JP2005227755A - Small imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small imaging lens used in imaging equipment for a portable phone, a personal digital assistant and an electronic still camera or the like, which gives priority to the miniaturization of configuration firstly, which has excellent imaging performance and distortion aberration characteristic, sufficient peripheral light quantity and appropriate back focus, and which realizes the miniaturization while securing the position of an exit pupil as long as possible. <P>SOLUTION: The small imaging lens is constituted of an aperture diaphragm and a 1st positive lens succeeding it, a 2nd negative lens and a 3rd positive or negative lens in order from an object side, and the respective lenses have at least one or more aspherical surfaces. The imaging lens satisfies following conditional expressions. (1) 0.9<f/f1<1.3, (2) 1.0<TL/f<1.6, (3) 0.25<fB/f<0.65 and(4) 45<ν1, provided that f: the focal distance of an entire lens system, f1: the focal distance of the 1st lens, TL: length from the first surface of the lens to an imaging surface (parallel plane part is converted to air length) fB: length from the final surface of the lens to the imaging surface (parallel plane part is converted to air length), and ν1: the Abbe number of the material of the 1st lens. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In particular, the present invention relates to a compact imaging lens used in an imaging device such as a mobile phone, a portable terminal, and an electronic still camera, and more particularly to a compact imaging lens in which the first priority is to be small in its configuration. It is.

  Imaging devices used in mobile phones, mobile terminals, electronic still cameras, etc., which have become very popular in recent years, have rapidly expanded their use range as information communication infrastructure has been improved and expanded, and various electronic devices have become more sophisticated and smaller. It is also diversifying.

  In particular, there is a remarkable explosive spread to portable terminals called mobile phones and PDAs. In particular, in the product group that adds an imaging function to these mobile phones and mobile terminals, the development and expansion of the information and communication infrastructure has led to the realization of an environment where image data can be transmitted and received without stress. Acquiring the position greatly contributes to the spread of mobile phones and mobile terminals.

  One of the features of mobile phones, PDAs, etc. is that they are small. For this reason, the imaging devices mounted on them are inevitably required to be small.

  In other words, an optical lens that forms an image on an imaging element such as a CCD or CMOS sensor used in an imaging device is first required to be small. In addition, it is required to have good imaging performance and distortion characteristics, a sufficient amount of peripheral light, an appropriate back focus, and an exit pupil position as long as possible.

  An imaging lens having an excellent imaging performance, a small size, and a three-lens configuration suitable for a videophone or a surveillance camera has been disclosed. (For example, see Patent Document 1)

JP 09-288234 A

  However, the speed of downsizing and thinning of recent mobile phones, PDAs, and electronic still cameras is extremely fast, and the same downsizing is required for imaging devices.

  Further, in CCD and CMOS sensors, the number of pixels is directly increased because it directly leads to an improvement in image quality such as an increase in resolution. Although details are omitted, in the aforementioned sensor manufactured by a semiconductor process, the increase in the number of pixels is determined by the number of sensors on the silicon wafer, and the pixel pitch is determined by the wiring rule on the silicon wafer. The two are not synchronized.

  Therefore, the physical area of the sensor, which is proportional to the product of the pitch and the number of pixels, often increases temporarily due to the increase in the number of pixels. Increasing the size of the CCD or CMOS sensor itself is an obstacle to downsizing and thinning, but the geometrical optical effect due to the increase in the size of the imaging area of the sensor is a more serious problem.

  This is because, in the optical system of these imaging devices, when the imaging size increases, the lens aperture and the dimension in the optical axis direction are set to correct aberrations on the imaging surface and to ensure brightness. This is because it becomes necessary to increase the size and it becomes difficult to reduce the size of the imaging lens system.

  In addition, in order to reduce the occurrence of color bias and moire interference found in CCDs and CMOS sensors, an infrared region cut filter and a low-pass filter must be arranged, and a certain amount of back focus is required. It must be ensured, and it is difficult to achieve miniaturization.

  The present invention has been made in view of such problems, and particularly relates to a small imaging lens used in an imaging device such as a mobile phone, a portable terminal, and an electronic still camera. Good imaging performance and distortion characteristics that give priority to certain things, sufficient peripheral light intensity, moderate back focus, and a compact connection that realizes compactness while keeping the exit pupil position as long as possible. An object of the present invention is to provide an image lens.

The small image-forming lens of the present invention includes, in order from the object side, an aperture stop, followed by a positive first lens, a negative second lens, and a positive or negative third lens. A compact imaging lens having a spherical surface and satisfying the following conditional expression.
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1
Where f: focal length of all lens systems f1: focal length of the first lens TL: length from the first lens surface to the image plane (parallel plane portion is converted to air length)
fB: Length from the last lens surface to the image plane (parallel plane portion is converted to air length)
ν1: Abbe number of the first lens material

  First, by setting the aperture stop on the object side, it is necessary to make the exit pupil position as large as possible with respect to the imaging plane. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action. If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it is difficult to reduce the size.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, miniaturization cannot be achieved, and if the lower limit is exceeded, miniaturization is possible, but the power of each lens becomes excessive and good performance cannot be maintained.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition becomes disadvantageous.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it must be made of a low dispersion material having a large Abbe number in order to correct chromatic aberration. If the lower limit is exceeded, chromatic aberration increases.

In the small imaging lens that satisfies the above-described conditional expressions (1) to (4), the second lens is further a small imaging lens that satisfies the following conditions.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5
Where f2: focal length of the second lens R4: paraxial radius of curvature of the image side surface of the second lens

  It is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens and the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby achieving both miniaturization and high performance. Is possible.

