JP4890607B2 - Imaging lens, camera module, and portable information device - Google Patents

Description

  The present invention relates to an imaging lens, a camera module, and a portable information device including a first lens having a convex surface on the subject side and a second lens disposed on the image plane side of the first lens.

  In recent years, various types of imaging modules mounted on digital cameras or digital video units have been developed that use solid-state imaging devices as imaging devices. Here, examples of the solid-state imaging device include those composed of a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor). The imaging module can be reduced in size and height by being configured using a solid-state imaging device.

  In particular, portable terminals such as portable information terminals and portable telephones are rapidly spreading in recent years. An imaging module mounted on the portable terminal is desired to have an imaging lens that has a high resolving power and is small and low in profile.

  As an example of an imaging lens having a high resolving power and having a small size and a low profile, Patent Document 1 discloses a first lens having a positive refractive power and a second lens having a negative refractive power. An imaging lens (a so-called telephoto imaging lens) configured using two lenses is disclosed.

  In the imaging lens disclosed in Patent Document 1, since the overall length of the imaging lens can be shortened compared to the focal length of the entire imaging lens, it is possible to reduce the size and height. In the imaging lens disclosed in Patent Document 1, the first and second lenses jointly correct various aberrations such as coma aberration, astigmatism, and field curvature aberration. Can be improved. Therefore, with the technique disclosed in Patent Document 1, it is possible to realize an imaging lens that is small and has good optical characteristics.

  As another example of an imaging lens having high resolving power and having a small size and low height, Patent Document 2 discloses a first lens having a positive refractive power and a positive or negative refractive power. An imaging lens configured by using two lenses including a second lens having a lens is disclosed.

  As still another example of an imaging lens having a high resolving power and having a small size and a low profile, a first lens having a positive refractive power and a second lens having a positive refractive power are two. Examples include an imaging lens configured using a single lens (see Patent Documents 4 to 7 and Patent Documents 9 to 11).

  By the way, Patent Document 3 discloses a wide-angle lens for a camera that maintains a high resolving power and can be easily manufactured.

  The lens disclosed in Patent Document 3 is configured by using two lenses, a first lens having a positive or negative refractive power and a second lens having a positive refractive power. Furthermore, in the lens disclosed in Patent Document 3, the film constituting the image plane is curved to improve spherical aberration and field curvature aberration.

  In each technique disclosed in Patent Documents 1 to 11, each surface on the object side and the image surface side in each of the first and second lenses is formed into a shape including a concave surface and / or a convex surface. Realizes a low-profile imaging lens.

JP 2008-309999 A (released on December 25, 2008) JP 2004-145183 A (published May 20, 2004) JP-A-8-334684 (published on December 17, 1996) JP 2002-296696 A (published on October 9, 2002) Japanese Patent No. 3717482 (published on September 2, 2004) Japanese Patent No. 4074203 (published on September 2, 2004) Japanese Patent No. 3717483 (published September 9, 2004) Japanese Patent No. 3717487 (published January 8, 2004) JP 2005-107254 A (published April 21, 2005) JP 2005-107368 A (published April 21, 2005) JP 2005-107369 A (published April 21, 2005)

  An imaging lens configured by using a plurality of lenses becomes difficult to manufacture with downsizing and low profile. That is, in an optical system that is downsized and reduced in height, very strict manufacturing tolerances are required with respect to thickness variations and decentering in each lens constituting the optical system. Here, “eccentricity” refers to an optical system misalignment that occurs between both surfaces of each lens constituting the optical system, a misalignment of the other lens with respect to one lens, and the like. It means various misalignments accompanied by displacement of the optical axis in the normal direction.

  In order to apply to an imaging module using a solid-state imaging device, an imaging lens that has been downsized and reduced in height has a thickness variation of each lens constituting the imaging lens and an error such as eccentricity of about 1 It is required to be controlled within the range of 5 μm to 2 μm, and it is necessary to satisfy this strict requirement, which makes manufacturing difficult. When manufacturing becomes difficult, in the imaging lens, the problem that the manufacturing cost required to satisfy the imposed requirements increases, and large manufacturing variations are likely to occur, so that it becomes difficult to maintain a desired resolving power. The problem occurs.

  It is no exception in the imaging lenses disclosed in Patent Documents 1 and 2 and 4 to 11 that the manufacture becomes difficult. Accordingly, in each of the imaging lenses disclosed in Patent Documents 1 to 2 and 4 to 11, a problem that the manufacturing cost required to satisfy the strict requirements imposed and a large manufacturing variation are likely to occur. Therefore, there arises a problem that it becomes difficult to maintain a desired resolving power.

  In general, the smaller the image pickup lens is, the lower the profile, the greater the MTF (Modulation Transfer Function) changes according to the amount of eccentricity. Therefore, as the imaging lens is made smaller and lower in height, it is required to produce a lens having an eccentricity closer to 0 μm, and therefore the manufacturing difficulty becomes very high.

