JP2005284110A - Photographing lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographing lens capable of simultaneously satisfying an aberration correcting effect and an infrared ray cutting effect while satisfactorily securing productivity by using a lens where infrared ray cutting components are uniformly mixed, and which is advantageous to the reduction of the number of components and the miniaturization. <P>SOLUTION: A 3rd lens G3 as a final lens is an aspherical lens, and also, the infrared ray cutting components are uniformly mixed into the lens material so as to give a function of cutting the infrared ray to the lens, and the lens is formed to such a shape that a thickness difference between the center part and the peripheral part is small, and also, the position through which the light passes of the aspherical lens is optimized. Thus, the aberration correcting effect and the infrared ray cutting effect are simultaneously attained while satisfactorily securing the productivity, then, the photographing lens can dispense with an infrared ray cut filter as another member, and the photographing lens advantageous to the reduction of the number of components and the miniaturization can be attained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photographic lens suitable for mounting on a small information terminal device such as a mobile phone with a camera or a PDA (Personal Digital Assistant).

  In recent years, with the spread of personal computers to ordinary homes and the like, digital still cameras (hereinafter simply referred to as digital cameras) capable of inputting image information such as photographed landscapes and human images to personal computers have rapidly spread. It's getting on. As mobile phones become more sophisticated, camera-equipped mobile phones equipped with a small imaging module are also rapidly spreading. In addition, small information terminal devices such as PDAs that are equipped with an imaging module have become widespread.

  In devices equipped with these imaging functions, imaging devices such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) are used. In recent years, these image sensors have been greatly reduced in size, so that the image pickup apparatus main body and the lens mounted thereon are also required to be smaller and lighter.

  In general, since the sensitivity of an imaging element such as a CCD extends to the near infrared region, it is necessary to cut off the harmful infrared component of an imaging device for normal use that requires only visible light. For this reason, in general, an infrared component is cut by, for example, disposing an infrared cut filter in front of the image sensor in the photographing optical system. However, in particular, a photographic lens attached to a mobile phone or the like has recently been required to be miniaturized, and it is difficult to make a space for inserting an infrared cut filter in a photographic optical system.

In view of this, it is conceivable that an infrared cut component is mixed in the lens material of the photographing lens so that the lens itself has an action of cutting infrared rays, and the infrared cut filter is omitted. For example, Patent Document 1 describes a plan in which a part of an endoscope objective lens is made of a material containing an infrared cut component. Japanese Patent Application Laid-Open No. H10-228561 describes a plan in which a part of an endoscope objective lens is a refractive index distribution lens and an infrared cut component is included in the lens material.
Japanese Patent Laid-Open No. 10-197787 JP 9-325285 A

  As described in Patent Document 1, in a method of simply including an infrared cut component in a normal lens, a lens shape for obtaining an aberration correction effect, and a lens shape for obtaining a uniform infrared cut effect for each angle of view; However, it was not possible to achieve a combination that satisfies both effects at the same time. That is, a normal lens used for obtaining an aberration correction effect has a shape having a thickness difference between the central portion and the peripheral portion. For this reason, the optical path length of the light beam that passes through the lens varies depending on the angle of view, and the effect of infrared cut varies depending on the angle of view. On the other hand, as described in Patent Document 2, in the method of optimizing the distribution density of the infrared cut component in the lens, it is necessary to design a lens shape that satisfies both the aberration correction effect and the infrared cut effect simultaneously. Considered easy. However, in reality, there are problems in terms of manufacturing cost, manufacturing accuracy, etc. at the stage of manufacturing, and at present, the feasibility is poor.

  The present invention has been made in view of such problems, and the object thereof is to simultaneously achieve the aberration correction effect and the infrared ray cut effect while ensuring sufficient manufacturability using a lens in which the infrared ray cut component is uniformly mixed. An object of the present invention is to provide a photographing lens that can be satisfied and is advantageous in reducing the number of parts and reducing the size.

  The photographic lens according to the present invention includes an aspheric lens having at least one aspheric surface, an infrared cut component is uniformly mixed in the lens material of the aspheric lens, and the shape of the aspheric lens is as follows. It is comprised so that Formula (1)-(3) may be satisfied.

0.8 <B / D <1.2 (1)
0.8 <A / B <1.2 (2)
2.0 <E / F (3)
Where A is the thickness at the maximum effective height of the aspheric lens, B is the thickness at half the maximum effective height of the aspheric lens, D is the thickness on the optical axis of the aspheric lens, E is the height from the optical axis when the principal ray having the maximum field angle passes through the image-side surface of the aspheric lens, and F is the principal ray at the half field angle of the maximum field angle. The height from the optical axis when passing through the image side surface is shown.

