JP4248379B2 - Photography lenses and portable devices - Google Patents

Description

  The present invention relates to a photographic lens, and more particularly to a photographic lens suitably used for capturing an image of a simple digital camera, a PC camera, a portable device or the like equipped with a high pixel CCD.

  In recent years, cellular phones having a photographing function are generally used, and a cellular phone is provided with a photographing lens (optical system) and a CCD (image reading means). In other words, mobile phones have the same functions as digital cameras. When a mobile phone was equipped with a photographing function, the number of CCD pixels was about 110,000 to 300,000, and the CCD size was also reduced to 1/7 to 1/4 inch. In this case, with respect to the required optical performance, a lens configuration of one to two lenses is sufficient. In addition, it has been relatively easy to secure a desired back focus while protecting the optical total length regulated by the thickness of the mobile phone body.

  However, the number of pixels of a CCD built in a mobile phone has been increasing year by year, and when the number of pixels is megapixels, the required optical performance is also increased. Therefore, the conventional one or two lens configuration is required. Unable to achieve performance. Therefore, it is necessary to configure the number of lenses, for example, four. In this case, there is a problem in that the back focus cannot be ensured while keeping the desired optical total length, and optical components such as an infrared cut filter cannot be arranged. Can occur. For example, as a four-lens photographic lens, techniques disclosed in Patent Documents 1 and 2 below are known. These are optical systems suitable for digital cameras. However, when scaling for a mobile phone that often uses a small CCD of 1/4 inch or less, for example, the back focus becomes short. It cannot be applied as a photographing lens for mobile phones.

Therefore, in order to ensure the back focus, it is conceivable to increase the CCD size and make the optical system longer in focal length. However, when such a configuration is adopted, the optical total length becomes long, and it cannot be arranged in a limited space such as a mobile phone, or even if it is arranged, the design is impaired. It can be.
Japanese Patent No. 3342030 JP 2003-255222 A

  The present invention has been made in view of the above circumstances, and a problem thereof is a photographic lens suitable for a high-pixel image reading unit, which can secure a back focus and can suppress the overall length of an optical system to the same level as in the past. To provide a photographing lens and a portable device incorporating the same.

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, a third lens, and a fourth lens from the object side,
The first lens is a biconvex positive lens,
The second lens is a biconcave shape in which the object side surface is joined to the image side surface of the first lens, or a negative lens having a planoconcave shape,
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 image side,
The fourth lens is a positive meniscus lens having an aspherical shape at least one refracting surface and a convex surface facing the object side.

  The operation and effect of the photographic lens with this configuration will be described. The optical system of this photographic lens is composed of four lenses, first to fourth lenses. Compared with Patent Document 2 having the same four-lens configuration, in Patent Document 2, the second lens is a meniscus lens (negative lens) having a concave surface facing the object side, and the second lens has a refractive index of 1.8 or more. High refractive index glass is used. However, since a meniscus lens is used, the negative power necessary to ensure a desired back focus cannot be obtained. In the present invention, a biconcave or planoconvex negative lens is used as the second lens, so that a relatively strong negative power can be secured and the back focus required for the portable device can be secured. In Patent Document 2, a material having a low refractive index (1.7 or less) is used for the first lens, which causes an increase in the lens thickness. If an optical system using a relatively large-diameter lens for a digital camera as in Patent Document 2 is used with a large number of high-refractive-index lenses, the cost increases. The photographic lens of the present invention is suitable for a portable device. Even if the first lens and the second lens are formed of a material having a high refractive index, since the size is small, the influence on the cost is small. From this viewpoint, the present invention can shorten the optical total length.

  Further, Patent Document 1 discloses about two examples in which the refractive index of the glass of the second lens is 1.8 or more, but the first lens and the second lens are not a junction type. It has become a separation type. Therefore, there is a problem that the optical total length is increased accordingly. Further, all of the junction type examples disclosed in Patent Document 1 have a refractive index of 1.8 or less. However, a large difference in refractive index between the cemented lenses is taken to increase the negative power and back focus. However, this is canceled by the positive power on the second lens image plane side. On the other hand, in the case of the present invention, the first lens and the second lens are cemented lenses, and as described above, the cemented surface has a concave surface facing the object side, and the second lens image side surface is concave on the image surface. Both lenses can be made of a material with a high refractive index. As a result, it is possible to provide a photographic lens suitable for an image reading unit having a high pixel, which can secure a back focus and can suppress the overall length of the optical system to the conventional level.

In the present invention, when the combined focal length of the entire lens system is f and the combined focal length of the third lens and the fourth lens is f ₃₄ ,
0.3 <f / f ₃₄ <0.65
It is preferable to satisfy the following conditional expression.

