JP4784068B2 - Photography lens and imaging device - Google Patents

Description

  The present invention relates to a photographic lens, and more particularly to a high-performance and compact photographic lens used in a small-sized imaging device using a solid-state imaging device such as a CCD or CMOS having high pixels.

In recent years, with the rapid spread of portable communication devices such as camera-equipped mobile phones, notebook PCs, and PDAs, high optical performance is desired. Various lenses have been developed as photographing lenses for this purpose (for example, cited documents 1, 2 and 3).
Japanese Patent Laid-Open No. 2004-4466 JP 2004-212467 A JP 2003-255222 A

  However, in recent years, in particular, along with the miniaturization of the above-described portable communication device, there is a strong demand for taking lenses with high optical performance and further miniaturization and cost reduction. Therefore, there is a demand for a photographic lens having a high optical performance equivalent to or higher than the conventional one while reducing the number of lenses, downsizing and simplifying the configuration. Moreover, the cost of glass is more than twice as high as that of plastic, and processing into a glass lens becomes more difficult as the diameter becomes smaller.

  The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a photographing lens that is compact and can correct aberrations satisfactorily without increasing the number of lenses.

An imaging lens according to the present invention is a photographing lens including a lens system including an aperture stop, a first lens, a second lens, and a third lens in order from the object side. The first lens is convex on the object side. The second lens is a meniscus lens that is concave on the object side and has negative refractive power, and the third lens is a meniscus lens that is convex on the object side and has positive refractive power. The first lens, the second lens, and the third lens are all made of a resin material, and the aperture stop is separated from the center position of the first lens to the object side in the vicinity of the center position of the first lens. The lens system satisfies the following conditions.

TL / f <1.22 (1)
1.1 <f / f1 <1.5 (2)
−1.6 <f / f2 <−0.5 (3)
−3.0 <(n2-1) f / r3 <−1.6 (4)
ν1-ν2> 20 (5)
However, TL is the distance (mm) on the optical axis from the aperture stop to the image side focal point, f is the focal length (mm) of the lens system, f1 is the focal length (mm) of the first lens, and f2 is the second lens. Focal length (mm), n2 is the refractive index of the second lens, r3 is the radius of curvature (mm) of the object side surface of the second lens, ν1 is the Abbe number of the first lens, and ν2 is the Abbe number of the second lens.

  In the photographic lens according to the above configuration, the first lens which is a meniscus lens having a positive refractive power on the object side, the second lens which is a meniscus lens having a negative refractive power on the object side, and a convex on the object side. The lens system is composed of three lenses, the third lens being a meniscus lens having a positive refractive power. The aperture stop is provided in front of the first lens (on the object side).

  Here, the conditional expression (1) in the present invention indicates a condition for defining the overall length of the photographing lens and achieving miniaturization.

  That is, when the ratio of the optical total length to the focal length of the lens system is larger than the upper limit value of the conditional expression (1), the total length of the photographing lens is increased.

  Conditional expression (2) in the present invention defines the refractive power of the first lens, and indicates conditions for obtaining compact and good aberration performance.

  That is, when the ratio of the focal length of the lens system to the focal length of the first lens is smaller than the lower limit value of the conditional expression (2), the positive refractive power of the first lens is excessively reduced, and the overall length of the photographing lens is reduced. It cannot be maintained. On the other hand, if it exceeds the upper limit value of the conditional expression (2), the positive refractive power of the first lens is excessively increased, resulting in an extremely small radius of curvature, resulting in poor workability.

  In addition, the conditional expression (3) in the present invention defines the refractive power of the second lens, and indicates conditions for obtaining a compact and good aberration performance.

  That is, when the ratio of the focal length of the lens system to the focal length of the second lens becomes smaller than the lower limit value of the conditional expression (3), the negative refractive power of the second lens increases and the downsizing of the overall length of the photographing lens is maintained. I can't. On the other hand, when the value exceeds the upper limit value of conditional expression (3), the negative refractive power of the second lens is excessively reduced, and spherical aberration, axial chromatic aberration, and distortion occurring in the first lens can be corrected well. I can't.

  In addition, the conditional expression (4) in the present invention indicates a condition for appropriately setting the negative refractive power on the object side surface of the second lens and performing the field curvature correction satisfactorily.

  That is, when the function (n2-1) f / r3 regarding the refractive index of the second lens, the focal length of the optical system, and the radius of curvature of the object side surface of the second lens is smaller than the lower limit value of the conditional expression (4), the second The negative refractive power on the object side surface of the lens becomes too large, and off-axis coma occurs. On the other hand, if the upper limit value of conditional expression (4) is exceeded, the negative refractive power of the second lens cannot be maintained, the positive Petzval sum increases, and it becomes difficult to correct field curvature. In addition, spherical aberration and coma generated in the first lens cannot be corrected well.

