JP2004199092A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which can be made small-sized and light-weight and can have manufacturability improved while maintaining optical performance. <P>SOLUTION: A first lens 2 being a positive-power meniscus lens having the convex turned to the object side, a stop 3, and a second lens 4 being a meniscus lens having the convex turned to the image surface side are arranged in order from the object side, and they satisfy conditional formulas 1.25×fl≥L≥0.8×fl, 1.26×fl≥f<SB>1</SB>≥0.85×fl, 0.8×d<SB>1</SB>≥d<SB>2</SB>≥0.35×d<SB>1</SB>, L≤6.25mm, d<SB>1</SB>≥0.225×fl, and d<SB>3</SB>≥0.242×fl, wherein L: overall length of the lens system, fl: focal length of the entire lens system, f<SB>1</SB>: focal length of the first lens 2, d<SB>1</SB>: center thickness of the first lens, d<SB>2</SB>: space between the first and second lenses, and d<SB>3</SB>: center thickness of the second lens. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an imaging lens, and in particular, forms an image of an object such as a landscape or a person on an imaging surface of a solid-state imaging device such as a CCD or a CMOS mounted on a portable computer, a videophone, a mobile phone, or the like. TECHNICAL FIELD The present invention relates to an imaging lens having a two-lens configuration made of a resin, which is used for an imaging device that is capable of reducing size and weight and improving productivity.

  In recent years, for example, there has been a remarkable increase in demand for cameras using solid-state imaging devices such as CCDs and CMOSs for mounting on mobile phones, portable computers, video phones, and the like. Since such a camera needs to be mounted in a limited installation space, it is desired that the camera be small and lightweight.

  Therefore, the imaging lens used for such a camera is also required to be small and lightweight, and such an imaging lens has conventionally been a single-lens lens using one lens. A system is used.

  Such a single-lens lens system can sufficiently cope with application to a solid-state imaging device having a resolution of about 110,000 pixels called CIF, but recently, about 300,000 called VGA is used. The use of a solid-state imaging device having a high resolution of about a pixel has been studied, and in order to sufficiently exhibit the resolution capability of such a high-resolution solid-state imaging device, a conventional single-lens lens system has been proposed. There is a problem that cannot be dealt with.

  Therefore, conventionally, various lens systems having a two-lens configuration or a three-lens configuration having excellent optical performance as compared with a single-lens configuration lens system have been proposed.

  In this case, in the three-lens lens system, it is possible to effectively correct each aberration that leads to a decrease in optical performance, so that extremely high optical performance can be obtained. However, since the number of parts is large, it is difficult to reduce the size and weight, and there is a problem that high accuracy is required for each component and the manufacturing cost is increased.

On the other hand, a two-lens lens system cannot obtain optical performance as high as a three-lens lens system, but can obtain higher optical performance than a one-lens lens system, and is small and high in size. It can be said that the lens system is suitable for a high-resolution solid-state imaging device.
As such a two-lens lens system, a number of lens systems called a retrofocus type in which a negative lens and a positive lens are combined have been conventionally proposed. However, in such a retrofocus type lens system, it is possible to reduce the cost by reducing the number of components, but since the back focus distance is long, it is possible to reduce the size and weight as much as a single lens system. In view of its configuration, it is virtually impossible.

  As another two-lens lens system, there is a lens system called a telephoto type in which a positive lens and a negative lens are combined. However, such a telephoto type lens system was originally developed for silver halide photography, and has a short back focus distance and also has a problem of telecentricity, so that it is directly used as an imaging lens for a solid-state imaging device. It is difficult to apply.

  Conventionally, a two-lens lens system combining two positive lenses has also been proposed (for example, see Patent Documents 1 to 5).

JP-A-7-181379 JP-A-7-287164 JP-A-10-206725 JP 2000-72079 A Japanese Patent No. 3313317

  However, since the imaging lenses according to Patent Literatures 1 to 3 are all developed as optical systems for silver halide photography or as copiers and facsimile machines, the focal lengths are extremely long, 20 mm or more, and The lens system has an extremely dark Fno of 4.0 or more, and has a very long overall length, and cannot be directly applied to a small-sized imaging device using a solid-state imaging device mounted on a mobile phone or the like. are doing.

