Table 1 is the combined focal length of the entire imaging lens 1a, “FNO” is the F number (F value) of the imaging lens 1a, and “ω” is the half angle of view of the imaging lens 1a. is there. In this embodiment, since the optical length d = 3.1 and f = 2.3, d / f = 1.3, which satisfies the above conditional expression (1). In this embodiment, since the focal length f1 of the first lens group 16a is 2.0 and the combined focal length f2 of the third lens 13a and the flat plate 14 is −2.2, f1 / f2 = −. 0.91 was achieved, thereby satisfying the above conditional expression (2).

In addition, the numerical value of each aspheric surface data in this specification and the like represents a power of 10 using “E”. That is, for example, 2.5 × 10 ⁻⁰² is represented as 2.5E-02.

  In the field of the surface number Si in the lens data shown in Tables 1 and 2, the surface of the constituent element closest to the subject is the first, and the i-th (i = i = The surface numbers of 1 to 8) are shown. The column of the curvature radius Ri shows the value of the curvature radius of the i-th surface from the subject side. The column of the surface interval Di indicates the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the subject side. The unit of Ri and Di is mm (millimeter). In the columns of the refractive index and the Abbe number, the refractive index with respect to the d-line (587.6 nm) of lens elements including the flat plate 14 (the first lens 11a, the second lens 12a, the third lens 13a, and the flat plate 14) and The Abbe number is shown.

  As shown in Table 1, in this embodiment, the image surface side surface S2 of the first lens 11a and both surfaces S4 and S5 of the second lens 12a are aspherical. In the basic lens data, numerical values of the radius of curvature near the optical axis are shown as the radius of curvature of these aspheric surfaces.

  FIG. 5 shows spherical aberration, astigmatism, and distortion in the imaging lens 1a. FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens 1a.

  Each aberration diagram shows aberration with 550 nm as a reference wavelength, but the spherical aberration diagram also shows aberrations for 440 nm and 660 nm. In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from Tables 1 and 2 above, in the imaging lens 1a, the first lens 11a uses a spherical lens on the object-side surface, and low-order aspherical coefficients are also obtained in other aspherical shapes. To form an aspherical surface. As a result, it is possible to increase the allowable amount of eccentricity deviation and inclination, and it is possible to suppress deterioration of the performance of the imaging lens 1a. Therefore, it is possible to provide an imaging lens 1a that is easy to assemble and has excellent mass productivity.

  Further, as can be seen from FIG. 7, by forming the third lens 13a on the flat plate 14, the power arrangement of the entire imaging lens 1a can be optimized, and the imaging lens with sufficient aberration correction. 1a can be realized.

(Example 2)
In Example 2, numerical examples in the imaging lens 1b described in Embodiment 2 will be described. Tables 3 and 4 show specific lens data for the configuration of the imaging lens 1b shown in FIG. Table 3 shows basic data portions in the imaging lens 1b, and Table 4 shows data related to the aspherical shape among the lens data in Table 3.

  In the present embodiment, the same terms as in the first embodiment are used in the same meaning as in the first embodiment, and therefore, the description thereof is omitted in the present embodiment.

  As can be seen from Tables 3 and 4, in the imaging lens 1b, the first lens 11b uses a spherical lens on the surface on the subject side, and other aspherical shapes are non-spherical due to low-order aspherical coefficients. A spherical surface is formed. Accordingly, it is possible to increase the allowable amount of eccentricity deviation and inclination, and it is possible to suppress deterioration of the performance of the imaging lens 1b. Therefore, it is possible to provide an imaging lens 1b that is easy to assemble and excellent in mass productivity.

  FIG. 7 shows spherical aberration, astigmatism, and distortion in the imaging lens 1b. FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens 1b.

  As can be seen from FIG. 7, by forming the third lens 13a on the flat plate 14, the power arrangement of the entire imaging lens 1b can be optimized, and the imaging lens 1b with sufficiently corrected aberration can be obtained. realizable.

  In this embodiment, unlike the first embodiment, the aperture stop 10 is disposed closest to the subject, that is, closer to the subject than the first lens 10b. That is, since the position of the aperture stop 10 is separated from the image plane, it is possible to realize a wider angle while minimizing the aberration reduction of the light beam outside the optical axis.

(Example 3)
In Example 3, a numerical example of the imaging lens 1c described in Embodiment 3 will be described. Tables 5 and 6 show specific lens data for the configuration of the imaging lens 1c shown in FIG. Table 5 shows basic data portions in the imaging lens 1c, and Table 6 shows data related to the aspherical shape among the lens data in Table 5.

  In the present embodiment, the same terms as those in the first and second embodiments are used in the same meaning as in the first and second embodiments, so that the description thereof is omitted in the present embodiment.

  As can be seen from Tables 5 and 6, the imaging lens 1b uses relatively low-order aspherical lenses on both sides of the first lenses 11c and 12c. As a result, the performance of the optical system can be maintained, and since it is a low-order aspherical surface, it is possible to increase the allowable deviation of eccentricity and inclination. Therefore, it is possible to provide an imaging lens 1c that is easy to assemble while maintaining performance and excellent in mass productivity.

