JP2017142363A - Wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle lens that offers improved resolution performance in a peripheral region.SOLUTION: A wide-angle lens consists of a first group having negative refractive power, second group having positive refractive power, aperture stop, and third group having positive refractive power in order from the object side. The first group comprises, in order from the object side, a first lens having negative refractive power and a meniscus shape that is convex on the object side, and a second lens having negative refractive power and a meniscus shape that is convex on the object side. The second group comprises, in order from the object side, a third lens having positive refractive power, and a fourth lens having positive refractive power and a concave surface on the object side. The third group comprises, in order from the object side, a cemented lens comprising fifth and sixth lenses cemented together and having negative refractive power, a seventh lens having positive refractive power, and an eighth lens having positive refractive power. Each of the second and eighth lenses is formed to have at least one aspherical surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wide-angle lens, and relates to a wide-angle lens that can improve the resolution performance of a peripheral portion.

  Conventionally, a wide-angle lens configured to obtain high imaging performance over the entire effective screen has been proposed (Patent Document 1).

Japanese Patent No. 5463265

  However, in the above conventional technique, the distortion (aberration) in the peripheral portion is not sufficiently corrected, and the imaging size in the peripheral portion is not sufficiently large, so that the resolution performance in the peripheral portion is insufficient.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a wide-angle lens capable of improving the resolution performance of the peripheral portion.

Means for Solving the Problems and Effects of the Invention

  In order to achieve this object, according to the wide-angle lens of claim 1, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, an aperture stop, And a third group having a positive refractive power. In order from the object side, the first lens unit includes 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. Is configured. Such a light beam incident on the first group is adjusted so that the angle formed with the optical axis gradually becomes gentle and is emitted from the second lens. As a result, the occurrence of aberration can be suppressed, and the angle of view can be widened while reducing the diameter of the first lens.

  Since the light beam emitted from the second lens has negative aberration, the aberration can be favorably corrected by the second group and the third group having positive refractive power. In order from the object side, the second lens group includes a third lens having positive refractive power and a fourth lens having positive refractive power and concave on the object side. Thereby, chromatic aberration can be favorably corrected.

  In order from the object side, a third lens unit including a cemented lens having a negative refractive power obtained by cementing the fifth lens and the sixth lens, a seventh lens having a positive refractive power, and an eighth lens having a positive refractive power. Is configured. Chromatic aberration can be favorably corrected by the cemented lens in which the fifth lens and the sixth lens are cemented.

  Since each of the second lens and the eighth lens has at least one aspherical surface, the image forming size at the central portion can be reduced and the image forming size at the peripheral portion can be increased. In addition, the aberration generated in the first group and the second group can be favorably corrected by the aspherical surface of the eighth lens. As a result, it is possible to increase the image forming size of the peripheral portion while favorably correcting the aberration, so that the resolution performance of the peripheral portion can be improved.

According to the wide-angle lens of claim 2, the distance from the apex of the object-side surface of the first lens to the aperture stop is TA, and from the apex of the object-side surface of the first lens to the image plane at the object infinite distance. When the distance of TT is TT, the following conditional expression (1) is satisfied.

  If the lower limit of conditional expression (1) is not reached, the aberration becomes large and it becomes difficult to correct the aberration. When the upper limit value of conditional expression (1) is exceeded, the effective diameter increases and the first lens increases in diameter. By satisfying conditional expression (1), in addition to the effect of the first aspect, there is an effect that the first lens can be reduced in diameter and the wide-angle lens can be reduced in size while correcting aberrations well.

According to the wide-angle lens of claim 3, when the focal length of the entire lens is f and the distance from the vertex of the object-side surface of the first lens to the image plane at infinity is TT, Conditional expression (2) is satisfied.

  If the lower limit of conditional expression (2) is not reached, the aberration becomes large and it becomes difficult to correct the aberration. If the upper limit of conditional expression (2) is exceeded, the total length (length in the optical axis direction) of the wide-angle lens becomes large. By satisfying conditional expression (2), in addition to the effect of the first or second aspect, there is an effect that the wide-angle lens can be reduced in size by reducing the overall length of the wide-angle lens while favorably correcting aberrations.

According to the wide angle lens of the fourth aspect, at least one surface of the seventh lens is formed as an aspherical surface. When the focal length of the second lens is f2, the focal length of the seventh lens is f7, and the focal length of the eighth lens is f8, the following conditional expression (3) is satisfied.

  If the lower limit value of conditional expression (3) is exceeded or the upper limit value of conditional expression (3) is exceeded, the balance of the focal lengths of the second lens, the seventh lens, and the eighth lens having an aspheric surface on at least one surface. As a result, it becomes difficult to correct aberrations, and it is difficult to increase the image size of the peripheral portion. When the conditional expression (3) is satisfied, the image forming size of the peripheral portion can be increased while correcting the aberration satisfactorily. Therefore, in addition to the effect of any one of claims 1 to 3, the resolution performance of the peripheral portion There is an effect that can be further improved.

  According to the wide-angle lens of claim 5, since the Abbe number of the second lens is larger than 50, in addition to the effect of any one of claims 1 to 4, there is an effect that chromatic aberration can be favorably corrected.

  According to the wide-angle lens of the sixth aspect, since the refractive index of the third lens is larger than 1.9, in addition to the effect of any one of the first to fifth aspects, there is an effect that chromatic aberration can be favorably corrected.