  The lens disclosed in Patent Document 3 can maintain a high resolution and can be easily manufactured. However, since the lens that forms the image plane is curved, a CCD or CMOS type image sensor is used. There arises a problem that it is difficult to apply to a conventional imaging module, that is, an imaging module using a solid-state imaging device.

  The present invention is an invention made in view of the above-mentioned problems, and its object is applicable to an imaging module using a solid-state imaging device, reducing manufacturing costs and maintaining a desired resolving power. Is to provide an imaging lens, a camera module, and a portable information device.

In the imaging lens according to the present invention, the first lens and the second lens are arranged in this order from the subject side to the image plane side, and the first lens has a convex surface formed on the subject side and an image. side and concave is formed on the front Stories second lens, and a image surface side surface directed to the image plane side and the object side surface directed to the object side, the object side surface, A convex object-side central part and a subject-side peripheral part formed in a concave shape around the subject-side central part, and the image surface side surface is a concave image-side central part; An imaging lens having an image plane side peripheral portion formed in a convex shape around the image plane side central portion , d1: center thickness of the first lens, d12: the first lens and the above The distance from the second lens, d: 0.35 <(d1 / d) <0.5, where 0 is the total optical length. .12 <(d12 / d) < 0.3, is characterized by satisfying the following relationship.

  Due to this feature, the second lens has a configuration in which the central portion of the surface directed toward the subject is traveling to the subject side, and the peripheral portion is recessed toward the image plane. According to this configuration, the light beam passing near the central portion of the second lens is closer to the subject side in the direction from the subject side to the image plane side (generally, the direction along the optical axis of the imaging lens). An image can be formed, and a light beam passing near the periphery of the second lens can be imaged on the image plane side in the same direction. For this reason, the imaging lens of the present invention can correct various aberrations such as curvature of field according to the degree of protrusion on the subject side and the degree of depression on the image side in the second lens. Further, according to this configuration, the second lens can be used as a lens having the same positive or negative refractive power as the first lens, and thereby the asymmetry between the first lens and the second lens. Can be small. As a result, in the imaging lens of the present invention, when an error such as eccentricity and thickness variation in each of the first and second lenses occurs, an adverse effect caused by this error can be reduced. The range of the error can be substantially widened.

  Furthermore, the present imaging lens can moderately change the shape of each surface of the first lens directed toward the subject side and the image plane side by satisfying the above 0.35 <(d1 / d). . That is, each of these surfaces can reduce the degree of protrusion or depression in the direction from the subject side to the image surface side. Furthermore, the interval between these surfaces in the same direction can be increased.

  Further, when 0.07 <(d12 / d) is satisfied, the light fluxes at the image heights incident on the second lens are separated from each other, and correction of distortion and astigmatism is further performed on the image side. Easy to do.

  As described above, the imaging lens of the present invention that satisfies the above-described mathematical expression can reduce the adverse effects of this error when errors such as eccentricity and thickness variations in the first and second lenses occur. Therefore, it is possible to substantially expand the range in which the adverse effect of the allowable error can be reduced.

  From the above, when the imaging lens of the present invention is downsized and reduced in height, severe demands may be imposed on eccentricity and thickness variations in each of the first and second lenses. Therefore, it is relatively easy to manufacture an imaging lens that satisfies the imposed requirements. For this reason, this imaging lens can reduce the manufacturing cost required to satisfy the imposed requirements, and it is easy to maintain a desired resolving power because manufacturing variations are less likely to occur.

  When d1 / d is less than or equal to 0.35, the thickness of the first lens is reduced. Therefore, in order to obtain a large refractive power, a change in the shape of the surface of the first lens directed toward the subject is increased. Since it is necessary to increase the degree of protrusion of the convex surface, it is not preferable. Therefore, in order to obtain the effect of the imaging lens, the value of d1 / d needs to satisfy the above 0.35 <(d1 / d).

  When d12 / d is 0.07 or less, the distance between the first lens and the second lens becomes narrow, so that the aberrations corrected by the first lens and the second lens are mixed, making it difficult to correct aberrations satisfactorily. Alternatively, even if aberration correction is performed satisfactorily, a strict value is required for the axial deviation error between lenses, and manufacturing becomes difficult.

  When d1 / d is 0.5 or more, it becomes difficult to correct lateral aberrations or the tolerance sensitivity becomes severe. Specifically, the light beam passing through the object side surface of the first lens is condensed, and the contribution to the correction of lateral aberration is reduced on this surface, and sufficient aberration correction cannot be performed. At this time, if the power of the first lens is weakened, the light beam passing through the object side surface of the first lens is not condensed, and lateral aberration can be corrected on this surface, but an effective image circle is secured. For this reason, a rapid bending of the light beam is required on this surface, and as a result, tolerance sensitivity such as eccentricity becomes severe.

  When d12 / d is 0.3 or more, it becomes difficult to correct curvature of field and astigmatism. That is, since the distance between the object side surface of the second lens and the image surface is too short with respect to the entire length, it is difficult to perform sufficient aberration correction.