  Although the imaging lenses according to Patent Documents 4 and 5 are imaging lenses applicable to solid-state imaging devices, they are not suitable for miniaturization and lightening because their overall length is too long. From the viewpoint of manufacturability such as processing accuracy at the time of manufacturing and accuracy at the time of measuring a mold and a product, there is a problem that it is not good.

  In particular, recently, demands for smaller and lighter imaging lenses and improved manufacturability have been increasing. However, in the conventional imaging lenses, such demands cannot be sufficiently satisfied. .

  As another optical system, an optical system using a glass material has been proposed. However, while it is possible to use the excellent optical characteristics of the optical system of a glass material, an imaging system mounted on a mobile phone or the like is used. It cannot meet the demand for an inexpensive optical system with good manufacturability, which is required for an optical system used in an apparatus.

  In this specification, the term “good manufacturability” means good manufacturability when mass-producing an imaging lens (for example, good moldability when mass-producing an imaging lens by injection molding). In addition, it also means that processing and manufacturing of equipment used for manufacturing an imaging lens are easy (for example, processing of a mold used for injection molding is easy).

  The present invention has been made in view of the above points, and an object of the present invention is to provide an imaging lens that can be reduced in size and weight and improved in manufacturability while maintaining optical performance.

The feature of the imaging lens according to claim 1 of the present invention for achieving the above object is an imaging lens used to form an image of an object on an imaging surface of a solid-state imaging device,
In order from the object side to the image surface side, a resin-made first lens, which is a meniscus lens having a positive power with the convex surface facing the object side, a diaphragm, and a meniscus lens with the convex surface facing the image surface side. A second lens made of resin is disposed, and the following conditional expressions (1) to (6) are provided.
1.25 × fl ≧ L ≧ 0.8 × fl (1)
1.26 × fl ≧ f ₁ ≧ 0.85 × fl (2)
0.8 × d ₁ ≧ d ₂ ≧ 0.35 × d ₁ (3)
L ≦ 6.25mm (4)
d ₁ ≧ 0.225 × fl (5)
d ₃ ≧ 0.242 × fl (6)
However,
L: Overall length of the lens system (distance from the object-side surface of the first lens to the imaging surface (air-equivalent length))
fl: focal length of the entire lens system f ₁ : focal length of the first lens d ₁ : center thickness of the first lens d ₂ : distance between the first and second lenses on the optical axis d ₃ : distance of the second lens The point is that the center thickness is satisfied.

  According to the first aspect of the present invention, by satisfying each of the conditional expressions (1) and (2), the entire optical system can be reduced in size and weight, and the exit pupil and the imaging surface ( By increasing the telecentricity by maintaining the distance between the sensor and the sensor, it is possible to effectively use the light beam incident on the end of the sensor. Further, it is possible to effectively correct coma and distortion to improve optical performance, and to improve manufacturability. Further, by satisfying the conditional expression (3), it is possible to more effectively secure manufacturability and maintain high optical performance. Further, by satisfying the conditional expression (4), it is possible to further reduce the size of the entire optical system. In addition, the first and second lenses are made of resin, and the center thickness of each lens is defined (conditional expressions (5) and (6)). An inexpensive lens can be provided.

  Further, a feature of the imaging lens according to claim 2 is that the second lens is formed as a meniscus lens having positive power.

  According to the second aspect of the invention, it is possible to more effectively secure telecentricity.

  According to a third aspect of the present invention, in the imaging lens according to the first or second aspect, the stop is on an optical axis connecting an image-side surface of the first lens and an object-side surface of the second lens. Is located closer to the first lens than the midpoint of the line segment.

  According to the third aspect of the present invention, the diaphragm is set at a position higher than the midpoint of a line segment on the optical axis connecting the image-side surface of the first lens and the object-side surface of the second lens. Since it is arranged so as to be located on the side of the first lens, the distance between the exit pupil and the imaging surface (sensor) can be more reliably maintained, and a load is not applied to the shape of each lens. , Telecentricity can be ensured.

A feature of the imaging lens according to a fourth aspect is that in any one of the first to third aspects, the brightness of the optical system is defined as follows.
4.0> Fno (7)
Where Fno is the brightness of the optical system

  According to the fourth aspect of the present invention, it is possible to exhibit better optical performance in a situation where the amount of light is small, such as at night or in a dark place, required for an imaging apparatus equipped with the imaging lens according to the present invention. It becomes possible.

