WO2004107008A1

WO2004107008A1 - Imaging lens and image pickup device using the same

Info

Publication number: WO2004107008A1
Application number: PCT/JP2004/006648
Authority: WO
Inventors: Junichi Nio
Original assignee: Seiko Precision Inc.
Priority date: 2003-05-30
Filing date: 2004-05-18
Publication date: 2004-12-09
Also published as: JP2004361440A; TW200426390A; TWI235845B

Abstract

An imaging lens consists of: a first lens (L1) of biconvex shape having positive power and having both convex surfaces which are aspheric surfaces; and a second lens (L2) of meniscus shape having a concave surface opposing to an object, having negative power, and having both surfaces which are aspheric surfaces. The first lens and the second lens are arranged in this order from the object side and the ratio of the lens back focus (bf) against the focal distance (f) of the entire lens system is regulated to a range from 0.6 to 0.8. Thus, it is possible to obtain sufficient back focus and reduce the lens optical length. Accordingly, it is possible to provide a compact imaging lens having a high performance.

Description

Specification

Shooting lens and imaging apparatus using the same

Technical field

[0001] The present invention relates to an extremely compact and high-performance photographing lens and an imaging device mainly applied to a mobile phone, a modular camera for a mobile phone, and the like provided with a CCD or CMOS type solid-state imaging device.

Background art

In a module camera provided with a solid-state imaging device such as a CCD, a space for disposing an optical member such as a low pass filter or a cover glass is secured between the imaging lens (or imaging lens) and the imaging device. In order to achieve this, a constant back focus (the distance between the lens final surface and the imaging surface) is required.

In addition, a camera module incorporated in a mobile phone or the like needs to be designed compactly by extremely shortening the optical length of the photographing lens. Furthermore, with the increase in the number of pixels of solid-state imaging devices, there is also a demand for high resolution of photographing lenses.

[0004] In order to satisfy such a requirement, a high resolution lens which is compact and has various aberrations corrected while having a photographing lens made up of a plurality of lenses has been developed. For example, Patent Document 1 discloses a photographing lens of this type.

Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-75719

Disclosure of the invention

Problem that invention tries to solve

However, the photographing lens disclosed in Patent Document 1 has the following problems. The imaging lens of Patent Document 1 is a lens in which a positive biconvex lens with an aspheric surface and a convex convex surface facing the image plane are disposed in order from the object side, with a positive meniscus lens having both aspheric surfaces. In the configuration, the back focus (the distance from the surface on the image side of the positive meniscus lens to the image forming surface) is too short, and the lens optical length (the distance from the surface of the aperture stop to the surface on the image side of the positive meniscus lens + back focus) Is too long to be suitable for incorporation in thin products such as mobile phones. That is, when the back focus is short, the optical This is because it is difficult to miniaturize if the lens optical length which makes it difficult to interpose an optical member such as a filter is long.

Therefore, the present invention is intended to solve the problems of the above-described conventional photographing lens, and to provide a high-performance photographing lens having a sufficient back focus and a short lens optical length, which is outside the scope of the present invention.

Another object of the present invention is to provide a compact image pickup apparatus provided with such a photographing lens.

Means to solve the problem

The photographing lens according to the present invention has a biconvex positive power and a biconvex aspheric first lens, and a meniscus negative power having a concave surface facing the object side and both surfaces non-convex. It has a second lens which is a spherical surface, and the first and second lenses are arranged in order from the object side, and satisfy the conditional expressions (1) and (2) described below.

[0010] [Number 1]-group ^{d 3} ■ ■ ■

[0011] [Number 2]

0. 6 <0. 8 ■ ■ ■ (2) where f is the focal length of the whole lens system, bf is the back focus (the distance from the image side surface of the second lens to the image forming surface), r is the Radius of paraxial curvature of the surface on the object side of the two lenses, r is the second lens

The paraxial radius of curvature of the surface on the image side of 3 4 z, d is the core thickness of the second lens on the optical axis, n is the second lens

3 3

Indicates the refractive index of d-line.

Conditional expression (1) defines that the second lens is a concave lens (negative lens). Condition (2) is to set the ratio of the back focus (bf) to the focal length (f) of the whole lens system within the range of 0.6 to 0.8, and thereby obtaining a sufficient back focus. At the same time, the lens optical length is shortened. That is, when the ratio is smaller than 0.6, the back focus becomes too small, and it becomes difficult to interpose an optical filter or the like between the second lens and the imaging surface. On the other hand, If the ratio is greater than 0.8, the lens optical length becomes too large, making it difficult to apply to a small camera such as a mobile phone or a thin camera.

