WO2010071077A1

WO2010071077A1 - Imaging lens

Info

Publication number: WO2010071077A1
Application number: PCT/JP2009/070708
Authority: WO
Inventors: 隆広三觜; 来未
Original assignee: 株式会社タムロン
Priority date: 2008-12-19
Filing date: 2009-12-10
Publication date: 2010-06-24
Also published as: JP2010145828A

Abstract

Disclosed is an imaging lens which is configured with, disposed in order from the object side, a first lens (L₁₁) having a negative refractive power and having a concave face facing the object, a second lens (L₁₂) having a positive refractive power, a third lens (L₁₃) having a positive refractive power, a fourth lens (L₁₄) having a negative refractive power, and a fifth lens (L₁₅) having a positive refractive power and having a convex face facing the image plane (IMG). An aperture diaphragm (STOP) is provided between the first lens (L₁₁) and the second lens (L₁₂). In addition, the third lens (L₁₃) and the fourth lens (L₁₄) are joined together. By fulfilling a prescribed condition, the various distortions generated by each lens can be corrected satisfactorily without losing the compactness of the optical system, while suppressing the generation of ghosts, and preventing a reduction in the amount of peripheral light.

Description

Imaging lens

The present invention relates to a small and lightweight imaging lens suitable for an imaging apparatus provided with a solid-state imaging device such as a CCD (Charged Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor).

In recent years, imaging devices (on-vehicle cameras) that can be mounted on vehicles have become widespread. In particular, some in-vehicle cameras use a high dynamic range camera and incorporate a technique for recognizing people and objects in a captured image. Such a vehicle-mounted camera is required to have a highly reliable lens capable of obtaining a bright image with a small size and a simple configuration.

Several imaging lenses having a small and simple configuration that can be mounted on such an in-vehicle camera have been proposed (see, for example, Patent Document 1).

JP 2007-127954 A

In-vehicle cameras are required to have a bright lens that allows a lot of light to enter the periphery so that the person or object captured can be accurately recognized even when the image is recognized, even at the periphery of the screen. This requirement is particularly strong in order to be able to withstand night use.

However, since the imaging lens described in Patent Document 1 has an exit pupil position close to the image plane, the incident angle of light on the image plane increases, and when a solid-state imaging device such as a CCD or CMOS is used, the peripheral light amount decreases. There is a problem of inviting. Although there is a simple configuration, there is also a problem that correction of astigmatism is insufficient.

The present invention eliminates the problems caused by the prior art described above, and suppresses the generation of ghosts, prevents the decrease in the amount of peripheral light, and can satisfactorily correct various aberrations occurring in each lens. An object is to provide a high-performance imaging lens.

In order to solve the above-described problems and achieve the object, an imaging lens according to the invention of claim 1 is arranged in order from the object side, and has a first lens having negative refractive power with a concave surface facing the object side. A second lens having a positive refractive power, a third lens having a positive refractive power, a fourth lens having a negative refractive power, and a fifth lens having a positive refractive power with a convex surface facing the image side And an aperture stop is disposed between the first lens and the second lens, and the third lens and the fourth lens are joined.

According to the first aspect of the present invention, the concave surface is formed on the most object side surface of the optical system, and the convex surface is formed on the most image side surface, thereby causing light reflected on the image side at the most object side surface. And the ghost generated between the most image side surface and the image sensor can be effectively suppressed. In addition, since an aperture stop is disposed between the first lens and the second lens, the amount of light at the periphery of the optical system increases, and a bright image can be obtained up to the periphery. Further, by joining the third lens and the fourth lens, it is possible to satisfactorily correct various aberrations generated in each lens.

An imaging lens according to a second aspect of the invention is characterized in that, in the first aspect of the invention, the following conditional expression is satisfied.
(1) EXP / (L / f)> 6.0
Here, EXP is the distance from the exit pupil position to the image plane in the imaging lens, L is the distance from the first surface (most object side surface) to the image plane, and f is the focal length of the imaging lens.

