JP3467155B2 - Imaging lens - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup lens for electronically picking up an image such as a video camera and an image pickup apparatus using the image pickup lens.

[0002]

2. Description of the Related Art In recent years, cameras for electronic imaging have become widespread, as seen in home video cameras, videophones, intercoms with cameras, and the like. The lens systems used in these cameras are required to be small and lightweight and low in cost. The lens system used for these cameras is generally composed of about 3 to 6 lenses with a fixed focal length.

Among the lens systems used in the above-mentioned camera for electronically picking up images, as a conventional example of a lens system having a fixed focal length, one having a structure as shown in FIG. 19 is known. In the system LS, a low pass filter F1 and an infrared cut filter F2 for eliminating moire are generally arranged on the image side.

Further, as a conventional example of an image pickup lens having a simple structure with the above-mentioned lens system, one using an aspherical lens as described in JP-A-4-191716 and JP-A-61-277913. The lens system described in the official gazette, which is composed of one axial GRIN lens, JP-A-60-140307, and JP-A 61-5.
As the lens system described in Japanese Patent No. 221, there is a lens system including one radial type GRIN lens.

[0005]

Of the above-mentioned conventional examples, 3
In a lens system composed of ~ 6 lenses, the number of lenses is large, and the lens frame structure for fixing the lenses is also complicated, resulting in high cost. In addition, there is a problem that the performance tends to deteriorate due to the eccentricity of each lens during processing and assembly.

The lens systems described in JP-A-4-191716, JP-A-61-277913 and the like are
Although the lens configuration is simple, correction of chromatic aberration and curvature of field is not sufficient, and optical performance cannot be said to be sufficiently good.

Further, the radial type G described in JP-A-60-140307 and JP-A-61-2221.
The one composed of one RIN lens has a large amount of astigmatism, and correction of chromatic aberration is not taken into consideration.

An object of the present invention is to provide an image pickup lens having a simple structure and excellent optical performance.

[0009]

The image pickup lens of the present invention comprises:
The radial type GRIN lens is composed of a radial type gradient index lens (GRIN lens) having a concave surface on the object side and having a positive refracting power as a whole, and a brightness diaphragm for limiting a light beam in the vicinity of the object side surface. The lens is characterized by satisfying the following conditions (1), (2) and (3). (1) -1 <φ _s1 / φ <0 (2) -2 <d · φ <0.5 (3) -0.015 <1 / V ₁ <0.015 where φ _s1 is a radial type refractive index Refractive power of the object side surface of the distribution lens, φ is the entire refractive power of the radial type gradient index distribution lens, d is the distance in the optical axis direction from the lens object surface of the aperture stop, V ₁ is the radial type GRIN lens It is a coefficient that represents the Abbe number of the medium.

According to the present invention, an imaging lens is constituted by one radial type GRIN lens having high optical ability. In this way, the imaging lens is used as a radial GRI.
The configuration is simple with one N lens, and the lens element itself can be manufactured at low cost, and the lens frame configuration for holding the lens can be simplified, and the assembling and adjustment are easy. As a result, it is possible to reduce the overall cost and size and weight, including the lens frame and assembly adjustment.
The influence of assembly error is small and good optical performance can be maintained.

In the radial type GRIN lens, the medium has a refractive index distribution in the direction perpendicular to the optical axis, and the refractive index distribution n (r) is expressed by the following equation (a). n (r) = N ₀ + N ₁ r ² + N ₂ r ⁴ + N ₃ r ⁶ + ... (a) where N ₀ is the refractive index on the optical axis and N _i (i = 1, 2, 3)
...) is a coefficient representing the refractive index distribution, and r is the distance from the optical axis in the vertical direction.

The Abbe number of the radial type GRIN lens is given by the following equations (b) and (c). _{V 0 = (N 0d -1)} / (N 0F -N 0C) (b) V i = N id / (N iF -N iC) (c) Is a coefficient, and therefore N _0d , N _0F and N _0C are d respectively.
Line, F line, C line optical axis refractive index, N _id , N _iF ,
_NiC is the 2i-th order refractive index distribution coefficient for the d-line, F-line and C-line, respectively.