A feature of the imaging lens according to the fifth aspect is that, in any one of the first to fourth aspects, the diagonal angle of view is defined as follows.
2ω ≧ 50 ° (8)
However, 2ω: diagonal angle of view

  According to the fifth aspect of the present invention, it is possible to sufficiently satisfy a demand for a wide angle of view required for an imaging apparatus equipped with the imaging lens according to the present invention.

According to a sixth aspect of the present invention, in the imaging lens according to any one of the first to fifth aspects, the following conditional expression (9) is further satisfied.
fl ≦ 5.0 mm (9)
Is satisfied.

  According to the sixth aspect of the present invention, it is possible to provide a more suitable configuration for realizing a miniaturized imaging lens while maintaining a wide angle of view.

  According to the imaging lens according to the first aspect of the present invention, it is possible to realize a small-sized imaging lens excellent in manufacturability while maintaining good optical performance.

  According to the imaging lens according to the second aspect, in addition to the effects of the imaging lens according to the first aspect, a small-sized imaging device that is further excellent in optical performance and can effectively use the amount of light incident on the solid-state imaging device. An imaging lens can be realized.

  According to the imaging lens of the third aspect, in addition to the effects of the imaging lens of the first or second aspect, a small-sized imaging lens capable of effectively utilizing the amount of light incident on the solid-state imaging device is realized. Can be.

  According to the imaging lens of the fourth aspect, in addition to the effects of the imaging lens of the first to third aspects, it is possible to exhibit more excellent optical performance at night or in a dark place or the like where the amount of light is small. An imaging lens that can be realized can be realized.

  According to the imaging lens according to the fifth aspect, in addition to the effects of the imaging lens according to the first to fourth aspects, a wide-angle imaging lens capable of photographing a wider range of landscapes and a large number of people is realized. can do.

  According to the imaging lens of the sixth aspect, in addition to the effects of the imaging lens of the first to fifth aspects, it is possible to realize an imaging lens having a reduced overall length while maintaining a wider angle of view. .

  Hereinafter, an embodiment of an imaging lens according to the present invention will be described with reference to FIGS. 1 to 9.

  As shown in FIG. 1, the imaging lens 1 according to the present embodiment is a resin-made first lens having a positive power and a meniscus lens having a convex surface facing the object side in order from the object side to the image plane side. 2, a stop 3, and a second resin lens 4 serving as a meniscus lens having a convex surface facing the image surface side. Here, the lens surfaces on the object side and the image plane side of the first lens 2 and the second lens 4 are respectively referred to as a first surface and a second surface.

  A light amount limiting plate 6 is provided between the diaphragm 3 and the second lens 4. On the second surface side of the second lens 4, various filters 7 such as a cover glass, an IR cut filter and a low-pass filter, and an imaging surface 8 which is a light receiving surface of an imaging device such as a CCD or a CMOS are provided. I have. Note that the light amount limiting plate 6 and the various filters 7 can be omitted as necessary.

In the present embodiment, the first lens 2 and the second lens 4 are configured to satisfy the following conditional expressions (1) and (2).
1.25 × fl ≧ L ≧ 0.8 × fl (1)
1.26 × fl ≧ f ₁ ≧ 0.85 × fl (2)

Here, L in the expression (1) is the total length of the lens system, that is, the distance (air-equivalent length) from the first surface of the first lens 2 to the image plane (imaging plane 8). Also, fl in equations (1) and (2) Is the focal length of the entire lens system. Further, f ₁ in the equation (2) is the focal length of the first lens 2.

  Here, if the value of L exceeds the value (1.25 × fl) shown in the expression (1), the entire optical system becomes large, which is against the demand for reduction in size and weight. On the other hand, if the value of L is smaller than the value (0.8 × fl) shown in the equation (1), it becomes difficult to maintain the assembly accuracy and the like, so that the manufacturability is reduced and the desired optical characteristics are maintained. It becomes difficult. Further, it becomes difficult to secure a back focus distance for inserting various filters 7 between the second lens 4 and the imaging surface 8.

  It is more preferable that the relationship between L and fl is 1.25 × fl ≧ L ≧ 1.0 × fl.

