JP2018194618A - Illumination optical system - Google Patents

Abstract

To provide an illumination optical system in which favorable observations not only in a far point observation but in a proximity observation can be achieved and distribution unevenness of illumination light is decreased.SOLUTION: The illumination optical system comprises, successively from an object side, a first lens having a positive refractive power, a second lens having a positive refractive power, and a third lens having a positive refractive power, in which the first lens has a convex surface on an object side and an aspherical surface on a light source side, and the optical system satisfies conditional expressions (1) and (2). They are: (1) 3<|r1/r2|<7 and (2) 2<φ/|Zasp-Zsph|<16, where r1 is a radius of curvature of the object side surface of the first lens, r2 is a radius of curvature of the light source side surface of the first lens, φ is a half length of a diameter of a luminous flux incident to the third lens, Zasp is a sag amount at a height φ of rays, on the aspherical surface on the light source side of the first lens, and Zsph is a sag amount of a paraxial reference spherical surface at the height φ of rays, on the aspherical surface on the light source side of the first lens.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an illumination optical system.

  It is desirable that the light distribution characteristic of the illumination optical system required for far-point observation (normal observation) of the endoscope can irradiate mainly in the depth direction as in a flashlight, for example.

  In close proximity (near point) observation (enlarged observation), the distance to the subject is very short. For example, the distance to the subject is 2 mm or less. For this reason, it is desirable for the illumination light to be irradiated to a wide field of view with the largest possible angle with respect to the subject.

  It is difficult to perform appropriate illumination in both the far-point observation and the close-up observation of the endoscope. For example, Patent Document 1 discloses an illumination optical system capable of preventing light distribution unevenness and controlling light distribution characteristics while suppressing a decrease in the total amount of illumination light.

JP 2010-115281 A

  However, Patent Document 1 does not specify a radius of curvature or an aspheric shape regarding the lens surface of the illumination optical system. Thus, in patent document 1, only the result of the light distribution characteristic is disclosed.

  The present invention has been made in view of the above, and in addition to far-point observation (normal observation), close observation (magnification observation) close to the subject can be performed with good observation, An object of the present invention is to provide an illumination optical system in which uneven distribution of illumination light is reduced.

In order to solve the above-described problems and achieve the object, an illumination optical system according to at least some embodiments of the present invention includes, in order from the object side, a first lens having positive refractive power, 2 lenses and a third lens having positive refracting power. The first lens has a convex surface facing the object side, and the light source side surface is aspherical. The following conditional expressions (1), ( 2) is satisfied.
3 <| r1 / r2 | <7 (1)
2 <φ / | Zasp-Zsph | <16 (2)
here,
r1 is the radius of curvature of the object side surface of the first lens;
r2 is the radius of curvature of the light source side surface of the first lens,
φ is half the diameter of the light beam incident on the third lens,
Zasp is the amount of zag at the ray height φ on the aspherical surface on the light source side of the first lens,
Zsph is a zag amount at the light ray height φ of the paraxial reference spherical surface on the light source side aspherical surface of the first lens,
It is.

  In addition to far-point observation (normal observation), the present invention can perform good observation in close-up observation (enlarged observation) approaching a subject to 2 mm or less, and illumination optics in which uneven distribution of illumination light is reduced. There is an effect that a system can be provided.

FIG. 2A is a lens cross-sectional view of an illumination optical system according to an embodiment. (B) is a figure explaining parameters Asph and Sph. It is a figure explaining parameters r (0) and r (α). 1A is a lens cross-sectional view of an illumination optical system according to Example 1. FIG. FIG. 6B is a lens cross-sectional view of the illumination optical system according to Example 2. (C) is a lens sectional view of the illumination optical system according to Example 3. FIG. FIG. 6D is a lens cross-sectional view of the illumination optical system according to Example 4; (A) is a lens cross-sectional view of the illumination optical system according to Example 5. FIG. 6B is a lens cross-sectional view of the illumination optical system according to Example 6. FIG. 10C is a lens cross-sectional view of the illumination optical system according to Example 7.

