JP2016148725A - Wide-angle lens and wide-angle lens unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle lens that has a five-lens configuration and is well corrected for aberrations.SOLUTION: A wide-angle lens 11 comprises a front group G1, and a rear group G2 having positive refractive power in order from the object side. The front group G1 comprises, in order from the object side, a first lens L1 having negative refractive power and a convex meniscus surface on the object side, a second lens L2 having negative refractive power and a convex meniscus surface on the object side, and a third lens L3 having positive refractive power, where at least two surfaces of the first group are rotationally asymmetric. The rear group G2 comprises, in order from the object side, a fourth lens L4 having one of positive and negative refractive power, and a fifth lens L5 having the other of positive and negative refractive power, where at least one surface of the group is rotationally asymmetric.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wide-angle lens and a wide-angle lens unit, and more particularly to a wide-angle lens and a wide-angle lens unit that can favorably correct various aberrations with a five-lens configuration.

  Conventionally, an inexpensive and small-sized wide-angle lens has been proposed by reducing the number of lenses (Patent Documents 1 and 2). The technologies disclosed in Patent Documents 1 and 2 are wide-angle lenses having four and six lenses, respectively, and have at least one rotationally asymmetric surface.

Japanese Patent No. 4748220 JP 2006-11093 A

  However, the above conventional technique has a problem that the image formed by the wide-angle lens is distorted because the distortion at the wide-angle end is large.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wide-angle lens and a wide-angle lens unit that can satisfactorily correct various aberrations with a five-lens configuration.

Means for Solving the Problems and Effects of the Invention

  According to the wide-angle lens of the first aspect, the wide-angle lens includes the front group and the rear group having a positive refractive power in order from the object side. In order from the object side, a first lens that is a meniscus lens having negative refractive power and convex toward the object side, a second lens that is negative meniscus lens having negative refractive power and convex toward the object side, and positive refraction The front lens group includes a third lens having force, and at least two surfaces have rotationally asymmetric surfaces. In order from the object side, a rear group is configured by a fourth lens having one of positive or negative refractive power and a fifth lens having the other positive or negative refractive power, and at least one surface has a rotationally asymmetric surface. . A first rotationally asymmetric surface that is one of the rotationally asymmetric surfaces of the front group is formed on the object side surface of the first lens or the second lens, and a second rotationally asymmetric surface that is one of the rotationally asymmetric surfaces of the front group is formed. It is formed on the image side surface of the first lens or the second lens.

  Orthogonal coordinates with the intersection of the first rotationally asymmetric surface and the second rotationally asymmetric surface and the optical axis as the origin, the optical axis direction as the Z axis, and the axes orthogonal to and orthogonal to the Z axis as the X axis and the Y axis Define the system (x, y, z). The distance in the Z-axis direction between the first rotationally asymmetric surface and the second rotationally asymmetric surface and the surface formed from rotationally symmetric components of the first rotationally asymmetric surface and the second rotationally asymmetric surface is defined as a sag difference, and the rotationally symmetric component The sag difference is (−) when there is a rotationally asymmetric surface on the object side with respect to the surface formed from, and the sag difference is (+) when there is a rotationally asymmetric surface on the image side with respect to the surface formed from rotationally symmetric components. It is defined as The first rotationally asymmetric surface is set so that the change in the sag difference in the direction in which the absolute value of y increases compared to the change in the sag difference in the direction in which the absolute value of x increases. Further, the sag difference of the XZ section including the origin increases in the (+) direction as the absolute value of x increases, and the principal ray traveling on the XZ plane including the origin passes through the second rotationally asymmetric surface. Among them, there is a maximum point in the (+) direction between the position farthest from the origin and the origin, and the sag difference of the YZ section including the origin and the sag difference of the YZ section including the maximum point increase the absolute value of y. As a result, the second rotationally asymmetric surface is set so as to increase in the (−) direction. By setting the first rotationally asymmetric surface and the second rotationally asymmetric surface in this manner, there is an effect that it is possible to satisfactorily correct the distortion at the wide-angle end in the five-lens wide-angle lens.

  Further, since at least one surface of the rear group has a rotationally asymmetric surface, there is an effect that the aberration generated in the front group can be favorably corrected.

但し、
ｚ：サグ量（原点から回転非対称面上の点までのＺ軸方向の距離）
ｃ：曲率（１／基準曲率半径Ｒ）
ｋ：円錐定数
ｈ：光軸垂直方向距離
Ｘ_ｍＹ_ｎ：自由曲面係数（ｍ＝０，１，２，３・・・）（ｎ＝０，１，２，３・・・）
ｘ，ｙ：Ｚ軸に直交するＸＹ平面上の位置 According to the wide-angle lens of the second aspect, the rotationally asymmetric surfaces of the front group and the rear group are expressed by the following conditional expression (1), and the following conditional expressions (2) and (3) are satisfied.