The value of f ₁ becomes larger beyond the value (1.26 × fl) shown in equation (2), becomes too long back focus distance, as a result, size and weight reduction becomes difficult. On the other hand, when the value of f ₁ becomes smaller than the value (0.85 × fl) shown in the equation (2), various filters 7 are inserted between the second lens 4 and the imaging surface 8 as described above. It is difficult to secure a certain back focus distance. In addition, telecentricity is reduced, causing shading. In addition, it becomes difficult to precisely process the first lens 2, particularly the first surface, and the productivity is reduced.

The relationship between _{f 1} and fl is a _{1.0 × fl ≧ f 1 ≧ 0.9} × fl, and more preferably.

Therefore, according to this embodiment, by so as to satisfy the value of L the expression (1), and, so as to satisfy the values of f ₁ the expression (2), the productivity It is possible to reduce the size and weight of the entire optical system while securing the same. In addition, by maintaining the distance between the exit pupil and the imaging surface 8 (sensor) to enhance the telecentricity, it is possible to effectively use the light rays incident on the sensor end of the imaging surface 8. Further, it is possible to effectively correct coma and distortion to improve optical performance.

In addition to the above configuration, the present embodiment is configured to further satisfy the conditional expression (3).
0.8 × d ₁ ≧ d ₂ ≧ 0.35 × d ₁ (3)

Here, d ₁ in the equation (3) is the center thickness of the first lens 2, and d ₂ is the distance between the second surface of the first lens 2 and the first surface of the second lens 4.

Here, when the value of d ₂ is larger than the (3) the value (0.8 × d ₁₎ shown in the expression must be a power of the first lens 2 and the second lens 4 is increased, respectively, the As a result, manufacturing of the lenses 2 and 4 becomes difficult. Further, the height of the light beam passing through the second surface of the second lens 4 from the optical axis 5 increases, and the power of the aspherical surface increases, so that the manufacturing becomes more difficult. On the other hand, when the value of d ₂ becomes smaller than the value (0.35 × d ₁ ) shown in the equation (3), the diaphragm 3 for effectively restricting the light amount between the first lens 2 and the second lens 4. Becomes difficult, and furthermore, the value of d ₁ becomes relatively large, and it becomes difficult to secure a sufficient back focus distance.

  Therefore, when the conditional expression (3) is satisfied, it is possible to more favorably secure manufacturability and maintain high optical performance.

The relationship _{d 2} and _{d 1,} and more preferably, it is desirable that there is a _{0.5 × d 1 ≧ d 2 ≧} 0.35 × d 1.

Further, in the present embodiment, the value of L, which is the overall length of the lens system described above, is configured to satisfy the following conditional expression (4).
L ≦ 6.25mm (4)

  Here, if the value of L exceeds Expression (4), the overall length of the lens system becomes too long, the overall length of the optical system becomes large, and the size of the imaging device to which the imaging lens according to the present invention is applied is reduced. Hinders

  Therefore, in the present embodiment, by making the value of L satisfy the expression (4), it is possible to further reduce the size of the entire optical system.

  Note that the second lens 4 may be formed as a meniscus lens having positive power.

  By doing so, it is possible to more effectively secure telecentricity.

  In addition to the above configuration, the stop 3 is further moved from the midpoint of the line segment on the optical axis 5 connecting the second surface of the first lens 2 and the first surface of the second lens 4 to the first lens 2. May be arranged so as to be located on the side of. In this case, the stop 3 may be arranged at a position in contact with the second surface of the first lens 2.

  By doing so, the distance between the exit pupil and the imaging surface 8 (sensor) can be more reliably maintained, and telecentricity is ensured without imposing a load on the shape of each of the lenses 2 and 4. It becomes possible. In addition, it is possible to effectively use the amount of light incident on the imaging surface 8.

In the present embodiment, the center thickness d ₁ of the first lens 2 (5) is defined as the center thickness d ₃ of the second lens 4 (6) is defined as equation.
d ₁ ≧ 0.225 × fl (5)
d ₃ ≧ 0.242 × fl (6)

  As described above, by defining the center thickness of the first lens 2 and the second lens 4, even if the imaging lens is mounted on the small-sized imaging device according to the present invention, the lenses have a certain thickness. Thereby, manufacturability can be appropriately secured.