It is sectional drawing containing the optical axis of the wide angle lens in 1st Example of this invention. (A) to (e) are lateral aberration diagrams in the tangential direction at each angle of view, and (f) to (j) are lateral aberration diagrams in the sagittal direction at each angle of view. (A) is a spherical aberration diagram, (b) is a field curvature and astigmatism diagram, and (c) is a distortion diagram. It is sectional drawing containing the optical axis of the wide angle lens in 2nd Example. (A) to (e) are lateral aberration diagrams in the tangential direction at each angle of view, and (f) to (j) are lateral aberration diagrams in the sagittal direction at each angle of view. (A) is a spherical aberration diagram, (b) is a field curvature and astigmatism diagram, and (c) is a distortion diagram. It is sectional drawing containing the optical axis of the wide angle lens in 3rd Example. (A) to (e) are lateral aberration diagrams in the tangential direction at each angle of view, and (f) to (j) are lateral aberration diagrams in the sagittal direction at each angle of view. (A) is a spherical aberration diagram, (b) is a field curvature and astigmatism diagram, and (c) is a distortion diagram. It is sectional drawing containing the optical axis of the wide angle lens in 4th Example. (A) to (e) are lateral aberration diagrams in the tangential direction at each angle of view, and (f) to (j) are lateral aberration diagrams in the sagittal direction at each angle of view. (A) is a spherical aberration diagram, (b) is a field curvature and astigmatism diagram, and (c) is a distortion diagram. It is sectional drawing containing the optical axis of the wide angle lens in 5th Example. (A) to (e) are lateral aberration diagrams in the tangential direction at each angle of view, and (f) to (j) are lateral aberration diagrams in the sagittal direction at each angle of view. (A) is a spherical aberration diagram, (b) is a field curvature and astigmatism diagram, and (c) is a distortion diagram.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. First, a wide-angle lens will be described with reference to FIG. FIG. 1 is a cross-sectional view including an optical axis Ax of a wide-angle lens (in the first example, a wide-angle lens 10) according to an embodiment (first example) of the present invention. 1 is the object side, and the right side of FIG. 1 is the image side (the same applies to FIGS. 4, 7, 10 and 13). In the present specification, the intersections of the lens surfaces R1 to R8, R10 to R16 and the optical axis Ax are the vertices of the lens surfaces R1 to R8 and R10 to R16, respectively.

  As shown in FIG. 1, the wide-angle lens is an imaging lens for in-vehicle or surveillance cameras, and has a maximum field angle of 150 ° or more and an F value (FNO) of 2.0 or less. The surface imaged by the wide-angle lens when the object is at infinity is the image plane R19, and a parallel plate-like glass filter 12 is disposed on the image plane R19 side of the wide-angle lens. The glass filter 12 has functions such as an infrared cut filter, an ultraviolet cut filter, and a polarizing filter. The glass filter 12 is not essential, and the glass filter 12 can be omitted.

  The wide-angle lens includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, an aperture stop 11, and a third group G3 having a positive refractive power. Composed. The first 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 meniscus lens having negative refractive power and convex toward the object side. And two lenses L2.

  Such a light beam incident on the first group G1 is adjusted so that the angle formed with the optical axis Ax becomes gradually gentle and is emitted from the second lens L2. As a result, the occurrence of aberration can be suppressed and the angle of view can be widened while reducing the diameter of the first lens L1. Since the light beam emitted from the second lens L2 has negative aberration, the second group G2 and the third group G3 having positive refractive power can favorably correct the aberration.

  The second group G2 includes, in order from the object side, a third lens L3 that is a biconvex lens having positive refractive power and a fourth lens L4 that is a meniscus lens having positive refractive power and concave on the object side. Is done. Thereby, chromatic aberration can be favorably corrected.

  The third group G3 includes, in order from the object side, a cemented lens L56 having a negative refractive power obtained by cementing a fifth lens L5 and a sixth lens L6 having different refractive powers, and a seventh lens having a positive refractive power. L7 and an eighth lens L8 having a positive refractive power. The chromatic aberration can be favorably corrected by the cemented lens L56.

  In particular, it is preferable that the fifth lens L5 has a low refractive index and a high Abbe number, and the sixth lens L6 has a high refractive index and a low Abbe number compared to each other. In this case, correction of chromatic aberration by the cemented lens L56 can be improved. Similarly, when the fifth lens L5 has a high refractive index and a low Abbe number, and the sixth lens L6 has a low refractive index and a high Abbe number, the chromatic aberration correction by the cemented lens L56 is improved. it can.

  In the wide-angle lens, the lens surfaces of the lenses L1 to L4 are arranged in order from the object side to surfaces R1 to R8, the aperture stop 11 is a surface R9, the object side surface of the cemented lens L56 is R10, the fifth lens L5 and the sixth lens L6. R11, the image side surface of the cemented lens L56, R12, the lens surfaces of the lenses L7 and L8 in order from the object side, the surfaces R13 to R16, the object side surface of the glass filter 12, R17, and the glass filter 12 Let the image side surface be R18.

  At least one of the surface R3 and the surface R4 and at least one of the surface R15 and the surface R16 is formed as an aspheric surface. Moreover, it is preferable that at least one of the surface R13 and the surface R14 is formed as an aspherical surface. The lens having an aspheric surface on at least one surface is preferably made of a resin that can be easily processed. It is preferable that the lens whose both surfaces are spherical is made of glass whose performance variation due to temperature change is small. Further, by making the lenses having different refractive power positive and negative from resin and reducing the total refractive power of the resin lenses, it is possible to cancel out performance fluctuations due to temperature changes of the resin lenses.