However,
z: Sag amount (distance in the Z-axis direction from the origin to a point on the rotationally asymmetric surface)
c: curvature (1 / reference radius of curvature R)
k: cone constant h: optical axis vertical direction distance X _m Y _n : free-form surface coefficient (m = 0, 1, 2, 3...) (n = 0, 1, 2, 3...)
x, y: position on the XY plane orthogonal to the Z axis

  Since the conditional expression (2) is satisfied, in the conditional expression (1), the free-form surface coefficient is 0 when the order of x and y is an odd number. That is, in the conditional expression (1), since the order of x and y is limited to an even number, there is an effect that the rotationally asymmetric surface can be prevented from being inclined and asymmetric with respect to the optical axis.

  Further, since the rotationally asymmetric surfaces of the front group and the rear group satisfy the conditional expression (3), the radius of curvature near the optical axis can be rotationally symmetric. Therefore, in addition to the effect of the first aspect, there is an effect that the astigmatism near the axis center can be favorably corrected.

  According to the wide-angle lens of the third aspect, the fourth lens having one of positive and negative refractive power and the fifth lens having the other positive or negative refractive power are joined to form a cemented lens. The chromatic aberration can be corrected well.

但し、
ΔＳａｇＶ_１：前記第１回転非対称面の原点を含むＹＺ断面における、原点を含むＹＺ面上を進む主光線が通過する位置のうち原点から最も離れた位置のサグ差
ΔＳａｇＨ_１：前記第１回転非対称面のＸＹ平面視において、ΔＳａｇＶ_１のサグ差を得た位置の同心円上、且つ、Ｘ軸上のサグ差
ΔＳａｇＨ_２：前記第１回転非対称面の原点を含むＸＺ断面における、原点を含むＸＺ面上を進む主光線が通過する位置のうち原点から最も離れた位置のサグ差
ＩｍｇＨ：前記撮像素子のＸ軸方向のサイズ
ＩｍｇＶ：前記撮像素子のＹ軸方向のサイズ According to a wide-angle lens unit according to a fourth aspect, the wide-angle lens according to any one of the first to third aspects and a substantially rectangular imaging element that converts an image formed by the wide-angle lens into an electrical signal. The long side direction and the short side direction of the image sensor are the X-axis direction and the Y-axis direction, respectively, and the first rotationally asymmetric surface satisfies at least one of the following conditional expressions (4) or (5). There is an effect that distortion at the wide-angle end can be corrected well.

However,
DerutaSagV _1: wherein in the YZ cross-section including a first origin of rotationally asymmetric surface sag difference farthest from the origin of the position where the principal ray passes traveling YZ Menjo including the origin DerutaSagH _1: the first rotating asymmetric In the XY plan view of the surface, the sag difference on the X axis on the concentric circle at the position where the sag difference of ΔSagV ₁ is obtained ΔSagH ₂ : XZ plane including the origin in the XZ cross section including the origin of the first rotationally asymmetric surface The sag difference at the position farthest from the origin among the positions through which the principal ray traveling upward passes. ImgH: Size in the X-axis direction of the image sensor ImgV: Size in the Y-axis direction of the image sensor

(A) is YZ sectional drawing of the wide angle lens unit in embodiment of this invention, (b) is XZ sectional drawing of a wide angle lens unit. It is a perspective view of the 1st sag difference surface which is a surface which consists of a sag difference of the 1st rotation asymmetric surface. It is XY top view of a 1st sag difference surface. It is a perspective view of the 2nd sag difference surface which is a surface which consists of a sag difference of the 2nd rotation asymmetric surface. It is XY top view of a 2nd sag difference surface. (A) is sectional drawing of the 2nd sag difference surface in the VIa-VIa line of FIG. 5, (b) is sectional drawing of the 2nd sag difference surface in the VIb-VIb line of FIG. 5, (c) is shown. It is sectional drawing of the 2nd sag difference surface in the VIc-VIc line | wire of FIG. It is XZ sectional drawing containing the origin of the 2nd sag difference surface in the wide angle lens of each angle of view. (A) is a spherical aberration diagram in this example, (b) is a field curvature and astigmatism diagram in the YZ section including the origin, and (c) is a distortion aberration diagram in the YZ section including the origin. (D) is a field curvature and astigmatism diagram in the XZ section including the origin, and (e) is a distortion diagram in the XZ section including the origin. It is the condensing position with respect to the imaginary height.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. First, the wide-angle lens unit 10 will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a YZ cross-sectional view of the wide-angle lens unit 10 in the embodiment of the present invention, and FIG. 1B is an XZ cross-sectional view of the wide-angle lens unit 10. The XZ sectional view and the YZ sectional view of the wide angle lens unit 10 are sectional views of the YZ section and the XZ section including the origin O in the wide angle lens unit 10, respectively. In this specification, an orthogonal coordinate system in which the intersection of an arbitrary lens surface and the optical axis Ax is the origin O, the optical axis Ax is the Z axis, and the axes orthogonal to the Z axis and orthogonal to each other are the X axis and the Y axis. Define (x, y, z).