The imaging lens according to the present invention, 0.12 <(d12 / d) , satisfy the relationship.

  With the above-described configuration, the manufacturing tolerance for the eccentricity between the first lens and the second lens can be further relaxed.

  In the imaging lens according to the present invention, the Abbe number of the material of the first lens and the second lens is preferably larger than 40.

  With the above-described configuration, the choice of materials is widened, and by using inexpensive materials, it is possible to reduce manufacturing costs and to apply various manufacturing processes that are not limited by material constraints.

  The imaging lens according to the present invention preferably has an F number of less than 3.

  By reducing the F-number to less than 3, the imaging lens of the present invention can increase the amount of received light and can obtain high resolution because chromatic aberration is corrected well.

  The imaging lens according to the present invention is preferably manufactured by a wafer level lens process.

  According to the above configuration, since the imaging lens according to the present invention has a wide tolerance, it is possible to manufacture a lens module at low cost by applying it to a wafer level process.

  In the imaging lens according to the present invention, it is preferable to provide an aperture stop on the subject side of the first lens.

  With the above configuration, a clear image can be provided by adjusting the amount of light.

The camera module according to the present invention includes an imaging lens according to the present invention, characterized by comprising an electronic imaging device for receiving light representing an image to be thus formed on the imaging lens.

  This feature makes it possible to realize an inexpensive, compact and high-performance digital camera.

  In the camera module according to the present invention, the electronic image pickup device is preferably a CMOS image pickup device or a CCD image pickup device having a pixel size of 2.5 μm or less.

  According to the above configuration, by configuring the sensor using a solid-state imaging device having a pixel pitch of 2.5 μm or less, it is possible to realize an imaging module that fully utilizes the performance of the high-pixel imaging device.

  In the camera module according to the present invention, the number of pixels of the CMOS image sensor or the CCD image sensor is preferably 300,000 pixels or more.

  According to the above configuration, by providing the sensor suitable for the resolution performance of the imaging lens, a digital camera module having a good resolution performance can be obtained. It is particularly suitable for VGA class sensors.

  In the camera module according to the present invention, it is preferable that a distance between the electronic imaging device and the cover glass is 0.195 mm or more.

  According to the above configuration, the present invention can be applied to both a wire bonding structure and a lens-on-wafer structure widely used in mobile digital camera modules using a solid-state imaging device. When the distance between the cover glass and the sensor is 0.195 mm or less, it interferes with the wire for electrical connection between the sensor and the substrate, and therefore cannot be applied to a wire bonding type module structure.

  The camera module according to the present invention preferably has a focus adjustment-less structure.

  According to the above configuration, since the lens of the present invention has a characteristic of excellent tolerance sensitivity, it is not necessary to adjust the position of the light receiving element with respect to the best image plane position in the optical axis direction, and focus adjustment is not performed in the assembly process. A camera module that does not have a mechanism for adjustment can be provided, and manufacturing costs can be reduced.

  In the camera module according to the present invention, it is preferable that the first and second lenses of the imaging lens are made of a heat resistant material.

  According to the above configuration, it is possible to provide a camera module that can be reflow mounted and has a low mounting cost. Since heat-resistant materials are advantageous in tolerances, they have a large tolerance for changes in the lens assembly state due to thermal history due to reflow, and can be applied to a process with a load.

  The camera module according to the present invention preferably has a barrelless structure.

  According to the above configuration, since the lens barrel is not provided, it is possible to realize cost reduction by reducing the number of processes and components.

  The camera module according to the present invention preferably has a holderless structure.

  According to the above configuration, since no casing is provided, it is possible to realize cost reduction by reducing processes and components.

Memory portable information apparatus according to the present invention, for storing the imaging lens according to the present invention, an electronic image pickup element for receiving light representing an image to be thus formed on the imaging lens, an image captured by the electronic image pickup device It is characterized by comprising.

  With this feature, it is possible to realize a portable information device that is inexpensive, compact, and has a high-performance imaging function.

In the imaging lens according to the present invention, the first lens and the second lens are arranged in this order from the subject side to the image plane side, and the first lens has a convex surface formed on the subject side and an image. A concave surface is formed on the surface side, and the second lens has a subject side surface directed toward the subject side and an image surface side surface directed toward the image surface side, and the subject side surface is convex. A subject-side central portion and a subject-side peripheral portion formed in a concave shape around the subject-side central portion, and the image plane side surface includes a concave image-plane-side central portion and the image plane An imaging lens having an image surface side peripheral portion formed in a convex shape around the side center portion, d1: center thickness of the first lens, d12: the first lens and the second lens spacing between, d: when the optical total length, 0.35 <(d1 / d) <0.5, .12 <(d12 / d) < 0.3, since satisfies the following relationship is applicable to an imaging module using the solid-state imaging device, imaging can reduce the manufacturing cost, and to maintain the resolution A lens, a camera module, and a portable information device can be provided.