The present invention focuses on the fact that slight field curvature and slight distortion are allowed in the case of an actual image pickup lens, and a single radial GRIN lens is practically acceptable as an image pickup lens. The objective is to realize a lens system in which the aberration is corrected within the range.

In the case of constructing an image pickup lens with one radial type GRIN lens, correction of field curvature, astigmatism, spherical aberration and chromatic aberration is a problem.

First, in order to satisfactorily correct the field curvature, it is necessary to correct the Petzval sum.

The Petzval sum PTZ of the radial type GRIN lens is expressed by the following equation (d). PTZ = (φ _s / N ₀ ) + (φ _m / N ₀ ² ) (d) where φ _s is the refractive power of the surface of the radial type GRIN lens,
φ _m is the refractive power of the medium of the radial type GRIN lens.

From the above expression (d), it is understood that the Petzval sum PTZ can be reduced by giving the medium of the radial type GRIN lens a positive refractive power.

According to the present invention, in an actual image pickup lens, a slight negative field curvature is left in consideration of the balance between spherical aberration and field curvature. For that purpose, it is necessary to give the surface a negative refracting power, but in consideration of the correction of off-axis aberrations, especially astigmatism, the refracting power required for the surface is given mainly to the object side surface. .

Therefore, the imaging lens of the present invention satisfies the above condition (1). As a result, the Petzval sum is made appropriately small to maintain a good image surface and balance with other aberrations.

When the lower limit of -1 of the condition (1) is exceeded, the Petzval sum becomes positive and large, and when the upper limit of 0 is exceeded, the Petzval sum becomes negative and it becomes difficult to maintain balance with other aberrations. .

The image pickup lens of the present invention has the radial GRIN as described above in order to satisfactorily correct astigmatism.
An aperture stop is arranged near the object side surface of the lens so as to satisfy the above condition (2).

This condition (2) defines the position of the aperture stop, and if the stop is arranged in the range shown in this condition (2), astigmatism can be corrected well.

When the lower limit of -2 of this condition (2) is exceeded,
The meridional image surface largely falls in the negative direction, and when the upper limit of 0.5 is exceeded, the meridional image surface largely falls in the positive direction and astigmatism deteriorates.

Further, in the imaging lens of the present invention, in order to satisfactorily correct chromatic aberration, particularly chromatic aberration of magnification, it is desirable that the Abbe number V _{1 of the} medium satisfies the above condition (3).

If the conditions (1) and (2) are satisfied in a lens system having a structure such as the image pickup lens of the present invention, it is possible to reduce the chromatic aberration of magnification that occurs on each surface. Therefore, in order to reduce the chromatic aberration of magnification in the entire imaging lens of the present invention, it is sufficient to suppress the occurrence of chromatic aberration of magnification in the medium. The condition therefor is the condition (3).

If the upper limit of 0.015 to condition (3) is exceeded, chromatic aberration in the medium will be large and the chromatic aberration of magnification in the whole will be too large, which is not preferable. The lower limit of -0.01
On the other hand, when it exceeds 5, chromatic aberration of magnification is overcorrected.

Next, in the imaging lens of the present invention, it is preferable that the following condition (4) is satisfied in order to well balance the spherical aberration with the image plane. (4) −0.2 <N ₂ / φ ⁴ <0.016

By changing the 4th-order refractive index distribution coefficient N ₂ of the radial type GRIN lens, spherical aberration can be controlled without changing the power arrangement of the entire lens system, but the field curvature can be controlled. Considering the degree of the above, it is preferable that the spherical aberration is slightly underexposed because the image positions of the center and the periphery of the image forming screen can be aligned. Therefore, the condition (4) is set in consideration of the spherical aberration generated on the concave surface on the object side.

If the lower limit of -0.2 of the condition (4) is exceeded, the spherical aberration will be excessive on the under side, and if it exceeds the upper limit of 0.016, the spherical aberration will be excessive on the over side.

In the imaging lens of the present invention, it is desirable that the image side surface of the radial type GRIN lens is a flat surface or a surface having a gentle curvature in order to satisfactorily correct astigmatism. Specifically, it is desirable that the refractive power φ _s2 of this image-side surface satisfies the following condition (5). (5) −0.1 <φ _s2 / φ <0.2 Even if the upper limit of 0.2 of this condition (5) is exceeded, the lower limit of −
Even if it exceeds 0.1, the refracting power of this surface becomes strong, and it becomes difficult to satisfactorily correct astigmatism.

