Illumination optical system

Abstract

An illumination optical system according to the present invention has, in order from an object to be illuminated, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. When the illumination optical system is regarded as an image forming optical system for a light beam incident from the illumination object side, the combined focal length is set to be f mm, the combined refractive power is set to be Pt = 1 / f, the surfaces of the three lenses are set to be first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is set to be P5, and the center thickness of the second lens is set to be L2. The following formula is satisfied: 1.3 < P5 / Pt 0.1 < L2 / f < 0.25.

Description

Technical Field

[0001] The present invention relates to an illumination optical system used in a headlight of a vehicle or the like. Background Art

[0002] In recent years, an illumination optical system for ADB (Adaptive Driving Beam) light distribution control has been developed in vehicle headlights (Patent Document 1). In ADB light distribution control, multiple LEDs (light emitting diodes) configured as light sources are individually controlled according to the conditions of other vehicles in front of the vehicle, thereby controlling the irradiation target area and irradiation intensity, etc. Therefore, in ADB light distribution control, it is required to be able to individually control the irradiation area of ​​each LED. Therefore, in the illumination optical system, it is necessary to reduce flare, which is a phenomenon of irradiating an undesired area, as much as possible. In addition, it is preferred that the illumination optical system is bright.

[0003] Therefore, in the field of vehicle headlights and the like, there is a demand for a lighting optical system that is bright and has little glare.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2019-573638 (Japanese Patent No. 002897) Summary of the invention

[0007] Problems to be solved by the invention

[0008] The technical object of the present invention is to provide a bright illumination optical system with little flare.

[0009] Means for solving problems

[0010] The illumination optical system of the present invention has a first lens, a second lens, and a third lens in order from the illumination object side, the first lens has a positive refractive power, the second lens has a negative refractive power, and the third lens has a positive refractive power. When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the synthetic focal length is set to f mm, the synthetic refractive power is set to Pt=1 / f, the surfaces of the three lenses are set to the first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is set to P5, and the center thickness of the second lens is set to L2, then the following formula is satisfied:

[0011] 1.3<P5 / Pt

[0012] 0.1<L2 / f<0.25.

[0013] According to the present invention, coma aberration is reduced when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, and flare of the illumination optical system corresponding to coma aberration is reduced.

[0014] In the illumination optical system of the first embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the proportion of light beams that reach the image plane among the light beams that are incident on the surface of the first lens on the illumination object side at an angle of 25 degrees relative to the optical axis is in the range of 14% to 20%.

[0015] In the illumination optical system of the second embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the following equation is satisfied, assuming that the F value is F:

[0016] F<0.7.

[0017] According to the illumination optical system of this embodiment, sufficient luminous intensity can be obtained.

[0018] In the illumination optical system of the third embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the focus movement range of the axial chromatic aberration of the light beam with a wavelength of 0.420 μm to 0.680 μm based on the d line (588 nm) is set to c mm, and the following equation is satisfied:

[0019] c / f<0.00292.

[0020] According to the illumination optical system of this embodiment, dispersion in the irradiation surface is reduced.

[0021] In the illumination optical system of the fourth embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the distortion of the light beam incident on the surface of the first lens on the illumination object side at an angle of 20 degrees relative to the optical axis is negative, and its absolute value is greater than 5%.

[0022] According to the illumination optical system of this embodiment, a wider range can be illuminated compared to a case where there is no distortion.

[0023] In the illumination optical system according to the fifth embodiment of the present invention, the materials of the first lens, the second lens, and the third lens are acrylic, polycarbonate, and acrylic, respectively.

[0024] According to the illumination optical system of this embodiment, by using acrylic and polycarbonate having different refractive indices as the materials of the three lenses, the axial chromatic aberration when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side is reduced, thereby reducing the dispersion in the irradiation surface.

[0025] In the illumination optical system according to the third embodiment of the present invention, the first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram showing an example of the illumination optical system of the present invention.