  As shown in FIGS. 1A and 1B, the wide-angle lens unit 10 includes, in order from the object side, an IR-cut filter 13 that includes a wide-angle lens 11 and a glass plate with a coating that cuts infrared rays. And a cover glass 14 of the image pickup device 15 and a substantially rectangular image pickup device 15 that converts an optical image obtained from the wide-angle lens 11 into an electrical signal. The wide-angle lens 11 is composed of a front group G1 and a rear group G2 in order from the object side, and includes a diaphragm 12 between the front group G1 and the rear group G2. The wide-angle lens 11 has a wider angle of view in the X-axis direction than the angle of view in the Y-axis direction. In the image sensor 15, the long side direction is the X-axis direction, and the short side direction is the Y-axis direction.

Note that the angle of view of the wide-angle lens 11 may be widened in the Y-axis direction as compared to the X-axis direction, the long-side direction of the image sensor 15 may be the Y-axis direction, and the short-side direction may be the X-axis direction. In that case, values and expressions relating to the X axis and Y axis (x and y) described later are all opposite values and expressions for the X axis and Y axis (x and y) (for example, free in the embodiments described later). The value of the curved surface coefficient X ₄ Y _{0 is} the value of X ₀ Y _{4 and} the value of X ₀ Y _{4 is} the value of X ₄ Y ₀ ).

  Further, the IR cut filter 13 is not always necessary and can be omitted, and other filters (for example, an ultraviolet cut filter or a polarization filter) can be used instead of the IR cut filter 13. Furthermore, a coating for cutting infrared rays (a coating for cutting ultraviolet rays, a polarizing coating) can be applied to any lens surface.

  The front group G1, in order from the object side, is a first lens L1 that is a meniscus lens having negative refractive power and convex toward the object side, and a second meniscus lens having negative refractive power and convex toward the object side. The lens L2 and a third lens L3 having a positive refractive power. The lens surfaces of the lenses in the front group G1 are changed from the surface R1 to the surface R6 in order from the object side, and at least two of the surfaces R1 to R6 have rotationally asymmetric surfaces. The rotationally asymmetric surface of the front group G1 includes a first rotationally asymmetric surface formed on a surface R1 that is an object side surface of the first lens L1 or a surface R3 that is an object side surface of the second lens L2, and And a second rotationally asymmetric surface formed on the surface R2 that is the image side surface of the first lens L1 or the surface R4 that is the image side surface of the second lens L2.

  The rear group G2 includes, in order from the object side, a fourth lens L4 having one of positive or negative refractive power and a fifth lens L5 having the other positive or negative refractive power, and positive refraction as a whole. Have power. In the present embodiment, the fourth lens L4 and the fifth lens L5 are cemented to form a cemented lens L45. The cemented lens L45 has an object side surface as R8, a cemented surface between the fourth lens L4 and the fifth lens L5 as a surface R9, an image side surface as a surface R10, and at least one of the surfaces R8 to R10 rotates. It has an asymmetric surface. The diaphragm 12 is the surface R7, the object side surface of the IR cut filter 13 is the surface R11, the image side surface is the surface R12, the object side surface of the cover glass 14 is the surface R13, and the image side surface is the surface R14. And

  The first lens L1 is made of glass, and the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are each made of plastic. When the fourth lens L4 and the fifth lens L5 are compared with each other, one of the fourth lens L4 and the fifth lens L5 has a low refractive index and a high Abbe number, and the fourth lens L4 or the fifth lens L5. The other of them preferably has a high refractive index and a low Abbe number. In the present embodiment, the fourth lens L4 has a low refractive index and a high Abbe number, and the fifth lens L5 has a high refractive index and a low Abbe number.

但し、
ｚ：サグ量（原点Ｏから回転非対称面上の点までのＺ軸方向の距離）
ｃ：曲率（１／基準曲率半径Ｒ）
ｋ：円錐定数
ｈ：光軸垂直方向距離
Ｘ_ｍＹ_ｎ：自由曲面係数（ｍ＝０，１，２，３・・・）（ｎ＝０，１，２，３・・・）
ｘ，ｙ：Ｚ軸に直交するＸＹ平面上の位置 The rotationally asymmetric surface is represented by the following conditional expression (1). Furthermore, it is preferable that the following conditional expressions (2) and (3) are satisfied.