Further, in the present embodiment, the brightness of the optical system is defined as in the following equation (7).
4.0> Fno (7)
However, Fno in equation (7) is the brightness of the optical system.

  Here, the sensitivity of the solid-state imaging device and the fact that a camera mounted on a mobile phone or a PDA using the imaging lens 1 of the present embodiment is used at night or in a dark place or the like with a small amount of light are considered. In this case, if the brightness of the optical system exceeds the value (4.0) of the equation (7), the image on the imaging surface becomes too dark even if the strobe function is used. As a result, noise or the like may be generated, and the image may be deteriorated.

Therefore, in the present embodiment, by setting the value of Fno so as to satisfy the expression (7), it is possible to shoot a brighter and better image under a situation where the amount of light is small. In order to obtain a good image with little noise and the like without using a strobe, it is more preferable to set the brightness Fno of the optical system as follows.
2.8 ≧ Fno (7-2)

In the present embodiment, the diagonal angle of view (full angle of view) is defined as in the following equation (8).
2ω ≧ 50 ° (8)
Here, 2ω in the equation (8) is a diagonal angle of view.

  Here, the imaging lens 1 according to the present embodiment is used for a camera mounted on a mobile phone, a PDA, or the like as described above, and this type of camera captures a wide range of landscapes and a large number of people. However, if the diagonal angle of view is smaller than the value (50 °) in the expression (8), the requirement cannot be satisfied.

  Therefore, in the present embodiment, by setting the value of the diagonal angle of view to satisfy Expression (8), it is possible to sufficiently satisfy the specifications required for a camera mounted on a mobile phone, a PDA, or the like. It becomes.

Furthermore, in the present embodiment, fl, which is the value of the focal length of the entire lens system, satisfies the following conditional expression (9).
fl ≦ 5.0 mm (9)

  Thereby, it is possible to make the configuration more suitable for realizing miniaturization and widening the angle of view.

  Further, as described above, since the first lens 2 and the second lens 4 are formed of a resin material, the weight of the lenses can be reduced as compared with a glass material, and the lenses 2 and 4 can be formed by resin molding. It can be formed easily and the production efficiency can be improved. Further, by using an inexpensive material, it is possible to further reduce the manufacturing cost.

  The resin material used for molding the first lens 2 and the second lens 4 may have any composition as long as it has transparency used for molding optical components, such as acrylic, polycarbonate, and amorphous polyolefin resin. However, from the viewpoint of further improving the manufacturing efficiency and further reducing the manufacturing cost, it is desirable to unify the resin materials of both lenses 2 and 4 to the same resin material.

  Next, an embodiment of the present invention will be described with reference to FIGS.

Here, in this embodiment, fl is the focal length of the entire lens system, L is the distance from the full-length or first surface of the first lens 2 of the lens system to the imaging surface 8 (air reduced length), f ₁ is , The focal length of the first lens 2, Fno is the F number, 2ω is the diagonal angle of view (full angle of view), r Indicates the radius of curvature of the optical surface (the center radius of curvature in the case of a lens). D indicates the distance to the next optical surface. Further, nd indicates the refractive index of each optical system when irradiating d-line (yellow), and νd indicates the Abbe number of each optical system in the case of d-line.

  k, A, B, C, and D indicate each coefficient in the following equation (10). That is, the shape of the aspherical surface of the lens has a Z axis in the direction of the optical axis 5, an X axis in a direction perpendicular to the optical axis 5, the traveling direction of light is positive, and k is a conic coefficient, A, B, C, When D is an aspheric coefficient and r is a radius of curvature, it is expressed by the following equation.

^{Z (X) = r -1 X} 2 / [1+ {1- (k + 1) r -2 X 2} 1/2]
+ AX ⁴ + BX ⁶ + CX ⁸ + DX ¹⁰ (10)

<First embodiment>
FIG. 2 shows a first embodiment of the present invention. In this embodiment, similarly to the imaging lens 1 having the configuration shown in FIG. 1, an aperture 3 is provided near the second surface of the first lens 2. At the same time, a light amount limiting plate 6 is arranged between the stop 3 and the first surface of the second lens 4. Note that a cover glass 7 is disposed on the image plane side of the second lens 4 as an example of a filter.