[0027] Figure 2 The figure shows that when a parallel beam of light with an angle of 25 degrees to the optical axis of the illumination optical system is Figure 1 The diagram shows the path of light when the illumination object side of the illumination optical system is incident on the surface S1.

[0028] Figure 3 The diagram shows a region of the surface S1 through which light rays that reach a surface perpendicular to the optical axis and that includes the point O without vignetting pass, among parallel light beams that are parallel to the optical axis and that enter the surface S1 of the optical system.

[0029] Figure 4 The diagram shows a region of the surface S1 through which light rays that reach a surface perpendicular to the optical axis and that includes the point O without vignetting pass, among parallel light beams that form an angle of 25 degrees with the optical axis and that enter the surface S1 of the optical system.

[0030] Figure 5 1 is a diagram showing the ratio of light rays that reach a surface perpendicular to the optical axis and include the point O, without vignetting, among parallel light beams incident on the surface S1 of the optical system.

[0031] Figure 6 The figure shows that when a parallel beam of light with an angle of 23 degrees to the optical axis of the illumination optical system is Figure 1 The diagram shows the path of light when the illumination object side of the illumination optical system is incident on the surface S1.

[0032] Figure 7 The figure shows that when a parallel beam of light with an angle of 23 degrees to the optical axis of the illumination optical system is Figure 1 The diagram shows the path of light when the illumination object side of the illumination optical system is incident on the surface S1.

[0033] Figure 8 1 is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis of the illumination optical system enters the surface S1 from the illumination object side of the illumination optical system of the comparative example.

[0034] Fig. 9 1 is a diagram showing flare on a plane perpendicular to the z-axis due to a light source arranged at a point on the x-axis away from point O by the distance between point O and point E″.

[0035] Fig.10 This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 4.0 mm in which the center thickness of the second lens is changed.

[0036] Fig.11 This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 5.5 mm in which the center thickness of the second lens is changed.

[0037] Fig.12 This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 8.5 mm in which the center thickness of the second lens is changed.

[0038] Fig.13 It is a diagram showing the field curvature when the embodiment is regarded as an imaging optical system.

[0039] Fig.14 1 is a diagram showing distortion when the embodiment is regarded as an imaging optical system.

[0040] Fig.15 Graphs showing axial chromatic aberration when the embodiment is regarded as an imaging optical system. DETAILED DESCRIPTION

[0041] Figure 1 : is a diagram showing an example of an illumination optical system of the present invention. The illumination optical system has a first lens L1, a second lens L2, and a third lens L3, and is configured to irradiate light from a light source having a center at a point O to an object. The first lens L1 is closest to the illumination object, and the third lens L3 is closest to the light source. The surfaces on the illumination object side of the first lens L1, the second lens L2, and the third lens L3 are represented by S1, S3, and S5, respectively, and the surfaces on the light source side of the first lens L1, the second lens L2, and the third lens L3 are represented by S2, S4, and S6, respectively. The illumination optical system is configured in such a way that its optical axis passes through the point O. Figure 1 The path of light rays when a parallel light beam parallel to the optical axis of the illumination optical system is incident on the surface S1 from the illumination object side of the illumination optical system is shown.

[0042] The surface of each lens is expressed by the following formula.

[0043]

[0044] z represents the coordinate of a point on the surface along the optical axis from the vertex of the lens surface. r represents the distance of the point on the surface from the optical axis. c represents the curvature, k represents the cone constant, and αi represents the aspheric coefficient. The sign of the curvature c is determined to be positive when the surface is convex toward the illumination object side, and is determined to be negative when it is concave toward the illumination object side.

[0045] Table 1 is a table showing the shapes, materials, and positions of lenses of the illumination optical system of the embodiment.

[0046]

Table 1

[0047]

[0048] The radius of curvature is the reciprocal of the curvature c. The "thickness or distance" in the S1 row indicates the thickness (center thickness) of the first lens L1, and the "thickness or distance" in the S6 row indicates the distance from the surface S6 to the point O at the center of the light source along the optical axis.

[0049] Table 2 is a table showing the values ​​of the aspheric coefficients of the lens surfaces. The values ​​of the aspheric coefficients not shown in the table are 0.