  In the photographic lens according to the present invention, an infrared cut component is uniformly mixed in the lens material of the aspherical lens, and the conditional expressions (1) and (2) are satisfied with respect to the aspherical lens, and the thickness difference is small from the center to the periphery. By adopting the lens shape, the optical path length difference due to the angle of view of the light rays passing through the aspherical lens is reduced, and an infrared cut effect can be obtained uniformly over the entire photographing screen. In addition, an aspheric lens is used as the lens that contains the infrared cut component, and the position of the light beam that passes through the aspheric lens is made appropriate by satisfying conditional expression (3), so that the aberration correction effect, particularly the image plane correction. The effect can be expected. As a result, an aberration correction effect and an infrared ray cutting effect can be obtained at the same time, which is advantageous in reducing the number of parts and reducing the size.

  In this photographic lens, it is preferable that the aspherical lens into which the infrared cut component is mixed is disposed closest to the image plane side and both surfaces are aspherical. In particular, in the case of a photographic lens with a small number of lenses, since the final lens is expected to correct aberration by an aspherical surface rather than a power, it is preferable that the final lens is the above-mentioned aspherical lens.

  According to the photographic lens of the present invention, the infrared cut component is uniformly mixed in the lens material of the aspheric lens, and the center of the aspheric lens satisfies the predetermined conditional expressions (1) and (2). The shape of the light beam passing through the aspherical lens is made appropriate by satisfying the conditional expression (3) while making the shape having a small wall thickness difference from the outer periphery to the periphery. Since the optical path length difference due to corners is reduced, it is possible to satisfy the aberration correction effect and the infrared cut effect at the same time while ensuring sufficient manufacturability using a lens in which the infrared cut component is uniformly mixed. . Thereby, since the infrared cut filter as a separate member can be omitted, it is possible to realize a photographing lens that is advantageous for reducing the number of parts and reducing the size.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration example of a photographic lens according to an embodiment of the present invention. In FIG. 1, L1 indicates a light ray group having an angle of view of 0 ° (center angle of view) passing through the photographing lens, L3 indicates a light ray group having a maximum angle of view, and L2 indicates an angle of view that is ½ of the maximum angle of view. The ray group at. C3 indicates a chief ray having a maximum angle of view, and C2 indicates a chief ray having an angle of view that is ½ the maximum angle of view. H1 indicates the maximum image height of the photographing lens, and H1 / 2 indicates an image height that is ½ of the maximum image height.

  This photographic lens is mounted and used in an imaging device using a small image sensor, such as a small information terminal device such as a mobile phone with a camera or a digital camera. This photographing lens has a configuration in which a first lens G1, a second lens G2, and a third lens G3 are arranged in this order from the object side along the optical axis Z1.

  An imaging element such as a CCD (not shown) is disposed on the imaging surface (imaging surface) of the photographing lens. A cover glass CG for protecting the imaging surface is disposed near the imaging surface of the CCD.

  The first lens G1 is, for example, a plano-convex lens having a convex surface facing the object side. The second lens G2 is, for example, a negative meniscus lens having a convex surface facing the image side.

  The third lens G3 is an aspheric lens having at least one aspheric surface. The third lens G3 is, for example, a meniscus lens having a convex surface facing the object side in the vicinity of the paraxial axis. The third lens G3 is preferably aspheric on both sides for aberration correction.

The third lens G3 is configured such that an infrared cut component is uniformly mixed as a lens material and satisfies the following conditional expressions (1) to (3).
0.8 <B / D <1.2 (1)
0.8 <A / B <1.2 (2)
2.0 <E / F (3)

  The concept of parameters A, B, D, E, and F in conditional expressions (1) to (3) is shown in FIG. In conditional expressions (1) to (3), A is the thickness at the maximum effective height of the third lens G3, which is an aspheric lens for cutting infrared rays, and B is 1 / the maximum effective height of the third lens G3. The thickness at 2 and D indicate the thickness of the third lens G3 on the optical axis. E is the height from the optical axis Z1 when the principal ray C3 having the maximum angle of view passes through the image side surface of the third lens G3, and F is the principal ray C2 having an angle of view that is ½ of the maximum angle of view. The height from the optical axis Z1 when passing through the image side surface of the third lens G3 is shown.