According to the second aspect of the present invention, it is possible to define a good exit pupil position, and it is possible to prevent a decrease in the amount of peripheral light that occurs when the exit pupil position is too close to the image plane.

An imaging lens according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the following conditional expression is satisfied.
(2) -0.4 <(L / f) / R ₁ <-0.2
Where L is the distance from the first surface (the most object side surface) to the image plane in the imaging lens, f is the focal length of the imaging lens, and R ₁ is the radius of curvature of the first surface (the most object side surface) in the imaging lens. Indicates.

According to the third aspect of the present invention, it is possible to more effectively suppress a ghost generated due to light reflected to the image side on the most object side surface of the optical system. In addition, astigmatism can be effectively corrected.

According to the present invention, it is possible to effectively suppress the ghost generated due to the light reflected to the image side on the most object side surface of the optical system and the ghost generated between the most image side surface and the image sensor. On the other hand, there is an effect that it is possible to provide a small-sized and high-performance imaging lens that can prevent a decrease in the amount of peripheral light and can satisfactorily correct various aberrations generated in each lens.

FIG. 1 is a diagram for explaining the exit pupil position of the imaging lens according to the embodiment of the present invention. FIG. 2 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the first example. FIG. 3 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the first example. FIG. 4 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the second example. FIG. 5 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the second example. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the third example. FIG. 7 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the third example.

Hereinafter, preferred embodiments of the imaging lens according to the present invention will be described in detail.

An imaging lens according to an embodiment of the present invention includes, in order from the object side, a first lens having a negative refractive power with a concave surface facing the object side, a second lens having a positive refractive power, A third lens having a positive refractive power; a fourth lens having a negative refractive power; and a fifth lens having a positive refractive power with a convex surface facing the image side.

It is assumed that the imaging lens according to this embodiment is used for a digital video camera. Generally, the light receiving surface of an image sensor mounted on a digital video camera has a high light reflectivity of about several tens of percent, so that the reflected light causes a ghost. Therefore, special consideration is required for the configuration of the imaging lens in order to suppress the occurrence of such a ghost.

In the imaging lens according to this embodiment, as described above, the convex surface is formed on the image side surface of the fifth lens corresponding to the final surface of the imaging lens, so that the reflection on the imaging element is reflected again on the final surface. Light originating from light can be directed away from the optical axis, and the luminance of ghost light can be reduced. In addition, by forming a concave surface on the object side surface of the first lens, it is possible to reduce ghosts caused by light reflected from the outermost object side surface of the imaging lens toward the image side.

In the imaging lens according to this embodiment, since the aperture stop is disposed between the first lens and the second lens, the amount of light at the periphery of the optical system increases, and a bright image is obtained up to the periphery. It is done. Further, by joining the third lens and the fourth lens, it is possible to satisfactorily correct various aberrations generated in each lens.

In addition, digital video cameras, especially in-vehicle cameras, may be used at night, so when recognizing images, even if you are at the periphery of the screen, A bright lens that can receive a lot of light is required. That is, a lens that does not cause a decrease in the amount of peripheral light is required. In order to suppress a decrease in the amount of peripheral light, it is necessary to optimize the exit pupil position.

FIG. 1 is a diagram for explaining an exit pupil position of an imaging lens according to an embodiment of the present invention. As shown in FIG. 1, the exit pupil is located at the intersection of the principal ray (the central ray of the oblique ray bundle) of the outermost luminous flux from the outermost image side surface (final surface) of the imaging lens and the optical axis. The decrease in the amount of peripheral light occurs when the exit pupil position is too close to the image plane. In order to suppress the decrease in the peripheral light amount, it is necessary to appropriately set the distance from the image plane to the exit pupil position.

Therefore, in the imaging lens according to this embodiment, EXP is the distance from the exit pupil position of the imaging lens to the image plane, L is the distance from the first surface (most object side surface) to the image plane of the imaging lens, When the focal length of the imaging lens is f, it is preferable that the following conditional expression is satisfied.
(1) EXP / (L / f)> 6.0

Conditional expression (1) is an expression for defining an appropriate exit pupil position. By satisfying this conditional expression (1), it is possible to prevent a decrease in the amount of peripheral light.