[0050]

Table 2

[0051]

[0052] Below, we will Figure 1 The illumination optical system shown is studied as an imaging optical system. As mentioned above, Figure 1 The path of the light when a parallel light beam parallel to the optical axis of the illumination optical system is incident on the surface S1 from the illumination object side. The parallel light beam converges at point O.

[0053] Figure 2 The figure shows that when a parallel beam of light with an angle of 25 degrees to the optical axis of the illumination optical system is Figure 1 The path of the light beam when the illumination object side of the illumination optical system is incident on the surface S1 is shown in FIG. The parallel light beams mentioned above reach the periphery of point E on the surface that includes point O and is perpendicular to the optical axis. If we consider Figure 1 and Figure 2 As for the path of the light ray shown, if a light source such as an LED (light emitting diode) is arranged in a plane including point O and perpendicular to the optical axis and within a range where the distance from point O is less than the distance between point O and point E, it is inferred that the range within an angle of 25 degrees with the optical axis centered on the light source can be illuminated.

[0054] Table 3 is a table showing the refractive power of each lens surface of the embodiment and the composite refractive power of the imaging optical system. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. In Table 3, "ratio" refers to the ratio of the refractive power of each surface to the composite refractive power. The composite focal length of the imaging optical system is 34.697 mm. In addition, the F value is 0.65. Generally, the F value is preferably less than 0.7.

[0055]

Table 3

[0056] Refractive power (1 / mm) ratio Synthetic refractive power 0.029 1 S1 0.0194 0.673 S2 0.0186 0.645 S3 -0.0479 -1.662 S4 -0.0097 -0.337 S5 0.0475 1.648 S6 0.0146 0.507

[0057] As shown in Table 3, in this embodiment, the refractive power of the surface S5 is relatively large. The reason why the refractive power of the surface S5 is relatively large is described below.

[0058] In the illumination optical system, irradiation to an undesired area, called flare, sometimes occurs. Flare becomes a major obstacle in ADB light distribution control, which requires high-precision determination of the irradiation position of each LED. The flare of the illumination optical system corresponds to the coma when the illumination optical system is regarded as an imaging optical system. That is, the larger the coma when regarded as an imaging optical system, the larger the flare of the illumination optical system. Therefore, in order to reduce the flare of the illumination optical system, it is necessary to reduce the coma when regarded as an imaging optical system. One method of reducing the coma is to reduce the proportion of light reaching the surface perpendicular to the optical axis in a parallel light beam that forms a relatively large angle with the optical axis by vignetting.

[0059] Figure 3 The diagram shows a region of the surface S1 through which light rays that reach a surface perpendicular to the optical axis and that includes the point O without vignetting pass, among parallel light beams that are parallel to the optical axis and that enter the surface S1 of the optical system. Figure 3 The figure on the left side shows a top view of surface S1, Figure 3 The figure on the right is Figure 1 Similarly, the path of the optical system is shown. Figure 3 , the light rays passing through substantially the entire area of ​​the surface S1 reach the surface including the point O and perpendicular to the optical axis without vignetting. Figure 3 The figure on the right is Figure 1 The same is true for the path of light.

[0060] Figure 4 The diagram shows a region of the surface S1 through which light rays that reach a surface perpendicular to the optical axis and that includes the point O without vignetting pass, among parallel light beams that form an angle of 25 degrees with the optical axis and that enter the surface S1 of the optical system. Figure 4 The figure on the left side shows a top view of surface S1, Figure 4 The figure on the right is Figure 2 Similarly, the path of the optical system is shown. Figure 4The area of ​​the surface S1 through which the light rays that reach the surface that includes the point O and is perpendicular to the optical axis without vignetting passes is less than 20% of the entire area.