  The characteristic part of the photographing lens according to the present embodiment is an aspherical lens (third lens G3) for cutting infrared rays, and the configuration of the other lenses is not limited to that shown in the figure, and the number of lenses and the lenses thereof are not limited. Other configurations may be taken with respect to shape and the like. The aspherical lens for cutting infrared rays is preferably used as the final lens closest to the image plane. However, a lens other than the final lens may be an aspherical lens for cutting infrared rays. Also, the number of aspherical lenses for cutting infrared rays is not limited to one, but may be two or more.

  Next, operations and effects of the photographic lens configured as described above will be described.

  In this photographing lens, an infrared cut component is uniformly mixed in the lens material of the third lens G3, which is an aspheric lens, and the conditional expressions (1) and (2) are satisfied with respect to the aspheric lens. The optical path length difference due to the angle of view of the light beam passing through the aspherical lens is determined by making the lens shape with a small thickness difference and making the position of the light beam passing through the aspherical lens satisfying the conditional expression (3). Is reduced as much as possible, and the infrared cut effect is obtained uniformly over the entire shooting screen.

  If the numerical range of conditional expressions (1) and (2) is exceeded, the difference in lens thickness between the central part and the peripheral part becomes large, and it becomes difficult to obtain an infrared cut effect uniformly over the entire screen. . Further, in this photographing lens, the lens that incorporates the infrared cut component is an aspherical lens, and the light ray position that passes through the aspherical lens is made appropriate by satisfying conditional expression (3), so that the aberration correction effect, In particular, an image plane correction effect is obtained. If the lower limit of conditional expression (3) is not reached, the image surface correction effect by the aspherical lens becomes dilute, which is not preferable.

  Usually, in the case of a photographic lens having a small number of lenses, such as a portable photographic lens having three or four lenses, the final lens is expected to have an aberration correction effect by an aspherical surface rather than power. For this reason, in this photographing lens, the third lens G3 as the final lens is an aspherical lens for cutting infrared rays, thereby making the aberration correction effect by the aspherical surface more effective.

  As described above, according to the photographing lens according to the present embodiment, the third lens G3 as the final lens is an aspheric lens, and the infrared cut component is uniformly mixed in the lens material to have the role of infrared cut. In addition, the lens shape has a small thickness difference from the center to the periphery, and the position of the light beam that passes through the aspherical lens is optimized, so aberration correction is ensured while ensuring sufficient manufacturability. The effect and the infrared cut effect can be satisfied at the same time. Thereby, since the infrared cut filter as a separate member can be omitted, it is possible to realize a photographing lens that is advantageous for reducing the number of parts and reducing the size.

  Next, specific numerical examples of the photographing lens according to the present embodiment will be described. FIG. 3 shows a configuration of a photographing lens according to an embodiment of the present invention. The basic configuration of this photographing lens is the same as that of the photographing lens shown in FIG. In FIG. 3, reference numeral Ri is attached so that the surface of the component on the most object side, including the cover glass CG, is first, and sequentially increases toward the image side (imaging side). The curvature radius of the i-th (i = 1 to 8) surface is shown. The symbol Di indicates the surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface.

  Tables 1 and 2 show specific lens data corresponding to the configuration of the photographing lens shown in FIG. Table 1 shows the basic data portion of the lens data, and Table 2 shows the data portion related to the aspheric shape of the lens data.

  In the field of the surface number Si in the lens data shown in Table 1, the surface of the lens element closest to the object side, including the cover glass CG, is taken as the first surface of the photographic lens of the present embodiment, and the order is gradually increased toward the image side. The number of the i-th surface (i = 1 to 8), which is assigned a code so as to increase, is shown. In the column of the radius of curvature Ri, the value of the radius of curvature of the i-th surface from the object side is shown in correspondence with the symbol Ri attached in FIG. Also in the column of the surface interval Di, the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side is shown in correspondence with the reference numerals attached in FIG. The unit of the value of the curvature radius Ri and the surface interval Di is millimeter (mm). In the columns of ndj and νdj, the values of the refractive index and Abbe number for the d-line (587.6 nm) of the j-th lens element (j = 1 to 4) from the object side, including the cover glass CG, are shown. .

  Table 1 also shows the paraxial focal length f (mm), F number (FNO.), And angle of view 2ω (ω: half angle of view) of the entire system as various data.