Furthermore, in the imaging lens according to this embodiment, the distance from the first surface (the most object side surface) to the image plane in the imaging lens is L, the focal length of the imaging lens is f, and the first surface ( when the radius of curvature of the most object side surface) and R _1, it is preferable to satisfy the following condition.
(2) -0.4 <(L / f) / R ₁ <-0.2

Conditional expression (2) is an expression that defines the curvature of the first surface (most object side surface) of the imaging lens. By satisfying this conditional expression (2), it is possible to more effectively suppress a ghost generated due to light reflected to the image side on the most object side surface of the imaging lens. In addition, astigmatism can be effectively corrected.

By the way, when the upper limit is exceeded in the conditional expression (2), the curvature of the most object side surface of the imaging lens becomes large and becomes a shape close to a plane. The light reflected by the light-receiving surface of the image sensor is re-reflected even on the most object side of the imaging lens, but when the re-reflected surface is close to a flat surface, the re-reflected light follows an optical path close to the incident light, thus forming an image. A ghost image with high brightness is formed near the state. On the other hand, if the lower limit of conditional expression (1) is not reached, it will be difficult to correct astigmatism, and image deterioration will be noticeable at the periphery.

As described above, the imaging lens according to this embodiment has the above-described characteristics, so that the optical system can be compacted between the most image side surface of the imaging lens and the imaging element without impairing the compactness of the optical system. It is possible to suppress the ghost generated and the ghost generated due to the light reflected to the image side on the most object side surface of the imaging lens. In addition, the peripheral light amount can be prevented from being reduced, and various aberrations generated in each lens can be corrected well.

Hereinafter, examples of the imaging lens according to the present invention will be described.

Example 1
FIG. 2 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the first example. This imaging lens is a single focus lens, and in order from an object side (not shown), a first lens L ₁₁ having a negative refractive power with a concave surface directed toward the object side, and a second lens L ₁₂ having a positive refractive power. A third lens L ₁₃ having a positive refractive power, a fourth lens L ₁₄ having a negative refractive power, a fifth lens L ₁₅ having a positive refractive power with a convex surface facing the image plane IMG, Are arranged and configured. The object side surface of the second lens L _12, the aperture stop STOP is provided. The third lens L ₁₃ and the fourth lens L ₁₄ are cemented. Note that a light receiving surface of an image sensor such as a CCD or a CMOS is disposed on the image plane IMG. Further, if necessary, an optical element such as a cover glass or a filter can be disposed between the fifth lens L ₁₅ and the image plane IMG.

Hereinafter, various numerical data regarding the imaging lens according to Example 1 are shown.

Focal length (f) of entire imaging lens system = 7.0
F number = 2.0
Half angle of view (ω) = 24.2 °
Object distance (distance from the first surface of the imaging lens to the object) = ∞
Distance from the exit pupil position to the image plane in the imaging lens (EXP) = 13.1
Distance from first surface (most object side surface) to image surface in imaging lens (L) = 14.6
Radius of curvature (R ₁ ) of the first surface of the imaging lens = -7.000
Maximum image height = 3.0

(Numerical values related to conditional expression (1))
EXP / (L / f) = 6.25

(Numerical value related to conditional expression (2))
(L / f) / R ₁ = -0.29

r ₁ = -7.000
d ₁ = 1.00 nd ₁ = 1.58913 νd ₁ = 61.18
r ₂ = 6.037
d ₂ = 0.36
r ₃ = 24.238
d ₃ = 1.45 nd ₂ = 1.88300 νd ₂ = 40.78
r ₄ = -7.279
d ₄ = 0.10
r ₅ = 5.725
d ₅ = 2.74 nd ₃ = 1.88300 νd ₃ = 40.78
r ₆ = -10.401
d ₆ = 0.50 nd ₄ = 1.92286 νd ₄ = 20.88
r ₇ = 5.368
d ₇ = 0.80
r ₈ = -21.359
d ₈ = 1.55 nd ₅ = 1.88300 νd ₅ = 40.78
r ₉ = -5.372
d ₉ = 6.10
r ₁₀ = ∞ (image plane)

FIG. 3 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the first example. Note that symbols S and T in the astigmatism diagram represent sagittal and tangential aberrations, respectively.