The imaging lens 1 of the first embodiment is set under the following conditions.

Lens data

fl = 4.54 mm, Fno = 2.8, L = 5.04 mm, f ₁ = 4.37 mm, 2ω = 55 °, d ₁ = 1.2 mm, d ₂ = 0.6 mm, d ₃ = 1.1 mm

Surface number rd nd νd
(Object point)
1 (first lens first surface) 1.333 1.200 1.525 56.0
2 (first lens second surface) 2.200 0.100
3 (aperture) 0.000 0.150
4 (light limit plate) 0.000 0.350
5 (2nd lens 1st surface) -4.400 1.100 1.525 56.0
6 (2nd lens 2nd surface) -4.000 0.000
7 (1st cover glass) 0.000 0.300 1.516 64.1
8 (2nd cover glass) 0.000 1.778
(Image plane)

Surface number k A B C D
10 -7.6E-3 1.79E-5 5.5E-3 -7.0E-3
2 -1.0E + 1 1.3E-1 -7.30E-2 0 0
5 0 -2.1E-1 2.10E-1 -7.5E-1 0
6 4.6E -5.4E-2 -1.00E-2 1.5E-2 -1.3E-2

Under these conditions, L / fl = 1.11 was achieved, thereby satisfying the expression (1). _Further, f 1 _/fl=0.96 was achieved, thereby satisfying the expression (2). _Furthermore, d ₂ / d 1 = 0.5 was achieved, thereby satisfying the expression (3). _Moreover, d 1 _/fl=0.264 was achieved, thereby satisfying the expression (5). _Further, d 3 _/fl=0.242 was achieved, thereby satisfying the expression (6). It is obvious that the condition (L = 5.04 mm) of the present embodiment satisfies the expression (4) with respect to the total length L (air conversion length) of the lens system.

  FIG. 3 shows the spherical aberration, astigmatism, and distortion of the imaging lens 1 of the first embodiment.

  According to the result, each of the spherical aberration, astigmatism, and distortion was almost satisfied. It can be seen from the result that sufficient optical characteristics can be obtained.

<Second embodiment>
FIG. 4 shows a second embodiment of the present invention. In this embodiment, similarly to the imaging lens 1 having the configuration shown in FIG. 1, the stop 3 is provided near the second surface of the first lens 2. At the same time, a light amount limiting plate 6 is arranged between the stop 3 and the first surface of the second lens 4. Note that a cover glass 7 is disposed on the image plane side of the second lens 4 as an example of a filter.

The imaging lens 1 of the second embodiment is set under the following conditions.

Lens data

fl = 3.97 mm, Fno = 2.8, L = 4.64 mm, f ₁ = 3.64 mm, 2ω = 60 °, d ₁ = 1.1 mm, d ₂ = 0.4 mm, d ₃ = 1.1 mm

Surface number rd nd νd
(Object point)
1 (first lens first surface) 1.143 1.100 1.525 56.0
2 (first lens second surface) 1.905 0.100
3 (aperture) 0.000 0.150
4 (light quantity limiting plate) 0.000 0.150
5 (1st surface of 2nd lens) -3.704 1.100 1.525 56.0
6 (2nd lens 2nd surface) -3.922 0.000
7 (1st cover glass) 0.000 0.500 1.516 64.1
8 (2nd cover glass) 0.000 1.327
(Image plane)

Surface number k A B C D
10 -5.7E-3 1.8E-2 -2.8E-2 1.8E-2
2 0 8.3E-2 -1.6E-1 4.4E-1 0
5 0 -2.2E-1 2.9E-2 -9.5E-1 0
6 8.08 -2.3E-2 -2.7E-2 1.7E-2 -1.0E-2

Under such conditions, L / fl = 1.17 was achieved, thereby satisfying the expression (1). _Further, f 1 _/fl=0.92 was achieved, thereby satisfying the expression (2). _Furthermore, d ₂ / d 1 = 0.36 was achieved, thereby satisfying the expression (3). _Moreover, d 1 _/fl=0.277 was achieved, thereby satisfying the expression (5). _Further, d 3 _/fl=0.277 was achieved, thereby satisfying the expression (6). It is obvious that the condition (L = 4.64 mm) of the present embodiment satisfies the expression (4) with respect to the total length L (air conversion length) of the lens system.