但し、
ｚ：サグ量（光軸Ａｘとの交点から非球面上の点までの光軸Ａｘ方向の距離）
ｃ：曲率（レンズ面の頂点での曲率）
ｒ：径方向（光軸Ａｘに関して垂直方向）の光軸Ａｘから非球面上の点までの距離
ｋ：コーニック定数
Ａ、Ｂ、Ｃ、Ｄ：非球面係数（順に４次、６次、８次、１０次） The shape of the aspheric surface is represented by the following formula (4).

However,
z: Sag amount (distance in the optical axis Ax direction from the intersection with the optical axis Ax to a point on the aspheric surface)
c: Curvature (curvature at the apex of the lens surface)
r: distance from the optical axis Ax in the radial direction (perpendicular to the optical axis Ax) to a point on the aspheric surface k: conic constant A, B, C, D: aspheric coefficients (in order 4th order, 6th order, 8th order) 10th)

  Since at least one of the surface R3 and the surface R4 and at least one of the surface R15 and the surface R16 is formed as an aspheric surface, the wide-angle lens becomes a three-dimensional projection system by appropriately setting the shape of the aspheric surface. The imaging size of the peripheral part can be reduced and the imaging size of the peripheral part can be increased. In the correction to the stereoscopic projection method, the aspherical surface of the second lens L2 greatly contributes and fine adjustment is performed by the aspherical surface of the eighth lens L8. In addition, since at least one of the surface R15 and the surface R16 is formed as an aspheric surface, the aberration generated in the first group G1 and the second group G2 can be corrected satisfactorily. As a result, the image forming size of the peripheral portion can be increased while correcting aberrations satisfactorily, so that the resolution performance of the peripheral portion can be improved.

  Note that by forming both the surface R3 and the surface R4 as aspherical surfaces, the image correction by the aspherical surface (correction to the aberration correction and the stereoscopic projection method) is performed as compared with the case where the surface R3 or the surface R4 is formed as an aspherical surface. ) Can be assigned to each lens surface. Thereby, it is easy to correct aberrations, and lens design can be facilitated. Similarly, when both the surface R15 and the surface R16 are formed as aspherical surfaces, the aberration can be easily corrected and the lens design can be facilitated as compared with the case where at least one of the surface R15 and the surface R16 is formed as an aspherical surface. Further, by forming at least one of the surface R13 and the surface R14 as an aspheric surface, the correction of the image by the aspheric surface can be shared by each lens surface, so that the aberration can be easily corrected and the lens design can be facilitated.

  Since the lens surface farther from the aperture stop 11 (surface R9) is more easily separated from the light beam passing through the lens surface, the lens surface farther from the aperture stop 11 (surface R9) has an effect of correcting aberrations due to the aspherical surface. It is easy to influence the image size. Therefore, by forming at least one of the surface R3 and the surface R4 and at least one of the surface R15 and the surface R16 as an aspherical surface, it is easy to correct aberrations and to facilitate lens design.

The wide-angle lens has TA as the distance from the vertex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9), and TT as the distance from the vertex of the surface R1 to the image surface R19 when the object is at infinity. It is preferable that the following conditional expression (1) is satisfied.

  If the lower limit of conditional expression (1) is not reached, the aberration becomes large and it becomes difficult to correct the aberration. When the upper limit value of conditional expression (1) is exceeded, the effective diameter increases and the first lens L1 increases in diameter. By satisfying conditional expression (1), it is possible to reduce the diameter of the first lens L1 and reduce the size of the wide-angle lens while correcting aberrations well.

The wide-angle lens preferably satisfies the following conditional expression (2), where f is the focal length of the entire lens.

  If the lower limit of conditional expression (2) is not reached, the aberration becomes large and it becomes difficult to correct the aberration. If the upper limit of conditional expression (2) is exceeded, the total length of the wide-angle lens (the length in the optical axis Ax direction) becomes large. By satisfying conditional expression (2), it is possible to reduce the overall length of the wide-angle lens and to reduce the size of the wide-angle lens while correcting aberrations well.

The wide-angle lens satisfies the following conditional expression (3) when the focal length of the second lens L2 is f2, the focal length of the seventh lens L7 is f7, and the focal length of the eighth lens L8 is f8. It is preferable.

  If the lower limit value of conditional expression (3) is exceeded or the upper limit value of conditional expression (3) is exceeded, the focal points of the second lens L2, the seventh lens L7, and the eighth lens L8 having an aspheric surface on at least one surface. The balance of the distance is lost, making it difficult to correct aberrations and increasing the image size of the peripheral portion. By satisfying conditional expression (3), it is possible to increase the imaging size of the peripheral part while satisfactorily correcting the aberration, so that the resolution performance of the peripheral part can be further improved.

  In the wide-angle lens, the Abbe number of the second lens L2 is preferably set to be larger than 50. When the Abbe number of the second lens L2 is 50 or less, it becomes difficult to correct chromatic aberration. By setting the Abbe number of the second lens L2 to be greater than 50, chromatic aberration can be corrected satisfactorily.

  In the wide-angle lens, it is preferable to set the refractive index of the third lens L3 to be larger than 1.9. When the refractive index of the third lens L3 is smaller than 1.9, it is difficult to correct chromatic aberration. Chromatic aberration can be favorably corrected by setting the refractive index of the third lens L3 to be larger than 1.9.