  In the present invention, as described above, it is necessary to secure a certain amount of back focus. Therefore, it is inappropriate to use a positive lens, and the negative lens should be as close to the object side as possible from the exit pupil condition. It is advantageous. Therefore, in the present invention, this is achieved by giving a negative power to the second lens as in the conditional expression (5). If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. If the lower limit is exceeded, sufficient back focus cannot be obtained.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. If the upper limit of conditional expression (6) is exceeded, concentricity will be insufficient and coma will become large, and if it exceeds the lower limit, coma will be overcorrected.

In the small imaging lens that satisfies the above-described conditional expressions (1) to (4), the third lens is further a small imaging lens that satisfies the following conditions.
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0
Where f3: focal length of the third lens R5: paraxial radius of curvature of the object side surface of the third lens

  Conditional expression (7) defines the power of the third lens, but various aberrations remaining in the positive first lens and the negative second lens are finally corrected by the third lens having a small power. The range that can be properly balanced is shown. Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. When the negative power is increased beyond the lower limit, the exit pupil condition is deteriorated.

  Conditional expression (8) defines a paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes. If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous, but the exit pupil condition is deteriorated.

In the small imaging lens that satisfies the above-described conditional expressions (1) to (4), the second lens further satisfies the following conditions (5) and (6):
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5
In addition, the third lens is a small imaging lens characterized by further satisfying the following conditional expressions (7) and (8).
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0
However,
f2: focal length R4 of the second lens: paraxial radius of curvature of the image side surface of the second lens f3: focal length of the third lens R5: paraxial radius of curvature of the object side surface of the third lens

  The meanings defined by the above conditional expressions (5) to (8) are described in (0017) to (0023). By adopting a configuration that satisfies these conditions at the same time, it is possible to obtain a higher quality compact imaging lens.

  Further, in the compact imaging lens satisfying the conditional expressions (1) to (8) described above, the aspherical shapes of the second lens and the third lens further increase in shape toward the periphery with respect to the paraxial radius of curvature. Is a small imaging lens having an aspherical shape with a large radius of curvature at least once.

  As described above, the aspherical shape has a configuration in which the radius of curvature increases at least once as it goes to the peripheral portion with respect to the paraxial radius of curvature, particularly for the second lens. The negative power at the center is weakened at the periphery, and the peripheral luminous flux can pass smoothly.

  Also for the third lens, it is possible to correct the non-concentricity of the curvature radius of the center of the lens with respect to the peripheral light beam, thereby improving the distortion aberration and improving the exit pupil condition.

  Further, the above-mentioned conditional expressions (1) to (8) are satisfied, and the aspherical shapes of the second lens and the third lens are at least once as the shape goes to the peripheral part with respect to the paraxial radius of curvature. In a compact imaging lens having an aspherical shape with a large radius of curvature, each lens is a compact imaging lens made of a resin material.

  By using a resin material as the lens material, injection molding becomes possible, and a uniform and high-quality compact imaging lens component can be mass-produced inexpensively.

  According to the first aspect of the present invention, it is necessary to set the exit pupil position as large as possible with respect to the imaging plane by first placing the aperture stop on the object side. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action.

If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it is difficult to reduce the size.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, miniaturization cannot be achieved, and if the lower limit is exceeded, miniaturization is possible, but the power of each lens becomes excessive and good performance cannot be maintained.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition becomes disadvantageous.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it must be made of a low dispersion material having a large Abbe number in order to correct chromatic aberration. If the lower limit is exceeded, chromatic aberration increases.

  According to the invention of claim 2, it is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (5) is to obtain an appropriate back focus, and this is achieved by giving negative power to the second lens. If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. If the lower limit is exceeded, sufficient back focus cannot be obtained.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. If the upper limit of conditional expression (6) is exceeded, concentricity will be insufficient and coma will become large, and if it exceeds the lower limit, coma will be overcorrected.

  According to the invention of claim 3, it is desirable that the third lens satisfies the conditions of the conditional expressions (7) and (8). By giving auxiliary power and shape to the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (7) is for obtaining an improvement in aberrations, and defines the power of the third lens. Various aberrations remaining in the positive first lens and the negative second lens are converted into the first power with a small power. The range that can be finally corrected and properly balanced by three lenses is shown.

  Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. When the negative power is increased beyond the lower limit, the exit pupil condition is deteriorated.

  Conditional expression (8) is for obtaining improvement in aberration and taking the exit pupil far, and in particular defines the paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes.

  If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous, but the exit pupil condition is deteriorated.

  According to the invention of claim 4, the second lens satisfies the conditions of the conditional expressions (5) and (6), and the third lens satisfies the conditional expressions (7) and (8). By using these simultaneously, the overall effect of the invention can be expected.

  By giving auxiliary power and shape to the second lens and the third lens, respectively, the condition of the first lens and the third lens can be changed. Various aberrations that cannot be corrected only by the combination are corrected, and this makes it possible to achieve both miniaturization and high performance.

  According to the invention of claim 5, the aspherical shape has a configuration in which the radius of curvature increases at least once as it goes to the peripheral portion with respect to the paraxial radius of curvature, particularly for the second lens. As a result, the negative power at the center of the lens is weakened at the periphery, and the peripheral luminous flux can be passed smoothly.

  Also for the third lens, it is possible to correct the non-concentricity of the curvature radius of the center of the lens with respect to the peripheral light beam, thereby improving the distortion aberration and improving the exit pupil condition.

  As in the sixth aspect of the invention, by using a resin material as the lens material, injection molding becomes possible, and a uniform and high-quality compact imaging lens component can be mass-produced at low cost.

