JP4442184B2 - Imaging lens - Google Patents

Description

  The present invention relates to an imaging lens, and more particularly to a high-performance and compact imaging lens suitable for a digital input device (digital still camera, digital video camera, etc.) that captures a subject image with a solid-state imaging device. .

  In recent years, with the spread of personal computers and the like, digital still cameras, digital video cameras and the like (hereinafter simply referred to as “digital cameras”) that can easily capture image information into digital devices are becoming popular at the individual user level. Such digital cameras are expected to become increasingly popular as image information input devices.

  In addition, miniaturization of solid-state imaging devices such as CCDs (Charge Coupled Devices) mounted on digital cameras has progressed, and accordingly, further miniaturization of digital cameras is required. For this reason, there is a strong demand for a compact imaging lens that occupies the largest volume in a digital input device. Although the easiest way to reduce the size of the imaging lens is to reduce the size of the solid-state imaging device, it is necessary to reduce the size of the light-receiving device, which increases the difficulty of manufacturing the solid-state imaging device. The performance required for the imaging lens is also increased.

  On the other hand, if the size of the imaging lens is reduced while leaving the size of the solid-state imaging device as it is, the exit pupil position will inevitably approach the image plane. When the exit pupil position approaches the image plane, the off-axis light beam emitted from the imaging lens is obliquely incident on the image plane, so that the condensing performance of the microlens provided in front of the solid-state imaging device is sufficient This causes a problem that the brightness of the image changes extremely between the central portion of the image and the peripheral portion of the image. In order to solve this problem, if it is attempted to move the exit pupil position of the imaging lens far away, it is inevitable that the entire imaging lens is enlarged.

In addition, due to the recent competition for lower prices, there is an increasing demand for cost reduction in imaging lenses. In response to the above demand, Patent Documents 1 and 2 propose an imaging lens for a solid-state imaging device having two lenses.
JP-A-10-90597 JP 2002-296696 A

  However, the imaging lenses described in Patent Documents 1 and 2 have a weak first lens, resulting in a large overall length and lack of compactness.

  The present invention has been made in view of such a situation, and an object thereof is to provide an imaging lens for a solid-state imaging device that has good optical performance, is low-cost, and is compact.

In order to achieve the above object, an imaging lens according to a first aspect of the present invention is a two-lens imaging lens that forms an image on a solid-state imaging device, and is a positive lens with a convex surface facing the object side in order from the object side. It is composed of a meniscus first lens and a second lens having a convex surface facing the image surface side, and satisfies the following conditional expressions (1) to (3) .
0.51 <f / f1 <1.17 (1)
-0.84 <(R21 + R22) / (R21−R22) ≦ 1.11 (2)
0.15 ≦ TA / f <0.29… (3)
However,
f: focal length of the entire system,
f1: focal length of the first lens,
R21: radius of curvature of the object side surface of the second lens,
R22: radius of curvature of the image side surface of the second lens,
TA: On-axis air gap between the first lens and the second lens,
It is.

The imaging lens of the second invention is characterized in that, in the first invention, the following conditional expression (4) is satisfied.
1.19 <f / Y '<2.06 (4)
However,
f: focal length of the entire system,
Y ': Maximum image height,
It is.

An imaging lens according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, an aperture stop is further provided on the object side of the first lens.

  According to the present invention, it is possible to realize a low-cost and compact imaging lens for a solid-state imaging device having good optical performance. If the imaging lens according to the present invention is used in a digital input device such as a camera mounted on a mobile phone or a digital camera, it can contribute to high performance, high functionality, low cost, and compactness of the device.

  Hereinafter, embodiments of an imaging lens according to the present invention will be described with reference to the drawings. 1 to 3 show optical configurations of the lens configurations of the first to third embodiments, respectively. The imaging lens of each embodiment is a single-focus lens for imaging (for example, for a digital camera) that forms an optical image on a solid-state imaging device (for example, CCD). Then, in order from the object side, an aperture stop ST, a positive meniscus first lens L1 having a convex surface facing the object side, and a second lens L2 having a convex surface facing the image surface side, have a two-lens configuration. A parallel plane plate-like glass filter GF corresponding to an optical low-pass filter or the like is disposed on the image side. In each lens configuration diagram (FIGS. 1 to 3), the surface with ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side, and ri * The marked surface is an aspherical surface.