In the imaging lens of the present invention, if the power of the object side surface of the radial type GRIN lens is made too strong, the refractive index gradient of the medium must be increased in order to maintain the power of the entire system. Therefore, the maximum refractive index difference Δ
Since n becomes too large, it becomes difficult to manufacture the material. Considering the ease of manufacturing this material, it is preferable that the following condition (1-1) is satisfied instead of the condition (1). (1-1) -0.7 <φ _s1 / φ <0 If the lower limit of this condition (1-1) is exceeded, a radial type GRI will be obtained.
It becomes difficult to manufacture the material for the N lens.

Further, when the image pickup lens of the present invention is used in an image pickup device having a large number of pixels, it is necessary to further suppress spherical aberration. For that purpose, it is desirable that the following condition (4-1) is satisfied instead of the condition (4). (4-1) −0.1 <N ₂ / φ ⁴ <0.01

When an image pickup device having a large number of pixels is used, in order to further suppress the chromatic aberration of magnification,
It is desirable that the following condition (3-1) is satisfied instead of the condition (3). (3-1) −0.01 <1 / V ₁ <0.01

If the above-described conditions are satisfied, the distortion will be slightly negative and will be a so-called barrel distortion, but this is practically acceptable. If it is necessary to reduce this distortion, it can be electrically corrected.

The above-described image pickup lens of the present invention is composed of only a radial type GRIN lens. However, it may be composed of a concave flat lens having a concave object side surface and a radial GRIN lens having a flat object side surface.

The homogeneous lens and the radial type GR as described above
The above conditions (1) and (2) are also applicable to an imaging lens which is a cemented lens having a positive refracting power as a whole and cemented with an IN lens, and which has a brightness diaphragm for limiting a light beam in the vicinity of the most object side surface of the cemented lens. , (3) should be satisfied. The condition (1) is required not to be the object-side surface of the radial GRIN lens, but the object-side concave surface of the homogeneous lens to satisfy this condition. Therefore, when the lens system is composed of a cemented lens in which a homogeneous lens and a radial GRIN lens are cemented as described above, the refractive power of the most object side surface (concave surface of the homogeneous lens on the object side) is φ _sh1. It is desirable that the following conditions (6), (2) and (3) be satisfied. (6) -1 <φ _sh1 / φ <0 (2) -2 <d · φ <0.5 (3) -0.015 <1 / V ₁ <0.015

Of the above conditions, it is more desirable to satisfy the following condition (6-1) instead of condition (6). (6-1) −0.7 <φ _sh1 <0 Further, in addition to these conditions, it is desirable to satisfy the condition (5).

When the number of pixels of the image pickup device is large, it is desirable to satisfy the condition (3-1) instead of the condition (3) as described above.

In the case of the image pickup lens having the above structure, N ₂ / φ ⁴
It is desirable that the value of satisfies the following condition (4-2) instead of the condition (4) or the condition (4-1). _{(4-2) -0.23 <N 2 /} φ 4 <-0.01

The spherical aberration generated on the concave surface of the lens is different between the homogeneous lens and the radial type GRIN lens. Normally, a positive spherical aberration occurs on a concave surface, so it works to correct spherical aberration in the entire system to the over side. However, when the radial GRIN lens used in the present invention has a concave surface, due to the influence of the refractive index distribution, the spherical aberration generated on this concave surface has a small positive spherical aberration amount or a negative spherical aberration. Therefore, when the concave surface of the radial type GRIN lens is replaced with the concave surface of the homogeneous lens, a positive spherical aberration is generated on the surface like a spherical aberration generated on a normal concave surface, so that the spherical aberration in the entire system is positive. Will shift to the side.

Therefore, in order to balance the whole, the conditions regarding N ₂ / φ are the condition (4) and the condition (4-
It is desirable that the above condition (4-2) is satisfied instead of 1).

In the imaging lens of the present invention including the above-mentioned cemented lens, if the lower limit of the condition (4-2) is exceeded, the spherical aberration becomes excessive on the under side, and if it exceeds the upper limit, the spherical aberration becomes excessive on the over side.