  The best embodiment of the compact imaging lens in the present invention will be shown below, but the present invention is not limited to this without departing from the gist of the present invention.

Here, symbols used in the description of the embodiments are as follows.
F: F number of lens f: Focal length of all lens systems f *: Focal length of each lens (* is a number corresponding to each lens)
R *: Radius of curvature of lens surface (* has a number corresponding to each surface)
D: Distance (interval) between each surface
nd: Refractive index νd of each lens material at d-line: Abbe number of each lens ν *: Abbe number of each lens (* has a number corresponding to each lens)
TL: Length from the first lens surface to the image plane (parallel plane portion is air length converted)
fB: Length from the last lens surface to the image plane (parallel plane portion is air length converted)
ω: Half angle of view (unit: degrees)

  Equation 1 when the lens is aspherical is described as follows.

ただし、ｋ＝α_１＋１ とし、
Ｃ ：非球面頂点の曲率
α_１ ：円錐係数
α_２〜α_１０ ：非球面係数
ρ ：光軸からの高さ
Ｚ ：レンズ面頂点における接平面から光軸方向への距離
である。

Where k = α ₁ +1 and
C: curvature of the aspherical vertex α ₁ : conical coefficient α _{2 to} α ₁₀ : aspherical coefficient ρ: height from the optical axis Z: distance from the tangential plane at the vertex of the lens surface to the optical axis direction.

  Hereinafter, the best embodiment of the present invention will be described with reference to FIGS. 1-1, 1-2, Table 1-1, Table 1-2, and Table 3. FIG. FIG. 1-1 illustrates a lens layout and an optical path according to the configuration of the present invention. FIG. 1-2 is an aberration diagram of this example, and spherical, astigmatism, and distortion aberrations are illustrated as A, B, and C in FIG. 1-2. In Table 1-1, each lens surface used in the compact imaging lens of the present invention is numbered, and each surface has a radius of curvature R, a distance (interval) D, a refractive index nd, an Abbe number for each lens. It is a table compiled by entering νd. Table 1-2 describes the aspherical coefficient when the surface of Table 1-1 is described by the above-described Equation 1.

  Table 3 is a table summarizing specific numerical values to be substituted into the conditional expressions (1) to (3) and (5) to (8) described in the claims, and the calculated results. The numerical values are those that give better results within a given range of conditions. Table 3 also shows the calculation results in Examples 1 to 3 in addition to the best example. Further, in the items in Table 3, the description of the calculation part that is not directly related to the present invention is omitted.

  FIG. 1-1 illustrates a lens layout, and there is an object (not shown) to be imaged on the left side of the drawing. Next, an aperture stop 1-1-5, a first lens 1-1-1, A second lens 1-1-2, a third lens 1-1-3, an LPF (optical low-pass filter) 1-1-4, and an imaging sensor surface 1-1-6 as an imaging surface are disposed. . The thickness of the imaging sensor is not shown. Reference numeral 1-1-7 denotes a lens optical axis.

  In FIG. 1-1, numbers from 1 to 9 are assigned to the surface of the optical element from the object side surface of the first lens 1-1-1 to the imaging sensor surface 1-1-6. It matches the surface number used in. 1-1 and Table 1-1, regarding the aperture stop, the thickness is regarded as 0 and the surface number is 0.

  In the optical paths 1 (1-1-8) to 4 (1-1-11) shown in FIG. 1-1, the angle formed with the lens optical axis 1-1-7 when entering the lens is a half angle of view ω. Is shown by three line segments. FIG. 1-1 shows the total angle of view 2ω in this embodiment.

From Tables 1-1 and 3, in this example, f / f1 is 1.118, TL / f is 1.341, fB / f is 0.478, and the Abbe number ν1 of the first lens is 56.2. It can be seen that the following conditional expression defined in claim 1 is satisfied.
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1

  First, by placing the aperture stop on the object side, the exit pupil position can be made as large as possible with respect to the imaging plane. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action. If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it becomes difficult to reduce the size. However, in this embodiment, an appropriate value is adopted with f / f1 being 1.118. ing.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, downsizing cannot be achieved, and if the lower limit is exceeded, downsizing is possible, but the power of each lens is excessive and good performance cannot be maintained. An appropriate value is adopted with TL / f set to 1.341.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition is disadvantageous. However, in this embodiment, an appropriate value is adopted with fB / f being 0.478.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it is necessary to use a low dispersion material having a large Abbe number in order to correct chromatic aberration. When the lower limit is exceeded, chromatic aberration increases. An appropriate value is adopted as 56.2.

From Table 1-1 and Table 3, f / f2 is -0.418 and f / R4 is -1.360 in this embodiment, and the following conditional expression defined in claim 2 is satisfied. I understand.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5

  According to the invention of claim 2, it is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (5) is to obtain an appropriate back focus, and this is achieved by giving negative power to the second lens. If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. When the lower limit is exceeded, sufficient back focus cannot be obtained. However, in this embodiment, an appropriate value is adopted with f / f2 set to -0.418.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. When the upper limit of conditional expression (6) is exceeded, concentricity is insufficient and coma becomes large. When the lower limit is exceeded, coma is overcorrected, but in this embodiment, f / R4 is set to −1.360. The value is adopted.

From Table 1-1 and Table 3, it can be seen that f / f3 is 0.282 and f / R5 is 2.192 in this embodiment, which satisfies the following conditional expression defined in claim 3. .
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0

  According to the invention of claim 3, it is desirable that the third lens satisfies the conditions of the conditional expressions (7) and (8). By giving auxiliary power and shape to the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (7) is for obtaining an improvement in aberrations, and defines the power of the third lens. Various aberrations remaining in the positive first lens and the negative second lens are converted into the first power with a small power. The range that can be finally corrected and properly balanced by three lenses is shown.

  Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. When the negative power increases beyond the lower limit, the exit pupil condition deteriorates. In this embodiment, f / f3 is set to 0.282, and an appropriate value is adopted.

  Conditional expression (8) is for obtaining improvement in aberration and taking the exit pupil far, and in particular defines the paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes.

  If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous but the exit pupil condition deteriorates, but f / R5 is set to 2 . 192 is an appropriate value.

  According to Table 1-2, it can be seen that the curvature of the lens surface of each aspheric lens of the present example increases as it goes from the vicinity of the optical axis to the periphery, and satisfies the condition of claim 5. Yes.

  As described above, the compact imaging lens of the present example satisfies all the conditions of claims 1 to 3, and further, since these are realized at the same time, the condition of claim 4 is also satisfied. While having image performance and distortion characteristics, a sufficient amount of peripheral light, and an appropriate back focus, the exit pupil position can be made as long as possible and a small size can be realized.

  In addition, by forming the three lenses with a resin material, injection molding becomes possible, and a uniform and high-quality compact imaging lens can be mass-produced at low cost.

This embodiment is the best embodiment in which the balance between size and aberration is well taken. Aberration diagrams of the present example are shown in FIGS. In the figure, 1-2-1 is spherical aberration at the C line, 1-2-2 is spherical aberration at the d line, 1-2-3 is spherical aberration at the e line, and 1-2-4 is spherical aberration at the F line. 1-2-5 is spherical aberration in g-line, 1-2-6 is sagittal, 1-2-7 is tangential, 1-2-8 indicates distortion.

  Hereinafter, Example 1 is demonstrated using FIGS. 2-1, 2-2, Table 2-1, Table 2-2, and Table 3. FIG. FIG. 2A illustrates a lens layout and an optical path according to the configuration of the present invention. FIG. 2-2 is an aberration diagram of this example, and spherical, astigmatism, and distortion aberrations are illustrated as A, B, and C in FIG. 2-2. Table 2-1 numbers each lens surface used in the compact imaging lens of the present invention, the radius of curvature R, the distance (interval) D for each surface, the refractive index nd, the Abbe number for each lens. It is a table compiled by entering νd. Table 2-2 describes the aspherical coefficients when the surface of Table 2-1 is described by the above-described Equation 1.

  Table 3 is a table summarizing specific numerical values to be substituted into the conditional expressions (1) to (3) and (5) to (8) described in the claims, and the calculated results. The numerical values are those that give better results within a given range of conditions. Table 3 also shows the calculation results in the best example and the examples 2 and 3 in addition to the example 1. Further, in the items in Table 3, the description of the calculation part that is not directly related to the present invention is omitted.

  FIG. 2-1 shows the layout of the lens, and there is an object (not shown) to be imaged on the left side of the drawing. Next, the aperture stop 2-1-5, the first lens 2-1-1. A second lens 2-1-2, a third lens 2-1-3, an LPF (optical low-pass filter) 2-1-4, and an imaging sensor surface 2-1-6 that is an imaging surface. Yes. The thickness of the imaging sensor is not shown. Reference numeral 2-1-7 denotes a lens optical axis.

  2A, numbers from 1 to 9 are assigned to the surfaces of the optical elements from the object side surface of the first lens 2-1-1 to the imaging sensor surface 2-1-6. It matches the surface number used in -1. In both FIGS. 2-1 and 2-1, regarding the aperture stop, the thickness is regarded as 0 and the surface number is set to 0.

  The optical paths 1 (2-1-8) to 4 (2-1-11) shown in FIG. 2-1 each have an angle formed by the lens optical axis 2-1-7 when incident on the lens with a half angle of view ω. Is shown by three line segments. FIG. 2A shows the total angle of view 2ω in this embodiment.

From Tables 2-1 and 3, in this example, f / f1 is 1.075, TL / f is 1.186, fB / f is 0.404, and the Abbe number ν1 of the first lens is 56.2. It can be seen that the following conditional expression defined in claim 1 is satisfied.
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1

  First, by placing the aperture stop on the object side, the exit pupil position can be made as large as possible with respect to the imaging plane. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action. If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it becomes difficult to reduce the size. However, in this embodiment, an appropriate value is adopted with f / f1 being 1.075. ing.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, downsizing cannot be achieved, and if the lower limit is exceeded, downsizing is possible, but the power of each lens is excessive and good performance cannot be maintained. An appropriate value is adopted with TL / f being 1.186.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition becomes disadvantageous. However, in this embodiment, an appropriate value is adopted with fB / f being 0.404.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it is necessary to use a low dispersion material having a large Abbe number in order to correct chromatic aberration. When the lower limit is exceeded, chromatic aberration increases. An appropriate value is adopted as 56.2.

From Tables 2-1 and 3, f / f2 is -0.441 and f / R4 is -1.592 in this embodiment, and the following conditional expression defined in claim 2 is satisfied. I understand.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5

  According to the invention of claim 2, it is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (5) is to obtain an appropriate back focus, and this is achieved by giving negative power to the second lens. If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. If the lower limit is exceeded, sufficient back focus cannot be obtained, but in this embodiment, f / f2 is set to -0.441, and an appropriate value is adopted.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. When the upper limit of conditional expression (6) is exceeded, concentricity is insufficient and coma becomes large. When the lower limit is exceeded, coma is overcorrected, but in this embodiment, f / R4 is set to -1.592. The value is adopted.