  The wide-angle lens does not have to satisfy all of the conditional expressions (1), (2), and (3). As the number satisfying conditional expressions (1), (2) and (3) increases, the performance of the wide-angle lens can be improved. Similarly, the Abbe number condition of the second lens L2 and the refractive index condition of the third lens L3 need not all be satisfied, and the performance of the wide-angle lens can be improved as the number satisfying the condition increases.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely with reference to an Example, this invention is not limited to this Example.

(First embodiment)
As shown in FIG. 1, in the wide-angle lens 10 in the first embodiment, the fifth lens L5 is a biconvex lens, the sixth lens L6 is a biconcave lens, and both surfaces R3, R4, and the seventh lens of the second lens L2. Both surfaces R13 and R14 of L7 and both surfaces R15 and R16 of the eighth lens L8 are aspheric. In the wide-angle lens 10, the second lens L2, the seventh lens L7, and the eighth lens L8 are made of resin, and the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of resin. It is made of glass.

The optical values and lens data of the wide-angle lens 10 are shown in Table 1, and the focal length of each lens is shown in Table 2. In addition, * symbol of the surface number of Table 1 has shown the aspherical surface (Table 7, 13, 19, 25 is also the same). The wide-angle lens 10 can satisfactorily correct chromatic aberration because the Abbe number ν2 of the second lens L2 is larger than 50. The wide-angle lens 10 can satisfactorily correct chromatic aberration because the refractive index N3 of the third lens L3 is larger than 1.9. The wide-angle lens 10 can correct chromatic aberration better because the fifth lens L5 has a low refractive index and a high Abbe number, and the sixth lens L6 has a high refractive index and a low Abbe number.

The distance TA from the apex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9) is the sum of the axial upper surface distances D1 to D8, and the distance from the apex of the surface R1 to the image plane R19 when the object is at infinity. TT is the sum of the shaft upper surface distances D1 to D18. Table 3 shows numerical values of conditional expressions (1), (2), and (3) in the wide-angle lens 10 based on Tables 1 and 2.

  Since the wide-angle lens 10 satisfies the conditional expression (1), it is possible to reduce the size of the wide-angle lens 10 by reducing the diameter of the first lens L1 while favorably correcting the aberration. Since the wide-angle lens 10 satisfies the conditional expression (2), the wide-angle lens 10 can be reduced in size by reducing the overall length of the wide-angle lens 10 while favorably correcting aberrations. Since the wide-angle lens 10 satisfies the conditional expression (3), it is possible to increase the imaging size of the peripheral part while improving the aberration well, and to improve the resolution performance of the peripheral part.

The conic constants and aspheric coefficient data of the surfaces R3 and R4 of the second lens L2 in the wide-angle lens 10 are shown in Table 4, the conic constants and aspheric coefficient data of the surfaces R13 and R14 of the seventh lens L7 are shown in Table 5, and the eighth Table 6 shows conic constants and aspheric coefficient data of the surfaces R15 and R16 of the lens L8. In this specification, a power of 10 is expressed using E (for example, 1.6 × 10 ⁻⁴ is 1.6E-4). In the wide-angle lens 10, the 10th-order aspheric coefficient D of the surfaces R3, R4, R13, R14, R15, and R16 is zero.

  In the wide-angle lens 10, the aspherical shape of the surfaces R3, R4, R13, R14, R15, and R16 is set as shown in Tables 4 to 6, so that the wide-angle lens 10 becomes a three-dimensional projection system, and the image formation size at the center portion. Can be reduced to increase the image size of the peripheral portion. Further, since the wide-angle lens 10 can share the correction of the image by the aspheric surface with the six lens surfaces, it is easy to correct the aberrations and the lens design. As a result, the lens design can be facilitated while the aberrations are favorably corrected, and the resolution performance of the peripheral portion can be improved.

  The aberration diagrams obtained from the wide-angle lens 10 are shown in FIGS. 2 (a) to (j) and FIGS. 3 (a) to (c). FIGS. 2A to 2E are transverse aberration diagrams in the tangential direction when the angles of view of principal rays with respect to the optical axis Ax are 90 °, 76 °, 57 °, 38 °, and 0 ° in this order. FIGS. 2F to 2J are lateral aberration diagrams in the sagittal direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. 2A to 2J, the horizontal axis represents the entrance pupil coordinates (value obtained by normalizing the entrance height to the pupil by the maximum height), and the vertical axis represents the lateral aberration (mm). 2A to 2J show a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  3A is a spherical aberration diagram, FIG. 3B is a field curvature and astigmatism diagram, and FIG. 3C is a distortion diagram. In FIG. 3A, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the entrance pupil coordinates. FIG. 3A shows a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  In FIG. 3B, 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 (°) of the principal ray with respect to the optical axis Ax. FIG. 3B shows the aberration S on the sagittal surface when the wavelength of the light beam is 588 nm as a solid line, and the aberration T on the tangential surface when the wavelength is 588 nm as a broken line. FIG. 3C shows a case where the horizontal axis represents distortion (%), the vertical axis represents the field angle (°) of the principal ray with respect to the optical axis Ax, and the wavelength of the ray is 588 nm.