The above-described image pickup lens of the present invention is used as a single radial GRIN lens or a single cemented lens in which a homogenous lens and a radial GRIN lens are cemented, but this is used as a part of a lens system composed of a plurality of lenses. It is also possible to use For example, a lens system having a configuration in which an afocal converter is arranged on the object side of the radial GRIN lens of the lens system of the present invention can be realized very easily.

The radial type GRIN lens used in the image pickup lens of the present invention is a single lens or a plurality of radial type GRIN lenses.
It is also possible to use a lens in which an IN lens is attached. However, it is preferable to use a single lens because it is easy to manufacture and inexpensive.

By providing an image pickup device in the lens system of each constitution of the above-described image pickup lens of the present invention, an image pickup apparatus of the present invention as will be described in, for example, the following embodiments can be constructed.

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the image pickup lens and the image pickup apparatus of the present invention will be described.

First, an embodiment of the image pickup lens of the present invention will be described based on each example.

As shown in FIG. 1, the first embodiment is composed of a radial GRIN lens G having a concave surface on the object side and a flat surface on the image side, and an aperture stop S on the object side surface of the lens G. It is provided. I is an image plane.

The lens data of Example 1 are as follows. f = 6, F / 2.0, maximum image height 1.8, angle of view 2ω = 35.0 °, f _B = 0.05 r ₁ = -12.5053 (aperture) d ₁ = 19.8761 n ₁ (GRIN lens) r ₂ = ∞ GRIN lens N ₀ = 1.664, N ₁ = -7.50 × 10 ^-3 , N ₂ = 0 V ₀ = 38.2, V ₁ = 655 φ _S1 / φ = -0.32, φ _S2 / φ = 0, d · φ = 0, 1 / V ₁ == 0.002 N ₂ / φ ⁴ = 0 The aberration situation when the object distance of this lens system is infinity is as shown in FIG. 7, and each aberration is well corrected.

As shown in FIG. 2, the second embodiment comprises a radial GRIN lens G having a concave surface on the object side and a flat surface on the image side. The aperture stop S is located closer to the object side than the lens object side surface. I is an image plane, and the image side of the lens is filled with resin P. The lens data of Example 2 is as shown below. f = 6, F / 1.0, maximum image height 1.5, angle of view 2ω = 28.8 °, f _B = 0.0 r ₁ = ∞ (aperture) d ₁ = 5.0 r ₂ = -300.0 d ₂ = 14.9300 n ₁ (GRIN lens) r ₃ = ∞ d ₃ = 1.0 n ₂ = 1.49216 ν ₂ = 57.5 GRIN lens N ₀ = 1.70, N ₁ = -8.2716 × 10 ^-3 , N ₂ = 1.1257 × 10 ^-5 V ₀ = 50.0, V ₁ = 1000.0 , V ₂ = 1000.0 φ _S1 / φ = -0.014, φ _S2 / φ = 0, d · φ = -0.83, 1 / V ₁ == 0.001 N ₂ / φ ⁴ = 0.015 In the case of infinity of this lens system The aberrations are as shown in FIG. 8, and each aberration is well corrected. Further, this lens system is a bright lens with an F number of 1.0.

In Example 3, as shown in FIG. 3, a radial GRIN lens G having a concave surface on the object side and a flat surface on the image side is provided, and an aperture stop S is provided inside the lens. . I is an image plane. The lens data of Example 3 is as shown below. f = 4, F / 4.0, maximum image height 1.5, angle of view 2ω = 44.9 °, f _B = 1.0 r ₁ = -4.5815 d ₁ = 1.0 n ₁ (GRIN lens) r ₂ = ∞ (aperture) d ₂ = 14.5548 n ₂ (GRIN lens) r ₃ = ∞ GRIN lens N ₀ = 1.664, N ₁ = -1.33 × 10 ^-2 , N ₂ = -8.0 × 10 ^-5 V ₀ = 38.2, V ₁ = 655, V ₂ = 655 _{φ S1 /φ=-0.58, φ S2 / φ} = 0, d · φ = 0.2, 1 / V 1 == 0.002 N 2 / φ 4 = -0.20 aberration when the object distance of the lens system of infinity Is as shown in FIG. 9, and each aberration is well corrected.