However,
z: Sag amount (distance in the Z-axis direction from the origin O to a point on the rotationally asymmetric surface)
c: curvature (1 / reference radius of curvature R)
k: cone constant h: optical axis vertical direction distance X _m Y _n : free-form surface coefficient (m = 0, 1, 2, 3...) (n = 0, 1, 2, 3...)
x, y: position on the XY plane orthogonal to the Z axis

但し、
Ａ，Ｂ，Ｃ・・・：非球面係数 The rotationally symmetric aspherical surface is expressed by the following conditional expression (6).

However,
A, B, C ...: Aspheric coefficient

  Next, the first rotationally asymmetric surface will be described with reference to FIGS. 2 and 3. 2 is a perspective view of the first sag difference surface S1, which is a surface formed by the sag difference ΔSag of the first rotationally asymmetric surface, and FIG. 3 is an XY plan view of the first sag difference surface S1. The sag difference ΔSag is the distance in the Z-axis direction between the rotationally asymmetric surface and the surface formed from the rotationally symmetric component of the rotationally asymmetric surface, and the rotationally asymmetric surface is closer to the object side than the surface formed from the rotationally symmetric component. In this case, (−) is defined as (+) when there is a rotationally asymmetric surface on the image side of the surface formed from rotationally symmetric components. 2 and 3 show the first sag difference surface S1 when the angle of view of the wide-angle lens 11 is 120 °, the contour lines of the sag difference ΔSag are shown by broken lines, and the contour lines are made equal. Has been. In FIG. 2, the direction indicated by the arrow of ΔSag from the origin O is (+), and the direction opposite to the direction indicated by the arrow of ΔSag from the origin O is (−).

但し、
ΔＳａｇＶ_１：第１サグ差面Ｓ１（第１回転非対称面）の原点Ｏを含むＹＺ断面における、原点Ｏを含むＹＺ面上を進む主光線が通過する位置のうち原点Ｏから最も離れた位置のサグ差ΔＳａｇ
ΔＳａｇＨ_１：第１サグ差面Ｓ１（第１回転非対称面）のＸＹ平面視において、サグ差ΔＳａｇＶ_１を得た位置の同心円上、且つ、Ｘ軸上のサグ差ΔＳａｇ
ΔＳａｇＨ_２：第１サグ差面Ｓ１（第１回転非対称面）の原点Ｏを含むＸＺ断面における、原点Ｏを含むＸＺ面上を進む主光線が通過する位置のうち原点Ｏから最も離れた位置のサグ差ΔＳａｇ
ＩｍｇＨ：撮像素子１５のＸ軸方向のサイズ
ＩｍｇＶ：撮像素子１５のＹ軸方向のサイズ As shown in FIGS. 2 and 3, the first sag difference surface S1 (first rotationally asymmetric surface) is plane-symmetric in the XZ section including the origin O and the YZ section including the origin O, and is x or y. As at least one absolute value increases, the sag difference ΔSag increases in the (−) direction. Further, in the first sag difference surface S1, the change in the sag difference ΔSag in the direction in which the absolute value of y increases is larger than the change in the sag difference ΔSag in the direction in which the absolute value of x increases. Further, the contour lines of the sag difference ΔSag are provided in a substantially rectangular shape in the XY plan view. Furthermore, it is preferable that the first sag difference surface S1 satisfies at least one of the following conditional expressions (4) and (5).

However,
ΔSagV ₁ : In the YZ cross section including the origin O of the first sag difference surface S1 (first rotationally asymmetric surface), the position farthest from the origin O among the positions through which the principal ray traveling on the YZ plane including the origin O passes. Sag difference ΔSag
ΔSagH ₁ : In the XY plan view of the first sag difference surface S1 (first rotationally asymmetric surface), the sag difference ΔSag on the concentric circle at the position where the sag difference ΔSagV ₁ is obtained and on the X axis
ΔSagH ₂ : In the XZ cross section including the origin O of the first sag difference surface S1 (first rotationally asymmetric surface), the position farthest from the origin O among the positions through which the principal ray traveling on the XZ plane including the origin O passes. Sag difference ΔSag
ImgH: Size of the image sensor 15 in the X-axis direction ImgV: Size of the image sensor 15 in the Y-axis direction

