JP4183132B2 - Shooting lens - Google Patents

Description

  The present invention relates to a photographing lens arranged in order of an aperture stop, a first lens, a second lens, and a third lens from the object side.

  In recent years, mobile phones having a photographing function have become common, and a solid-state imaging device such as a CCD sensor or a CMOS sensor and a photographing lens are incorporated in the mobile phone. With the downsizing and high performance of solid-state imaging devices, there is an increasing demand for further downsizing of photographing lenses. Also, with the widespread use of mobile phones, a wide variety of image sensors have been developed, and a highly difficult optical design including the limitation of the overall length and the manufacturing conditions for each image sensor is required.

  For example, a photographic lens disclosed in Patent Document 1 below achieves downsizing with a three-lens configuration lens. That is, in order from the object side, an aperture stop, a biconvex first lens having positive refractive power, a second lens having negative refractive power and having a concave surface facing the object side, and a meniscus having a convex surface facing the object side A third lens having a shape is arranged.

However, such a lens arrangement has the following problems. Since the first lens has a biconvex shape, the power is strong, and at the same time, the power of the second lens, which is a negative lens, needs to be increased for aberration correction. When the power of each lens is increased in this way, the sensitivity of eccentricity as a whole increases.
Japanese Patent Laid-Open No. 2004-4466

  The present invention has been made in view of the above circumstances, and its object is to provide a photographic lens having a three-lens configuration in which the power of each lens is reduced to reduce the sensitivity to eccentricity and various aberrations are corrected satisfactorily. That is.

In order to solve the above problems, a photographic lens according to the present invention provides:
A photographing lens arranged in order of an aperture stop, a first lens, a second lens, and a third lens from the object side,
The first lens is a plano-convex lens or a positive meniscus lens having a convex surface facing the object side,
The second lens is a negative meniscus lens in which at least one refracting surface has an aspherical shape and a convex surface faces the image side,
The third lens is a positive meniscus lens in which at least one refracting surface has an aspherical shape and a convex surface faces the object side.

  The operation and effect of such a photographic lens will be described. The optical system of the photographing lens has a three-lens configuration of first to third lenses. Compared with the photographic lens of Patent Document 1 having the same three-lens configuration, in Patent Document 1, the first lens is a biconvex lens, whereas the first lens of the present invention is a plano-convex lens with a convex surface facing the object side or Place a positive meniscus lens. Thereby, while suppressing the increase in the power of a 1st lens, the power of a 2nd lens can also be suppressed. In addition, with respect to the second lens and the third lens, various aberrations can be corrected while suppressing power by making the at least one refracting surface an aspherical shape. As described above, it is possible to provide a three-lens photographic lens in which the power of each lens is suppressed to reduce the eccentric sensitivity and various aberrations are corrected favorably.

The present invention further provides that when the focal length of the first lens is f ₁ and the focal length of the third lens is f ₃ ,
1.296 ≦ f ₃ / f ₁ <2.7
It satisfies the following conditional expression .

When f ₃ / f ₁ <1.296 , power distribution between the first lens and the third lens becomes inappropriate, and aberration correction becomes difficult. Further, when f ₃ / f ₁ ≧ 2.7, the power of the first lens becomes too large, and the eccentricity sensitivity becomes high.

In the present invention when the combined focal length of the entire lens system is f, the thickness of the second lens and the d _2,
5.0 <f / d ₂ <11.0
It is preferable to satisfy the following conditional expression.

When f / d ₂ ≦ 5.0, the larger the image sensor, the thicker the lens becomes, and the total length becomes longer. When f / d ₂ ≧ 11.0, if the image sensor becomes small, the lens becomes too thin and manufacturing becomes difficult. Therefore, according to the structure of this invention, it can adapt to the magnitude | size of a wide image pick-up element.

  The second lens and the third lens according to the present invention are preferably plastic lenses. Thereby, a lens having an aspherical shape can be easily manufactured.

The present invention further provides that when the radius of curvature of the third lens on the object side is R ₃₁ and the radius of curvature of the third lens on the image side is R ₃₂ ,
1.0 <R ₃₂ / R ₃₁ ≦ 3.725
It satisfies the following conditional expression .

When R ₃₂ / R ₃₁ ≦ 1.0, the amount of sag at the peripheral portion increases and the flange back to the image plane becomes shorter. When R ₃₂ / R ₃₁ > 3.725 , the difference in lens thickness between the central portion and the peripheral portion increases, and in the case of a plastic lens, manufacturing variations such as temperature changes and molding errors increase.

In the present invention, when the combined focal length of the second lens and the third lens is f ₂₃ and the combined focal length of the entire lens system is f,
f / | f ₂₃ | <0.4
It is preferable to satisfy the following conditional expression.