  FIG. 5 shows the spherical aberration, astigmatism, and distortion of the imaging lens 1 of the SECOND EXAMPLE.

  According to the result, each of the spherical aberration, astigmatism, and distortion was almost satisfied. It can be seen from the result that sufficient optical characteristics can be obtained.

<Third embodiment>
FIG. 6 shows a third embodiment of the present invention. In this embodiment, similarly to the imaging lens 1 having the configuration shown in FIG. 1, the stop 3 is provided near the second surface of the first lens 2. At the same time, a light amount limiting plate 6 is arranged between the stop 3 and the first surface of the second lens 4. Note that a cover glass 7 is disposed on the image plane side of the second lens 4 as an example of a filter.

The imaging lens 1 of the third embodiment is set under the following conditions.

Lens data

fl = 4.01 mm, Fno = 2.8, L = 4.29 mm, f ₁ = 3.51 mm, 2ω = 61 °, d ₁ = 1.1 mm, d ₂ = 0.4 mm, d ₃ = 1.25 mm

Surface number rd nd νd
(Object point)
1 (first lens first surface) 1.124 1.100 1.525 56.0
2 (first lens second surface) 1.905 0.100
3 (aperture) 0.000 0.150
4 (light quantity limiting plate) 0.000 0.150
5 (first surface of second lens) -3.636 1.250 1.525 56.0
6 (2nd lens 2nd surface) -4.545 0.000
7 (1st cover glass) 0.000 0.500 1.516 64.1
8 (2nd cover glass) 0.000 1.198
(Image plane)

Surface number k A B C D
10 -8.3E-3 1.7E-2 -2.6E-2 1.6E-2
2 -1.7E + 1 3.5E-1 -2.3E-1 0 0
5 0 -2.3E-1 1.1E-1 -1.1 0
6 9.8 -3.0E-2 -2.4E-2 1.8E-2 -9.3E-3

Under such conditions, L / fl = 1.07 was achieved, thereby satisfying the expression (1). _Further, f 1 _/fl=0.88 was achieved, thereby satisfying the expression (2). _Furthermore, d ₂ / d 1 = 0.36 was achieved, thereby satisfying the expression (3). _Moreover, d 1 _/fl=0.274 was achieved, thereby satisfying the expression (5). _Further, d 3 _/fl=0.312 was achieved, thereby satisfying the expression (6). It is obvious that the condition (L = 4.29 mm) of the present embodiment satisfies the expression (4) with respect to the total length L (equivalent air length) of the lens system.

  FIG. 7 shows the spherical aberration, astigmatism, and distortion of the imaging lens 1 of the THIRD EXAMPLE.

  According to the result, each of the spherical aberration, astigmatism, and distortion was almost satisfied. It can be seen from the result that sufficient optical characteristics can be obtained. Also, as in the present embodiment, even if the second lens 4 is a lens having a negative power, good optical characteristics can be obtained similarly to the lenses of the other embodiments depending on the design.

<Fourth embodiment>
FIG. 8 shows a fourth embodiment of the present invention. In this embodiment, similarly to the imaging lens 1 having the configuration shown in FIG. 1, the stop 3 is provided near the second surface of the first lens 2. At the same time, a light amount limiting plate 6 is arranged between the stop 3 and the first surface of the second lens 4. Note that a cover glass 7 is disposed on the image plane side of the second lens 4 as an example of a filter.

The imaging lens 1 of the FOURTH EXAMPLE is set under the following conditions.

Lens data

fl = 2.39 mm, Fno = 2.8, L = 2.95 mm, f ₁ = 2.98 mm, 2ω = 58 °, d ₁ = 0.7 mm, d ₂ = 0.3 mm, d ₃ = 0.7 mm

Surface number rd nd νd
(Object point)
1 (first lens first surface) 0.952 0.700 1.525 56.0
2 (first lens second surface) 1.818 0.050
3 (aperture) 0.000 0.150
4 (light limiter) 0.000 0.100
5 (first surface of second lens) -5.000 0.700 1.525 56.0
6 (2nd lens 2nd surface) -1.818 0.000
7 (1st cover glass) 0.000 0.700 1.516 64.1
8 (2nd cover glass) 0.000 0.788
(Image plane)