  Next, the second rotationally asymmetric surface will be described with reference to FIGS. 4, 5, 6 (a), 6 (b), and 6 (c). 4 is a perspective view of the second sag difference surface S2, which is a surface formed by the sag difference ΔSag of the second rotationally asymmetric surface, and FIG. 5 is an XY plan view of the second sag difference surface S2, and FIG. FIG. 6 is a sectional view of the second sag difference surface S2 along the VIa-VIa line in FIG. 5, and FIG. 6B is a sectional view of the second sag difference surface S2 along the VIb-VIb line in FIG. (c) is sectional drawing of 2nd sag difference surface S2 in the VIc-VIc line | wire of FIG. 4, 5, 6 (a), 6 (b), and 6 (c) illustrate the second sag difference surface S <b> 2 when the angle of view of the wide-angle lens 11 is 120 °. 4 and 5, the contour lines of the sag difference ΔSag are shown by broken lines, and the contour lines are shown to be equal. In FIGS. 4, 6A, 6B, and 6C, the direction indicated by the ΔSag arrow from the origin O is (+), and the direction opposite to the direction indicated by the ΔSag arrow from the origin O is opposite. (-).

  As shown in FIGS. 4 and 5, the second sag difference surface S <b> 2 (second rotationally asymmetric surface) is symmetrical with respect to the XZ section including the origin O and the YZ section including the origin O. As shown in FIG. 6 (a), the second sag difference surface S2 has a maximum point M (change after the sag difference ΔSag in the XZ section including the origin O increases in the (+) direction as the absolute value of x increases. It increases in the (−) direction beyond the music point I). Further, as shown in FIG. 6B, the sag difference ΔSag of the YZ cross section including the origin O increases in the (−) direction as the absolute value of y increases. As shown in FIG. 6C, the sag difference ΔSag of the YZ cross section including the maximum point M increases in the (−) direction as the absolute value of y increases. Further, the sag difference ΔSag of the YZ section including the maximum point M in the direction in which the absolute value of y increases is compared with the change of the sag difference ΔSag including the origin O in the direction in which the absolute value of y increases. The change is great.

  Next, the maximum point M of the second sag difference surface S2 in this specification will be described with reference to FIG. FIG. 7 is an XZ cross-sectional view including the origin O of the second sag difference surface S2 in the wide-angle lens 11 of each field angle. FIG. 7 shows a position E farthest from the origin O by a broken line among positions where the principal ray traveling on the XZ plane including the origin O passes through the second sag difference surface S2 (second rotationally asymmetric surface). ing.

  The maximum point M is a point where the sag difference ΔSag of the XZ cross section including the origin O is the maximum value in the (+) direction between the position E and the origin O. As shown in FIG. 7, the sag difference ΔSag of the XZ section including the origin O is such that the inflection point I moves away from the origin O as the angle of view increases (θ1 <θ2 <θ3 <θ4). When the angle of view of the wide-angle lens 11 is θ1 (120 ° in the present embodiment), the inflection point I of the sag difference ΔSag exists between the position E and the origin O, so the maximum point M is the sag difference ΔSag. Is the inflection point I. When the angle of view of the wide-angle lens 11 is θ2, the inflection point I of the sag difference ΔSag exists at substantially the same position as the position E, and when the angle of view of the wide-angle lens 11 is θ3 and θ4, the change of the sag difference ΔSag. Since the curvature point I exists at a position farther from the origin O than the position E, the maximum point M is the position E of the sag difference ΔSag. As in the case where the maximum point M is the inflection point I, even when the maximum point M is the position E, the sag difference ΔSag of the YZ cross section including the maximum point M increases as the absolute value of y increases in the (−) direction. To increase.

  Next, the influence of the configuration of the wide-angle lens unit 10 on various aberrations will be described. The object side surface (surface R1 or surface R3) of the first lens L1 or the second lens L2, which is a meniscus lens having negative refractive power and convex to the object side, among the lens surfaces of the front group G1 of the wide angle lens 11. Are formed on the first rotationally asymmetric surface, and the image side surface (surface R2 or surface R4) of the first lens L1 or the second lens L2 is formed on the second rotationally asymmetric surface. Further, the first rotationally asymmetric surface is set so that the change in the sag difference ΔSag in the direction in which the absolute value of y increases compared to the change in the sag difference ΔSag in the direction in which the absolute value of x increases. Further, the sag difference ΔSag of the XZ section including the origin O increases in the (+) direction as the absolute value of x increases, and the chief ray traveling on the XZ plane including the origin O passes through the second rotationally asymmetric surface. The maximum point M in the (+) direction is between the position E farthest from the origin O and the origin O, and the sag difference ΔSag of the YZ section including the origin O and the YZ section including the maximum point M The second rotationally asymmetric surface is set so that the sag difference ΔSag increases in the (−) direction as the absolute value of y increases. As a result, it is possible to satisfactorily correct distortion at the wide-angle end in the five-lens wide-angle lens 11.