The imaging lens of the present invention preferably has an aperture stop on the object side of the first lens, and satisfies the following conditional expressions (3) and (4).

[0014] [Number 3]

1. 9 <<2.5 ■ ■ ■ (3)

Φ

[0015] [Number 4]

However, Φ is the combined refractive power of the entire lens system, Φ is the refracting power of the surface on the image side of the first lens, and 開 is open

2

The distance from the object-side surface of the aperture stop to the image-side surface of the second lens is shown.

Condition (3) is obtained by combining the combined refractive power Φ of the entire lens system and the refractive power 面面 of the surface of the first lens on the image side.

The ratio to 2 shall be in the range of 1.9 to 2.5. If the ratio is less than 1.9, the refracting power of the surface on the image side of the first lens becomes too weak, as a result, the focal length becomes long, making it suitable for miniaturization. On the other hand, if the ratio is 2.5 or more, the curvature of the surface on the image side of the first lens becomes too tight, and it becomes difficult to mold the lens.

Conditional expression (4) sets the ratio of the lens optical length (T + bf) to the focal length (f) of the entire lens system in the range of 1.2 to 1.8. If the ratio is less than 1.2, the power of the first lens becomes too small, and it becomes difficult to correct the aberration. On the other hand, if the ratio is 1.8 or more, the overall length becomes long, which makes it unsuitable for miniaturization. As described above, by setting the lens optical length (T + bf) to the size of 1.2 to 1.8 of the focal distance (f) of the entire lens system, it is compact and the number of pixels of the imaging device is increased. It is possible to obtain a high-performance photographing lens corresponding to

An image pickup apparatus according to the present invention has a photographing lens having the above-described features, and an image pickup element for picking up an image formed by the photographing lens. As the imaging device, for example, a solid-state imaging device such as a CCD is used. Since such an imaging device has a compact configuration, it can be used for a miniaturized camera or a thin camera. Preferably, an optical filter such as an IR (infrared) cut filter or a low pass filter is disposed between the photographing lens and the imaging device. By doing this, the imaging performance is improved.

Effect of the invention

According to the imaging lens and the imaging device of the present invention, since the first biconvex lens and the second meniscus lens are configured to satisfy the conditional expressions (1) and (2), a sufficient back focus can be obtained. It is possible to provide an imaging lens and an imaging device with high cost performance, as well as extremely compact high-performance imaging performance with a short chip and optical length.

Brief description of the drawings

FIG. 1 is a view showing the configuration of a taking lens according to an example of the present invention and showing the configuration of the taking lens of Example 1.

FIG. 2 is a view showing a configuration of a photographing lens of Embodiment 2.

FIG. 3 is a view showing the configuration of a photographing lens of Example 3;

FIG. 4 is a view showing the configuration of a photographing lens of Example 4;

FIG. 5 is a view showing a configuration of a photographing lens of Example 5.

FIG. 6 is a diagram showing lens data of Example 1.

FIG. 7 is a view showing spherical aberration according to Example 1.

FIG. 8 is a diagram showing astigmatism according to Example 1.

FIG. 9 is a diagram showing distortion according to Example 1.

FIG. 10 shows lens data of the second embodiment.

FIG. 11 is a view showing spherical aberration according to Example 2.

FIG. 12 is a diagram showing astigmatism according to Example 2.

FIG. 13 is a diagram showing distortion according to Example 2.

FIG. 14 is a diagram showing lens data of Example 3.

FIG. 15 is a view showing spherical aberration according to Example 3.

FIG. 16 is a diagram showing astigmatism according to Example 3.

FIG. 17 is a diagram showing distortion according to Example 3.

FIG. 18 is a diagram showing lens data of Example 4.

FIG. 19 shows spherical aberration according to Example 4.

FIG. 20 is a diagram showing astigmatism according to Example 4. FIG. 21 is a diagram showing distortion according to Example 4.

FIG. 22 shows lens data of the fifth embodiment.

FIG. 23 shows spherical aberration according to Example 5.

FIG. 24 is a diagram showing astigmatism according to Example 5.

FIG. 25 is a diagram showing distortion according to Example 5.

FIG. 26 is a view comparing lens performances of the photographing lens of each example according to the present invention and the photographing lens of each example of Patent Document 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will now be described with reference to the attached drawings.