  Hereinafter, the illumination optical system according to the embodiment will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

FIG. 1A is a lens cross-sectional view of the illumination optical system 100 according to the embodiment. In order from the object side, the first lens L1 having positive refractive power, the second lens L2 having positive refractive power, and the third lens L3 having positive refractive power,
The first lens L1 has the convex surface r1 facing the object side, and the light source side surface r2 is aspherical, and satisfies the following conditional expressions (1) and (2).
3 <| r1 / r2 | <7 (1)
2 <φ / | Zasp-Zsph | <16 (2)
here,
r1 is a radius of curvature of the object side OBJ-d surface of the first lens L1,
r2 is a radius of curvature of the surface of the light source side LS-d of the first lens L2,
φ is half the diameter of the light beam LG1 incident on the third lens L3,
Zasp is a zag amount at the light beam height φ on the aspheric surface Asph (= r2) on the light source side LS-d of the first lens L1,
Zsph is a zag amount at the light ray height φ of the paraxial reference spherical surface Sph in the aspheric surface Asph on the light source side LS-d of the first lens L1,
It is.

FIG. 1B is a diagram for explaining a zag amount that is a parameter. The zag amount means a length at a light beam height φ between a plane passing through the top of the surface and perpendicular to the optical axis AX (z axis) and an aspherical surface or a spherical surface. Zasp is a zag amount at the light beam height φ on the aspheric surface Asph on the light source side LS-d of the first lens L1. Zsph is a zag amount at the light ray height φ of the paraxial reference spherical surface Sph in the aspheric surface Asph on the light source side LS-d of the first lens L1,
It is.

  The description of Zasp and Zsph will be continued. The zag amount of the aspheric surface Asph is expressed by the following equation.

here,
Zasp is the amount of aspherical zag,
s is the distance from the optical axis AX,
C is the curvature (the reciprocal of the radius of curvature = 1 / r)
k is the cone coefficient,
_An is an aspheric coefficient,
It is.
Zsph is the Z value in the spherical shape, and k = 0 and A _n = 0 in the above formula.

  Conditional expression (1) defines an appropriate range of the absolute value of the ratio between r1 and r2. By satisfying conditional expression (1), it is possible to efficiently refract a light beam having a large angle propagating from the rearmost side (light source side LS-d). Thereby, the surrounding light distribution performance is improved. Further, the light beam around the optical axis AX on the aspherical side of the first lens L1 can be efficiently refracted. Thereby, the light beam around the optical axis AX can be emitted in the central direction.

  Conditional expression (2) defines an appropriate relationship among the light beam height φ, the zig amount of the spherical surface of the first lens L1, and the zig amount of the aspheric surface of the first lens L1. By satisfying conditional expression (2), the illumination light propagated from the rear side (light source side LS-d) can be efficiently refracted on the aspherical side of the first lens L1. As a result, more rays having a large angle can be propagated.

  When the lower limit value of conditional expression (1) is not reached, the refractive effect of the object side surface r1 of the first lens L1 becomes large, and the peripheral luminous flux decreases. Alternatively, since the refraction effect at the light source side surface r2 of the first lens L1 is reduced, a sufficiently large angle light beam does not reach the object side surface r1 of the first lens L1. As a result, the peripheral luminous flux is reduced.

  If the upper limit of conditional expression (1) is exceeded, a light beam having a large angle incident on the object side surface r1 of the first lens L1 will be kicked. As a result, the luminous flux having a large angle is reduced.

  In addition, a light beam having a sufficiently large angle can be generated on the light source side surface r2 of the first lens L1. However, the luminous flux in the central direction is reduced accordingly. For this reason, it is not preferable for far-point observation with an endoscope.

  If the lower limit value of conditional expression (2) is not reached, the contribution of the aspherical surface (light source side surface r2) of the first lens L1 increases. As a result, a light beam having a large angle is increased and the close-up observation is improved. However, this is not preferable because the amount of the light beam having a small angle is reduced.

  If the upper limit value of conditional expression (2) is exceeded, the contribution of the aspherical surface (light source side surface r2) of the first lens L1 becomes small. As a result, the light beam having a large angle is reduced, and the far point observation is improved. However, this is not preferable because the amount of the light beam having a large angle is reduced.