(Second embodiment)
The wide angle lens 20 in the second embodiment will be described with reference to FIG. FIG. 4 is a cross-sectional view including the optical axis Ax of the wide-angle lens 20 in the second embodiment. As shown in FIG. 4, in the wide-angle lens 20 of the present embodiment, the fifth lens L5 is a biconvex lens, the sixth lens L6 is a biconcave lens, both surfaces R3 and R4 of the second lens L2, and the seventh lens L7. Both surfaces R13 and R14 and both surfaces R15 and R16 of the eighth lens L8 are aspherical. In the wide-angle lens 20, the second lens L2, the seventh lens L7, and the eighth lens L8 are made of resin, and the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of resin. It is made of glass.

Table 7 shows optical values and lens data of the wide-angle lens 20, and Table 8 shows the focal length of each lens. The wide-angle lens 20 can correct chromatic aberration satisfactorily because the Abbe number ν2 of the second lens L2 is larger than 50. The wide-angle lens 20 can correct chromatic aberration satisfactorily because the refractive index N3 of the third lens L3 is larger than 1.9. In the wide-angle lens 20, the fifth lens L5 has a low refractive index and a high Abbe number, and the sixth lens L6 has a high refractive index and a low Abbe number, so that the chromatic aberration can be corrected more favorably.

The distance TA from the apex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9) is the sum of the axial upper surface distances D1 to D8, and the distance from the apex of the surface R1 to the image plane R19 when the object is at infinity. TT is the sum of the shaft upper surface distances D1 to D18. Table 9 shows numerical values of conditional expressions (1), (2), and (3) in the wide-angle lens 20 based on Tables 7 and 8.

  Since the wide-angle lens 20 satisfies the conditional expression (1), it is possible to reduce the size of the wide-angle lens 20 by reducing the diameter of the first lens L1 while correcting aberrations favorably. Since the wide-angle lens 20 satisfies the conditional expression (2), it is possible to reduce the overall length of the wide-angle lens 20 and to reduce the size of the wide-angle lens 20 while favorably correcting aberrations. Since the wide-angle lens 20 satisfies the conditional expression (3), it is possible to increase the image forming size of the peripheral portion and improve the resolution performance of the peripheral portion while satisfactorily correcting the aberration.

Table 10 shows the conic constants and aspheric coefficient data of the surfaces R3 and R4 of the second lens L2 in the wide-angle lens 20, Table 11 shows the conic constants and aspheric coefficient data of the surfaces R13 and R14 of the seventh lens L7, and Table 12 shows the conic constants and aspheric coefficient data of the surfaces R15 and R16 of the lens L8. In the wide-angle lens 20, the tenth-order aspheric coefficient D of the surfaces R4, R13, R14, R15, and R16 is zero.

  In the wide-angle lens 20, the aspherical shape of the surfaces R3, R4, R13, R14, R15, and R16 is set as shown in Tables 10 to 12, so that the wide-angle lens 20 becomes a three-dimensional projection system, and the imaging size of the central portion is set. Can be reduced to increase the image size of the peripheral portion. Further, since the wide-angle lens 20 can share the correction of the image by the aspheric surface with the six lens surfaces, it is easy to correct the aberration and to facilitate the lens design. As a result, the lens design can be facilitated while the aberrations are favorably corrected, and the resolution performance of the peripheral portion can be improved.

  The aberration diagrams obtained from the wide-angle lens 20 are shown in FIGS. 5 (a) to (j) and FIGS. 6 (a) to (c). FIGS. 5A to 5E are lateral aberration diagrams in the tangential direction when the angles of view of principal rays with respect to the optical axis Ax are 90 °, 76 °, 57 °, 38 °, and 0 ° in order. FIGS. 5F to 5J are lateral aberration diagrams in the sagittal direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. In FIGS. 5A to 5J, the horizontal axis represents the entrance pupil coordinates (value obtained by normalizing the entrance height to the pupil by the maximum height), and the vertical axis represents the lateral aberration (mm). 5A to 5J show a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  6A is a spherical aberration diagram, FIG. 6B is a field curvature and astigmatism diagram, and FIG. 6C is a distortion diagram. In FIG. 6A, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the entrance pupil coordinates. FIG. 6A shows a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  In FIG. 6B, 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 (°) of the principal ray with respect to the optical axis Ax. FIG. 6B shows the aberration S on the sagittal surface when the wavelength of the light beam is 588 nm, and the broken line shows the aberration T on the tangential surface when the wavelength is 588 nm. FIG. 6C shows the case where the horizontal axis is distortion (%), the vertical axis is the field angle (°) of the principal ray with respect to the optical axis Ax, and the wavelength of the ray is 588 nm.

(Third embodiment)
A wide-angle lens 30 in the third embodiment will be described with reference to FIG. FIG. 7 is a cross-sectional view including the optical axis Ax of the wide-angle lens 30 in the third embodiment. As shown in FIG. 7, in the wide-angle lens 30 of the present embodiment, the fifth lens L5 is a biconvex lens, the sixth lens L6 is a biconcave lens, both surfaces R3 and R4 of the second lens L2, and the seventh lens L7. Both surfaces R13 and R14 and both surfaces R15 and R16 of the eighth lens L8 are aspherical. In the wide-angle lens 30, the second lens L2, the seventh lens L7, and the eighth lens L8 are made of resin, and the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of resin. It is made of glass.