Surface number k A B C D
10 -4.5E-2 1.5E-1 -5.5E-1 2.0E-1
2 0 -1.8E-1 -7.0E-1 0 0
5 0 -6.0E-1 -8.1E-1 -1.0E + 1 0
6 3.1 -3.0E-2 -4.4E-1 7.9E-1 -1.2

Under these conditions, L / fl = 1.23 was achieved, thereby satisfying the expression (1). _Further, f 1 _/fl=1.25 was achieved, thereby satisfying the expression (2). _Furthermore, d ₂ / d 1 = 0.43 was achieved, thereby satisfying the expression (3). _Moreover, d 1 _/fl=0.293 was achieved, thereby satisfying the expression (5). _Further, d 3 _/fl=0.293 was achieved, thereby satisfying the expression (6). It is obvious that the condition (L = 2.95 mm) of the present embodiment satisfies the expression (4) with respect to the total length L (air conversion length) of the lens system.

  FIG. 9 shows the spherical aberration, astigmatism, and distortion of the imaging lens 1 of the FOURTH EXAMPLE.

  According to the result, each of the spherical aberration, astigmatism, and distortion was almost satisfied. It can be seen from the result that sufficient optical characteristics can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made as necessary.

1 is a schematic configuration diagram illustrating an embodiment of an imaging lens according to the present invention. 1 is a schematic configuration diagram showing a first embodiment of an imaging lens according to the present invention. Explanatory diagram showing spherical aberration, astigmatism, and distortion in the imaging lens shown in FIG. Schematic configuration diagram showing a second embodiment of the imaging lens according to the present invention Explanatory diagram showing spherical aberration, astigmatism, and distortion in the imaging lens shown in FIG. Schematic configuration diagram showing a third embodiment of the imaging lens according to the present invention. Explanatory diagram showing spherical aberration, astigmatism, and distortion in the imaging lens shown in FIG. Schematic configuration diagram showing a fourth embodiment of the imaging lens according to the present invention Explanatory diagram showing spherical aberration, astigmatism, and distortion in the imaging lens shown in FIG.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 imaging lens 2 first lens 3 aperture 4 second lens 5 optical axis 6 light quantity limiting plate 7 filter 8 imaging surface

Claims (6)

An imaging lens used to form an image of an object on an imaging surface of a solid-state imaging device,
In order from the object side to the image surface side, a resin-made first lens, which is a meniscus lens having a positive power with the convex surface facing the object side, a diaphragm, and a meniscus lens with the convex surface facing the image surface side. A second lens made of resin is disposed, and the following conditional expressions (1) to (6) are provided.
1.25 × fl ≧ L ≧ 0.8 × fl (1)
1.26 × fl ≧ f ₁ ≧ 0.85 × fl (2)
0.8 × d ₁ ≧ d ₂ ≧ 0.35 × d ₁ (3)
L ≦ 6.25mm (4)
d ₁ ≧ 0.225 × fl (5)
d ₃ ≧ 0.242 × fl (6)
However,
L: Overall length of the lens system (distance from the object-side surface of the first lens to the imaging surface (air-equivalent length))
fl: focal length of the entire lens system f ₁ : focal length of the first lens d ₁ : center thickness of the first lens d ₂ : distance between the first and second lenses on the optical axis d ₃ : distance of the second lens An imaging lens characterized by satisfying the center thickness.   The imaging lens according to claim 1, wherein the second lens is formed as a meniscus lens having a positive power.   The stop is arranged so as to be located closer to the first lens than a midpoint of a line segment on the optical axis connecting the image-side surface of the first lens and the object-side surface of the second lens. The imaging lens according to claim 1, wherein the imaging lens is provided. The imaging lens according to any one of claims 1 to 3, wherein the brightness of the optical system is defined as follows.
4.0> Fno (7)
Where Fno is the brightness of the optical system The imaging lens according to any one of claims 1 to 4, wherein a diagonal angle of view is defined as follows.
2ω ≧ 50 ° (8)
However, 2ω: diagonal angle of view Further, the following conditional expression (9):
fl ≦ 5.0 mm (9)
The imaging lens according to any one of claims 1 to 5, wherein the following condition is satisfied.