  Φ is half the diameter of the light beam LG1 incident on the third lens L3. Here, the diameter of the light beam LG1 is the outer diameter (radius) of the light guide fiber in the case of a light guide fiber that guides light from a light source (not shown), and the light emitting surface of the LED in the case of a light emitting diode (LED). The outer diameter (radius).

Also, φ may be the effective diameter fe of the aspherical lens of the first lens L1 instead of half the diameter of the light beam LG1 incident on the third lens L3, as will be described below.
fe / | Zasp-Zsph |
fe is the effective diameter of the aspherical lens of the first lens L1,
It is.

Moreover, according to a preferable aspect of this embodiment, it is desirable that the following conditional expression (3) is satisfied.
1.2 <f1 / f <1.8 (3)
here,
f1 is the focal length of the first lens L1,
f is the focal length of the illumination optical system 100,
It is.

  Conditional expression (3) defines an appropriate ratio between f1 and f. When the conditional expression (3) is satisfied, the central light beam and the peripheral light beam can be efficiently generated in the first lens L1.

  If the lower limit of conditional expression (3) is not reached, the refractive power (power) of the first lens L1 will increase and the performance of refracting light rays will improve. However, since the ratio of the central beam is reduced, it is not preferable for far-point observation.

  When the value exceeds the upper limit value of the conditional expression (3), the refractive power (power) of the first lens L1 is reduced, and the performance of refracting light rays is reduced. However, since the ratio of the central light flux is increased, it is not preferable for close-up (near-point) observation.

Moreover, according to a preferable aspect of the present embodiment, it is desirable that the following conditional expression (4) is satisfied.
2 <f3 / f1 <7 (4)
here,
f1 is the focal length of the first lens L1,
f3 is the focal length of the third lens L3,
It is.

  Conditional expression (4) defines an appropriate ratio between f3 and f1. When the conditional expression (4) is satisfied, the illumination light can be adjusted and incident on the first lens L1. Further, it can greatly contribute to the adjustment of the object side surface r5 of the third lens L3 with respect to the spread of the light beam LG1 incident on the third lens L3.

  If the lower limit value of conditional expression (4) is not reached, the refractive power of the third lens L3 increases, that is, the focal length decreases, and the light rays are refracted greatly. As a result, reflection or the like is caused in a portion of the lens holding frame 101 that holds the second lens L2 and the third lens L3. As a result, the light beam effectively does not enter the lens surface of the first lens L1.

  If the upper limit value of conditional expression (4) is exceeded, the force that refracts the light rays traveling from the light source side LS-d becomes too small. As a result, the light having a large angle cannot be properly guided to the object side, and the illumination efficiency is lowered.

Further, according to a preferred aspect of the present embodiment, the absolute value of the radius of curvature of the object side surface r3 of the second lens L2 and the absolute value of the radius of curvature of the light source side surface r4 are the same, and the following conditional expression (5 ) Is desirable.
0.6 <r3 / r5 <1.4 (5)
here,
r3 is a radius of curvature of the object side surface r3 of the second lens L2,
r5 is a radius of curvature of the object side surface r5 of the third lens L3,
It is.

  Conditional expression (5) defines an appropriate ratio between r3 and r5. If the lower limit value of conditional expression (5) is not reached, the refractive power of the second lens L2 becomes large, and it becomes difficult to efficiently refract light rays at the light source side surface r2 of the first lens L1.

  If the upper limit value of the upper limit formula (5) is exceeded, the light beam incident on the periphery of the second lens L2 cannot be sufficiently propagated. For this reason, the loss of light quantity will arise.

According to a preferred aspect of the present embodiment, it is desirable that the angular distribution of the intensity of the illumination light emitted from the object side surface r1 of the first lens L1 satisfies the following conditional expressions (6) and (7). .
4.5 <r (30) / r (60) <7.5 (6)
1.2 <r (0) / r (30) <1.8 (7)
here,
r (0) is the light intensity at the object of the illumination light emitted from the illumination optical system 100 at an emission angle of 0 °,
r (30) is the light intensity at the object of the illumination light emitted from the illumination optical system 100 at an emission angle of 30 °,
r (60) is the light intensity at the object of the illumination light emitted from the illumination optical system 100 at an emission angle of 60 °,
It is.