From Table 2-1 and Table 3, it can be seen that f / f3 is 0.296 and f / R5 is 2.332 in this example, which satisfies the following conditional expression defined in claim 3. .
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0

  According to the invention of claim 3, it is desirable that the third lens satisfies the conditions of the conditional expressions (7) and (8). By giving auxiliary power and shape to the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (7) is for obtaining an improvement in aberrations, and defines the power of the third lens. Various aberrations remaining in the positive first lens and the negative second lens are converted into the first power with a small power. The range that can be finally corrected and properly balanced by three lenses is shown.

  Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. If the negative power increases beyond the lower limit, the exit pupil condition deteriorates. In this embodiment, f / f3 is set to 0.296 and an appropriate value is adopted.

  Conditional expression (8) is for obtaining improvement in aberration and taking the exit pupil far, and in particular defines the paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes.

  If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous but the exit pupil condition deteriorates, but f / R5 is set to 2 .332 is an appropriate value.

  According to Table 2-2, it can be seen that the curvature of the lens surface of each aspherical lens of the present example increases as it goes from the vicinity of the optical axis to the periphery, and the condition of claim 5 is satisfied. Yes.

  As described above, the compact imaging lens of this example satisfies all the conditions of claims 1 to 3, and further, since these are realized at the same time, the condition of claim 4 is also satisfied. While having image performance and distortion characteristics, a sufficient amount of peripheral light, and an appropriate back focus, the exit pupil position can be made as long as possible and a small size can be realized.

  In addition, by forming the three lenses with a resin material, injection molding becomes possible, and a uniform and high-quality compact imaging lens can be mass-produced at low cost.

The lens system of the present embodiment is sufficiently small but slightly larger than the other embodiments. Instead, the aberration can be reduced. Aberration diagrams of this example are shown in FIGS. In the figure, 2-2-1 is the spherical aberration at the C line, 2-2-2 is the spherical aberration at the d line, 2-2-3 is the spherical aberration at the e line, and 2-2-4 is the spherical aberration at the F line. 2-2-5 indicates spherical aberration at g-line, 2-2-6 indicates sagittal, 2-2-7 indicates tangential, and 2-2-8 indicates distortion.

  Hereinafter, Example 2 of the present invention will be described with reference to FIG. 3-1, FIG. 3-2, Table 3-1, Table 3-2, and Table 3. FIG. 3A illustrates a lens layout and an optical path according to the configuration of the present invention. FIG. 3-2 is an aberration diagram of this example, and spherical, astigmatism, and distortion aberrations are illustrated as A, B, and C in FIG. 3-2. Table 3-1 numbers each lens surface used in the compact imaging lens of the present invention, the radius of curvature R, the distance (interval) D for each surface, the refractive index nd, the Abbe number for each lens. It is a table compiled by entering νd. Table 3-2 shows the aspherical coefficients when the surface of Table 3-1 is described by the above-described Equation 1.

  Table 3 is a table summarizing specific numerical values to be substituted into the conditional expressions (1) to (3) and (5) to (8) described in the claims, and the calculated results. The numerical values are those that give better results within a given range of conditions. Table 3 also shows the calculation results in the best example and the examples 1 and 3 in addition to the example 2. Further, in the items in Table 3, the description of the calculation part that is not directly related to the present invention is omitted.

  FIG. 3A shows a lens layout, and there is an object (not shown) to be imaged on the left side of the drawing. Next, an aperture stop 3-1-5, a first lens 3-1-1, A second lens 3-1-3, a third lens 3-1-3, an LPF (optical low-pass filter) 3-1-4, and an imaging sensor surface 3-1-6 that is an imaging surface are arranged. . The thickness of the imaging sensor is not shown. Reference numeral 3-1-7 denotes a lens optical axis.

  In FIG. 3A, numbers from 1 to 9 are assigned to the surfaces of the optical elements from the object side surface of the first lens 3-1-1 to the imaging sensor surface 3-1-6. It matches the surface number used in -1. In both FIGS. 3A and 3B, regarding the aperture stop, the thickness is regarded as 0 and the surface number is set to 0.

  The optical paths 1 (3-1-8) to 4 (3-1-11) shown in FIG. 3A each have an angle of half angle of view ω with the lens optical axis 3-1-7 when entering the lens. Is shown by three line segments. FIG. 3A shows the total angle of view 2ω in this embodiment.

From Tables 3-1 and 3, in this example, f / f1 is 1.128, TL / f is 1.236, fB / f is 0.475, and the Abbe number ν1 of the first lens is 56.2. It can be seen that the following conditional expression defined in claim 1 is satisfied.
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1

  First, by placing the aperture stop on the object side, the exit pupil position can be made as large as possible with respect to the imaging plane. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action. If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it becomes difficult to reduce the size. However, in this embodiment, an appropriate value is adopted with f / f1 being 1.128. ing.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, downsizing cannot be achieved, and if the lower limit is exceeded, downsizing is possible, but the power of each lens is excessive and good performance cannot be maintained. An appropriate value is adopted with TL / f being 1.236.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition becomes disadvantageous. However, in this embodiment, an appropriate value is adopted with fB / f being 0.475.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it is necessary to use a low dispersion material having a large Abbe number in order to correct chromatic aberration. When the lower limit is exceeded, chromatic aberration increases. An appropriate value is adopted as 56.2.