[0061] Figure 5 1 is a diagram showing the ratio of light rays that reach a surface perpendicular to the optical axis and include the point O, without vignetting, among parallel light beams incident on the surface S1 of the optical system. Figure 5 The horizontal axis represents the angle between the parallel light beam and the optical axis. Figure 5 The vertical axis of represents the proportion of light rays that reach the surface that includes point O and is perpendicular to the optical axis without vignetting. Figure 5 When the angle between the parallel light beam and the optical axis is 25 degrees, the proportion of light rays that reach the surface that includes point O and is perpendicular to the optical axis without vignetting is approximately 15%.

[0062] like Figure 4 As shown, when the angle between the parallel light beam and the optical axis is 25 degrees, by reducing the radius of curvature of surface S5 and increasing the refractive power, a portion of the light rays diverged from surface S4 is prone to vignetting, and the proportion of light rays that reach the surface containing point O and perpendicular to the optical axis without vignetting is reduced.

[0063] Generally speaking, the ratio of the refractive power of surface S5 to the composite refractive power is preferably greater than 1.3. In addition, when the angle between the parallel light beam and the optical axis is 25 degrees, the proportion of light rays that reach the surface including point O and perpendicular to the optical axis without vignetting is preferably in the range of 14% to 20%.

[0064] Table 4 is a table showing the values ​​of various aberrations of various surfaces of the imaging optical system.

[0065]

Table 4

[0066]

[0067] "Total" is the sum of the aberrations of each surface, indicating the aberration of the entire imaging optical system. According to Table 4, the aberration of surface S5 helps to reduce the aberration of the entire imaging optical system. When the radius of curvature of surface S5 is increased (reducing the refractive power), the aberration of the entire imaging optical system tends to become larger. From this point of view, it is also preferred that the ratio of the refractive power of surface S5 to the composite refractive power is within the above range.

[0068] Figure 6 The figure shows that when a parallel beam of light with an angle of 23 degrees to the optical axis of the illumination optical system is Figure 1 The path of the light beam when the illumination object side of the illumination optical system shown in FIG. 1 is incident on the surface S1. The parallel light beams mentioned above reach the periphery of point E' on the surface that includes point O and is perpendicular to the optical axis. Figure 6 In this example, point O is the origin and the optical axis of the optical system is the z-axis. The x-axis is Figure 6The direction perpendicular to the paper.

[0069] Figure 7 This is a diagram showing flare on a plane perpendicular to the z-axis caused by a light source disposed at a point on the x-axis away from point O by the distance between point O and point E'. As an example, the light source is a light emitting diode. Figure 7 The horizontal axis represents the angle between the z-axis and the straight line obtained by projecting the light emitted from the light source onto the xz plane. Figure 7 The vertical axis represents the angle between the z-axis and the straight line obtained by projecting the light emitted from the light source onto the yz plane.

[0070] Next, other illumination optical systems will be considered as comparative examples.

[0071] Table 5 is a table showing the shapes, materials, and positions of lenses of the illumination optical system of the comparative example.

[0072]

Table 5

[0073]

[0074] The “thickness or spatial length” in the S1 row indicates the thickness (center thickness) of the first lens L1 , and the “thickness or spatial length” in the S6 row indicates the distance from the surface S6 to the point O at the center of the light source along the optical axis.

[0075] Table 6 is a table showing the aspheric coefficients of each lens surface.

[0076]

Table 6

[0077] S1 S2 S3 S4 S5 S6 α1 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 α2 5.158E-06 6.260E-05 3.485E-05 1.201E-06 1.476E-05 1.125E-04 α3 -5.725E-09 -6.779E-08 -4.669E-08 2.152E-08 -7.654E-09 -2.936E-07 α4 1.103E-11 2.656E-11 2.069E-11 1.184E-11 4.666E-11 4.761E-10

[0078] Table 7 is a table showing the refractive power of each lens surface and the composite refractive power of the imaging optical system of the comparative example. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. The composite focal length of the imaging optical system is 34.799 mm. In addition, the F value is 0.66.