As shown in FIG. 4, the fourth embodiment comprises a radial GRIN lens G having a concave surface on the object side and a flat surface on the image side, and an aperture stop S provided on the lens object side surface. ing. Further, C is a protective glass of the image pickup element, and I is an image plane. The lens data of this Example 4 is as follows. f = 5, F / 2.8, maximum image height 1.2, angle of view 2ω = 27.9 °, f _B = 1.0 r ₁ = -50.0 (aperture) d ₁ = 8.6355 n ₁ (GRIN lens) r ₂ = ∞ d ₂ = 1.0 n ₂ = 1.51633 ν ₂ = 64.15 r ₃ = ∞ GRIN lens N ₀ = 1.55, N ₁ = -1.52383 × 10 ^-2 , N ₂ = -2.2319 × 10 ^-4 V ₀ = 55.0, V ₁ = -100.0, V ₂ = -100.0 φ _S1 / φ = -0.055, φ _S2 / φ = 0, d · φ = 0, 1 / V ₁ ==-0.01 N ₂ / φ ⁴ = -0.014 Object distance of this lens system is infinity The aberration situation in the case of is as shown in FIG. 10, and each aberration is well corrected.

The fifth embodiment, as shown in FIG. 5, is a radial GRIN lens having a concave surface on the object side and a convex surface on the image side, and an aperture stop S provided on the lens object side surface. There is. I is an image plane, and the space between the lens and the image plane I is filled with resin P. The lens data of this Example 5 is as follows. f = 4, F / 2.0, maximum image height 1.2, angle of view 2ω = 35.2 °, f _B = 0.0 r ₁ = -4.8476 (aperture) d ₁ = 15.8743 n ₁ (GRIN lens) r ₂ = -20.0 d ₂ = 1.0 n ₂ = 1.49216 ν ₂ = 57.5 r ₃ = ∞ GRIN lens N ₀ = 1.664, N ₁ = -1.33 × 10 ^-2 , N ₂ = 0 V ₀ = 38.2, V ₁ = 655 φ _{S 1} /φ=-0.55 , Φ _S2 / φ = 0.034, d · φ = 0, 1 / V ₁ == 0.002 N ₂ / φ ⁴ = 0 The aberrations of this lens system when the object distance is infinity are as shown in FIG. , Each aberration is well corrected.

In Example 6, as shown in FIG. 6, a concave flat homogenous concave plano lens L and a radial GRIN lens G on both planes are cemented in order from the object side. This embodiment has the same specifications as the first embodiment, but in the first embodiment, instead of processing the concave surface of the radial type GRIN lens G on the object side, a concave flat homogeneous lens L is formed on both sides of the radial type GRIN lens. It is attached to the lens G to obtain the same effect. The brightness stop S is provided on the side surface of the joint. I is an image plane. The lens data of this Example 6 is as follows. f = 6, F / 2.0, maximum image height 1.8, angle of view 2ω = 35.0 °, f _B = 0.05 r ₁ = -13.2508 d ₁ = 1.000 n ₁ = 1.51633 ν ₁ = 64.15 r ₂ = ∞ (aperture) d ₂ = 18.9467 n ₂ (GRIN lens) r ₃ = ∞ GRIN lens N ₀ = 1.664, N ₁ = −7.50 × 10 ⁻³ , N ₂ = −3.85 × 10 ⁻⁵ V ₀ = 38.2, V ₁ = 655, V ₂ = 655 φ _Sh1 / φ = -0.23, φ _S2 / φ = 0, d · φ = 0.2, 1 / V ₁ == 0.002 N ₂ / φ ⁴ = -0.05 When the object distance of this lens system is infinity The aberrations are as shown in FIG. 12, and each aberration is well corrected as in the first embodiment. From this, it is understood that the sixth embodiment, in which the homogeneous concave plano lens is cemented with the two-plane GRIN lens, has an operation optically equivalent to the configuration of the first embodiment.

In the sixth embodiment, as described above, the concave flat homogeneous lens and the double-sided planar radial GRIN lens are composed of cemented lenses, so that the most object side surface is the concave surface of the homogeneous lens. Is. Therefore, the condition (6) is satisfied instead of the condition (1).

Similarly, the condition regarding the fourth-order coefficient N ₂ of the radial type GRIN lens satisfies the condition (4-2). Thereby, the spherical aberration of the entire system is corrected well.