When f / f ₃₄ ≦ 0.3, the power burden of the cemented lens including the first lens and the second lens becomes excessive, and it becomes difficult to correct spherical aberration and coma. When f / f ₃₄ ≧ 0.65, if the third lens and the fourth lens are made of plastic, the movement of the focal position when the temperature changes becomes large.

In the present invention, when the total focal length of the entire lens system is f, and the radius of curvature of the image side of the second lens is R ₂₂ ,
0.0 ≦ f / R ₂₂ <0.75
It is preferable to satisfy the following conditional expression.

When f / R ₂₂ <0, the negative power of the second lens becomes small, so that sufficient back focus cannot be secured. When f / R ₂₂ ≧ 0.75, the radius of curvature R ₂₂ decreases, and it is necessary to increase the on-axis air clearance with the third lens in order to secure the height of the collision with the surface on the third lens object side. Therefore, downsizing becomes difficult. The radius of curvature represents a paraxial numerical value.

When in the present invention, a combined focal length of the entire lens system f, and the radius of curvature of the image side of the fourth lens and the R _42,
2.0 <f / R ₄₂ <3.7
It is preferable to satisfy the following conditional expression.

When f / R ₄₂ ≦ 2.0 , the shape difference between the lens peripheral part (near the inflection point / curved part) becomes large, and the performance deterioration from the screen center to the peripheral part becomes large. When f / R ₄₂ ≧ 3.7, the amount of sag at the peripheral portion increases, and the flange back to the image plane becomes shorter. The radius of curvature represents a numerical value on the paraxial axis.

  The photographic lens according to the present invention is particularly suitable for portable devices such as mobile phones.

  Preferred embodiments of the taking lens according to the present invention will be described with reference to the drawings. 1 to 7 show lens configuration diagrams (FIGS. 1A to 7A) from Example 1 to Example 7, aberration diagrams, and optical system characteristic data (FIGS. 1B to 7B). 8 to 10 are diagrams showing aspherical data of the lenses of the respective examples. The photographic lens according to the present invention has a structure suitable for a photographic lens built in a portable device, particularly a mobile phone.

<Lens configuration diagram>
As shown in FIGS. 1A to 7A, the photographing lens according to the present invention is configured by four lenses. The members constituting the photographic lens will be described in order from the object side. The aperture stop 1, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the parallel plane glass 2, and the imaging plane 3 are arranged in this order. Has been.

  The first lens L1 is a biconvex positive lens and is made of a material having a high refractive index. The second lens L2 is a biconcave negative lens or a plano-concave (object side concave) negative lens in which the object side surface is cemented with the image side surface of the first lens L1. Example 2 is a plano-concave negative lens, and other examples are biconcave negative lenses. The second lens L2 is also formed of a material having a high refractive index.

  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 image side. The fourth lens L4 is a positive meniscus lens having at least one refracting surface having an aspherical shape and a convex surface facing the object side. The third lens L3 and the fourth lens L4 are preferably formed by plastic molding and formed of a low refractive index material. In all of Examples 1 to 7, the third lens L3 and the fourth lens L4 are both formed in an aspheric shape.

  The plane parallel glass 2 has a function as an infrared cut filter. On the image plane 3, image reading means such as a CCD is arranged.

<Lens specifications and aberration diagrams>
1B to 7B will be described. At the top of the figure, the focal length, F number, and angle of view are shown as lens specifications. In the table below, S, 1, 2,... 9 indicate surface numbers in order from the object side (where S indicates an aperture stop). Since the first lens L1 and the second lens L2 are cemented, the second surface is a surface common to both.

  r represents the radius of curvature (mm) on the paraxial axis. Since the 8th surface and the 9th surface are parallel plane glasses, both are infinite. d is a numerical value indicating the surface separation (mm). nd represents the refractive index of each lens and parallel plane glass, and vd represents the Abbe number of each lens and plane parallel glass.

f represents the combined focal length of the entire lens system. f ₃₄ denotes a third lens L3 of the composite focal length of the fourth lens L4. R ₂₂ represents the radius of curvature of the second lens L2 on the image side. R ₄₂ represents a radius of curvature of the image side of the fourth lens L4.

  As aberration diagrams, diagrams of spherical aberration, astigmatism, and distortion are shown. Each aberration diagram 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).

The aspheric shape of FIGS. 8 to 10 will be described. The aspherical shape is expressed as follows: A, B, C, D, E, F, G are aspheric 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 .

For the photographic lens according to the present invention, it is preferable to set the numerical ranges relating to f, f ₃₄ , R ₂₂ , and R ₄₂ as follows.