  The lens configuration of each embodiment will be described in more detail. In the first embodiment (FIG. 1), the first lens L1 is a positive lens having a meniscus shape with a convex surface facing the object side, and the second lens L2 has a meniscus shape having a convex surface facing the image surface side. It is a positive lens. In the second embodiment (FIG. 2), the first lens L1 is a positive lens having a meniscus shape with a convex surface facing the object side, and the second lens L2 is a positive lens having a biconvex shape. In the third embodiment (FIG. 3), the first lens L1 is a positive lens having a meniscus shape with a convex surface facing the object side, and the second lens L2 is a positive lens having a biconvex shape. In any of the embodiments, all the lens surfaces (r2 to r5) are aspherical surfaces.

  As in each embodiment, the first lens L1 has a positive meniscus shape with a convex surface facing the object side, so that the total lens length can be shortened. Further, since the second lens L2 has a shape with the convex surface facing the image surface side, various aberrations can be corrected satisfactorily. Therefore, an imaging lens having a two-lens configuration includes, in order from the object side, a positive meniscus first lens L1 having a convex surface facing the object side, and a second lens L2 having a convex surface facing the image surface side. By doing so, it is possible to achieve compactness and cost reduction of the lens system while realizing high optical performance and an appropriate exit pupil position. Conditions for obtaining such effects in a balanced manner will be described below. In any of the embodiments, the power arrangement (power: an amount defined by the reciprocal of the focal length) of the two-lens configuration is positive / positive, but the application of the conditions described below is applied to this power arrangement. It is not limited.

  First, conditional expressions that should be satisfied by the imaging lens of each embodiment, that is, conditional expressions that should be satisfied in the imaging lens of the type as in each embodiment will be described. However, it is not necessary to satisfy all the conditional expressions described below at the same time, and it is possible to achieve the corresponding actions and effects as long as each conditional expression is satisfied independently according to the optical configuration. Needless to say, satisfying a plurality of conditional expressions is more desirable from the viewpoint of optical performance, miniaturization, manufacturing / assembly, and the like.

It is desirable that the following conditional expression (1) is satisfied.
0.51 <f / f1 <1.17 (1)
However,
f: focal length of the entire system,
f1: focal length of the first lens,
It is.

  Conditional expression (1) prescribes a preferable condition range mainly for balancing the total length and aberration with respect to the first lens. Exceeding the lower limit of conditional expression (1) is advantageous for aberration correction, but causes an increase in the total length. On the contrary, if the upper limit of conditional expression (1) is exceeded, it will be advantageous for shortening the total length, but aberration deterioration, in particular, distortion aberration and field curvature deterioration will be significant.

It is more desirable to satisfy the following conditional expression (1a).
0.66 <f / f1 <1.17 (1a)
This conditional expression (1a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1).

It is desirable to satisfy the following conditional expression (2).
-0.84 <(R21 + R22) / (R21−R22) ≦ 1.11 … (2)
However,
R21: radius of curvature of the object side surface of the second lens,
R22: radius of curvature of the image side surface of the second lens,
It is.

  Conditional expression (2) prescribes a preferable condition range for balancing the exit pupil position and distortion mainly for the second lens. Exceeding the lower limit of the conditional expression (2) is advantageous for the exit pupil position, but the deterioration of the distortion becomes significant. Conversely, exceeding the upper limit of conditional expression (2) is advantageous for distortion, but the exit pupil position is disadvantageous. Therefore, it is not preferable as an imaging lens for a solid-state imaging device.

It is more desirable to satisfy the following conditional expression (2a).
-0.45 <(R21 + R22) / (R21−R22) ≦ 1.11 … (2a)
This conditional expression (2a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2).

It is desirable to satisfy the following conditional expression (3).
0.15 ≦ TA / f <0.29 (3)
However,
TA: On-axis air gap between the first lens and the second lens,
f: focal length of the entire system,
It is.