  In this embodiment, since the optical length d = 3.0 and f = 2.5, d / f = 1.2, which satisfies the above conditional expression (1). In this embodiment, since the focal length f1 of the first lens group 16c is 2.6 and the combined focal length f2 of the third lens 13b and the flat plate 14 is 12.3, f1 / f2 = 0. 21, which satisfies the above conditional expression (2).

  FIG. 8 shows spherical aberration, astigmatism, and distortion in the imaging lens 1c. FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens 1c.

  As can be seen from FIG. 8, by forming the spherical third lens 13b having a convex surface on the object side on the flat plate 14, the incident angle of off-axis light rays onto the image sensor 15 is made perpendicular to the image sensor. It is possible to approach.

  In the present embodiment, as in the second embodiment, the aperture stop 10 is disposed closest to the subject, that is, closer to the subject than the first lens 11c. That is, since the position of the aperture stop 10 is separated from the image plane, it is possible to realize a wider angle while minimizing the aberration reduction of the light beam outside the optical axis. However, the position of the aperture stop is not limited to this.

  As mentioned above, although the specific Example of this invention was shown by Examples 1-3, this invention is not limited to the specific shape and numerical value of the Example shown previously, A desired optical characteristic and In order to obtain the optical length, each parameter can be appropriately changed.

  The imaging lens according to the present invention can be suitably used for imaging equipment such as a digital still camera. Further, it can be particularly preferably used for a small imaging device suitable for portable use. Specifically, a digital camera mounted on a portable information terminal or a mobile phone can be given.

It is sectional drawing of the imaging lens which concerns on 1st Embodiment. It is sectional drawing of the imaging lens which concerns on 2nd Embodiment. It is sectional drawing of the imaging lens which concerns on 3rd Embodiment. It is sectional drawing of the imaging unit which concerns on 4th Embodiment. It is an external view of the portable information terminal which concerns on 5th Embodiment, (a) is a front view, (b) is a rear view, (c) is a side view. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens in the first example. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens in the second example. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens in the third example.

Explanation of symbols

1a, 1b, 1c Imaging lens 10 Aperture stop 11a, 11b, 11c First lens 12a, 12b, 12c Second lens 13a, 13b, 13c Third lens (second lens group)
14 Plane plate 15 Image sensor 16a, 16b, 16c Lens group (first lens group)
DESCRIPTION OF SYMBOLS 21 Housing | casing 100 Imaging unit 101 Speaker part 102 Microphone part 103 Input part 104 Monitor part 106 Light part 108 Shutter button 200 Portable information terminal

Claims (14)

An imaging lens that forms a subject image on an imaging device,
A first lens group having positive refractive power disposed on the subject side;
A second lens group having a curved surface formed directly or indirectly on the subject-side surface of the image sensor;
An imaging lens comprising:   The imaging lens according to claim 1, wherein the second lens group is formed on a flat plate formed on the surface on the subject side.   The imaging lens according to claim 1, wherein the second lens group is formed directly on the surface on the subject side.   The imaging lens according to claim 1, wherein a surface of the second lens group on the imaging element side has a planar shape. The imaging lens according to claim 1, wherein the imaging lens is configured to satisfy the following conditional expression (1).
d / f <1.5 (1)
However,
d: Distance from the surface closest to the subject to the image plane (optical length)
f: Total focal length of the entire lens system The imaging lens according to claim 1, wherein the imaging lens is configured to satisfy the following conditional expression (2).
-2.0 <f1 / f2 <0.5 (2)
However,
f1: Composite focal length of the first lens group f2: Composite focal length of the second lens group   2. The imaging lens according to claim 1, wherein the curved surface shape on the subject side of the second lens group is an aspheric shape having positive refractive power in the peripheral portion. The lens arranged closest to the image plane side of the first lens group has a convex shape on the image plane side,
2. The imaging lens according to claim 1, wherein the lens arranged closest to the subject side of the second lens group has a concave shape on the subject side. The lens arranged closest to the image plane side of the first lens group has a concave shape on the image plane side,
The imaging lens according to claim 1, wherein a lens disposed closest to the subject side of the second lens group has a convex shape on the subject side.   The imaging lens according to claim 2, wherein the flat plate is made of glass having an optical coating film.   The imaging lens according to claim 1, wherein the second lens group is made of a resin material. The imaging lens according to claim 2, wherein a maximum value of the thickness of the second lens group satisfies the following conditional expression (3).
0 <d <d1 (3)
However,
d: Maximum thickness of the second lens group d1: Thickness of the flat plate An image sensor having an electrical converter that converts the light beam that has passed through the imaging lens into an electrical signal;
The imaging lens according to claim 1, wherein a subject image is formed on an electrical conversion unit of the imaging element;
An imaging unit comprising: a housing made of a light-shielding member having an opening for allowing light to enter the subject side.   A portable information terminal comprising the imaging unit according to claim 13.

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