From Tables 3-1 and 3, f / f2 is -0.455 and f / R4 is -1.454 in the present embodiment, and the following conditional expression defined in claim 2 is satisfied. I understand.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5

  According to the invention of claim 2, it is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (5) is to obtain an appropriate back focus, and this is achieved by giving negative power to the second lens. If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. If the lower limit is exceeded, sufficient back focus cannot be obtained, but in this embodiment, an appropriate value is adopted with f / f2 set to -0.455.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. When the upper limit of conditional expression (6) is exceeded, concentricity is insufficient and coma increases. When the lower limit is exceeded, coma is overcorrected, but in this embodiment, f / R4 is set to −1.454 and is appropriate. The value is adopted.

From Table 3-1 and Table 3, it can be seen that f / f3 is 0.303 and f / R5 is 2.373 in this example, which satisfies the following conditional expression defined in claim 3. .
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0

  According to the invention of claim 3, it is desirable that the third lens satisfies the conditions of the conditional expressions (7) and (8). By giving auxiliary power and shape to the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (7) is for obtaining an improvement in aberrations, and defines the power of the third lens. Various aberrations remaining in the positive first lens and the negative second lens are converted into the first power with a small power. The range that can be finally corrected and properly balanced by three lenses is shown.

  Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. If the negative power increases beyond the lower limit, the exit pupil condition deteriorates. However, in this embodiment, f / f3 is set to 0.303 and an appropriate value is adopted.

  Conditional expression (8) is for obtaining improvement in aberration and taking the exit pupil far, and in particular defines the paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes.

  If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous but the exit pupil condition deteriorates, but f / R5 is set to 2 . 373 is an appropriate value.

  According to Table 3-2, it can be seen that the curvature of the lens surface of each aspherical lens of the present example increases as it goes from the vicinity of the optical axis to the periphery, and the condition of claim 5 is satisfied. Yes.

  As described above, the compact imaging lens of the present example satisfies all the conditions of claims 1 to 3, and further, since these are realized at the same time, the condition of claim 4 is also satisfied. While having image performance and distortion characteristics, a sufficient amount of peripheral light, and an appropriate back focus, the exit pupil position can be made as long as possible and a small size can be realized.

  In addition, by forming the three lenses with a resin material, injection molding becomes possible, and a uniform and high-quality compact imaging lens can be mass-produced at low cost.

  The lens system of the present embodiment has a large back focus as compared with other embodiments of the present invention. This is an embodiment that can be miniaturized while allowing flexibility in the arrangement of LPFs and the like.

Aberration diagrams of the present example are shown in A, B, and C of FIG. In the figure, 3-2-1 is spherical aberration at C line, 3-2-2 is spherical aberration at d line, 3-2-3 is spherical aberration at e line, and 3-2-4 is spherical aberration at F line. 3-2-5 represents spherical aberration at g-line, 3-2-6 represents sagittal, 3-2-7 represents tangential, and 3-2-8 represents distortion.

  Hereinafter, Example 3 of the present invention will be described with reference to FIGS. 4-1, 4-2, Table 4-1, Table 4-2, and Table 3. FIG. FIG. 4A illustrates a lens layout and an optical path according to the configuration of the present invention. FIG. 4-2 is an aberration diagram of this example. The spherical, astigmatism, and distortion aberrations are shown as A, B, and C in FIG. 4-2. Table 4-1 numbers each lens surface used in the compact imaging lens of the present invention, the curvature radius R and distance (interval) D for each surface, the refractive index nd and the Abbe number for each lens. It is a table compiled by entering νd. Table 4-2 shows the aspherical coefficients when the surface of Table 4-1 is described by the above-described Equation 1.

  Table 3 is a table summarizing specific numerical values to be substituted into the conditional expressions (1) to (3) and (5) to (8) described in the claims, and the calculated results. The numerical values are those that give better results within a given range of conditions. Table 3 also shows the calculation results in the best example and the examples 1 and 2 in addition to the example 3. Further, in the items in Table 3, the description of the calculation part that is not directly related to the present invention is omitted.

  FIG. 4A shows the layout of the lens, and there is an object (not shown) to be imaged on the left side of the drawing. Next, the aperture stop 4-1-5, the first lens 4-1-1, A second lens 4-1-2, a third lens 4-1-3, an LPF (optical low-pass filter) 4-1-4, and an imaging sensor surface 4-1-6 that is an imaging surface are arranged. . The thickness of the imaging sensor is not shown. 4-1-7 is a lens optical axis.

  4A, numbers from 1 to 9 are assigned to the surfaces of the optical elements from the object side surface of the first lens 4-1-1 to the imaging sensor surface 4-1-6. It matches the surface number used in -1. In both FIG. 4-1 and Table 4-1, regarding the aperture stop, the thickness is regarded as 0 and the surface number is 0.

  The optical paths 1 (4-1-8) to 4 (4-1-11) shown in FIG. 4-1 each have an angle formed by the lens optical axis 4-1-7 when incident on the lens with a half angle of view ω. Is shown by three line segments.

From Tables 4-1 and 3, in this example, f / f1 is 1.063, TL / f is 1.209, fB / f is 0.446, and the Abbe number ν1 of the first lens is 56.2. It can be seen that the following conditional expression defined in claim 1 is satisfied.
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1

  First, by placing the aperture stop on the object side, the exit pupil position can be made as large as possible with respect to the imaging plane. Next, as shown in the conditional expression (1), the first lens is given a large positive power so as to be the center of the imaging action. If the upper limit of conditional expression (1) is exceeded, the power of the first lens will be excessive, and various aberrations will occur and good performance will not be obtained. If the lower limit of conditional expression (1) is exceeded, it is advantageous for aberration correction, but the total lens length becomes large and it becomes difficult to reduce the size. However, in this embodiment, an appropriate value is adopted with f / f1 being 1.063. ing.