  Since the first lens L1 and the second lens L2 are farther from the diaphragm 12 than the third lens L3, the third lens L3 is the lens surface (surface R1 to surface R4) of the first lens L1 and the second lens L2. Compared with the lens surfaces (surface R5 and surface R6), the luminous fluxes at each angle of view are separated. As a result, the first lens L1 and the second lens L2 can easily affect the correction of distortion due to the rotationally asymmetric surface. In addition, since at least one of the lens surfaces R8 to R10 of the rear group G2 has a rotationally asymmetric surface, the aberration generated in the front group G1 can be favorably corrected.

  Further, when the rotationally asymmetric surface satisfies the conditional expression (2), the free-form surface coefficient becomes 0 when the order of at least one of x or y is an odd number. That is, since the order of x and y is limited to an even number, it is possible to prevent the rotationally asymmetric surface from being inclined and asymmetric with respect to the optical axis Ax. Further, when the rotationally asymmetric surface satisfies the conditional expression (3), the radius of curvature near the optical axis Ax can be made rotationally symmetric, and astigmatism near the axis can be corrected well. Moreover, when the first rotationally asymmetric surface satisfies at least one of conditional expressions (4) and (5), the distortion at the wide-angle end can be corrected more favorably.

  In addition, since the first lens L1 that is the most object side lens is made of glass, the wide-angle lens 11 can be made strong against external scratches and dirt. Since the fourth lens L4 having a low refractive index and a high Abbe number and the fifth lens L5 having a high refractive index and a low Abbe number are composed of the cemented lens L45 as compared with each other, The chromatic aberration generated in the group G1 can be corrected satisfactorily. It should be noted that the chromatic aberration generated in the front group G1 can be corrected satisfactorily even when the mutual relationship between the refractive index and the Abbe number of the fourth lens L4 and the fifth lens L5 is reversed.

In this embodiment, the object-side surface R3 of the second lens L2 is formed as a first rotationally asymmetric surface, the image-side surface R4 of the second lens L2 is formed as a second rotationally asymmetric surface, and the third lens L3 is positive. The biconvex lens has refractive power, and the surface R5 and the surface R6 of the third lens L3 are each formed into a rotationally symmetric aspherical surface. Further, a cemented lens L45 is formed by cementing a fourth lens L4, which is a biconvex lens having positive refractive power, and a fifth lens L5, which is a meniscus lens having negative refractive power and convex on the image side, The surface R8 and the surface R9 of the cemented lens L45 are each formed as a rotationally symmetric aspheric surface, and the surface R10 of the cemented lens L45 is formed as a rotationally asymmetric surface. The X-axis direction is the horizontal direction, the Y-axis direction is the vertical direction, the XZ section including the origin O in each lens is the horizontal section, and the YZ section including the origin O is the vertical section. The optical values of this example are shown in Table 1.

Table 2 shows lens data of this example. The surface number * symbol indicates a rotationally symmetric aspheric surface, and the surface number ** symbol indicates a rotationally asymmetric surface. The fourth lens L4 and the fifth lens L5 constituting the cemented lens L45 are compared with each other. The fourth lens L4 has a low refractive index and a high Abbe number, the fifth lens L5 has a high refractive index, and Since the Abbe number is low, the chromatic aberration generated in the front group G1 can be corrected well.

Table 3 shows the aspheric coefficient data of the surface R5, the surface R6, the surface R8, and the surface R9 of this example. In the following, a power of 10 is expressed using E (for example, 1.6 × 10 ⁻⁴ is 1.6E-4). A blank in Table 3 indicates that the coefficient is 0.

The free surface coefficient data of the surface R3 of this embodiment is shown in Table 4, the free surface coefficient data of the surface R4 is shown in Table 5, and the free surface coefficient data of the surface R10 is shown in Table 6, respectively. Note that the estimated number of circles of the surface R3, the surface R4, and the surface R10 is 0, and the blanks in Tables 4 to 6 indicate that the coefficient is 0. In the present embodiment, by setting the first rotationally asymmetric surface R3 and the second rotationally asymmetric surface R4 in this way, the surfaces formed by the sag difference ΔSag between the first rotationally asymmetric surface R3 and the second rotationally asymmetric surface R4, respectively. It can be formed on the first sag difference surface S1 and the second sag difference surface S2. Further, since the surface R3, the surface R4, and the surface R10 satisfy the conditional expressions (2) and (3), the rotationally asymmetric surface can be prevented from being inclined and asymmetric with respect to the optical axis Ax. Astigmatism near the center can be corrected well.

Table 7 shows numerical values of conditional expressions (4) and (5) in this example. In this embodiment, since the first rotationally asymmetric surface R3 satisfies the conditional expressions (4) and (5), distortion can be corrected well.