(Example 2)
FIG. 4 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the second example. This imaging lens is a single focus lens, and in order from an object side (not shown), a first lens L ₂₁ having a negative refractive power with a concave surface directed toward the object side, and a second lens L ₂₂ having a positive refractive power. A third lens L ₂₃ having a positive refractive power, a fourth lens L ₂₄ having a negative refractive power, a fifth lens L ₂₅ having a positive refractive power with a convex surface facing the image plane IMG, Are arranged and configured. The object side surface of the second lens L _22, the aperture stop STOP is provided. The third lens L ₂₃ and the fourth lens L ₂₄ are cemented. Note that a light receiving surface of an image sensor such as a CCD or a CMOS is disposed on the image plane IMG. Further, if necessary, an optical element such as a cover glass or a filter can be disposed between the fifth lens L ₂₅ and the image plane IMG.

Hereinafter, various numerical data regarding the imaging lens according to Example 2 are shown.

Focal length (f) of entire imaging lens system = 7.0
F number = 2.0
Half angle of view (ω) = 24.2 °
Object distance (distance from the first surface of the imaging lens to the object) = ∞
Distance from the exit pupil position to the image plane in the imaging lens (EXP) = 12.6
Distance from first surface (most object side surface) to image surface in imaging lens (L) = 14.0
Radius of curvature (R ₁ ) of the first surface of the imaging lens = -5.368
Maximum image height = 3.0

(Numerical values related to conditional expression (1))
EXP / (L / f) = 6.31

(Numerical value related to conditional expression (2))
(L / f) / R ₁ = −0.37

r ₁ = -5.368
d ₁ = 0.50 nd ₁ = 1.51633 νd ₁ = 64.15
r ₂ = 6.014
d ₂ = 0.48
r ₃ = 24.279
d ₃ = 1.45 nd ₂ = 1.88300 νd ₂ = 40.78
r ₄ = -6.442
d ₄ = 0.10
r ₅ = 6.106
d ₅ = 2.74 nd ₃ = 1.88300 νd ₃ = 40.78
r ₆ = -7.552
d ₆ = 0.50 nd ₄ = 1.92286 νd ₄ = 20.88
r ₇ = 5.423
d ₇ = 0.80
r ₈ = -17.199
d ₈ = 1.55 nd ₅ = 1.88300 νd ₅ = 40.78
r ₉ = -5.346
d ₉ = 5.90
r ₁₀ = ∞ (image plane)

FIG. 5 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the second example. Note that symbols S and T in the astigmatism diagram represent sagittal and tangential aberrations, respectively.

(Example 3)
FIG. 6 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to the third example. This imaging lens is a single focus lens, and in order from an object side (not shown), a first lens L ₃₁ having a negative refractive power with a concave surface directed toward the object side, and a second lens L ₃₂ having a positive refractive power. A third lens L ₃₃ having a positive refractive power, a fourth lens L ₃₄ having a negative refractive power, a fifth lens L ₃₅ having a positive refractive power with a convex surface facing the image plane IMG, Are arranged and configured. An aperture stop STOP is provided on the side of the image plane IMG of the first lens L ₃₁ . The third lens L ₃₃ and the fourth lens L ₃₄ are cemented. Note that a light receiving surface of an image sensor such as a CCD or a CMOS is disposed on the image plane IMG. Further, if necessary, an optical element such as a cover glass or a filter can be disposed between the fifth lens L ₃₅ and the image plane IMG.

Hereinafter, various numerical data regarding the imaging lens according to Example 3 are shown.