In addition to the first to fifth embodiments, the sixth embodiment can be used not only as an image pickup lens in the lens system itself, but also as a part of a lens system including a plurality of lenses (lens components). . For example, it is extremely easy to realize a lens system in which an afocal converter is arranged on the object side of the lens system of the present invention.

In each of the above embodiments, the object side surface is concave G
GR with RIN lens or homogeneous lens with concave surface on object side
It is composed of a lens in which an IN lens is cemented, and an aperture stop is provided in the vicinity of the object side surface, and the most image side surface of the lens is a flat surface or a gentle curved surface.
The image plane is located near this plane. These are very convenient when constructing a device in which a lens system is integrated with an image pickup device such as a CCD. Next, an image pickup apparatus in which the lens system and the image pickup element of these examples are integrated will be described.

FIG. 13 shows a first embodiment of a device in which the lens of the present invention and an image pickup element are integrated, and the lens system of Example 1 or 6 of the lens of the present invention is used. ing. 13A is a side view,
(B) is a top view. In these figures, 1 is a lens system, 2
Is an image pickup chip of the image pickup element, 3 is an image pickup surface of the image pickup element, 4 is a ceramic substrate of the image pickup element, 5 is a connection portion of the image pickup chip 2, and an image is obtained by removing the protective glass from the plane portion which is the final surface of the lens system. It is directly bonded to the image pickup chip of the device. In the lens system of Example 1 or Example 6, the best image for an object at a distance of about 2000 is formed just near the final lens surface. Therefore, by the device directly bonded and integrated with the imaging chip in this way,
It is possible to take an image of an object at a predetermined distance. At this time, it is possible to image an object having a considerably wide range of object distances before and after a predetermined distance depending on the depth of field. Also,
At the time of bonding, in order to avoid interference between the outer shape of the lens and the wire connection portion, the image side portion of the lens is processed into a step shape so as to be smaller than the lens outer shape as shown in FIG.

FIG. 14 shows another second embodiment of the device in which the lens of the present invention and the image pickup device are integrated, and the lens system of Example 2 or Example 5 of the lens of the present invention is shown. The lens and the image sensor are filled with resin to be integrated. In FIG. 14, 6 is a lens system, 7 is an image pickup chip of an image pickup element, 8 is an image pickup surface of the image pickup element, 9 is a ceramic substrate of the image pickup element, and a resin 10 is filled between the lens system and the image pickup chip. There is. In the lens system of Example 2 or Example 5, the best image for an object located at infinity can be formed in the resin behind the lens system by about 0.9 or about 1, respectively. Therefore, if the thickness of the resin is adjusted to 0.9 or 1, an image of an object located at infinity can be captured. At this time,
Objects at a finite distance can be imaged over a fairly wide range due to the depth of field. As in Embodiments 2 and 5, the resin between the lens system and the image pickup element is used to prevent the marginal ray from having a large angle behind the lens. Image side N.E. A. There is also an advantage that it is easy to increase. In Example 5, the lens surface (lens final surface) in contact with the resin has a curvature, but by using the resin, integration with the image pickup element is easy.

Further, when the resin is integrated, the thickness of the resin is slightly changed from the design value and the resin is attached so that the image of the object at a predetermined distance is accurately formed on the image pickup surface. Variation due to error can be adjusted.

FIG. 15 shows a third embodiment of the device in which the lens of the present invention and the image pickup element are integrated, and the lens system of Example 3 of the lens of the present invention is used.
In FIG. 15, 11 is a lens system, 12 is an image pickup chip of an image pickup device, 13 is an image pickup surface of the image pickup device, and 14 is a ceramic substrate of the image pickup device. The image pickup device is directly bonded to the ceramic substrate. In the lens system of Example 3, the best image for an object at infinity is formed at about 1 behind the final lens surface. Therefore, if the distance between the last lens surface and the image pickup surface is set to 1, an image of an object at infinity can be picked up by this integrated device. At this time, an object at a finite distance can be imaged over a fairly wide range depending on the depth of field.