  Conditional expression (3) prescribes a preferable condition range for mainly balancing the total length of the imaging lens and the second lens diameter. When the lower limit of conditional expression (3) is exceeded, the diameter of the second lens is reduced, but the total length is increased. Conversely, if the upper limit of conditional expression (3) is exceeded, it will be advantageous for shortening the overall length, but aberrations will deteriorate significantly, and in particular, the second lens diameter will become larger. Will be invited. In addition, since the back focus is shortened, there arises a problem that the glass filter cannot be disposed on the image plane side.

It is more desirable to satisfy the following conditional expression (3a).
0.17 <TA / f <0.29… (3a)
This conditional expression (3a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3).

It is desirable to satisfy the following conditional expression (4).
1.19 <f / Y '<2.06 (4)
However,
f: focal length of the entire system,
Y ': Maximum image height,
It is.

  Conditional expression (4) defines a preferable condition range for balancing the total length of the imaging lens and the first lens diameter. If the lower limit of conditional expression (4) is exceeded, the diameter of the first lens will increase, leading to an increase in the radial direction of the imaging lens device and making it difficult to correct distortion. On the contrary, if the upper limit of conditional expression (4) is exceeded, the total length of the imaging lens increases, leading to an increase in the size of the imaging lens device in the optical axis direction.

It is more desirable to satisfy the following conditional expression (4a).
1.50 <f / Y '<1.70 (4a)
This conditional expression (4a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (4).

It is desirable to satisfy the following conditional expression (5).
0.69 <| f2 / f1 |… (5)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
It is.

  Conditional expression (5) defines a conditional range that is preferably satisfied with respect to the focal length ratio between the first lens and the second lens. Exceeding the lower limit of conditional expression (5) is advantageous for aberration correction, but increases the total length.

It is more desirable to satisfy the following conditional expression (5a).
2.00 <| f2 / f1 |… (5a)
Conditional expression (5a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by conditional expression (5).

  As in each embodiment, it is desirable to have an aperture stop on the object side of the first lens. By disposing the aperture stop on the object side of the first lens, the exit pupil position can be further distant. In addition to the aperture stop, a light flux restricting plate or the like for cutting unnecessary light may be arranged as necessary. In addition, by arranging prisms (for example, right-angle prisms), mirrors (for example, plane mirrors), etc. in the optical path, imaging is performed on surfaces that do not have optical power (for example, reflective surfaces, refractive surfaces, and diffractive surfaces) A bending optical system {for example, an optical system that reflects a light beam by bending the optical axis by approximately 90 ° (that is, 90 ° or substantially 90 °)} is formed by bending the optical path before, after, or in the middle of the lens. Also good. The bending position may be set as necessary, and it is possible to achieve an apparent thinness and compactness of a digital device (digital camera, etc.) on which an imaging lens is mounted by appropriately bending the optical path. .

  As in each embodiment, it is desirable that at least one surface of all the lenses is aspheric. Providing at least one aspheric surface on each of the first and second lenses has a great effect on correcting spherical aberration, coma aberration, and distortion. Moreover, it is desirable that all the lenses are plastic lenses. Constructing both the first and second lenses with plastic lenses is effective in achieving cost reduction of the imaging lens.

  The imaging lens of each embodiment is composed only of a refractive lens that deflects incident light by refraction (i.e., a lens that deflects at the interface between media having different refractive indexes). The possible lenses are not limited to this. For example, a diffractive lens that deflects incident light by diffracting action, a refractive / diffractive hybrid lens that deflects incident light by combining diffractive action and refracting action, and a refractive index distribution that deflects incident light by a refractive index distribution in the medium A mold lens or the like may be used. However, since the refractive index distribution type lens whose refractive index changes in the medium increases the cost due to its complicated manufacturing method, it is desirable to use homogeneous material lenses as the first and second lenses in the imaging lens according to the present invention. .