Focal length (f) of entire imaging lens system = 7.0
F number = 2.0
Half angle of view (ω) = 24.2 °
Object distance (distance from the first surface of the imaging lens to the object) = ∞
Distance from the exit pupil position to the image plane in the imaging lens (EXP) = 13.8
Distance from first surface (most object side surface) to image surface in imaging lens (L) = 14.6
Curvature radius (R ₁ ) of the first surface of the imaging lens = -6.520
Maximum image height = 3.0

(Numerical values related to conditional expression (1))
EXP / (L / f) = 6.65

(Numerical value related to conditional expression (2))
(L / f) / R ₁ = -0.31

r ₁ = -6.520
d ₁ = 1.00 nd ₁ = 1.58913 νd ₁ = 61.18
r ₂ = 6.021
d ₂ = 0.36
r ₃ = 21.122
d ₃ = 1.43 nd ₂ = 1.88300 νd ₂ = 40.78
r ₄ = -6.940
d ₄ = 0.10
r ₅ = 5.973
d ₅ = 2.87 nd ₃ = 1.88300 νd ₃ = 40.78
r ₆ = -8.200
d ₆ = 0.50 nd ₄ = 1.92286 νd ₄ = 20.88
r ₇ = 5.548
d ₇ = 0.70
r ₈ = -15.467
d ₈ = 1.50 nd ₅ = 1.88300 νd ₅ = 40.78
r ₉ = -5.078
d ₉ = 5.90
r ₁₀ = ∞ (image plane)

FIG. 7 is a diagram of various aberrations at the d-line (λ = 587.6 nm) of the imaging lens according to the third example. Note that symbols S and T in the astigmatism diagram represent sagittal and tangential aberrations, respectively.

In the above numerical data, r ₁ , r ₂ ,... Are the curvature radii of the lenses and the like, d ₁ , d ₂ ,... Are the thicknesses of the lenses or their surface spacings, nd ₁ , nd ₂ ,... Is the refractive index of each lens at the d-line (λ = 587.6 nm), and νd ₁ , νd ₂ ,... Are the Abbe numbers of each lens at the d-line (λ = 587.6 nm). Show.

As described above, according to the imaging lens of each of the above embodiments, by satisfying the conditional expression, it occurs between the most image side surface of the imaging lens and the imaging element without impairing the compactness of the optical system. And the ghost generated due to the light reflected to the image side on the most object side surface of the imaging lens can be suppressed. In addition, the peripheral light amount can be prevented from being reduced, and various aberrations generated in each lens can be corrected well.

As described above, the imaging lens of the present invention is useful for a digital video camera equipped with a solid-state imaging device, and particularly, it is required to accurately recognize a person or an object captured even at the periphery of the screen. It is most suitable for in-vehicle cameras.

L ₁₁ , L ₂₁ , L ₃₁ 1st lens L ₁₂ , L ₂₂ , L ₃₂ 2nd lens L ₁₃ , L ₂₃ , L ₃₃ 3rd lens L ₁₄ , L ₂₄ , L ₃₄ 4th lens L ₁₅ , L ₂₅ , L ₃₅ 5th lens STOP Aperture IMG Image surface

Claims

A first lens having a negative refractive power and a second lens having a positive refractive power, a third lens having a positive refractive power, arranged in order from the object side, and negative A fourth lens having a refractive power of 5 and a fifth lens having a positive refractive power with a convex surface facing the image side,
An aperture stop is disposed between the first lens and the second lens;
An imaging lens, wherein the third lens and the fourth lens are cemented.
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
(1) EXP / (L / f)> 6.0
Here, EXP is the distance from the exit pupil position to the image plane in the imaging lens, L is the distance from the first surface (most object side surface) to the image plane, and f is the focal length of the imaging lens.
The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
(2) -0.4 <(L / f) / R 1 <-0.2
Where L is the distance from the first surface (the most object side surface) to the image plane in the imaging lens, f is the focal length of the imaging lens, and R 1 is the radius of curvature of the first surface (the most object side surface) in the imaging lens. Indicates.