2 is a diagram illustrating a configuration of an imaging lens according to Embodiment 1. FIG. It is the figure which described the data of the aspherical formula, material, shape, etc. of each lens which comprises the said imaging lens. It is the figure which described the specification and various optical characteristics of the said imaging lens. It is a graph which shows the MTF and the spatial frequency characteristic of the said imaging lens. 4 is a graph showing MTF / defocus characteristics of the imaging lens. It is a graph which shows the astigmatism and distortion aberration of the said imaging lens. It is a graph which shows the spherical aberration of the said imaging lens. It is a graph which shows the MTF change with respect to the axial shift | offset | difference of the surface of the 1st lens provided in the said imaging lens. It is a graph which shows the MTF change with respect to the axial shift between the 1st lens provided in the said imaging lens, and a 2nd lens. It is sectional drawing which shows the structure of the wire bonding type of the focus adjustment-less structure camera module using the said imaging lens. (A)-(d) is sectional drawing for demonstrating the wafer level lens process which manufactures the wire bonding type of the said focus adjustment-less structure camera module. It is sectional drawing which shows the structure of the glass on wafer type of the said focus adjustment-less structure camera module. (A) And (b) is sectional drawing for demonstrating the wafer level lens process which manufactures the glass-on-wafer type of the said focus adjustment-less structure camera module. (A)-(c) is sectional drawing for demonstrating the conventional injection molding process which manufactures the wire bonding type of a focus adjustment-less structure camera module. FIG. 6 is a diagram describing data such as an aspherical expression, material, shape, and the like of each lens constituting the imaging lens according to Embodiment 2. It is the figure which described the specification and various optical characteristics of the said imaging lens. It is a figure which shows the layout of the said imaging lens typically. It is a graph which shows the MTF and the spatial frequency characteristic of the said imaging lens. 4 is a graph showing MTF / defocus characteristics of the imaging lens. FIG. 6 is a diagram describing data such as an aspheric expression, material, shape, and the like of each lens constituting the imaging lens according to Embodiment 3. It is the figure which described the specification and various optical characteristics of each lens which comprise the said imaging lens. It is a figure which shows the layout of the said imaging lens typically. It is a graph which shows the MTF and the spatial frequency characteristic of the said imaging lens. 4 is a graph showing MTF / defocus characteristics of the imaging lens.

  Embodiments relating to the imaging lens of the present invention will be described below with reference to FIGS.

(Embodiment 1)
(Configuration of Imaging Lens 1 According to Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of an imaging lens 1 according to the first embodiment. The imaging lens 1 includes a lens 2. The lens 2 has a convex surface 6 on the subject 4 side, a concave surface on the image surface 5 side, and has a center thickness d1. An aperture stop 10 is provided on the subject 2 side of the lens 2.

  The lens 3 is provided on the image plane 5 side of the lens 2 with a distance d12 from the lens 2. The lens 3 has a surface 7 directed toward the subject 4, and the surface 7 has a convex central portion 8 and a peripheral portion 9 formed in a concave shape around the central portion 8. ing.

  A cover glass 11 is provided between the lens 3 and the image plane 5. On the image plane 5 side of the cover glass 11, the electronic image sensor 12 is disposed at a position in contact with the image plane 5.

The imaging lens 1 has an optical total length d,
0.35 <(d1 / d) <0.5 Formula (1),
0.07 <(d12 / d) <0.3 Expression (2),
Satisfy the relationship.

  When the imaging lens 1 satisfies the above 0.35 <(d1 / d), the shape change of the convex surface 6 directed toward the subject 4 in the lens 2 and the shape change of the concave surface directed toward the image surface 5 side. Can be relaxed. That is, each of these surfaces can reduce the degree of protrusion or depression in the direction from the subject 4 side to the image surface 5 side. Furthermore, the interval between these surfaces in the same direction can be increased.

  Further, when 0.07 <(d12 / d) is satisfied, the light fluxes incident on the lens 3 are separated from each other, and correction of distortion and astigmatism is further performed on the image plane 5 side. Easy to do.

  When d1 / d is 0.35 or less, the thickness of the lens 2 is reduced. Therefore, in order to obtain a large refractive power, the shape change of the convex surface 6 directed toward the subject 4 in the lens 2 is increased. Since it is necessary to increase the degree of protrusion of the convex surface 6, it is not preferable. Accordingly, in order to obtain the effect of the imaging lens 1, the value of d1 / d needs to satisfy the above 0.35 <(d1 / d).

  When d12 / d is 0.07 or less, the distance between the lens 2 and the lens 3 is narrowed, so that the aberrations to be corrected by the lens 2 and the lens 3 are mixed, and it becomes difficult to perform good aberration correction, or Even if the aberration correction is performed satisfactorily, as a result, a severe value is required for the axial deviation error between the lens 2 and the lens 3, and the manufacturing becomes difficult.