As shown in FIG. 1, taking the left side of the drawing as the object side, the taking lens 1 has an aperture stop S and a biconvex positive power along the optical axis 順 in order from the object side. And a second lens L2 having a negative power in the form of a meniscus with its concave surface facing the object side. The lens surfaces of the first and second lenses L1 and L2 are all aspheric. As described above, the shooting lens 1 is a lens configured with two lenses and two lenses.

In the figure, r is the radius of curvature near the optical axis of the object-side surface of the first lens, and r is the first lens.

A radius of curvature near the optical axis of the surface at the side of the 1 2 z image, r is near the optical axis of the surface at the object side of the second lens

3

The radius of curvature _r represents the radius of curvature near the optical axis of the image-side surface of the second lens. dO is the aperture stop

Four

Distance between the lens and the first lens L1, dl is the core thickness on the optical axis of the first lens, d2 is the distance on the optical axis between the first lens and the second lens, d3 is the core on the optical axis of the second lens The thickness d4 indicates the distance between the second lens and the plane parallel glass (optical filter) 10, d5 indicates the thickness of the plane parallel glass, and d6 indicates the distance between the plane parallel glass 10 and the cover glass 20. These distances are lengths along the optical axis O. f is the focal length of the whole lens system, bf is the back focus (the distance from the surface on the image side of the second lens to the imaging surface M), T is the surface on the object side of the aperture stop S to the image side of the second lens Indicates the distance on the optical axis to the surface.

The parallel flat glass 10 disposed between the second lens L2 and the imaging surface M on the image side is preferably an optical filter such as a low pass filter or an IR cut filter required for a solid-state imaging device. Furthermore, a flat plate of the cover glass 20 is disposed between the plane-parallel glass 10 and the imaging surface M. The cover glass 20 is for protecting the surface of a solid-state imaging device such as a CCD. Used.

In addition, in the imaging lens 1, the aperture stop S is disposed on the object side of the first lens L1 in order to make the incident angle of incident light to the imaging device smaller and to facilitate the assembly. ing. With such a configuration, by satisfying the following conditional expressions (1) and (2), it is possible to provide a photographing lens with excellent imaging performance, which is extremely compact and has a sufficient back focus. S can.

[0026] [Number 5] — ^{dd 3} ■ ■ ■

[0027] [Number 6]

0 6 ^ ^! 0 0. 8 ■ ■ ■ (2)

The conditional expression (1) defines the composite refractive power of the second lens L2, and the paraxial composite refractive power has negative refractive power. Second lens L2 radius of curvature r, r, second lens core thickness d2 and its

3 4

When the correlation with the refractive index n3 satisfies the conditional expression (1), the balance of the positive refractive power of the first lens L1 can be properly maintained, and the total length can be shortened.

The conditional expression (2) defines the range of the lens back focus (bf) with respect to the entire system focal length f, and when the lower limit is exceeded, the back focus is too short, and interference with the plane parallel glass 10 or lens back The adjustment becomes difficult and the shading of the ambient light becomes worse. If the upper limit is exceeded, the overall length becomes long, and it becomes impossible to obtain the desired compact and thin shooting lens.

It is preferable that the photographing lens 1 further satisfy the conditional expressions (3) and (4).

[0031] [Number 7]

1. 9 Part 2.5 5 ■ ■ ■ (3)

Φ

[0032] [Number 8]

1. 2 <1. 8 ■ ■ ■ (4) Where Φ is the combined refractive power of the entire lens system, and Γ is the refractive power of the surface on the image side of the first lens.

2

Condition (3) further defines the refracting power of the surface r on the image side of the first lens L 1.

2

If the lower limit value is exceeded, the total length becomes long, and if the upper limit value is exceeded, the radius of curvature of the second lens L2 becomes small, lens formation becomes difficult, and correction of field curvature becomes difficult.

Conditional expression (4) defines the relative ratio of the lens optical length (T + bf) to the focal length f of the entire system in the configuration satisfying the conditional expression (3). Below the lower limit, the refractive power of the first lens L1 becomes stronger than necessary, and the balance with the second lens L2 can not be achieved, so that it is not possible to obtain good image performance. If the upper limit is exceeded, it becomes close to a retrofocus type, and the overall length becomes too long to obtain a compact taking lens.

Next, examples of the present invention will be described. In each embodiment, FNo. Is an F number, ω is a half angle of view, d is a lens surface distance, n is a refractive index of each lens to the d line (587. 6 nm) d

, V d is the Abbe number of each lens. Also, each lens surface (r, r, r, r) is aspheric.