  The imaging lens of each embodiment is suitable for use as a small imaging lens for a digital device with an image input function (for example, a mobile phone with a camera), and by combining this with an optical low-pass filter or a solid-state imaging device, An imaging lens device that optically captures an image of a subject and outputs it as an electrical signal can be configured. The imaging lens device is a main component of a camera used for still image shooting and moving image shooting of a subject.For example, an imaging lens that forms an optical image of an object in order from the object (subject) side, and an optical An optical filter such as a low-pass filter and an infrared cut filter, and an image sensor that converts an optical image formed by the imaging lens into an electrical signal. Examples of cameras include digital cameras; video cameras; surveillance cameras; in-vehicle cameras; video phone cameras; door phone cameras; personal computers, mobile computers, mobile phones, personal digital assistants (PDAs), and their surroundings. Examples include cameras (mouse, scanner, printer, etc.) and other cameras built in or external to digital devices. Therefore, it is possible not only to configure a camera by using an imaging lens device, but also to add a camera function by mounting the imaging lens device on various devices.

  As the imaging device, for example, a solid-state imaging device such as a CCD or CMOS (Complementary Metal Oxide Semiconductor) sensor composed of a plurality of pixels is used, and an optical image formed by the imaging lens is converted into an electrical signal by the solid-state imaging device. The An optical image to be formed by the imaging lens is generated when it is converted into an electrical signal by passing through an optical low-pass filter having a predetermined cutoff frequency characteristic determined by the pixel pitch of the solid-state imaging device. The spatial frequency characteristics are adjusted so that so-called aliasing noise is minimized. The signal generated by the solid-state image sensor is subjected to predetermined digital image processing, image compression processing, etc. as necessary, and is recorded as a digital video signal in a memory (semiconductor memory, optical disk, etc.). Or is converted into an infrared signal and transmitted to another device. Note that the optical low-pass filter disposed between the final surface of the imaging lens and the solid-state imaging device is composed of the glass filter GF in each embodiment, but it depends on the digital input device used. I just need it. For example, a birefringent low-pass filter made of quartz or the like with a predetermined crystal axis direction adjusted, or a phase-type low-pass filter that achieves the required optical cutoff frequency characteristics by the diffraction effect can be applied. is there.

  As can be understood from the above description, the following configurations are included in each of the above-described embodiments and each example described later. With this configuration, it is possible to realize a compact imaging lens device with good optical performance and low cost. By applying it to cameras, digital devices, etc., its high performance, high functionality, low cost and compactness are achieved. It can contribute to the conversion.

  (U1) An imaging lens device comprising an imaging lens that forms an optical image and an imaging device that converts an optical image formed by the imaging lens into an electrical signal, wherein the imaging lens is on the object side In order from the first lens having a positive meniscus shape having a convex surface facing the object side and a second lens having a convex surface facing the image surface side, and the conditional expressions (1), (1a ), (2), (2a), (3), (3a), (4), (4a), (5), (5a) .

  (U2) The imaging lens device according to (U1), further including an aperture stop on the object side of the first lens.

  (C1) A camera comprising the imaging lens device according to (U1) or (U2) and used for at least one of still image shooting and moving image shooting of a subject.

  (C2) Digital camera; video camera; or camera as described in (C1) above, which is a personal computer, mobile computer, mobile phone, personal digital assistant, or a camera built in or externally attached to these peripheral devices .

  (D1) A digital device provided with the imaging lens device according to (U1) or (U2), to which at least one function of still image shooting and moving image shooting of a subject is added.

  (D2) The digital device according to (D1), which is a personal computer, a mobile computer, a mobile phone, a portable information terminal, or a peripheral device thereof.

  Hereinafter, the imaging lens embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 3 listed here are numerical examples corresponding to the first to third embodiments, respectively, and are lens configuration diagrams showing the first to third embodiments (FIGS. 1 to 3). 3) shows the lens configurations of the corresponding first to third embodiments.

  In the construction data of each example, ri (i = 1, 2, 3, ...) is the radius of curvature (mm) of the i-th surface counted from the object side, di (i = 1, 2, 3,. ..) indicates the i-th axis top surface distance (mm) counted from the object side, and Ni (i = 1,2,3) and νi (i = 1,2,3) are counted from the object side. The refractive index (Nd) and Abbe number (νd) for the d-line of the i-th optical element are shown. The focal length (f, mm) and F number (FNO) of the entire system are shown together with other data. Table 1 shows values corresponding to the parameters defined in each conditional expression for each example.