[0079]

Table 7

[0080] Refractive power (1 / mm) ratio Synthetic refractive power 0.029 1 S1 0.0195 0.679 S2 0.0225 0.783 S3 -0.0271 -0.943 S4 -0.0404 -1.406 S5 0.048 1.670 S6 0.0224 0.779

[0081] Figure 8 : is a diagram showing the path of light when a parallel light beam at an angle of 23 degrees to the optical axis of the illumination optical system is incident on the surface S1 from the illumination object side of the illumination optical system of the comparative example. The parallel light beam reaches the periphery of point E" on the surface that includes point O and is perpendicular to the optical axis. Figure 8 In this example, point O is the origin and the optical axis of the optical system is the z-axis. The x-axis is Figure 8 The direction perpendicular to the paper.

[0082] Fig. 91 is a diagram showing flare on a plane perpendicular to the z-axis based on a light source arranged at a point on the x-axis away from point O by a distance between point O and point E". As an example, the light source is a light emitting diode. Fig. 9 The horizontal axis represents the angle between the z-axis and the straight line obtained by projecting the light emitted from the light source onto the xz plane. Fig. 9 The vertical axis represents the angle between the z-axis and the straight line obtained by projecting the light emitted from the light source onto the yz plane.

[0083] The flare of the illumination optical system of the embodiment will be shown. Figure 7 The flare of the illumination optical system of the comparative example is shown. Fig. 9 For comparison, Fig. 9 Large inward flare is observed in the image. The inward flare of the illumination optical system corresponds to the outward coma in the imaging optical system. Therefore, it is considered that the coma in the case of the comparative example as the illumination optical system is not sufficiently reduced.

[0084] Comparing Table 3 and Table 7, the refractive power of surface S5 is substantially the same. On the other hand, according to Table 2, the center thickness of the second lens of the embodiment is 6.992 mm, and according to Table 5, the center thickness of the second lens of the comparative example is 2.500 mm.

[0085] according to Figure 6 When a parallel beam is incident at an angle of 23 degrees to the optical axis, the light is incident on the surface S5 of the embodiment above the optical axis. Figure 8 , when a parallel light beam is incident at an angle of 23 degrees to the optical axis, in the surface S5 of the comparative example, the light is incident on both the area above and the area below the optical axis. In the comparative example, it is considered that the light incident on both the area above and the area below the optical axis in the surface S5 increases the coma. If the shapes of the lenses of the embodiment and the comparative example are considered, it is considered that by adjusting the center thickness of the second lens, when a parallel light beam is incident at an angle of 23 degrees to the optical axis, the area on the surface S5 where the light is incident can be adjusted.

[0086] Therefore, for the optical system in which the center thickness of the second lens is changed in the optical system of the embodiment, the path of the light beam when a parallel light beam forming an angle of 23 degrees with the optical axis is incident is obtained. In addition, the data other than the center thickness of the second lens of the optical system in which the center thickness of the second lens is changed are the same as those in Example 1.

[0087] Fig.10 This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 4.0 mm in which the center thickness of the second lens is changed.

[0088] Fig.11This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 5.5 mm in which the center thickness of the second lens is changed.

[0089] Fig.12 This is a diagram showing the path of light rays when a parallel light beam forming an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 8.5 mm in which the center thickness of the second lens is changed.

[0090] according to Figures 10 to 12 , when a parallel light beam is incident at an angle of 23 degrees to the optical axis, in the surface S5 of each imaging optical system, the light is incident on an area above the optical axis. Therefore, it is considered that coma can be reduced. The center thickness of the second lens is 4.0 mm, 5.5 mm and 8.5 mm, and the values ​​after being standardized according to the synthetic focal length (34.697 mm) of the imaging optical system of the embodiment are 0.115, 0.159 and 0.245. On the other hand, if the center thickness of the lens is too large, the molding time during manufacturing becomes longer, and the material cost also increases, so it is not preferred. Therefore, it is preferred that the center thickness of the second lens is standardized according to the synthetic focal length of the imaging optical system to a value in the range of 0.1 to 0.25.