When f / | f ₂₃ | ≧ 0.4, when the second and third lenses are made of plastic, the movement of the focal position when the temperature changes is large.

  Preferred embodiments of the taking lens according to the present invention will be described with reference to the drawings. 1 to 5 show lens configuration diagrams (FIGS. 1A to 12A) from Example 1 to Example 7, optical system characteristic data, and aberration diagrams (FIGS. 1B to 12B). 13 to 17 are diagrams showing aspheric data of each example. The three-lens imaging lens according to the present invention has a configuration particularly suitable as an optical system built in a portable device, particularly a cellular phone.

<Lens configuration diagram>
1A to 7A show the arrangement of the optical system in each example. When the bifocal lens system according to the first example is set on the wide angle side, the aperture stop 1, the first lens L 1, the second lens L 2, the third lens L 3, and the parallel plane are sequentially arranged from the object side along the optical axis. A glass 2 and an image plane 3 are arranged. That is, the optical system is constituted by three lenses.

  The first lens L1 is a plano-convex lens or a positive meniscus lens having a convex surface facing the object side. Examples 7 and 12 are examples using plano-convex lenses. Another example is a positive meniscus lens. The first lens L1 in the present invention can suppress an increase in power compared to a biconvex lens. The second lens L2 is a negative lens in which at least one refractive surface has an aspherical shape and a convex surface faces the image side. Examples 1 to 12 show examples in which both surfaces have aspherical shapes. The third lens L3 is a positive meniscus lens in which at least one refracting surface has an aspherical shape and a convex surface faces the object side. Examples 1 to 12 show examples in which both surfaces have aspherical shapes.

  The plane parallel glass 2 has a function as an infrared cut filter. A solid-state image sensor such as a CCD is disposed on the image plane 3. In Examples 7, 8, 9, and 11, two parallel flat glasses 2 are provided, and functions as an infrared cut filter and a CCD cover glass. When a CMOS sensor is configured on a chip-on-board as a solid-state imaging device, the sensor can be protected with a thin resin film, so that a cover glass is not necessary.

<Lens specifications and aberration diagrams>
1B to 12B will be described. The focal length f, F number F, and field angle 2ω are shown as lens specifications at the top of the figure. In the table below, 1, 2,... 8 (9, 10) indicate the surface numbers in order from the object side. r indicates the radius of curvature (mm) on the paraxial axis. For example, in the first embodiment, since the seventh surface and the eighth surface are the parallel flat glass 2, both are infinite. d is a numerical value indicating the surface separation (mm). nd indicates the refractive index of each of the lenses L1 to L3 and the plane parallel glass 2, and vd indicates the Abbe number of each of the lenses L1 to L3 and the plane parallel glass 2.

F ₁ is the focal length of the first lens L1, and f ₃ is the focal length of the third lens L3. f is the focal length of the entire lens system, f ₂₃ and the second lens L2 combined focal length of the third lens L3, d ₂ is the thickness of the second lens L2, R ₃₁ is the radius of curvature of the object side of the third lens L3 radius, R ₃₂ represents a curvature radius of the image side of the third lens L3.

  FIGS. 1B to 12B show diagrams of spherical aberration, astigmatism, and distortion for each example. Each figure is data about the d-line, and astigmatism shows both data about the sagittal image plane (S) and data about the meridional image plane (M). As can be seen from these aberration diagrams, it can be seen that the aberration is corrected to a level where there is no practical problem.

The aspheric shape of FIGS. 13 to 17 will be described. The aspherical shape is expressed as follows: A, B, C, D, E, F, G are aspherical coefficients, and the displacement X in the optical axis direction at the position of the height H from the optical axis is expressed with respect to the surface vertex. ^{X = (1 / R) H} 2 / [1+ {1- (1 + K) (H / R) 2} 1/2]
+ AH ⁴ + BH ⁶ + CH ⁸ + DH ¹⁰ + EH ¹² + FH ¹⁴ + GH ¹⁶
It becomes. R is a paraxial radius of curvature, and K is a conical coefficient. An aspherical coefficient such as E-03 means 10 ⁻³ .

In the present invention, it is preferable to set the numerical ranges relating to f ₁ , f ₃ , d ₂ , R ₃₁ , R ₃₂ , and f ₂₃ as follows.

(1) 0.9 <f ₃ / f ₁ <2.7
In f ₃ / f ₁ ≦ 0.9, the first lens L1 power distribution of the third lens L3 becomes inadequate, making it difficult to correct aberrations. In addition, when f ₃ / f ₁ ≧ 2.7, the power of the first lens L1 becomes too large, and the eccentricity sensitivity becomes high.

(2) 5.0 <f / d ₂ <11.0
When f / d ₂ ≦ 5.0, the larger the image sensor, the thicker the lens becomes, and the total length becomes longer. When f / d ₂ ≧ 11.0, if the image sensor becomes small, the lens becomes too thin and manufacturing becomes difficult.