The surface marked with * in the radius of curvature ri is an aspherical surface (aspherical refractive optical surface, a surface having a refractive action equivalent to an aspherical surface, etc.), and the following equation representing the aspherical surface shape ( AS). The aspheric data of each example is shown together with other data.
X (H) = (C0 · H ² ) / {1 + √ (1-ε · C0 ² · H ² )} + Σ (Aj · H ^j )… (AS)
However, in the formula (AS)
X (H): Displacement amount in the optical axis AX direction at the position of height H (based on the surface vertex),
H: height in a direction perpendicular to the optical axis AX,
C0: Paraxial curvature (= 1 / ri),
ε: quadric surface parameter,
Aj: j-th order aspheric coefficient (data when Aj = 0 is omitted),
It is.

  4 to 6 are aberration diagrams corresponding to Examples 1 to 3. In FIGS. 4 to 6, (A) is a spherical aberration diagram, (B) is an astigmatism diagram, and (C) is an astigmatism diagram. {FNO: F number, Y ': Maximum image height (mm)} which is a distortion diagram. In the spherical aberration diagram, the solid line d represents the d-line, the alternate long and short dash line g represents the g-line, the two-dot chain line c represents the amount of spherical aberration (mm) with respect to the c-line, and the broken line SC represents the unsatisfactory sine condition (mm). ing. In the astigmatism diagram, the broken line DM represents the meridional image plane (mm), and the solid line DS represents the sagittal image plane (mm). In the distortion diagram, the solid line represents the distortion (%) with respect to the d-line.

Example 1
f = 4.775, FNO = 5.6
[Curve radius] [Axis spacing] [Refractive index] [Abbe number]
r1 = ∞ (ST)
d1 = 0.000
r2 * = 1.329
d2 = 0.972 N1 = 1.53048 ν1 = 55.72 (L1)
r3 * = 1.909
d3 = 1.021 (= TA)
r4 * =-186.885 (= R21)
d4 = 1.493 N2 = 1.53048 ν2 = 55.72 (L2)
r5 * = -10.011 (= R22)
d5 = 0.500
r6 = ∞
d6 = 0.500 N3 = 1.51680 ν3 = 64.20 (GF)
r7 = ∞

[Aspherical data of 2nd surface (r2)]
ε = 0.88424, A4 = -0.28071 × 10 ^-1 , A6 = 0.36019, A8 = -0.71467, A10 = -0.83498
[Aspherical data of 3rd surface (r3)]
ε = 0.10000 × 10, A4 = 0.11743, A6 = -0.93281 × 10 ^-1 , A8 = 0.58148, A10 = -0.70643
[Aspherical data of 4th surface (r4)]
ε = 0.10000 × 10, A4 = 0.27640 × 10 ^-1 , A6 = -0.13393, A8 = 0.72650 × 10 ^-1 , A10 = -0.11419 × 10 ^-1
[Aspherical data of 5th surface (r5)]
ε = 0.10000 × 10, A4 = 0.16011 × 10 ⁻¹ , A6 = −0.23202 × 10 ⁻¹ , A8 = 0.24903 × 10 ⁻² , A10 = −0.27956 × 10 ^-5

Example 2
f = 4.669, FNO = 5.6
[Curve radius] [Axis spacing] [Refractive index] [Abbe number]
r1 = ∞ (ST)
d1 = 0.000
r2 * = 1.409
d2 = 0.972 N1 = 1.53048 ν1 = 55.72 (L1)
r3 * = 2.064
d3 = 1.062 (= TA)
r4 * = 12.304 (= R21)
d4 = 1.452 N2 = 1.53048 ν2 = 55.72 (L2)
r5 * = -22.844 (= R22)
d5 = 0.500
r6 = ∞
d6 = 0.500 N3 = 1.51680 ν3 = 64.20 (GF)
r7 = ∞