  Conditional expressions (6) and (7) define an appropriate ratio of the intensity of illumination light. FIG. 2 shows the angular distribution r (α) of the illumination light intensity. The horizontal axis represents the position of the subject OBJ, and the vertical axis represents the arbitrary light intensity I. The intensity of light emitted from the illumination optical system 100 at an emission angle of 0 ° is α (0). The intensity of light emitted from the illumination optical system 100 at the emission angle α ° is α (α).

  Satisfying conditional expressions (6) and (7) makes it possible to satisfactorily perform both far-point observation and proximity (near-point) observation. When the upper limit value of conditional expression (6) is exceeded, the peripheral portion becomes dark at the time of proximity (near point) observation. When the lower limit value of conditional expression (6) is not reached, the surrounding area becomes bright. However, if it becomes too smaller than the lower limit value, it becomes dark during far-point observation.

  When the upper limit value of conditional expression (7) is exceeded, the central portion of the subject OBJ becomes bright during close-up (near-point) observation. However, when it becomes larger than an upper limit, a peripheral part will become dark.

  If the lower limit value of conditional expression (7) is not reached, it will be dark in far-point observation.

It is preferable to satisfy the following conditional expression (1 ′) instead of conditional expression (1).
4 <| r1 / r2 | <6.5 (1 ′)
It is preferable to satisfy the following conditional expression (2 ′) instead of conditional expression (2).
3 <φ / | Zasp-Zsph | <10 (2 ′)
It is preferable to satisfy the following conditional expression (3 ′) instead of conditional expression (3).
1.4 <f1 / f <1.6 (3 ′)
It is preferable to satisfy the following conditional expression (4 ′) instead of conditional expression (4).
2.8 <f3 / f1 <5.2 (4 ′)
It is preferable to satisfy the following conditional expression (5 ′) instead of conditional expression (5).
0.7 <r3 / r5 <1.3 (5 ′)
It is preferable to satisfy the following conditional expression (6 ′) instead of conditional expression (6).
5.5 <r (30) / r (60) <6.5 (6 ′)
It is preferable to satisfy the following conditional expression (7 ′) instead of conditional expression (7).
1.4 <r (0) / r (30) <1.7 (7 ′)

  Each example will be described below.

Example 1
An illumination optical system according to Example 1 will be described. 3A is a lens cross-sectional view of the illumination optical system of Example 1. FIG.

  The illumination optical system 200 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 with a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

(Example 2)
An illumination optical system according to Example 2 will be described. FIG. 3B is a lens cross-sectional view of the illumination optical system of Example 2.

  The illumination optical system 201 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 having a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

Example 3
An illumination optical system according to Example 3 will be described. FIG. 3C is a lens cross-sectional view of the illumination optical system of Example 3.

  The illumination optical system 202 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 with a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

(Example 4)
An illumination optical system according to Example 4 will be described. FIG. 3D is a lens cross-sectional view of the illumination optical system of Example 4.

  The illumination optical system 203 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 having a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

(Example 5)
An illumination optical system according to Example 5 will be described. 4A is a lens cross-sectional view of the illumination optical system of Example 5. FIG.

  The illumination optical system 204 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 with a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

(Example 6)
An illumination optical system according to Example 6 will be described. FIG. 4B is a lens cross-sectional view of the illumination optical system of Example 6.

  The illumination optical system 205 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 having a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

(Example 7)
An illumination optical system according to Example 7 will be described. FIG. 4C is a lens cross-sectional view of the illumination optical system of Example 7.

  The illumination optical system 206 includes, in order from the object side, a biconvex positive lens L1, a biconvex positive lens L2, and a planoconvex positive lens L3 having a plane facing the illumination side. Light from the light source LS is guided to the planoconvex positive lens L3, which is the third lens, by the light guide fiber LG.

  Below, the numerical data of each said Example are shown. Symbols r are the radius of curvature of each lens surface, d is the distance between the lens surfaces, nd is the refractive index of the d-line of each lens, and * is an aspherical surface.