  Conditional expression (5) in the present invention defines the Abbe number of the first lens and the Abbe number of the second lens, and indicates the condition for obtaining good chromatic aberration correction.

  That is, by making the difference between the Abbe number of the first lens and the Abbe number of the second lens larger than the lower limit value of the conditional expression (5), it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

  In addition, it is preferable that the first lens, the second lens, and the third lens are all made of a resin material. Thereby, cost can be suppressed low and production can be facilitated.

  According to the photographic lens of the present invention, the lens system has a very simple configuration of 3 elements in 3 groups, but satisfies the conditional expressions (1) to (5), so that the total length is short and the angle is sufficiently wide. At the same time, good aberration performance can be obtained. Further, by using a resin material for all the lenses, the cost can be kept low and the production can be facilitated.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a cross-sectional view of a photographic lens in the first embodiment of the present invention.

  As shown in FIG. 1, the photographing lens according to the present embodiment includes a lens system including an aperture stop 4, a first lens 1, a second lens 2, and a third lens 3 in order from the object side. The first lens 1 is a meniscus lens that uses a resin material, has a convex refractive power on the object side (lens surface R1), and the second lens 2 uses a resin material that has a positive refractive power. The lens surface R3) is a meniscus lens having a negative refractive power and a concave lens surface. The third lens 3 is a meniscus lens made of a resin material and having a positive refractive power on the object side (lens surface R5). is there.

  Each parameter value of the photographic lens in the present embodiment having the above configuration is as follows.

  Here, rj is the radius of curvature (mm) at the j-th surface number Rj in order from the object side, dj is the j-th surface center distance (mm) in order from the object side, Nd is the refractive index of the d-th lens, and νd is Abbe number of the d-th lens, f is the focal length (mm) of the lens system, Fno. Is the open F number, and 2Y is the diagonal length (mm) of the effective screen.

Also, the aspherical shape is such that the distance (sag amount) in the optical axis direction from the tangent plane of the surface vertex is x, the height h from the optical axis, r is the paraxial radius of curvature, κ is the conic constant, and a _m ( When m = 4, 6, 8,..., 14) is an m-th aspherical coefficient, it is expressed by the following equation.

x = {(1 / r) h ² } / [1+ {1− (1 + κ) (1 / r) ² h ² } ^1/2 ]
+ A ₄ h ⁴ + a ₆ h ⁶ + a ₈ h ⁸ + a ₁₀ h ¹⁰ (X)
Therefore, in the following, it represents the value of a _m in the formula (X), and specifies a non-spherical shape.

なお、本実施形態においては、開口絞りから像側焦点までの光軸上の距離ＴＬ＝４．５６であり、レンズ系の焦点距離ｆ＝３．８２であるので、ＴＬ／ｆ＝１．２０＜１．２２となり、条件式（１）を満足している。また、第１レンズ１の焦点距離ｆ１＝３．０８であるので、１．１＜ｆ／ｆ１＝１．２４＜１．５となり、条件式（２）を満足している。また、第２レンズ２の焦点距離ｆ２＝２．７７であるので、−１．６＜ｆ／ｆ２＝−１．３８＜−０．５となり、条件式（３）を満足している。さらに、第２レンズ２の屈折率ｎ２＝１．５８であり、第２レンズ２の物体側面Ｒ３の曲率半径ｒ３＝−１．１２８であるので、−３．０＜（ｎ２−１）ｆ／ｒ３＝−２．０６＜−０．５となり、条件式（４）を満足している。最後に、第１レンズ１のアッベ数ν１＝５６．４０であり、第２レンズ２のアッベ数ν２＝２９．９０であるので、ν１−ν２＝２６．５０＞２０となり、条件式（５）を満足している。

In the present embodiment, since the distance TL on the optical axis from the aperture stop to the image side focal point is 4.56 and the focal length f of the lens system is 3.82, TL / f = 1.20. <1.22, which satisfies the conditional expression (1). In addition, since the focal length f1 of the first lens 1 is 3.08, 1.1 <f / f1 = 1.24 <1.5, which satisfies the conditional expression (2). Further, since the focal length f2 of the second lens 2 is 2.77, −1.6 <f / f2 = −1.38 <−0.5, which satisfies the conditional expression (3). Further, since the refractive index n2 of the second lens 2 is 1.58 and the radius of curvature r3 of the object side surface R3 of the second lens 2 is −1.128, −3.0 <(n2-1) f / r3 = −2.06 <−0.5, which satisfies the conditional expression (4). Finally, since the Abbe number ν1 of the first lens 1 is 56.40 and the Abbe number ν2 of the second lens 2 is 29.90, ν1−ν2 = 26.50> 20, and the conditional expression (5) Is satisfied.