FIG. 16 shows a fourth embodiment of the device in which the lens of the present invention and the image pickup element are integrated, and the lens system of Example 4 of the lens of the present invention is used. In FIG. 16, reference numeral 15 is a lens system, 16 is an image pickup chip of an image pickup element, 17 is an image pickup surface of the image pickup element, 18 is a ceramic substrate of the image pickup element, and 19 is a protective glass.
The final flat surface of the lens system is directly bonded to the protective glass of the image sensor. The adhesive surface of the protective glass 19 is not coated. The lens system of Example 4 is
The best image for an object at infinity is formed 0.9 behind the side of the protective glass image. Therefore, if the distance between the image side surface of the protective glass and the image pickup surface is set to 0.9, an image of an object at infinity can be picked up by this integrated device.
At this time, an object at a finite distance can be imaged over a fairly wide range depending on the depth of field.

As described above, the lens system of the present invention is also suitable when forming an image pickup device integrated with an image pickup device. In particular, a lens whose final surface is a flat surface can be easily integrated with the image pickup device.

At this time, in the conventional image pickup system, the low-pass filter and the infrared cut filter, which are arranged behind the lens system, cannot be arranged as in the conventional case. However, by taking the following measures, Integration of the device including such a filter can be achieved.

First, regarding the infrared cut filter,
Figure 17 how made to contain an element that absorbs infrared light of copper ions or the like in the glass material constituting the lens 21 as shown in (A), as shown in Matazu 17 (B) Lens 22
A method of applying a coating 23 that cuts infrared light to the surface of the is considered.

As for the low-pass filter, due to the aberration and diffraction blur of the lens system, the point image intensity distribution may be increased to about the pixel pitch causing the moire, or the moire may be formed on the object side surface of the lens. A method of forming a diffraction pattern for erasing is considered. Further, as shown in FIG. 18, the crystal low-pass filter 27 is connected to the radial GRIN lens 25 and the image pickup device (the image pickup chip 2).
It may be integrated by sandwiching between 6). At this time, the crystal low-pass filter is a radial GRIN
It may be attached to a lens or an image sensor.

The image pickup lens and the image pickup apparatus of the present invention described in detail above can achieve the object of the present invention not only by the ones described in each of the claims but also by the following items.

(1) An image pickup lens characterized by satisfying the following condition (5) with the lens system according to claim 1, 2 or 3 of the claims. (5) -0.1 <φ _s2 / φ <0.2

(2) In the lens system according to claim 1 or 2 of the claims or the above (1), the following condition (1-1) should be satisfied instead of the condition (1). Characteristic imaging lens. (1-1) -0.7 <φ _s1 / φ <0

(3) In the lens system described in claim 1, claim 2 or claim 3 or in claim (1) or claim 2, the following condition (3-1) is used instead of condition (3). An imaging lens characterized by satisfying: (3-1) −0.01 <1 / V ₁ <0.01

(4) In the lens system described in the item (1) or (2), the following condition (4-) is used instead of condition (4).
An imaging lens characterized by satisfying 1). (4-1) −0.1 <N ₂ / φ ⁴ <0.01

(5) In the lens system according to claim 3 of the claims, the following condition (6-1) is used instead of condition (6).
An imaging lens characterized by satisfying: (6-1) -0.7 <φ _sh1 / φ <0

(6) In the lens system described in claim 3 or (5), the following condition (4)
An image pickup lens characterized by satisfying -2). _{(4-2) -0.23 <N 2 /} φ 4 <-0.01

(7) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4),
The lens system according to item (5) or (6), wherein the image side surface of the radial GRIN lens is a flat surface.

(8) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4),
In the lens system described in item (5), (6) or (7),
An imaging lens having an infrared light cutting function inside or on the lens surface.

(9) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4),
In the lens system described in item (5), (6) or (7),
An imaging lens having a low-pass filter function inside or near the lens surface.

(10) Claims 1, 2 or 3 of the claims or (1), (2), (3), (4),
An image pickup lens according to the item (5), (6), (7), or (8), wherein a crystal low-pass filter is arranged on the image side of the lens.

(11) Claims 1, 2 or 3 or (1), (2), (3), (4), (5),
(6), (7), (8), (9) or (10) The imaging device characterized by integrating the radial GRIN lens of the lens system described in the item and the imaging device.

(12) In the image pickup apparatus described in the item (11), the outer peripheral portion near the image side surface of the radial type GRIN lens is processed to be smaller than the outer diameter of the lens system. An imaging device characterized by the above.