  Further, the condition for miniaturization is as shown in conditional expression (2). If the upper limit of conditional expression (2) is exceeded, downsizing cannot be achieved, and if the lower limit is exceeded, downsizing is possible, but the power of each lens is excessive and good performance cannot be maintained. An appropriate value is adopted with TL / f set to 1.209.

  Conditional expression (3) is to obtain an appropriate back focus. If the lower limit is exceeded, the space space is too small, and it is difficult to place a filter or the like. Alternatively, the negative power of the third lens becomes excessive and the performance deteriorates, and the exit pupil condition is disadvantageous. However, in this embodiment, an appropriate value is adopted with fB / f being 0.446.

  Conditional expression (4) is a condition for correcting chromatic aberration. Since the first lens has a strong positive power, it is necessary to use a low dispersion material having a large Abbe number in order to correct chromatic aberration. When the lower limit is exceeded, chromatic aberration increases. An appropriate value is adopted as 56.2.

From Table 4-1 and Table 3, f / f2 is -0.477 and f / R4 is -2.035 in this embodiment, and the following conditional expression defined in claim 2 is satisfied. I understand.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5

  According to the invention of claim 2, it is desirable that the second lens satisfies the conditions of the conditional expressions (5) and (6). By providing auxiliary power and shape to the second lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (5) is to obtain an appropriate back focus, and this is achieved by giving negative power to the second lens. If the upper limit of conditional expression (5) is exceeded, negative power becomes excessive and distortion and lateral chromatic aberration are deteriorated. If the lower limit is exceeded, sufficient back focus cannot be obtained, but in this embodiment, an appropriate value is adopted with f / f2 set to -0.477.

  Conditional expression (6) is a condition for coma aberration correction. Coma aberration is reduced by concentrically arranging the paraxial radius of curvature of the image side surface of the second lens with respect to the light beam incident on the second lens. When the upper limit of conditional expression (6) is exceeded, concentricity is insufficient and coma increases. When the lower limit is exceeded, coma is overcorrected, but in this embodiment, f / R4 is set to -2.035. The value is adopted.

From Tables 4-1 and 3, f / f3 is -0.027 and f / R5 is 2.259 in this embodiment, and the following conditional expression defined in claim 3 is satisfied. Understand.
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0

  According to the invention of claim 3, it is desirable that the third lens satisfies the conditions of the conditional expressions (7) and (8). By giving auxiliary power and shape to the third lens, various aberrations that cannot be corrected only by the first lens are corrected, thereby making it possible to achieve both miniaturization and high performance. .

  Conditional expression (7) is for obtaining an improvement in aberrations, and defines the power of the third lens. Various aberrations remaining in the positive first lens and the negative second lens are converted into the first power with a small power. The range that can be finally corrected and properly balanced by three lenses is shown.

  Therefore, if the upper limit of conditional expression (7) is exceeded, the positive power of the third lens will be excessive, reducing the back focus and deteriorating chromatic aberration of magnification. If the negative power increases beyond the lower limit, the exit pupil condition deteriorates. In this embodiment, f / f3 is set to -0.027 and an appropriate value is adopted.

  Conditional expression (8) is for obtaining improvement in aberration and taking the exit pupil far, and in particular defines the paraxial shape among the shapes of the third lens. This has the effect of reducing the occurrence of spherical and coma aberrations for low image heights near the paraxial axis and keeping the exit pupil position away from off-axis light fluxes.

  If the upper limit of conditional expression (8) is exceeded, the exit pupil condition is advantageous, but the off-axis coma aberration becomes excessive. If the lower limit is exceeded, spherical aberration and coma aberration are advantageous but the exit pupil condition deteriorates, but f / R5 is set to 2 .259 is an appropriate value.

  According to Table 4-2, it can be seen that the curvature of the lens surface of each aspherical lens of the present example increases as it goes from the vicinity of the optical axis to the periphery, and the condition of claim 5 is satisfied. Yes.

  In addition, by forming the three lenses with a resin material, injection molding becomes possible, and a uniform and high-quality compact imaging lens can be mass-produced at low cost.

  As described above, the compact imaging lens of the present example satisfies all the conditions of claims 1 to 3, and further, since these are realized at the same time, the condition of claim 4 is also satisfied. While having image performance and distortion characteristics, a sufficient amount of peripheral light, and an appropriate back focus, the exit pupil position can be made as long as possible and a small size can be realized.

Aberration diagrams of the present example are shown in FIGS. In the figure, 4-2-1 is the spherical aberration at the C line, 4-2-2 is the spherical aberration at the d line, 4-2-3 is the spherical aberration at the e line, and 4-2-4 is the spherical aberration at the F line. 4-2-5 represents spherical aberration at g-line, 4-2-6 represents sagittal, 4-2-7 represents tangential, and 4-2-8 represents distortion.