Table 13 shows optical values and lens data of the wide-angle lens 30, and Table 14 shows the focal length of each lens. The wide-angle lens 30 can satisfactorily correct chromatic aberration because the Abbe number ν2 of the second lens L2 is larger than 50. The wide-angle lens 30 can correct chromatic aberration satisfactorily because the refractive index N3 of the third lens L3 is larger than 1.9. In the wide-angle lens 30, the fifth lens L5 has a low refractive index and a high Abbe number, and the sixth lens L6 has a high refractive index and a low Abbe number, so that chromatic aberration can be corrected more favorably.

The distance TA from the apex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9) is the sum of the axial upper surface distances D1 to D8, and the distance from the apex of the surface R1 to the image plane R19 when the object is at infinity. TT is the sum of the shaft upper surface distances D1 to D18. Table 15 shows numerical values of conditional expressions (1), (2), and (3) in the wide-angle lens 30 based on Tables 13 and 14.

  Since the wide-angle lens 30 satisfies the conditional expression (1), it is possible to reduce the size of the wide-angle lens 30 by reducing the diameter of the first lens L1 while favorably correcting the aberration. Since the wide-angle lens 30 satisfies the conditional expression (2), it is possible to reduce the overall length of the wide-angle lens 30 and reduce the size of the wide-angle lens 30 while correcting aberrations well. Since the wide-angle lens 30 satisfies the conditional expression (3), it is possible to increase the peripheral imaging size and improve the peripheral resolution performance while correcting aberrations well.

Table 16 shows the conic constants and aspheric coefficient data of the surfaces R3 and R4 of the second lens L2 in the wide-angle lens 30, Table 17 shows the conic constants and aspheric coefficient data of the surfaces R13 and R14 of the seventh lens L7, and Table 18 shows the conic constants and aspheric coefficient data of the surfaces R15 and R16 of the lens L8. In the wide-angle lens 30, the 10th-order aspheric coefficient D of the surfaces R3, R4, R13, R14, R15, and R16 is zero.

  The wide-angle lens 30 has the aspherical shape of the surfaces R3, R4, R13, R14, R15, and R16 as shown in Tables 16 to 18, so that the wide-angle lens 30 becomes a three-dimensional projection system, and the imaging size at the center portion. Can be reduced to increase the image size of the peripheral portion. Further, since the wide-angle lens 30 can share the correction of the image by the aspheric surface with the six lens surfaces, it is easy to correct the aberration and to design the lens easily. As a result, the lens design can be facilitated while the aberrations are favorably corrected, and the resolution performance of the peripheral portion can be improved.

  The aberration diagrams obtained from the wide-angle lens 30 are shown in FIGS. 8 (a) to 8 (j) and FIGS. 9 (a) to 9 (c). FIGS. 8A to 8E are lateral aberration diagrams in the tangential direction when the angles of view of principal rays with respect to the optical axis Ax are 90 °, 76 °, 57 °, 38 °, and 0 ° in order. FIGS. 8F to 8J are lateral aberration diagrams in the sagittal direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. In FIGS. 8A to 8J, the horizontal axis represents the entrance pupil coordinates (value obtained by normalizing the entrance height to the pupil by the maximum height), and the vertical axis represents the lateral aberration (mm). 8A to 8J show a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  9A is a spherical aberration diagram, FIG. 9B is a field curvature and astigmatism diagram, and FIG. 9C is a distortion diagram. In FIG. 9A, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the entrance pupil coordinates. FIG. 9A shows a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  In FIG. 9B, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the field angle (°) of the principal ray with respect to the optical axis Ax. FIG. 9B shows the aberration S on the sagittal surface when the wavelength of the light beam is 588 nm, and the broken line shows the aberration T on the tangential surface when the wavelength is 588 nm. FIG. 9C shows a case where the horizontal axis is distortion (%), the vertical axis is the principal ray field angle (°) with respect to the optical axis Ax, and the wavelength of the light beam is 588 nm.

(Fourth embodiment)
A wide-angle lens 40 in the fourth embodiment will be described with reference to FIG. FIG. 10 is a cross-sectional view including the optical axis Ax of the wide-angle lens 40 in the fourth embodiment. As shown in FIG. 10, in the wide-angle lens 40 of the present embodiment, the fifth lens L5 is a biconvex lens, the sixth lens L6 is a biconcave lens, both surfaces R3 and R4 of the second lens L2, and the seventh lens L7. Both surfaces R13 and R14 and both surfaces R15 and R16 of the eighth lens L8 are aspherical. In the wide-angle lens 40, the second lens L2, the seventh lens L7, and the eighth lens L8 are made of resin, and the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of resin. It is made of glass.

Table 19 shows the optical values and lens data of the wide-angle lens 40, and Table 20 shows the focal length of each lens. The wide-angle lens 40 can correct chromatic aberration satisfactorily because the Abbe number ν2 of the second lens L2 is larger than 50. In the wide-angle lens 40, the refractive index N3 of the third lens L3 is larger than 1.9, so that chromatic aberration can be corrected well. In the wide-angle lens 40, the fifth lens L5 has a low refractive index and a high Abbe number, and the sixth lens L6 has a high refractive index and a low Abbe number, so that the chromatic aberration can be corrected more favorably.

The distance TA from the apex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9) is the sum of the axial upper surface distances D1 to D8, and the distance from the apex of the surface R1 to the image plane R19 when the object is at infinity. TT is the sum of the shaft upper surface distances D1 to D18. Table 21 shows numerical values of conditional expressions (1), (2), and (3) in the wide-angle lens 40 based on Tables 19 and 20.