  When d1 / d is 0.5 or more, it becomes difficult to correct lateral aberrations or the tolerance sensitivity becomes severe. Specifically, the light beam passing through the object side surface of the lens 2 is condensed, and the contribution to the correction of lateral aberration is reduced on this surface, and sufficient aberration correction cannot be performed. At this time, if the power of the lens 2 is weakened, the light beam passing through the object side surface of the lens 2 is not condensed and lateral aberration can be corrected on this surface, but in order to secure an effective image circle. In this plane, a sharp bending of the light beam is required, and as a result, tolerance sensitivity such as eccentricity becomes severe.

  When d12 / d is 0.3 or more, it becomes difficult to correct curvature of field and astigmatism. That is, since the distance between the object side surface of the lens 3 and the image surface is too short with respect to the entire length, it is difficult to perform sufficient aberration correction.

  The Abbe number of the material of the lens 2 and the lens 3 is preferably larger than 40. The choice of materials is widened, and by using inexpensive materials, it is possible to reduce manufacturing costs and to apply various manufacturing processes that are not limited by material constraints. For example, the materials of the lenses 2 and 3 are made of a thermoplastic material, and are ZEON's E48R (Nd: 1.531, νd: 56), 330R (Nd: 1.509, νd: 56), or 480R (Nd: 1.525). Νd: 56) can be used. Materials with low dispersion (high Abbe number) are useful in imaging lenses, but are difficult to develop. As a thermoplastic material used for injection molding, a material having an Abbe number of about 56 has been developed as in the above example. In the embodiment of the present invention, a design example using an Abbe number 46 material is given.

  The imaging lens preferably has an F number of less than 3. By reducing the F-number to less than 3, the imaging lens 1 can increase the amount of received light and can obtain a high resolving power because chromatic aberration is corrected well. The F number is a kind of quantity indicating the brightness of the optical system. The F number of the imaging lens 1 is represented by a value obtained by dividing the equivalent focal length of the imaging lens 1 by the entrance pupil diameter of the imaging lens 1.

  The electronic image pickup device 12 is preferably constituted by a CMOS image pickup device or a CCD image pickup device having a pixel size of 2.5 μm or less. According to this configuration, it is possible to realize an imaging module that sufficiently utilizes the performance of a high-pixel imaging device by configuring the sensor using a solid-state imaging device having a pixel pitch of 2.5 μm or less.

  The number of pixels of the CMOS image pickup device or the CCD image pickup device constituting the electronic image pickup device 12 is preferably 300,000 pixels or more. By providing a sensor suitable for the resolution performance of the imaging lens, a digital camera module having a good resolution performance can be obtained. It is particularly suitable for VGA class sensors.

  The distance between the electronic image sensor 12 and the cover glass 11 is preferably 0.195 mm or more.

  According to the above configuration, the present invention can be applied to both a wire bonding structure and a lens-on-wafer structure widely used in mobile digital camera modules using a solid-state imaging device. When the distance between the cover glass 11 and the electronic image pickup device 12 is less than 0.195 mm, it interferes with a wire for electrical connection between the sensor and the substrate, and thus cannot be applied to a wire bonding type module structure.

  The lenses 2 and 3 are preferably made of a heat resistant material. Accordingly, it is possible to provide a camera module that can be reflow mounted and has a low mounting cost. Since heat-resistant materials are advantageous in tolerances, they have a large tolerance for changes in the lens assembly state due to thermal history due to reflow, and can be applied to a process with a load.

(Design specifications and optical characteristics of imaging lens according to Embodiment 1)
FIG. 2 is a diagram describing data such as the aspherical formula, material, and shape of each lens constituting the imaging lens 1. “L1” in the “element” column in FIG. 2 indicates the lens 2 shown in FIG. 1, and “L2” indicates the lens 3. “CG” means cover glass.

  “Nd” in the “Material” column of FIG. 2 is the refractive index of each material constituting each lens with respect to the d-line (wavelength 587.6 nm), and “νd” is the Abbe number of each material with respect to the d-line. is there. The “center thickness” is a distance along the optical axis from the center of the corresponding surface to the center of the next surface toward the image surface side. “Effective radius” is the radius of a circular region in the lens where the range of the luminous flux can be regulated. The “aspheric coefficient” means a coefficient Ai (i is an even number of 4 or more) in the aspheric expression of FIG. 2, which is an aspheric expression constituting the aspheric surface.

  The (d1 / d) of the imaging lens 1 configured by the aspherical formula, material, shape, etc. of each lens shown in FIG. 2 is 0.39, and (d12 / d) is 0.14.

FIG. 3 is a diagram describing specifications of the imaging lens 1 and various optical characteristics. MTF (Modulation Transfer Function) was calculated by weighting the following wavelengths.
404.66 nm = 0.13,
435.84 nm = 0.49,
486. 1327 nm = 1.57,
546.07 nm = 3.12,
587.5618 nm = 3.18,
656.2725 nm = 1.51
The object distance was 500 mm.