  The aberration diagrams obtained from this example are shown in FIGS. 8 (a) to 8 (e). 8A is a spherical aberration diagram, FIG. 8B is a field curvature and astigmatism diagram in the YZ section (vertical section) including the origin O, and FIG. 8C includes the origin O. FIG. 8D is a distortion aberration diagram in the YZ section (vertical section), FIG. 8D is a field curvature and astigmatism diagram in the XZ section (horizontal section) including the origin O, and FIG. It is a distortion aberration figure in the XZ cross section (horizontal cross section) including. 8A shows the case of a wavelength of 486 nm as a solid line, the case of a wavelength of 588 nm as a one-dot chain line, the case of a wavelength of 656 nm as a two-dot chain line, and FIGS. 8B to 8E show a wavelength of 588 nm. Shows the case.

  In FIG. 8A, the horizontal axis is the amount of deviation (mm) in the direction of the optical axis Ax from the image plane near the optical axis Ax, and the vertical axis is the incident height to the pupil (0.2908 mm). ) (Ie, relative pupil height). In FIGS. 8B and 8D, the horizontal axis is the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis is the angle of view (deg) with respect to the optical axis Ax. The aberration S on the sagittal surface is indicated by a solid line, and the aberration T on the tangential surface is indicated by a broken line. In FIG. 8C and FIG. 8E, the horizontal axis is distortion (%), and the vertical axis is the angle of view (deg) with respect to the optical axis Ax.

The condensing position with respect to the ideal image height in the present embodiment is shown in FIG. In FIG. 9, the intersection point with the optical axis Ax is the origin O, the horizontal axis is the height (mm) of the optical image in the X-axis (horizontal) direction, and the vertical axis is the height of the optical image in the Y-axis (vertical) direction. Distortion is shown as (mm). Each intersection of the grid indicates the height of the ideal image (ideal image height), each circle indicates the height of the optical image (condensing position) of the present embodiment, and the closer each circle is to each intersection of the grid It is determined that the distortion is corrected well. Table 8 shows the coordinates (x (mm), y (mm)) of the condensing position in FIG. 10 and the angle of view (deg) with respect to the optical axis Ax where the coordinates of the condensing position are obtained. The ideal image height is obtained by multiplying the focal length in this embodiment by the tangent function of the half field angle, and Table 9 shows the relationship between the field angle and the ideal lattice.

  As shown in FIG. 9, the condensing position is located substantially parallel to the lattice of the ideal image height. From here, an optical image is formed without distortion like a barrel-shaped optical image where the wide-angle end is bent inward with respect to the ideal image and a pincushion-type optical image where the wide-angle end is bent outward with respect to the ideal image. Can be judged. That is, in this embodiment, it can be determined that the distortion at the wide-angle end is corrected well.

  The present invention has been described above based on the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various improvements can be made without departing from the spirit of the present invention. It can be easily inferred that deformation is possible. For example, in the above-described embodiment, the case where the surface R3 and the surface R4 of the second lens L2 are formed on the first rotationally asymmetric surface and the second rotationally asymmetric surface, respectively, is not limited to this. Among the lens surfaces of the group G1, if the object side surface of the meniscus lens having negative refractive power and convex to the object side is formed on the first rotationally asymmetric surface, the image side surface is formed on the second rotationally asymmetric surface. good. For example, the surface R1 of the first lens L1 can be formed as a first rotationally asymmetric surface, and the surface R2 of the first lens L1 can be formed as a second rotationally asymmetric surface. It is naturally possible to form the surface R1 of the first lens L1 on the first rotationally asymmetric surface and form the surface R4 of the second lens L2 on the second rotationally asymmetric surface. In addition to the first rotationally asymmetric surface and the second rotationally asymmetric surface, the surface R1 to the surface R6 of the front group G1 can be formed as rotationally asymmetric surfaces.

  In the above embodiment, the case where the surface R10 of the cemented lens L45 is formed as a rotationally asymmetric surface has been described. It is possible. Of course, two or more surfaces R8 to R10 of the cemented lens L45 can be rotationally asymmetric surfaces.

  In the embodiments and examples described above, the case where the fourth lens L4 and the fifth lens L5 are cemented to form the cemented lens L45 is described. However, the present invention is not necessarily limited thereto, and the fourth lens L4 and Each of the fifth lenses L5 can be an independent lens. At this time, if at least one of the total four surfaces including the object-side surface and the image-side surface of the fourth lens L4 and the object-side surface and the image-side surface of the fifth lens L5 is a rotationally asymmetric surface. good.