[0091] Fig.13 It is a diagram showing the field curvature when the embodiment is regarded as an imaging optical system. Fig.13 The horizontal axis represents the coordinate of the image point in the Z-axis direction. The origin of the coordinate is point O, and the sign of the coordinate is negative on the illuminated object side. The unit is millimeter. Fig.13 The vertical axis represents the angle between the parallel light beam incident on the surface S1 and the optical axis. The unit is degree. 0.42T represents the position of the image point of the light beam with a wavelength of 0.42 microns on the meridian plane, and 0.42S represents the position of the image point of the light beam with a wavelength of 0.42 microns on the sagittal plane. 0.68T represents the position of the image point of the light beam with a wavelength of 0.68 microns on the meridian plane, and 0.68S represents the position of the image point of the light beam with a wavelength of 0.68 microns on the sagittal plane.

[0092] Fig.14 1 is a diagram showing distortion when the embodiment is regarded as an imaging optical system. Distortion is the ratio of the lateral magnification of the imaging optical system to the lateral magnification of an ideal lens. Fig.14 The horizontal axis represents the distortion. The unit is percentage. Fig.14 The vertical axis represents the angle between the parallel light beam incident on the surface S1 and the optical axis. The unit is degree. The distortion at an angle of 20 degrees is about -5%. Since the distortion is negative at a relatively large angle, the illumination range of the illumination optical system is greater than the illumination range of an ideal optical system with zero distortion.

[0093] Generally speaking, when the angle between the parallel light beam incident on the surface S1 and the optical axis is 20 degrees, the distortion is negative, and its absolute value is preferably greater than 5%.

[0094] Fig.15 Graphs showing axial chromatic aberration when the embodiment is regarded as an imaging optical system. Fig.15 The horizontal axis represents the coordinate of the image point in the Z-axis direction. The origin of the coordinate is point O, and the sign of the coordinate is negative on the illuminated object side. The unit is micrometer. Fig.15 The vertical axis represents the wavelength of the light. The unit is micrometer. The imaging optical system becomes an achromatic lens with the d-line (588 nanometers) as the main wavelength and the coordinates of the horizontal axis of the d-line are the same as the coordinates of the horizontal axis of the light with a wavelength of 488 nanometers, and the dispersion on the irradiation surface of the illumination optical system becomes smaller. Generally speaking, in order to reduce the dispersion on the irradiation surface of the illumination optical system, it is preferred to set the focus movement range of the axial chromatic aberration of the light with a wavelength of 0.420 micrometers to 0.680 micrometers based on the d-line (588 nanometers) to c millimeters when the illumination optical system is regarded as an imaging optical system for the light beam incident from the illumination object side, so as to satisfy c / f<0.00292.

Claims

1. An illumination optical system, comprising, in order from the illumination object side, a first lens, a second lens and a third lens, the first lens having a positive refractive power, the second lens having a negative refractive power, the third lens having a positive refractive power, wherein: When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the synthetic focal length is set to f mm, the synthetic refractive power is set to Pt=1 / f, the surfaces of the three lenses are set to the first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is set to P5, and the center thickness of the second lens is set to L2, then the following equation is satisfied: 1.3<P5 / Pt 0.1<L2 / f<0.

25.

2. The illumination optical system according to claim 1, wherein: When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the proportion of light beams that reach the image plane among the light beams incident on the surface of the first lens on the illumination object side at an angle of 25 degrees relative to the optical axis is in the range of 14% to 20%.

3. The illumination optical system according to claim 1, wherein: When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, and the F value is set to F, the following equation is satisfied: F＜0.7。 4. The illumination optical system according to claim 1, wherein: When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the focus movement range of the axial chromatic aberration of the light beam with a wavelength of 0.420 μm to 0.680 μm based on the d line (588 nm) is set to c mm, and the following equation is satisfied: c / f<0.00292.

5. The illumination optical system according to claim 1, wherein: When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the distortion of the light beam incident on the illumination object side surface of the first lens at an angle of 20 degrees relative to the optical axis is negative, and its absolute value is greater than 5%.

6. The illumination optical system according to claim 1, wherein: The materials of the first lens, the second lens and the third lens are acrylic, polycarbonate and acrylic respectively.

7. The illumination optical system according to claim 1, wherein: The first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens.

Images