(Effect of the imaging lens of Embodiment 1)
FIG. 4 is a graph showing the MTF / spatial frequency characteristics of the imaging lens 1. The horizontal axis represents spatial frequency, and the vertical axis represents MTF. The imaging lens 1 according to Embodiment 1 exhibits high MTF characteristics with respect to spatial frequencies.

  FIG. 5 is a graph showing the MTF / defocus characteristics of the imaging lens 1. The horizontal axis represents the focus shift amount, and the vertical axis represents the MTF. With the imaging lens 1 according to Embodiment 1, defocus characteristics with the best image plane position are obtained.

  FIG. 6 is a graph showing astigmatism and distortion of the imaging lens 1. The left graph in FIG. 6 is a graph showing astigmatism, and the right graph is a graph showing distortion. The horizontal axis indicates the displacement of the image plane 5, and the vertical axis indicates the magnitude of astigmatism and distortion, respectively. According to the imaging lens 1 according to the present embodiment, astigmatism and distortion can be favorably corrected as shown in FIG.

  FIG. 7 is a graph showing the spherical aberration of the imaging lens 1. The horizontal axis indicates the displacement of the image plane 5, and the vertical axis indicates the magnitude of spherical aberration. According to the imaging lens 1 according to the present embodiment, it is possible to satisfactorily correct spherical aberration as shown in FIG.

  FIG. 8 is a graph showing the MTF change with respect to the axial displacement of the lens 2 provided in the imaging lens 1. The horizontal axis represents the error amount (axis deviation amount), and the vertical axis represents the MTF. The solid line graph shows the MTF change in sagittal, and the broken line graph shows the MTF change in tangential.

  FIG. 9 is a graph showing the MTF change with respect to the axial deviation between the lens 2 and the lens 3 provided in the imaging lens 1. The horizontal axis represents the error amount (axis deviation amount), and the vertical axis represents the MTF. As in FIG. 8, the solid line graph shows the sagittal MTF change, and the broken line graph shows the tangential MTF change.

(Focus adjustment-less structure camera module using the imaging lens of Embodiment 1)
FIG. 10 is a cross-sectional view showing a wire bonding type configuration of the focus adjustment-less structure camera module 15 using the imaging lens 1. The wire bonding type camera module 15 includes the imaging lens 1. The imaging lens 1 is provided with lenses 2 and 3. The camera module 15 includes a substrate 13. An electronic image sensor 12 is provided on the substrate 13. The electronic image sensor 12 and the substrate 13 are connected by wire bonding. A cover glass 11 is provided between the lens 3 and the electronic image sensor 12. A casing 14 is provided on the substrate 13 so as to cover the lenses 2 and 3, the cover glass 11, and the electronic image sensor 12. The camera module 15 configured as described above has a barrel (lens barrel) -less structure.

  11A to 11D are cross-sectional views for explaining a wafer level lens process for manufacturing the wire bonding type of the focus adjustment-less structure camera module 15. First, as shown in FIG. 11A, the lens array 2a is molded by the array-shaped mold 2k. Then, the lens array 3a is molded with another array mold. Next, as shown in FIG. 11B, the lens array 2a and the lens array 3a are bonded together. Thereafter, the lens arrays 2a and 3a are cut to form a lens unit in which the lens 3 is bonded to the lens 2 as shown in FIG. Then, as shown in FIG. 11 (d), the lens unit and the cover glass 11 are assembled in a housing (holder) 14, and the housing 14 is mounted on a substrate 13 on which the electronic image pickup device 12 is provided. To complete.

  FIG. 12 is a cross-sectional view showing a glass-on-wafer type configuration of the focus adjustment-less structure camera module 16 using the imaging lens 1. The glass-on-wafer type camera module 16 includes the imaging lens 1. The imaging lens 1 is provided with lenses 2 and 3 and an aperture stop 10. The camera module 16 includes a glass substrate 17. An electronic image sensor 12 is formed so as to cover the glass substrate 17. A cover glass 11 is provided between the electronic image sensor 12 and the lens 3. The camera module 16 configured in this manner has a holder (chassis) -less structure.

  FIGS. 13A and 13B are cross-sectional views for explaining a wafer level lens process for manufacturing a glass-on-wafer type of the focus adjustment-less structure camera module 16. First, as described above with reference to FIG. 11A, the lens arrays 2a and 3a are molded by an array mold. Then, as shown in FIG. 13A, the lens arrays 2a and 3a are bonded together, and the aperture stop array 10a is bonded onto the lens array 2a. Then, the cover glass array 11a is attached under the lens array 3a. Next, the glass substrate array 17a and the electronic image pickup device array 12a are pasted under the cover glass array 11a. Thereafter, as shown in FIG. 13B, the aperture stop array 10a, the lens arrays 2a and 3a, the cover glass array 11a, the electronic image sensor array 12a, and the glass substrate array 17a are cut to complete the camera module 16. .