_{(3) 1.0 <R 32 /} R 31 <7.0
When R ₃₂ / R ₃₁ ≦ 1.0, the amount of sag at the peripheral portion increases and the flange back to the image plane becomes shorter. When R ₃₂ / R ₃₁ ≧ 7.0, the difference in lens thickness between the central portion and the peripheral portion increases, and in the case of a plastic lens, manufacturing variations such as temperature changes and molding errors increase.

(4) f / | f ₂₃ | <0.4
When f / | f ₂₃ | ≧ 0.4, when the second and third lenses are made of plastic, the movement of the focal position when the temperature changes is large.

  The actual data of Examples 1 to 12 are as shown in Table 1.

また、実施例１〜１２について、ｄ（面間隔）のデータの総和を光学全長（ただし、平行平面ガラスの部分は空気換算距離に直して求めた。）として考えると、表２のようになる。

In addition, regarding Examples 1 to 12, when the total sum of d (surface distance) data is considered as the optical total length (however, the portion of the plane parallel glass was determined by correcting the air conversion distance), it is as shown in Table 2. .

この表２からも分かるように、携帯電話に内蔵するのに好適な大きさになっていることが理解される。

As can be seen from Table 2, it is understood that the size is suitable for incorporation in a mobile phone.

  The photographing lens according to the present invention is particularly suitable for a portable device such as a cellular phone, but can also be used for a digital camera or the like.

  In the present invention, each lens L1, L2, L3 is preferably molded from plastic. In particular, when it has an aspherical shape, it is preferably molded from plastic.

FIG. 5 is a diagram illustrating a lens configuration of Example 1. Aberration diagram and optical system characteristic data of Example 1 FIG. 5 is a diagram illustrating a lens configuration of Example 2. Aberration diagram and optical system characteristic data of Example 2 FIG. 5 is a diagram illustrating a lens configuration of Example 3. Aberration diagram and optical system characteristic data of Example 3 FIG. 5 is a diagram illustrating a lens configuration of Example 4. Aberration diagram and optical system characteristic data of Example 4 FIG. 10 is a diagram illustrating a lens configuration of Example 5. Aberration diagram and optical system characteristic data of Example 5 FIG. 6 shows a lens configuration of Example 6. Aberration diagram and optical system characteristic data of Example 6 FIG. 10 shows a lens configuration of Example 7. Aberration diagram and optical system characteristic data of Example 7 FIG. 10 shows a lens configuration of Example 8. Aberration diagram and optical system characteristic data of Example 8 FIG. 10 shows a lens configuration of Example 9. Aberration diagrams and optical system characteristic data of Example 9 FIG. 10 shows a lens configuration of Example 10. Aberration diagram and optical system characteristic data of Example 10 FIG. 11 shows a lens configuration of Example 11. FIG. 10 is a diagram showing aberration diagrams and optical system characteristic data in Example 11. FIG. 10 shows a lens configuration of Example 12. FIG. 10 is a diagram showing aberration diagrams and optical system characteristic data in Example 12. The figure which shows the aspherical surface coefficient of Example 1- Example 3. The figure which shows the aspherical surface coefficient of Example 4-Example 6. The figure which shows the aspherical surface coefficient of Example 7-9. The figure which shows the aspherical surface coefficient of Example 10 and Example 11. The figure which shows the aspherical surface coefficient of Example 12.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aperture stop 2 Parallel plane glass 3 Imaging surface L1 1st lens L2 2nd lens L3 3rd lens

Claims (2)

A photographing lens arranged in order of an aperture stop, a first lens, a second lens, and a third lens from the object side,
The first lens is a plano-convex lens or a positive meniscus lens having a convex surface facing the object side,
The second lens is a negative meniscus lens made of plastic , having at least one refracting surface aspherical, and a convex surface facing the image side,
The third lens is a positive meniscus lens formed of plastic , having at least one refracting surface as an aspherical shape, and having a convex surface facing the object side ,
When the focal length of the first lens is f ₁ and the focal length of the third lens is f ₃ ,
1.296 ≦ f ₃ / f ₁ <2.7
Satisfying the conditional expression of
When the combined focal length of the entire lens system is f and the thickness of the second lens is d ₂ ,
5.0 <f / d ₂ <11.0
Satisfying the conditional expression of
When the radius of curvature on the object side of the third lens is R ₃₁ and the radius of curvature on the image side of the third lens is R ₃₂ ,
1.0 <R ₃₂ / R ₃₁ ≦ 3.725
Shooting lens that satisfies the conditional expression When the composite focal length of the second lens and the third lens and f _23, the composite focal length of the lens whole system is f,
f / | f ₂₃ | <0.4
The photographic lens according to claim 1, wherein the conditional expression is satisfied.

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