FIG. 2 is a diagram illustrating the arrangement of lenses and the optical path in the best embodiment of the present invention, and illustrates an aperture stop, a first lens, a second lens, a third lens, an LPF (optical low-pass filter), and an imaging surface. Furthermore, the optical paths at four different angles of view are represented by three line segments. FIG. 6 is an aberration diagram representing aberrations in the best example of the present invention. A: aberration diagram representing spherical aberration B: aberration diagram representing astigmatism C: aberration diagram representing distortion aberration FIG. 2 is a diagram illustrating the arrangement of lenses and the optical path in Example 1 of the present invention, and illustrates an aperture stop, a first lens, a second lens, a third lens, an LPF (optical low-pass filter), and an imaging surface. In addition, the optical paths at four different angles of view are represented by three line segments. FIG. 6 is an aberration diagram illustrating the aberration in Example 1 of the present invention. A: aberration diagram representing spherical aberration B: aberration diagram representing astigmatism C: aberration diagram representing distortion aberration FIG. 6 is a diagram illustrating the arrangement of lenses and the optical path in Example 2 of the present invention, in which an aperture stop, a first lens, a second lens, a third lens, an LPF (optical low-pass filter), and an imaging surface are illustrated. In addition, the optical paths at four different angles of view are represented by three line segments. FIG. 9 is an aberration diagram illustrating the aberration in Example 2 of the present invention. A: aberration diagram representing spherical aberration B: aberration diagram representing astigmatism C: aberration diagram representing distortion aberration FIG. 7 is a diagram illustrating the arrangement of lenses and the optical path in Example 4 of the present invention, and illustrates an aperture stop, a first lens, a second lens, a third lens, an LPF (optical low-pass filter), and an imaging surface. In addition, the optical paths at four different angles of view are represented by three line segments. FIG. 10 is an aberration diagram illustrating the aberration in Example 4 of the present invention. A: aberration diagram representing spherical aberration B: aberration diagram representing astigmatism C: aberration diagram representing distortion aberration

Explanation of symbols

1-1-1 First lens 1-1-2 Second lens 1-1-3 Third lens 1-1-4 LPF
1-1-5 Aperture stop 1-1-6 Sensor surface 1-1-7 Optical axis 1-1-8 Optical path 1
1-1-9 Optical path 2
1-1-10 Optical path 3
1-1-11 Optical path 4
1-2-1 Spherical Aberration at C Line 1-2-2 Spherical Aberration at d Line 1-2-3 Spherical Aberration at e Line 1-2-4 Spherical Aberration at F Line 1-2-5 Spherical Aberration at g Line 1-2-6 Sagittal 1-2-7 Tangential 1-2-8 Distortion 2-1-1 First Lens 2-1-2 Second Lens 2-1-3 Third Lens 2-1-4 LPF
2-1-5 Aperture stop 2-1-6 Sensor surface 2-1-7 Optical axis 2-1-8 Optical path 1
2-1-9 Optical path 2
2-1-10 Optical path 3
2-1-11 Optical path 4
2-2-1 Spherical aberration at C line 2-2-2 Spherical aberration at d line 2-2-3 Spherical aberration at e line 2-2-4 Spherical aberration at F line 2-2-5 Spherical aberration at g line 2-2-6 sagittal 2-2-7 tangential 2-2-8 distortion 3-1-1 first lens 3-1-2 second lens 3-1-3 third lens 3-1-4 LPF
3-1-5 Aperture stop 3-1-6 Sensor surface 3-1-7 Optical axis 3-1-8 Optical path 1
3-1-9 Optical path 2
3-1-10 Optical path 3
3-1-11 Optical path 4
3-2-1 Spherical aberration at C line 3-2-2 Spherical aberration at d line 3-2-3 Spherical aberration at e line 3-2-4 Spherical aberration at F line 3-2-5 Spherical aberration at g line 3-2-6 Sagittal 3-2-7 Tangential 3-2-8 Distortion 4-1-1 First lens 4-1-2 Second lens 4-1-3 Third lens 4-1-4 LPF
4-1-5 Aperture stop 4-1-6 Sensor surface 4-1-7 Optical axis 4-1-8 Optical path 1
4-1-9 Optical path 2
4-1-10 Optical path 3
4-1-11 Optical path 4
4-2-1 Spherical aberration at C line 4-2-2 Spherical aberration at d line 4-2-3 Spherical aberration at e line 4-2-4 Spherical aberration at F line 4-2-5 Spherical aberration at g line 4-2-6 Sagittal 4-2-7 Tangential 4-2-8 Distortion

Claims (6)

In order from the object side, an aperture stop, followed by a positive first lens, a negative second lens, and a positive or negative third lens, each lens has at least one aspheric surface, and the following conditional expression A compact imaging lens characterized by satisfying
(1) 0.9 <f / f1 <1.3
(2) 1.0 <TL / f <1.6
(3) 0.25 <fB / f <0.65
(4) 45 <ν1
Where f: focal length of all lens systems f1: focal length of the first lens TL: length from the first lens surface to the image plane (parallel plane portion is converted to air length)
fB: Length from the last lens surface to the image plane (parallel plane portion is converted to air length)
ν1: Abbe number of the first lens material 2. The small imaging lens according to claim 1, wherein the second lens further satisfies the following conditional expression.
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5
Where f2: focal length of the second lens R4: paraxial radius of curvature of the image side surface of the second lens 2. The small imaging lens according to claim 1, wherein the third lens further satisfies the following conditional expression.
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0
Where f3: focal length of the third lens R5: paraxial radius of curvature of the object side surface of the third lens The small imaging lens according to claim 1, wherein the second lens further satisfies the following conditional expressions (5) and (6):
(5) -0.7 <f / f2 <-0.3
(6) -4.0 <f / R4 <-0.5
The third lens further satisfies the following conditional expressions (7) and (8):
(7) -0.3 <f / f3 <0.6
(8) 1.5 <f / R5 <4.0
However,
f2: focal length R4 of the second lens: paraxial radius of curvature of the image side surface of the second lens f3: focal length of the third lens R5: paraxial radius of curvature of the object side surface of the third lens 5. The small image forming lens according to claim 1, wherein the aspherical shape of the second lens and the third lens is at least once as the shape moves toward the periphery with respect to the paraxial radius of curvature. A small imaging lens having an aspherical shape with a large radius of curvature. 6. The small imaging lens according to claim 1, wherein each lens is made of a resin material.

Images