  Since the wide-angle lens 40 satisfies the conditional expression (1), it is possible to reduce the size of the wide-angle lens 40 by reducing the diameter of the first lens L1 while favorably correcting aberrations. Since the wide-angle lens 40 satisfies the conditional expression (2), it is possible to reduce the overall length of the wide-angle lens 40 and reduce the size of the wide-angle lens 40 while favorably correcting aberrations. Since the wide-angle lens 40 satisfies the conditional expression (3), it is possible to increase the imaging size of the peripheral part while improving the aberration well, and to improve the resolution performance of the peripheral part.

Table 22 shows the conic constants and aspheric coefficient data of the surfaces R3 and R4 of the second lens L2 in the wide-angle lens 40, Table 23 shows the conic constants and aspheric coefficient data of the surfaces R13 and R14 of the seventh lens L7, and Table 24 shows conic constants and aspheric coefficient data of the surfaces R15 and R16 of the lens L8. In the wide-angle lens 40, the tenth-order aspheric coefficient D of the surfaces R3, R4, R13, R14, R15, and R16 is zero.

  In the wide angle lens 40, the aspherical shape of the surfaces R3, R4, R13, R14, R15, and R16 is set as shown in Tables 22 to 24, so that the wide angle lens 40 becomes a three-dimensional projection system, and the imaging size of the central portion is set. Can be reduced to increase the image size of the peripheral portion. Further, since the wide-angle lens 40 can share the correction of the image by the aspheric surface with the six lens surfaces, it is easy to correct the aberration and to facilitate the lens design. As a result, the lens design can be facilitated while the aberrations are favorably corrected, and the resolution performance of the peripheral portion can be improved.

  The aberration diagrams obtained from the wide-angle lens 40 are shown in FIGS. 11 (a) to 11 (j) and FIGS. 12 (a) to 12 (c). FIGS. 11A to 11E are lateral aberration diagrams in the tangential direction when the angles of view of principal rays with respect to the optical axis Ax are 90 °, 76 °, 57 °, 38 °, and 0 ° in this order. FIGS. 11F to 11J are lateral aberration diagrams in the sagittal direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. In FIGS. 11A to 11J, the horizontal axis represents the entrance pupil coordinates (value obtained by normalizing the entrance height to the pupil by the maximum height), and the vertical axis represents the lateral aberration (mm). FIGS. 11A to 11J show a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  12A is a spherical aberration diagram, FIG. 12B is a field curvature and astigmatism diagram, and FIG. 12C is a distortion diagram. In FIG. 12A, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the entrance pupil coordinates. FIG. 12A shows a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  In FIG. 12B, 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 (°) of the principal ray with respect to the optical axis Ax. FIG. 12B shows the aberration S on the sagittal surface when the wavelength of the light beam is 588 nm as a solid line, and the aberration T on the tangential surface when the wavelength is 588 nm as a broken line. FIG. 12C shows a case where the horizontal axis represents distortion (%), the vertical axis represents the field angle (°) of the principal ray with respect to the optical axis Ax, and the wavelength of the ray is 588 nm.

(5th Example)
A wide-angle lens 50 in the fifth embodiment will be described with reference to FIG. FIG. 13 is a cross-sectional view including the optical axis Ax of the wide-angle lens 50 in the fifth embodiment. As shown in FIG. 13, the wide-angle lens 50 of the present embodiment is a concave meniscus lens on the object side where the fifth lens L5 has a positive refractive power and the sixth lens L6 has a negative refractive power. Both surfaces R3 and R4 of the second lens L2, both surfaces R13 and R14 of the seventh lens L7, and both surfaces R15 and R16 of the eighth lens L8 are formed as aspheric surfaces. The fifth lens L5 has a surface R10 that is substantially flat (slightly convex on the object side) and a surface R11 that is convex on the image side. In the wide-angle lens 50, the second lens L2, the seventh lens L7, and the eighth lens L8 are made of resin, and the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of resin. It is made of glass.

Table 25 shows the optical values and lens data of the wide-angle lens 50, and Table 26 shows the focal length of each lens. In the wide-angle lens 50, since the Abbe number ν2 of the second lens L2 is larger than 50, chromatic aberration can be corrected well. In the wide-angle lens 50, the refractive index N3 of the third lens L3 is larger than 1.9, so that chromatic aberration can be corrected well.

The distance TA from the apex of the surface R1 of the first lens L1 to the aperture stop 11 (surface R9) is the sum of the axial upper surface distances D1 to D8, and the distance from the apex of the surface R1 to the image plane R19 when the object is at infinity. TT is the sum of the shaft upper surface distances D1 to D18. Table 27 shows numerical values of conditional expressions (1), (2), and (3) in the wide-angle lens 50 based on Tables 25 and 26.

  Since the wide-angle lens 50 satisfies the conditional expression (1), it is possible to reduce the size of the wide-angle lens 50 by reducing the diameter of the first lens L1 while correcting aberrations favorably. Since the wide-angle lens 50 satisfies the conditional expression (2), the wide-angle lens 50 can be reduced in size by reducing the overall length of the wide-angle lens 50 while favorably correcting aberrations. Since the wide-angle lens 50 satisfies the conditional expression (3), it is possible to increase the image forming size of the peripheral part and improve the resolution performance of the peripheral part while correcting the aberration well.