  14A to 14C are cross-sectional views for explaining a conventional injection molding process for manufacturing a wire bonding type of a focus adjustment-less structure camera module. First, as shown in FIG. 14A, the lens 2 is molded by a mold 92k, and as shown in FIG. 14B, the molded lens 2 is taken out from the mold 92k, and the lens 2 is cut out. The lens 3 is created in the same manner as the lens 2. Next, as shown in FIG. 14C, the lens 3 is bonded to the lens 2 to form a lens unit, the lens unit and the cover glass 11 are assembled in a housing (holder) 14, and the electronic imaging device 12 is mounted. The housing 14 is mounted on the provided substrate 13 to complete the camera module 15.

  The wafer level lens process shown in FIG. 11 and FIG. 13 attracts attention because it is more advantageous than the injection molding process shown in FIG. 14 in the manufacturing time of the imaging module and other comprehensive findings. In carrying out the wafer level lens process, it is necessary to suppress the occurrence of plastic deformation in the lens arrays 2a and 3a due to heat. In view of this necessity, it is preferable that the lenses 2 and 3 are made of a thermosetting resin material or an ultraviolet curable resin material that is not easily deformed even when heat is applied and that is extremely excellent in heat resistance.

(Embodiment 2)
(Design specifications and optical characteristics of imaging lens according to Embodiment 2)
FIG. 15 is a diagram describing data such as an aspherical expression, material, and shape of each lens constituting the imaging lens according to Embodiment 2. The basic configuration of the imaging lens according to Embodiment 2 is the same as the configuration of the imaging lens 1 shown in FIG.

  As in FIG. 2 described in the first embodiment, “L1” in the “element” column indicates the lens 2 illustrated in FIG. 1 and “L2” indicates the lens 3. “CG” means cover glass. “Nd” in the “Material” column is the refractive index of each material constituting each lens with respect to the d-line (wavelength 587.6 nm), and “νd” is the Abbe number of each material with respect to the d-line. The “center thickness” is a distance along the optical axis from the center of the corresponding surface to the center of the next surface toward the image surface side. “Effective radius” is the radius of a circular region in the lens where the range of the luminous flux can be regulated. The “aspheric coefficient” means a coefficient Ai (i is an even number of 4 or more) in the aspheric expression of FIG. 2, which is an aspheric expression constituting the aspheric surface.

  The (d1 / d) of the imaging lens 1 configured by the aspherical formula, material, shape, etc. of each lens shown in FIG. 15 is 0.40, and (d12 / d) is 0.08.

FIG. 16 is a diagram describing specifications and various optical characteristics of the imaging lens according to the second embodiment. Similar to FIG. 3 described in the first embodiment, the MTF (modulation transfer function) is calculated by weighting the following wavelengths.
404.66 nm = 0.13,
435.84 nm = 0.49,
486. 1327 nm = 1.57,
546.07 nm = 3.12,
587.5618 nm = 3.18,
656.2725 nm = 1.51
The object distance was 500 mm.

  FIG. 17 is a diagram showing a layout of the imaging lens according to the second embodiment, and shows a path of light that forms an image on the image plane 5 through the lens 2, the lens 3, and the cover glass 11. Similarly to the imaging lens of the first embodiment shown in FIG. 1, the imaging lens according to the second embodiment also has a lens 2 having a convex surface on the subject side and a lens 3 arranged on the image plane 5 side of the lens 2. The lens 3 has a surface directed toward the subject side, and this surface has a convex central portion and a peripheral portion formed in a concave shape around the central portion. .

(Effect of the imaging lens of Embodiment 2)
FIG. 18 is a graph showing the MTF / spatial frequency characteristics of the imaging lens according to the second embodiment. The horizontal axis represents spatial frequency, and the vertical axis represents MTF. The imaging lens according to Embodiment 2 exhibits high MTF characteristics with respect to spatial frequencies.

  FIG. 19 is a graph showing the MTF / defocus characteristics of the imaging lens according to the second embodiment. The horizontal axis represents the focus shift amount, and the vertical axis represents the MTF. With the imaging lens according to Embodiment 2, defocus characteristics with the best image plane position are obtained.

(Embodiment 3)
(Design specifications and optical characteristics of imaging lens according to Embodiment 3)
FIG. 20 is a diagram describing data such as an aspherical expression, a material, and a shape of each lens constituting the imaging lens according to Embodiment 3. The basic configuration of the imaging lens according to Embodiment 3 is the same as the configuration of the imaging lens 1 shown in FIG.

  As in FIG. 2 described in the first embodiment, “L1” in the “element” column indicates the lens 2 illustrated in FIG. 1 and “L2” indicates the lens 3. “CG” means cover glass. “Nd” in the “Material” column is the refractive index of each material constituting each lens with respect to the d-line (wavelength 587.6 nm), and “νd” is the Abbe number of each material with respect to the d-line. The “center thickness” is a distance along the optical axis from the center of the corresponding surface to the center of the next surface toward the image surface side. “Effective radius” is the radius of a circular region in the lens where the range of the luminous flux can be regulated. The “aspheric coefficient” means a coefficient Ai (i is an even number of 4 or more) in the aspheric expression of FIG. 2, which is an aspheric expression constituting the aspheric surface.