  The aspheric shape is expressed by the following formula.

here,
Zasp is the amount of aspherical zag,
s is the distance from the optical axis AX,
C is the curvature (the reciprocal of the radius of curvature = 1 / r)
k is the cone coefficient,
_An is an aspheric coefficient,
It is.
In the aspheric coefficient, “e−n” (n is an integer) indicates “10 ⁻ⁿ ”. The symbols of these specification values are common to the numerical data of the examples described later.

Numerical example 1
Unit mm

Surface data surface number rd nd
1 6.000 1.60 1.883
2 * -1.243 0.06
3 3.500 0.77 1.883
4 -3.500 0.12
5 3.904 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = -3e-1, A6 = 0, A8 = 0, A10 = 0

Various data φ = 0.85

Numerical example 2
Unit mm

Surface data surface number rd nd
1 6.000 1.60 1.883
2 * -1.243 0.06
3 3.500 0.77 1.883
4 -3.500 0.12
5 3.904 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = -3e-1, A6 = -1e-1, A8 = 1e-1, A10 = 2e-1

Various data φ = 0.85

Numerical Example 3
Unit mm

Surface data surface number rd nd
1 6.000 1.60 1.883
2 * -1.243 0.06
3 3.500 0.77 1.883
4 -3.500 0.12
5 3.904 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = -3e-1, A6 = 0, A8 = 0, A10 = 2.5e-1

Various data φ = 0.85

Numerical Example 4
Unit mm

Surface data surface number rd nd
1 6.000 1.60 1.883
2 * -2.000 0.06
3 3.500 0.77 1.883
4 -3.500 0.12
5 3.904 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = -5e-1, A6 = 0, A8 = 0, A10 = 2.5e-1

Various data φ = 0.85

Numerical Example 5
Unit mm

Surface data surface number rd nd
1 7.000 1.60 1.883
2 * -1.100 0.06
3 3.200 0.77 1.883
4 -3.200 0.12
5 4.500 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = 0, A6 = -2e-1, A8 = 0, A10 = 2.5e-1

Various data φ = 0.85

Numerical Example 6
Unit mm

Surface data surface number rd nd
1 7.000 1.75 1.883
2 * -1.350 0.06
3 3.400 0.77 1.883
4 -3.400 0.12
5 3.000 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0.1
A4 = -2e-1, A6 = -2e-1, A8 = -2e-1, A10 = 0

Various data φ = 0.85

Numerical Example 7
Unit mm

Surface data surface number rd nd
1 5.500 1.40 1.883
2 * -1.050 0.06
3 3.400 0.77 1.883
4 -3.400 0.12
5 2.730 3.40 1.728
6 ∞ 0

Aspheric data
Second side
k = 0
A4 = -1e-1, A6 = 0, A8 = 0, A10 = 0

Various data φ = 0.85

The values corresponding to the conditional expressions in each example are shown below.

Conditional Example 1 Example 2 Example 3
(1) | r1 / r2 | 4.8 4.8 4.8
(2) φ / | Zasp-Zsph | 5.4 6.7 7.9
(3) f1 / f 1.48 1.48 1.48
(4) f3 / f1 4.1 4.1 4.1
(5) r3 / r5 0.90 0.90 0.90
(6) r (30) / r (60) 6.13 5.73 5.68
(7) r (0) / r (30) 1.60 1.57 1.56

Conditional Example 4 Example 5
(1) | r1 / r2 | 3.0 6.4
(2) φ / | Zasp-Zsph | 4.0 32.4
(3) f1 / f 1.80 1.46
(4) f3 / f1 2.9 5.2
(5) r3 / r5 0.90 0.71
(6) r (30) / r (60) 6.41 5.87
(7) r (0) / r (30) 1.61 1.58

Conditional Example 6 Example 7
(1) | r1 / r2 | 5.2 5.2
(2) φ / | Zasp-Zsph | 3.4 16.3
(3) f1 / f 1.60 1.41
(4) f3 / f1 2.9 3.4
(5) r3 / r5 1.13 1.25
(6) r (30) / r (60) 6.90 6.16
(7) r (0) / r (30) 1.59 1.52

  The illumination optical system described above may satisfy a plurality of configurations at the same time. This is preferable for obtaining a good illumination optical system. Moreover, the combination of a preferable structure is arbitrary. For each conditional expression, only the upper limit value or lower limit value of the numerical range of the more limited conditional expression may be limited.

  Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and may be implemented by appropriately combining the configurations of these embodiments without departing from the spirit of the present invention. The form is also within the scope of the present invention.

(Appendix)
In addition, the invention of the following structures is guide | induced from these Examples.
(Additional item 1)
In order from the object side, the first lens having positive refractive power,
An illumination optical system characterized in that the first lens has a convex surface facing the object side, and the light source side surface is aspherical, and satisfies the following conditional expressions (1) and (2).
3 <| r1 / r2 | <7 (1)
2 <φ / | Zasp-Zsph | <16 (2)
here,
r1 is the radius of curvature of the object side surface of the first lens;
r2 is a radius of curvature of the light source side surface of the first lens,
φ is half the diameter of the light beam incident on the first lens,
Zasp is a zag amount at a light beam height φ on the aspheric surface on the light source side of the first lens,
Zsph is a zag amount at a ray height φ of a paraxial reference spherical surface on the aspherical surface on the light source side of the first lens,
It is.

  As described above, the present invention can perform good observation not only in the far point observation (normal observation) but also in the close observation (enlarged observation) approaching the subject to 2 mm or less, and uneven distribution of the illumination light. Useful for reduced illumination optics.

100, 200, 201, 202, 203, 204, 205, 206 Illumination optical system 101 Lens holding frame L1 First lens L2 Second lens L3 Third lens r1 Object side surface of the first lens r2 Light source side surface of the first lens r3 First Object side surface of two lenses r4 Light source side surface of second lens r5 Object side surface of third lens LG1 Light beam LG Light guide fiber LS Light source

Claims (5)

In order from the object side, the first lens having a positive refractive power, a second lens having a positive refractive power, and a third lens having a positive refractive power,
An illumination optical system characterized in that the first lens has a convex surface facing the object side, and the light source side surface is aspherical, and satisfies the following conditional expressions (1) and (2).
3 <| r1 / r2 | <7 (1)
2 <φ / | Zasp-Zsph | <16 (2)
here,
r1 is the radius of curvature of the object side surface of the first lens;
r2 is a radius of curvature of the light source side surface of the first lens,
φ is half the diameter of the light beam incident on the third lens,
Zasp is a zag amount at a light beam height φ on the aspheric surface on the light source side of the first lens,
Zsph is a zag amount at a ray height φ of a paraxial reference spherical surface on the aspherical surface on the light source side of the first lens,
It is. The illumination optical system according to claim 1, wherein the following conditional expression (3) is satisfied.
1.2 <f1 / f <1.8 (3)
here,
f1 is the focal length of the first lens,
f is the focal length of the illumination optical system,
It is. The illumination optical system according to claim 1, wherein the following conditional expression (4) is satisfied.
2 <f3 / f1 <7 (4)
here,
f1 is the focal length of the first lens,
f3 is the focal length of the third lens,
It is. The absolute value of the radius of curvature of the object side surface of the second lens is the same as the absolute value of the radius of curvature of the light source side surface, and satisfies the following conditional expression (5): The illumination optical system according to any one of the above.
0.6 <r3 / r5 <1.4 (5)
here,
r3 is the radius of curvature of the object side surface of the second lens;
r5 is a radius of curvature of the object side surface of the third lens;
It is. 5. The angular distribution of the intensity of illumination light emitted from the object side surface of the first lens satisfies the following conditional expressions (6) and (7): 5. The illumination optical system described.
4.5 <r (30) / r (60) <7.5 (6)
1.2 <r (0) / r (30) <1.8 (7)
here,
r (0) is the light intensity at the object of the illumination light emitted from the illumination optical system at an emission angle of 0 °,
r (30) is the light intensity at the object of the illumination light emitted at an emission angle of 30 ° from the illumination optical system,
r (60) is the light intensity at the object of the illumination light emitted from the illumination optical system at an emission angle of 60 °,
It is.

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