  In the lens data of Table 1, the symbol “*” attached to the left side of the surface number indicates that the lens surface is aspherical. In this photographic lens, both surfaces S3 and S4 of the second lens G2 and both surfaces S5 and S6 of the third lens G3 are aspherical. In the basic lens data, the numerical value of the radius of curvature near the optical axis (near the paraxial axis) is shown as the radius of curvature of these aspheric surfaces.

In the numerical values of the aspherical data in Table 2, the symbol “E” indicates that the subsequent numerical value is a “exponential exponent” with 10 as the base, and a numerical value represented by an exponential function with 10 as the base. Indicates that the numerical value before “E” is multiplied. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.

In the aspherical surface data, the values of the coefficients A _i and K in the aspherical surface expression expressed by the following expression (A) are described. More specifically, Z is the length (mm) of a perpendicular line drawn from a point on the aspheric surface at a height h from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the apex of the aspheric surface. Show. In this photographic lens, the aspheric shape is represented by effectively using only even-order coefficients A ₄ , A ₆ , A ₈ , and A ₁₀ as aspheric coefficients.

Z = C · h ² / {1+ (1−K · C ² · h ² ) ^1/2 } + A ₄ · h ⁴ + A ₆ · h ⁶ A ₈ · h ⁸ + A ₁₀ · h ¹⁰ (A)
However,
Z: Depth of aspheric surface (mm)
h: Distance from the optical axis to the lens surface (height) (mm)
K: eccentricity C: paraxial curvature = 1 / R
(R: paraxial radius of curvature)
A _i : i-th order (i = 4, 6, 8, 10) aspheric coefficient

The third lens G3 is configured by uniformly mixing an infrared cut component in the lens material. For example, one or more kinds of metal oxides (for example, CuO, FeO, CoO, VO ₂ ) are mixed as an infrared cut component in the glass material.

  Table 3 below shows values related to the conditional expressions (1) to (3). As shown in Table 3, the photographic lens of this example satisfies the conditional expressions (1) to (3).

  4A to 4C show spherical aberration, astigmatism, and distortion (distortion aberration) in the photographing lens of this example. Each aberration diagram shows aberrations with the d-line as a reference wavelength, while the spherical aberration diagram also shows aberrations for the g-line (wavelength 435.8 nm) and C-line (wavelength 656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal direction and the broken line indicates the tangential direction. ω indicates a half angle of view.

  FIG. 5 shows an example of the spectral transmittance of the third lens G3 in which an infrared cut component is mixed. The horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (%). As shown, the infrared component is well cut.

  As can be seen from the above numerical data and aberration diagrams, in this embodiment, the aberration is corrected well, and the shape of the third lens G3 for cutting infrared rays has a small thickness difference from the center to the periphery. Therefore, a good infrared cut effect can be obtained. As a result, a photographing lens advantageous in reducing the number of parts and reducing the size can be realized.

  In addition, this invention is not limited to the said embodiment and Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

It is a lens sectional view showing an example of composition of a photography lens concerning one embodiment of the present invention. It is explanatory drawing about the shape of the 3rd lens in the photographic lens which concerns on one embodiment of this invention. 1 is a lens cross-sectional view of a taking lens according to an embodiment of the present invention. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the photographing lens according to one example of the present invention. It is a characteristic view which shows the spectral transmittance of the photographic lens which concerns on one Example of this invention.

Explanation of symbols

CG ... cover glass, St ... stop, Gj ... jth lens from the object side, Ri ... radius of curvature of i-th lens surface from the object side, Di ... i-th and i + 1th lens surfaces from the object side , Z1... Optical axis.

Claims (2)

An aspheric lens having at least one aspheric surface;
An infrared cut component is uniformly mixed in the lens material of the aspheric lens,
In addition, the photographic lens is configured to satisfy the following conditional expressions (1) to (3) with respect to the shape of the aspheric lens.
0.8 <B / D <1.2 (1)
0.8 <A / B <1.2 (2)
2.0 <E / F (3)
However,
A: Thickness at the maximum effective height of the aspherical lens B: Thickness at half the maximum effective height of the aspherical lens D: Thickness on the optical axis of the aspherical lens E: Maximum field angle Height from the optical axis when the principal ray of the aspherical lens passes through the image side surface of the aspherical lens F: The principal ray at the angle of view of half the maximum field angle passes through the image side surface of the aspherical lens Height from the optical axis when passing The photographic lens according to claim 1, wherein the aspheric lens is disposed closest to the image plane, and both surfaces are aspheric.

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