  The (d1 / d) of the imaging lens 1 configured by the aspherical formula, material, shape, and the like of each lens shown in FIG. 20 is 0.40, and (d12 / d) is 0.08.

FIG. 21 is a diagram describing specifications and various optical characteristics of each lens constituting the imaging lens according to Embodiment 3. Similar to FIG. 3 described in the first embodiment, the MTF (modulation transfer function) is calculated by weighting the following wavelengths.
404.66 nm = 0.13,
435.84 nm = 0.49,
486. 1327 nm = 1.57,
546.07 nm = 3.12,
587.5618 nm = 3.18,
656.2725 nm = 1.51
The object distance was 500 mm.

  FIG. 22 is a diagram schematically illustrating a layout of the imaging lens according to the third embodiment. The path of light that forms an image on the image plane 5 through the lens 2, the lens 3, and the cover glass 11 is shown. Similarly to the imaging lens according to the first embodiment shown in FIG. 1, the imaging lens according to the third embodiment also includes a lens 2 having a convex surface formed on the subject side and a lens 3 disposed on the image plane 5 side of the lens 2. The lens 3 has a surface directed toward the subject side, and this surface has a convex central portion and a peripheral portion formed in a concave shape around the central portion. .

(Effect of the imaging lens of Embodiment 3)
FIG. 23 is a graph showing MTF / spatial frequency characteristics of the imaging lens according to Embodiment 3. The horizontal axis represents spatial frequency, and the vertical axis represents MTF. The imaging lens according to Embodiment 3 exhibits high MTF characteristics with respect to spatial frequencies.

  FIG. 24 is a graph showing the MTF / defocus characteristics of the imaging lens according to the third embodiment. The horizontal axis represents the focus shift amount, and the vertical axis represents the MTF. With the imaging lens according to Embodiment 3, defocus characteristics with the best image plane position are obtained.

  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.

  The present invention is applied to an imaging lens, a camera module, and a portable information device including a first lens having a convex surface on the subject side and a second lens disposed on the image plane side of the first lens. In particular, the present invention can be applied to an imaging lens intended to be mounted on a digital camera using a solid-state imaging device mounted on a portable terminal.

1 imaging lens 2 lens (first lens)
3 Lens (second lens)
4 Subject 5 Image surface 6 Convex surface 7 Surface 8 Center portion 9 Peripheral portion 10 Aperture stop 11 Cover glass 12 Electronic imaging device 13 Substrate 14 Housing frame d1 Center thickness d12 Distance d Optical total length 2k Array-shaped mold 2a, 3a Lens array 10a Aperture Aperture array 11a Cover glass array 12a Electronic imaging device array 13a Substrate array 92k Mold

Claims (14)

The first lens and the second lens are arranged in this order from the subject side to the image plane side,
The first lens has a convex surface on the subject side and a concave surface on the image surface side ,
Before Stories second lens, and a image surface side surface directed to the image plane side and the object side surface directed to the object side, the object side surface, and the subject side central portion of the convex shape, the A subject-side peripheral portion formed in a concave shape around the subject-side central portion, and the image side surface protrudes around the concave image-side central portion and the image-side central portion. An imaging lens having an image plane side periphery formed in a shape ,
d1: center thickness of the first lens,
d12: an interval between the first lens and the second lens,
d: When the optical total length is assumed,
0.35 <(d1 / d) <0.5,
0.12 <(d12 / d) <0.3,
An imaging lens characterized by satisfying the following relationship: The imaging lens according to claim 1 , wherein an Abbe number of a material of the first lens and the second lens is larger than 40. The imaging lens according to claim 1 , wherein the F-number is less than 3. The imaging lens according to claim 1 manufactured by a wafer level lens process. The imaging lens according to claim 1 , wherein an aperture stop is provided on a subject side of the first lens. An imaging lens according to claim 1,
Camera module characterized by comprising an electronic imaging device for receiving light representing an image to be thus formed on the imaging lens. The camera module according to claim 6, wherein the electronic image sensor is a CMOS image sensor or a CCD image sensor having a pixel size of 2.5 μm or less. The camera module according to claim 7, wherein the number of pixels of the CMOS image sensor or the CCD image sensor is 300,000 pixels or more. The camera module according to claim 6, wherein a distance between the electronic image sensor and the cover glass is 0.195 mm or more. The camera module according to claim 6, having a focus adjustment-less structure. The camera module according to claim 6, wherein the first and second lenses of the imaging lens are made of a heat-resistant material. The camera module according to claim 6, having a barrelless structure. The camera module according to claim 6, which has a holderless structure. An imaging lens according to claim 1,
An electronic image pickup element for receiving light representing an image to be thus formed on the imaging lens,
A portable information device comprising a memory for storing an image picked up by the electronic image pickup device.

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