1 2 3 4

The shape of the aspheric surface is Z axis in the direction of the optical axis (O) and X axis in the direction perpendicular to the optical axis, and the traveling direction of light is positive, the conical constant is k, the aspheric coefficient is a, When b, c and d are given, they are expressed by equation (5)

[Number 9]

(Example 1)

The photographing lens 1 according to the first embodiment has a cross-sectional configuration shown in FIG. The lens data of the imaging lens 1 is as shown in FIG. 6, and the surface numbers in Table 1 are assigned in order from the object side along the optical axis 〇. The surface number 0 (ST〇) corresponds to the aperture stop S. The surface number 1 and 2 correspond to the first lens: L1 r and r, and the surface number 3 and 4 to the second lens: L2 r and r. Face number

1 2 3 4

No. 5 is the object-side surface r of the plane-parallel glass 10, and the surface number 6 is the surface of the plane-parallel glass 10 on the image side

Five

It corresponds to r. The spacing d is the spacing on the optical axis between the faces described above (dl, d2, d3, d4, d5, d

6

6) is shown. The numbers in Table 2 indicate powers, for example, “1. 04989E— 01” is “1. 04. It is 289 X 10-. The thickness of the cover glass 20 is 0 · 4 mm.

7 to 9 show various aberrations according to Example 1. FIG. 7 shows spherical aberration, FIG. 8 shows astigmatism, and FIG. 9 shows distortion. In FIG. 7, the dashed-dotted line is the d-line, the solid line is the F-line, and the broken line is the spherical aberration for the C-line. In FIG. 8, the solid line is the aberration of the tangential image plane, and the broken line is the aberration of the sagittal image plane. The distortion shown in FIG. 9 is for the d-line. The symbol of the aberration used in these figures is the same as in Example 2-5 below.

(Example 2-5)

Cross-sectional configurations of the photographing lenses of Examples 2 to 5 are shown in FIGS. 2 to 5. The lens data of Examples 2 to 5 are shown in FIGS. 10, 14, 18 and 22, and the spherical aberration according to Example 2-5 is shown in FIGS. 11, 15, 19 and 23, respectively. The astigmatism according to Example 2-5 is shown in FIG. 12, FIG. 16, FIG. 20 and FIG. 24, respectively, and the distortion according to Example 2-5 is shown in FIG. 13, FIG. 17, FIG. 21 and FIG.

Table 1 in FIG. 26 shows the numerical values of the conditional expressions (1) to (4) described above calculated based on the lens data of the example 15 according to the present invention. Table 2 shows the numerical values of conditional expressions (1) to (4) calculated based on lens data of the respective embodiments disclosed in Patent Document 1. As is apparent from these tables, the taking lens of each Example 15 of the present invention has sufficient back focus (bf) compared to Patent Document 1, but the lens The optical length (T + bf) is made sufficiently short. For this reason, a plane-parallel glass (optical filter) 10 is interposed between the second lens L2 and the image plane M to enable high-resolution imaging, and a photographing lens and an imaging device including such a photographing lens. It can be miniaturized and can be applied to small cameras and thin cameras.

Although the preferred embodiments of the present invention have been described above in detail, the present invention is not limited to the specific embodiments, but is within the scope of the present invention as set forth in the claims. Various variants are possible.

Claims

The scope of the claims

[1] A first lens having a positive power of a biconvex shape, and the biconvex surface is aspheric,

The second lens has negative meniscus power with its concave side facing the object side, and both sides are aspheric.

With two lenses,

An imaging lens characterized in that the first and second lenses are disposed in order from an object side, and the following conditional expressions (1) and (2) are satisfied.

[Equation 10]-" ³ (^) ■ ■ ■ ("

[Number 11]

0. 6 <-<0. 8 ■ ■ ■ (2) where f is the focal length of the whole lens system, bf is the back focus (the distance from the surface on the image side of the second lens to the image forming surface), r is Radius of paraxial curvature of the surface on the object side of the second lens, r is the second lens

The paraxial radius of curvature of the surface on the image side of 3 4 z, d is the core thickness on the optical axis of the second lens, n is the second lens

3 3

Indicates the refractive index of d-line.

[2] A photographic lens characterized by having an aperture stop on the object side of the first lens and satisfying the following conditional expressions (3) and (4).

[Number 12]

1. 9 <<2.5 ■ ■ ■ (3)

[Number 13]

However, Φ is the combined refractive power of the entire lens system, 但し is the refractive power of the surface on the image side of the first lens, and Τ is open

2

An image formed by the imaging lens according to claim 1 or 2 and the imaging lens is imaged. And an imaging device.

[4] The imaging device according to claim 3, wherein an optical filter is disposed between the imaging lens and the imaging element.