[Aspherical data of 2nd surface (r2)]
ε = 0.10000 × 10, A4 = -0.16310 × 10 ^-1 , A6 = -0.17271 × 10 ^-1 , A8 = 0.15342 × 10 ^-1 , A10 = -0.53822 × 10
[Aspherical data of 3rd surface (r3)]
ε = 0.10000 × 10, A4 = 0.38637 × 10 ^-1 , A6 = 0.22662, A8 = -0.26936, A10 = 0.65587 × 10 ^-1
[Aspherical data of 4th surface (r4)]
ε = 0.10000 × 10, A4 = -0.25355 × 10 ^-3 , A6 = -0.88791 × 10 ^-1 , A8 = 0.45081 × 10 ^-1 , A10 = -0.66598 × 10 ^-2
[Aspherical data of 5th surface (r5)]
ε = 0.10000 × 10, A4 = 0.13995 × 10 ⁻¹ , A6 = −0.26915 × 10 ⁻¹ , A8 = 0.47306 × 10 ⁻² , A10 = −0.330561 × 10 ^-3

Example 3
f = 5.213, FNO = 3.5
[Curve radius] [Axis spacing] [Refractive index] [Abbe number]
r1 = ∞ (ST)
d1 = 0.231
r2 * = 2.254
d2 = 1.615 N1 = 1.53048 ν1 = 55.72 (L1)
r3 * = 2.987
d3 = 0.765 (= TA)
r4 * = 4.775 (= R21)
d4 = 1.615 N2 = 1.53048 ν2 = 55.72 (L2)
r5 * = -17.100 (= R22)
d5 = 0.500
r6 = ∞
d6 = 0.500 N3 = 1.51680 ν3 = 64.20 (GF)
r7 = ∞

[Aspherical data of 2nd surface (r2)]
ε = -0.11878 × 10 ² , A4 = 0.11470, A6 = -0.60678 × 10 ^-1 , A8 = 0.14866 × 10 ^-1 , A10 = 0.52277 × 10 ^-2
[Aspherical data of 3rd surface (r3)]
ε = 0.10000 × 10, A4 = −0.31356 × 10 ⁻¹ , A6 = 0.48641 × 10 ⁻¹ , A8 = −0.32084 × 10 ⁻¹ , A10 = 0.10459 × 10 ⁻¹
[Aspherical data of 4th surface (r4)]
ε = 0.10000 × 10, A4 = -0.21634 × 10 ^-1 , A6 = -0.59534 × 10 ^-2 , A8 = 0.28085 × 10 ^-2 , A10 = -0.69251 × 10 ^-3
[Aspherical data of 5th surface (r5)]
ε = 0.10000 × 10, A4 = 0.77314 × 10 ^-2 , A6 = -0.84301 × 10 ^-2 , A8 = 0.16607 × 10 ^-2 , A10 = -0.16737 × 10 ^-3

The lens block diagram of 1st Embodiment (Example 1). The lens block diagram of 2nd Embodiment (Example 2). The lens block diagram of 3rd Embodiment (Example 3). FIG. 6 is an aberration diagram of Example 1. FIG. 6 is an aberration diagram of Example 2. FIG. 6 is an aberration diagram of Example 3.

Explanation of symbols

ST Aperture stop L1 First lens L2 Second lens GF Glass filter AX Optical axis

Claims (3)

An imaging lens having two lenses for forming an image on a solid-state imaging device, in order from the object side, a first meniscus first lens having a convex surface facing the object side, and a first lens having a convex surface facing the image surface side An imaging lens comprising two lenses and satisfying the following conditional expressions (1) to (3) :
0.51 <f / f1 <1.17 (1)
-0.84 <(R21 + R22) / (R21−R22) ≦ 1.11 (2)
0.15 ≦ TA / f <0.29… (3)
However,
f: focal length of the entire system,
f1: focal length of the first lens,
R21: radius of curvature of the object side surface of the second lens,
R22: radius of curvature of the image side surface of the second lens,
TA: On-axis air gap between the first lens and the second lens,
It is. The imaging lens according to claim 1, characterized by satisfying the following conditional expression (4);
1.19 <f / Y '<2.06 (4)
However,
f: focal length of the entire system,
Y ': Maximum image height,
It is. The imaging lens according to claim 1, further comprising an aperture stop on the object side of the first lens.

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