Table 28 shows the conic constants and aspheric coefficient data of the surfaces R3 and R4 of the second lens L2 in the wide-angle lens 50, Table 29 shows the conic constants and aspheric coefficient data of the surfaces R13 and R14 of the seventh lens L7. Table 30 shows conic constants and aspheric coefficient data of the surfaces R15 and R16 of the lens L8. In the wide-angle lens 50, the tenth-order aspheric coefficient D of the surfaces R3, R4, R13, R14, R15, and R16 is zero.

  In the wide-angle lens 50, the aspheric shapes of the surfaces R3, R4, R13, R14, R15, and R16 are set as shown in Tables 28 to 30, so that the wide-angle lens 50 becomes a three-dimensional projection system, and the image formation size at the center portion. Can be reduced to increase the image size of the peripheral portion. Further, since the wide-angle lens 50 can share the correction of the image by the aspherical surface with the six lens surfaces, it is easy to correct the aberration and to facilitate the lens design. As a result, the lens design can be facilitated while the aberrations are favorably corrected, and the resolution performance of the peripheral portion can be improved.

  The aberration diagrams obtained from the wide-angle lens 50 are shown in FIGS. 14 (a) to 14 (j) and FIGS. 15 (a) to 15 (c). FIGS. 14A to 14E are lateral aberration diagrams in the tangential direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. FIGS. 14F to 14J are lateral aberration diagrams in the sagittal direction when the angle of view of the principal ray with respect to the optical axis Ax is 90 °, 76 °, 57 °, 38 °, and 0 ° in order. In FIGS. 14A to 14J, the horizontal axis represents the entrance pupil coordinates (value obtained by normalizing the entrance height to the pupil by the maximum height), and the vertical axis represents the lateral aberration (mm). 14A to 14J show a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  15A is a spherical aberration diagram, FIG. 15B is a field curvature and astigmatism diagram, and FIG. 15C is a distortion diagram. In FIG. 15A, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the entrance pupil coordinates. FIG. 15A shows a one-dot chain line when the wavelength of the light beam is 436 nm, a solid line when the wavelength is 588 nm, and a two-dot chain line when the wavelength is 656 nm.

  In FIG. 15B, the horizontal axis represents the amount of deviation (mm) in the optical axis Ax direction from the image plane near the optical axis Ax, and the vertical axis represents the field angle (°) of the principal ray with respect to the optical axis Ax. FIG. 15B shows the aberration S on the sagittal surface when the wavelength of the light beam is 588 nm, and the broken line shows the aberration T on the tangential surface when the wavelength is 588 nm. FIG. 15C shows a case where the horizontal axis represents distortion (%), the vertical axis represents the field angle (°) of the principal ray with respect to the optical axis Ax, and the wavelength of the ray is 588 nm.

  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 each of the embodiments described above, the case where the maximum angle of view of the wide-angle lenses 10, 20, 30, 40, and 50 is 180 ° has been described. It is of course possible to construct more than °.

  In the above embodiment and each of the above examples, the case where the lens having an aspheric surface on at least one surface is made of resin has been described. However, the present invention is not limited to this, and a lens having an aspheric surface on at least one surface is used. Of course, it is possible to make it glass. Further, the lens having both spherical surfaces is not limited to glass, and a lens having both spherical surfaces can be made of resin.

  In each of the above-described embodiments, the case where the fifth lens L5 having positive refractive power and the sixth lens L6 having negative refractive power are cemented to form the cemented lens L56 having negative refractive power has been described. However, the present invention is not limited to this, and the fifth lens L5 having negative refractive power and the sixth lens L6 having positive refractive power are cemented to form a cemented lens L56 having negative refractive power. Is of course possible.

10, 20, 30, 40, 50 Wide-angle lens 11 Aperture stop G1 1st group G2 2nd group G3 3rd group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens L8 8th lens L56 Joint lens R19 Image plane

Claims (6)

A wide-angle lens including, in order from the object side, a first group having negative refractive power, a second group having positive refractive power, an aperture stop, and a third group having positive refractive power ,
The first group is a first lens 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, in order from the object side. Consisting of a lens and
The second group includes, in order from the object side, a third lens having positive refractive power and a fourth lens having positive refractive power and concave on the object side,
The third group includes, in order from the object side, a cemented lens having a negative refractive power obtained by cementing the fifth lens and the sixth lens, a seventh lens having a positive refractive power, and a first lens having a positive refractive power. Consisting of 8 lenses,
The second lens and the eighth lens each have at least one surface formed as an aspheric surface. TA is the distance from the vertex of the object side surface of the first lens to the aperture stop when the object is at infinity, and the distance from the vertex of the object side surface of the first lens to the image plane when the object is at infinity. The wide-angle lens according to claim 1, wherein, when TT is satisfied, the following conditional expression (1) is satisfied.

When the distance from the vertex of the object side surface of the first lens to the image plane at infinity is TT and the focal length of the entire lens is f, the following conditional expression (2) is satisfied. The wide-angle lens according to claim 1 or 2, characterized in that:

The seventh lens has an aspheric surface at least one surface,
The focal length of the second lens is f2, the focal length of the seventh lens is f7,
The wide-angle lens according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied when a focal length of the eighth lens is f8.

  5. The wide-angle lens according to claim 1, wherein an Abbe number of the second lens is larger than 50. 6. The wide-angle lens according to claim 1, wherein a refractive index of the third lens is larger than 1.9.

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