  FIG. 2 is an aberration diagram of the photographing lens of FIG. 2A shows spherical aberration, FIG. 2B shows astigmatism, and FIG. 2C shows distortion.

  As shown in FIG. 2, while satisfying the conditional expressions (1) to (5), the lens system has a very simple configuration of 3 elements in 3 groups, and the overall length is short and a sufficiently wide angle is good. Aberration performance can be obtained. Further, since all the lenses use a resin material, the cost is low and the lens can be easily produced.

Second Embodiment
FIG. 3 is a cross-sectional view of the taking lens according to the second embodiment of the present invention.

  In the second embodiment, the lens system is the same as that in the first embodiment. Each parameter value (including the aspheric coefficient) of the photographing lens in the present embodiment is as shown below.

なお、本実施形態においては、開口絞りから像側焦点までの光軸上の距離ＴＬ＝４．５６５であり、レンズ系の焦点距離ｆ＝３．８９であるので、ＴＬ／ｆ＝１．１８＜１．２２となり、条件式（１）を満足している。また、第１レンズ１の焦点距離ｆ１＝２．９０であるので、１．１＜ｆ／ｆ１＝１．３４＜１．５となり、条件式（２）を満足している。また、第２レンズ２の焦点距離ｆ２＝４．５８であるので、−１．６＜ｆ／ｆ２＝−０．８５＜−０．５となり、条件式（３）を満足している。さらに、第２レンズ２の屈折率ｎ２＝１．５８５５であり、第２レンズ２の物体側面Ｒ３の曲率半径ｒ３＝−１．０９５であるので、−３．０＜（ｎ２−１）ｆ／ｒ３＝−２．１＜−０．５となり、条件式（４）を満足している。最後に、第１レンズ１のアッベ数ν１＝５６．４０であり、第２レンズ２のアッベ数ν２＝２９．９０であるので、ν１−ν２＝２６．５０＞２０となり、条件式（５）を満足している。

In this embodiment, the distance TL on the optical axis from the aperture stop to the image-side focal point is TL = 4.565, and the focal length f of the lens system is 3.89, so TL / f = 1.18. <1.22, which satisfies the conditional expression (1). Since the focal length f1 of the first lens 1 is 2.90, 1.1 <f / f1 = 1.34 <1.5, which satisfies the conditional expression (2). Further, since the focal length f2 of the second lens 2 is 4.58, −1.6 <f / f2 = −0.85 <−0.5, which satisfies the conditional expression (3). Further, since the refractive index n2 of the second lens 2 is 1.5855 and the radius of curvature r3 of the object side surface R3 of the second lens 2 is −1.095, −3.0 <(n2-1) f / r3 = −2.1 <−0.5, which satisfies the conditional expression (4). Finally, since the Abbe number ν1 of the first lens 1 is 56.40 and the Abbe number ν2 of the second lens 2 is 29.90, ν1−ν2 = 26.50> 20, and the conditional expression (5) Is satisfied.

FIG. 4 is an aberration diagram of the photographing lens of FIG. 4A shows spherical aberration, FIG. 4B shows astigmatism, and FIG. 4C shows distortion.

Also in this embodiment, as shown in FIG. 4, although the lens system has a very simple configuration of 3 elements in 3 groups, the total length is sufficiently short by satisfying conditional expressions (1) to (5). In addition to a wide angle, good aberration performance can be obtained. Further, since all the lenses use a resin material, the cost is low and the lens can be easily produced.

<Third Embodiment>
FIG. 5 is a cross-sectional view of a taking lens according to the third embodiment of the present invention.

  The third embodiment is also composed of the same lens system as in the first embodiment. Each parameter value (including the aspheric coefficient) of the photographing lens in the present embodiment is as shown below.