  In the above embodiment, the case where the fourth lens L4 is a biconvex lens having a positive refractive power and the fifth lens L5 is a meniscus lens having a negative refractive power and convex to the image side has been described. The total refractive power of the fourth lens L4 and the fifth lens L5 only needs to be positive. For example, the fourth lens L4 can be a biconcave lens having negative refractive power, and the fifth lens L5 can be a biconvex lens having positive refractive power.

  In the above embodiment, the case where the first rotationally asymmetric surface R3 satisfies the conditional expressions (4) and (5) has been described. However, the present invention is not necessarily limited to this, and the first rotationally asymmetric surface R3 is defined by the conditional expression (4 ) Or (5) may be satisfied. Even in this case, distortion can be corrected well.

DESCRIPTION OF SYMBOLS 10 Wide-angle lens unit 11 Wide-angle lens 15 Image pick-up element Ax Optical axis E Maximum point G1 Front group G2 Rear group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L45 Joint lens

Claims (4)

A wide-angle lens composed of a front group and a rear group having a positive refractive power in order from the object side,
The front group includes, in order from the object side, a first lens that is a meniscus lens having negative refractive power and convex toward the object side, and a second lens that is negative meniscus lens having negative refractive power and convex toward the object side And a third lens having positive refractive power, at least two surfaces having rotationally asymmetric surfaces,
The rear group includes, in order from the object side, a fourth lens having one of positive or negative refractive power and a fifth lens having the other positive or negative refractive power, and at least one surface is a rotationally asymmetric surface. With
The rotationally asymmetric surface of the front group is formed on a first rotationally asymmetric surface formed on the object side surface of the first lens or the second lens and an image side surface of the first lens or the second lens. A second rotationally asymmetric surface
The intersection of the first rotationally asymmetric surface and the second rotationally asymmetric surface and the optical axis is the origin, the optical axis direction is the Z axis, and the axes orthogonal to the Z axis and orthogonal to each other are the X axis and the Y axis. In the orthogonal coordinate system (x, y, z), a surface formed from rotationally symmetric components of the first rotationally asymmetric surface and the second rotationally asymmetric surface and the first rotationally asymmetric surface and the second rotationally asymmetric surface. The distance in the Z-axis direction is a sag difference, and if there is a rotationally asymmetric surface on the object side of the surface formed from the rotationally symmetric component, the sag difference is (−), and the surface formed from the rotationally symmetric component. When the sag difference is defined as (+) when there is a rotationally asymmetric surface on the image side,
The first rotationally asymmetric surface is set to have a large change in sag difference in the direction in which the absolute value of y increases compared to a change in sag difference in the direction in which the absolute value of x increases.
In the second rotationally asymmetric surface, the sag difference of the XZ cross section including the origin increases in the (+) direction as the absolute value of x increases, and the principal ray traveling on the XZ plane including the origin is the second rotation. The maximum point in the (+) direction is between the position farthest from the origin and the position passing through the asymmetric surface, and the sag difference of the YZ section including the origin and the sag difference of the YZ section including the maximum point Are set so as to increase in the (−) direction as the absolute value of y increases, respectively. The wide-angle lens according to claim 1, wherein the rotationally asymmetric surfaces of the front group and the rear group satisfy the following conditional expressions (1), (2), and (3).

However,
z: Sag amount (distance in the Z-axis direction from the origin to a point on the rotationally asymmetric surface)
c: curvature (1 / reference radius of curvature R)
k: cone constant h: optical axis vertical direction distance X _m Y _n : free-form surface coefficient (m = 0, 1, 2, 3...) (n = 0, 1, 2, 3...)
x, y: position on the XY plane orthogonal to the Z axis   The wide-angle lens according to claim 1, wherein the fourth lens and the fifth lens are cemented to form a cemented lens. A wide-angle lens unit comprising: the wide-angle lens according to any one of claims 1 to 3; and a substantially rectangular imaging element that converts an image formed by the wide-angle lens into an electrical signal,
In the imaging device, the long side direction and the short side direction are the X-axis direction and the Y-axis direction, respectively.
The first rotationally asymmetric surface satisfies at least one of the following conditional expressions (4) and (5).

However,
DerutaSagV _1: wherein in the YZ cross-section including a first origin of rotationally asymmetric surface sag difference farthest from the origin of the position where the principal ray passes traveling YZ Menjo including the origin DerutaSagH _1: the first rotating asymmetric In the XY plan view of the surface, the sag difference on the X axis on the concentric circle at the position where the sag difference of ΔSagV ₁ is obtained ΔSagH ₂ : XZ plane including the origin in the XZ cross section including the origin of the first rotationally asymmetric surface The sag difference at the position farthest from the origin among the positions through which the principal ray traveling upward passes. ImgH: Size in the X-axis direction of the image sensor ImgV: Size in the Y-axis direction of the image sensor

Images