(13) In the image pickup apparatus described in the item (11), the radial GRIN lens and the image pickup element are filled with resin to be integrated with each other.

[0082]

The image pickup lens of the present invention is composed of one lens, is low in cost, and has sufficient optical performance. Further, the lens frame structure and the assembling adjustment are easy, the assembling lens system can be downsized and the cost can be reduced, and the assembling error is small. Further, the lens system of the present invention and the image pickup device can be integrated to form an image pickup apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view of Example 1 of the imaging lens of the present invention.

FIG. 2 is a sectional view of Example 2 of the imaging lens of the present invention.

FIG. 3 is a sectional view of Example 3 of the imaging lens of the present invention.

FIG. 4 is a sectional view of Example 4 of the imaging lens of the present invention.

5 is a sectional view of Example 5 of the imaging lens of the present invention. FIG.

FIG. 6 is a sectional view of Example 6 of the imaging lens of the present invention.

7 is an aberration curve diagram of Example 1. FIG.

8 is an aberration curve diagram of Example 2. FIG.

FIG. 9 is an aberration curve diagram of Example 3

FIG. 10 is an aberration curve diagram of Example 4.

11 is an aberration curve diagram of Example 5. FIG.

FIG. 12 is an aberration curve diagram for Example 6.

FIG. 13 is a diagram showing a first example of an image pickup apparatus in which an image pickup lens and an image pickup element are integrated.

FIG. 14 is a diagram showing a second example of an image pickup apparatus in which an image pickup lens and an image pickup element are integrated.

FIG. 15 is a diagram showing a third example of an image pickup apparatus in which an image pickup lens and an image pickup element are integrated.

FIG. 16 is a diagram showing a fourth example of an image pickup apparatus in which an image pickup lens and an image pickup element are integrated.

FIG. 17 is a diagram showing an example of an image pickup apparatus including a lens system having an infrared cut filter.

FIG. 18 is a diagram showing an example of an image pickup apparatus including a lens system having a low-pass filter.

FIG. 19 is a diagram showing a configuration of a conventional imaging lens.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (11)

(57) [Claims] 1. A radial GRIN lens having a concave surface on the object side and having a positive refracting power as a whole, and a brightness diaphragm for limiting a light beam in the vicinity of the object side surface of the radial GRIN lens. An imaging lens satisfying the following conditions (1), (2) and (3). (1) −1 <φ _S1 / φ <0 (2) −2 <d · φ <0.5 (3) −0.015 <1 / V ₁ <0.015 where φ _S1 is a radial GRIN lens Of the radial type GRIN lens, φ is the overall refractive power of the radial type GRIN lens, d is the distance from the object side surface of the radial type GRIN lens of the aperture stop in the optical axis direction, and V ₁ is the radial type GRI.
It is a coefficient representing the Abbe number of the medium of the N lens. 2. The image pickup lens according to claim 1, wherein the following condition (4) is satisfied. (4) −0.2 <N ₂ / φ ⁴ <0.016 where N ₂ is a fourth-order coefficient representing the refractive index distribution. 3. An image pickup apparatus comprising the image pickup lens according to claim 1 and an image pickup element. 4. The image pickup lens according to claim 1, further satisfying the following condition (5). (5) −0.1 <φ _s2 / φ <0.2 where φ _s2 is the refractive power of the image-side surface of the radial GRIN lens. 5. The image pickup lens according to claim 1, wherein the image side surface of the radial type GRIN lens is a flat surface. 6. The imaging lens according to claim 1, which has an infrared light cutting function inside or on the lens surface. 7. The imaging lens according to claim 1, which has a low-pass filter function inside the lens or near the lens surface. 8. The image pickup lens according to claim 1, further comprising a crystal low-pass filter arranged on the image side of the lens. 9. The image pickup apparatus according to claim 3, wherein the radial GRIN lens and the image pickup element are integrated. 10. The image pickup apparatus according to claim 9, wherein an outer peripheral portion near the image side surface of the radial type GRIN lens is processed to be smaller than an outer diameter of the lens system. 11. The image pickup device according to claim 9, wherein the radial type GRIN lens and the image pickup element are filled with resin to be integrated with each other.