なお、本実施形態においては、開口絞りから像側焦点までの光軸上の距離ＴＬ＝４．５６１であり、レンズ系の焦点距離ｆ＝３．８５であるので、ＴＬ／ｆ＝１．１９＜１．２２となり、条件式（１）を満足している。また、第１レンズ１の焦点距離ｆ１＝３．４０であるので、１．１＜ｆ／ｆ１＝１．１３＜１．５となり、条件式（２）を満足している。また、第２レンズ２の焦点距離ｆ２＝４．８１であるので、−１．６＜ｆ／ｆ２＝−０．８＜−０．５となり、条件式（３）を満足している。さらに、第２レンズ２の屈折率ｎ２＝１．５８５５であり、第２レンズ２の物体側面Ｒ３の曲率半径ｒ３＝−１．３９６であるので、−３．０＜（ｎ２−１）ｆ／ｒ３＝−１．６＜−０．５となり、条件式（４）を満足している。最後に、第１レンズ１のアッベ数ν１＝５６．４０であり、第２レンズ２のアッベ数ν２＝２９．９０であるので、ν１−ν２＝２６．５０＞２０となり、条件式（５）を満足している。

In this embodiment, since the distance TL on the optical axis from the aperture stop to the image-side focal point is 4.561 and the focal length f of the lens system is 3.85, TL / f = 1.19. <1.22, which satisfies the conditional expression (1). Further, since the focal length f1 of the first lens 1 is 3.40, 1.1 <f / f1 = 1.13 <1.5, which satisfies the conditional expression (2). Further, since the focal length f2 of the second lens 2 is 4.81, −1.6 <f / f2 = −0.8 <−0.5, which satisfies the conditional expression (3). Furthermore, since the refractive index n2 of the second lens 2 is 1.5855 and the radius of curvature r3 of the object side surface R3 of the second lens 2 is −1.396, −3.0 <(n2-1) f / r3 = −1.6 <−0.5, which satisfies the conditional expression (4). Finally, since the Abbe number ν1 of the first lens 1 is 56.40 and the Abbe number ν2 of the second lens 2 is 29.90, ν1−ν2 = 26.50> 20, and the conditional expression (5) Is satisfied.

FIG. 6 is an aberration diagram of the photographing lens of FIG. 6 (a) shows a spherical aberration, FIG. 6 (b) shows astigmatism, FIG. 6 (c) shows a distortion.

  In this embodiment as well, as shown in FIG. 6, although the lens system has a very simple configuration of three elements in three groups, the total length is sufficiently short by satisfying conditional expressions (1) to (5). In addition to a wide angle, good aberration performance can be obtained. Further, since all the lenses use a resin material, the cost is low and the lens can be easily produced.

  In the lens systems described in the above embodiments, lenses that are aspherical on the lens surfaces R1, R2, R3, R4, R5, and R6 are used, but the present invention is not limited to this. These can be selected as appropriate.

  The photographic lens according to the present invention is a lens system having a very simple configuration of three elements in three groups, and satisfying the conditional expressions (1) to (5), so that the total length is short and sufficiently wide, Good aberration performance can be obtained, and by using a resin material for all lenses, the cost can be reduced and the production can be easily performed. It is useful as a high-performance and compact photographing lens used in a small-sized imaging device using a solid-state imaging device such as a CMOS.

  The photographic lens according to the present invention is a lens system having a very simple configuration of three elements in three groups, and satisfying the conditional expressions (1) to (5), so that the total length is short and sufficiently wide, Good aberration performance can be obtained, and by using a resin material for all the lenses, it can be applied to applications such as technical fields that require low cost and can be easily produced.

Sectional drawing of the imaging lens in 1st Embodiment of this invention Aberration diagram of the photographic lens of FIG. Sectional drawing of the imaging lens in 2nd Embodiment of this invention Aberration diagram in the photographic lens of FIG. Sectional drawing of the imaging lens in 3rd Embodiment of this invention Aberration diagram of the photographic lens of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 Aperture stop

Claims (2)

In order from the object side, an aperture stop, a first lens, a composed photographic lens consisting essentially of a lens system of the second lens and the third lens, the first lens is a meniscus which the object side has a positive refractive power as a convex The second lens is a meniscus lens that is concave on the object side and has negative refractive power, and the third lens is a meniscus lens that is convex on the object side and has positive refractive power, and the first lens The second lens and the third lens are all made of a resin material, and the aperture stop is separated from the surface center position in the vicinity of the surface center position of the first lens toward the object side. A photographic lens characterized by satisfying the conditions.
TL / f <1.22 (1)
1.1 <f / f1 <1.5 (2)
−1.6 <f / f2 <−0.5 (3)
−3.0 <(n2-1) f / r3 <−1.6 (4)
ν1-ν2> 20 (5)
Where TL is the distance on the optical axis from the aperture stop to the image side focal point, f is the focal length of the lens system, f1 is the focal length of the first lens, f2 is the focal length of the second lens, and n2 is the focal length of the second lens. The refractive index, r3 is the radius of curvature of the object side surface of the second lens, ν1 is the Abbe number of the first lens, and ν2 is the Abbe number of the second lens. An imaging apparatus comprising: a photographing lens according to claim 1; and a solid-state imaging device disposed on a third lens side of the imaging lens.

Images