(1) 0.3 <f / f 34 <0.65
When f / f ₃₄ ≦ 0.3, the power burden of the cemented lens composed of the first lens L1 and the second lens L2 becomes excessive, and it becomes difficult to correct spherical aberration and coma. When f / f ₃₄ ≧ 0.65, when the third lens L3 and the fourth lens L4 are made of plastic, the movement of the focal position when the temperature changes becomes large.

(2) 0.0 ≦ f / R ₂₂ <0.75
When f / R ₂₂ <0, the negative power of the second lens becomes small, so that sufficient back focus cannot be secured. When f / R ₂₂ ≧ 0.75, the radius of curvature R ₂₂ decreases, and it is necessary to increase the on-axis air clearance with the third lens in order to secure the height of the collision with the surface on the third lens object side. Therefore, downsizing becomes difficult. Therefore, it becomes difficult to incorporate the mobile phone into a mobile phone having a limited arrangement space.

(3) 2.0 <f / _R42 <3.7
When f / R ₄₂ ≦ 2.0 , the shape difference between the lens peripheral part (near the inflection point / curved part) increases, and the performance degradation from the center of the screen to the peripheral part increases. When f / R ₄₂ ≧ 3.7, the amount of sag at the peripheral portion is increased, and the flange back to the imaging surface (referred to as the distance from the flange surface to which the lens is attached to the rear focal point) is shortened. As a result, a space for inserting the IR filter and the cover glass cannot be secured.

  The actual data of Examples 1 to 7 are as shown in Table 1.

各実施例のデータを見ても分かるように、第１レンズＬ１と第２レンズＬ２は、高屈折率の材料を使用している。第３レンズＬ３と第４レンズＬ４は、通常の低屈折率の材料でよい。ここで第１・第２レンズの好ましい屈折率の範囲は次のようになっている。

As can be seen from the data of each example, the first lens L1 and the second lens L2 are made of a material having a high refractive index. The third lens L3 and the fourth lens L4 may be made of a normal low refractive index material. Here, the preferable range of the refractive index of the first and second lenses is as follows.

First lens: 1.85>nd> 1.65
Second lens: 1.85>nd> 1.75
By selecting a refractive index in such a range, optical performance can be ensured and the optical total length can be suppressed. In the case of an optical system built in a mobile phone, the size of the lens is also small, so even if a high-refractive index material, which is generally an expensive material, is used, there is little impact on the cost. Therefore, in terms of cost, there is no problem even if a material having a high refractive index in the above range is used.

  Regarding Examples 1 to 7, when the total sum of d (surface spacing) data is considered as the optical total length (however, the portion of the plane parallel glass was obtained 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となっていることが理解される。また、バックフォーカスについても図１Ａ〜図７Ａの構成図から分かるように十分に確保できている。その結果、高画素ＣＣＤに好適な撮影レンズであって、バックフォーカスを確保できると共に光学系全長を従来並みに抑えることができる。例えば、小型で高画素の撮像素子に対応した撮影レンズとして好適であり、特に携帯電話に内蔵される撮影レンズとして好適である。

As can be seen from Table 2, it is understood that the size is suitable for incorporation in a mobile phone. Further, the back focus is sufficiently secured as can be seen from the configuration diagrams of FIGS. 1A to 7A. As a result, it is a photographing lens suitable for a high pixel CCD, which can ensure a back focus and can keep the entire length of the optical system as conventional. For example, it is suitable as a photographing lens corresponding to a small and high-pixel imaging device, and particularly suitable as a photographing lens incorporated in a mobile phone.

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 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 5. The figure which shows the aspherical surface coefficient of Example 6-7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aperture stop L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens 2 Parallel plane glass 3 Imaging surface

Claims (2)

A photographing lens arranged in order of an aperture stop, a first lens, a second lens, a third lens, and a fourth lens from the object side,
The first lens is a biconvex positive lens,
The second lens is a biconcave shape in which the object side surface is joined to the image side surface of the first lens, or a negative lens having a planoconcave shape,
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 image side,
The fourth lens at least one refractive surface an aspherical shape, Ri positive meniscus lens der having a convex surface directed toward the object side,
When the combined focal length of the entire lens system is f and the combined focal length of the third lens and the fourth lens is f ₃₄ ,
0.3 <f / f ₃₄ <0.65
Is satisfied,
When the total focal length of the entire lens system is f and the radius of curvature of the image side of the second lens is R ₂₂ ,
0.0 ≦ f / R ₂₂ <0.75
Is satisfied,
When the entire lens system in the composite focal distance f, and the radius of curvature of the image side of the fourth lens and the R _42,
2.0 <f / R ₄₂ <3.7
A photographic lens satisfying the following conditional expression: A portable device in which the photographing lens according to claim 1 is built.

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