JP2005345787A - Illumination optical system and endoscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate loss quantity of illuminating light emitted from a light guide and to uniformly emit illuminating light, such that the angle of luminous intensity distribution is wide. <P>SOLUTION: An illumination optical system 20 is disposed facing the emit end 11 of the light glass 10. The illumination optical system 20 includes, in order from the emit end, a first lens 21 having positive refracting power and a second lens group 22 having positive refracting power, as a whole. The first lens 21 has, in order from the emit end 11, a first face R<SB>1</SB>and a second face R<SB>2</SB>. The light guide 10 emits from the emit end 11 parallel rays of light that is parallel to the optical axis X of the first lens 21. Part (e.g., L5) of the parallel rays of light is totally reflected from the second face R<SB>2</SB>, then totally reflected from the first face R<SB>1</SB>again, passed through the second lens group 22, and emitted toward the object side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an illumination optical system disposed on an emission end side of a surface emitting light source such as a light guide, and an endoscope having the illumination optical system.

  An endoscope is usually provided with a light guide, and illumination light from the light source device is guided to the distal end portion of the endoscope by the light guide. In order to increase the illumination range of illumination light and eliminate unevenness in illuminance, it is known that an optical member is provided at the exit end of the light guide as described in Patent Documents 1 to 3, for example.

  Here, Patent Document 1 describes that two plano-convex lenses are disposed at the light guide emission end. In Patent Document 2, an optical element having a reflecting structure on the side surface and first and second lenses are arranged in order from the light emitting end of the light guide, and illumination light from the light guide is irradiated to the subject without loss. Has been described. Further, Patent Document 3 describes that an illumination optical system having a characteristic of h = fθ makes the illuminance distribution of the illumination light emitted from the light guide uniform and irradiates the subject with little loss of illumination light. Has been.

  However, in the optical system described in Patent Document 1, the orientation angle is narrow, and the illumination range of illumination light is not wide. Further, in Patent Document 2, since an optical element having a large lens thickness is used, the total length is long and it is not suitable for downsizing of the distal end portion of the endoscope, and processing and assembly take time and cost. Furthermore, in the optical system of Patent Document 3, an aspherical lens is required to obtain the characteristics in a limited space at the distal end portion of the endoscope, but the aspherical lens is not easily processed as compared with the spherical lens. .

Furthermore, in Patent Document 1, the light loss caused by the total reflection of light rays on the surface of the light distribution lens is not considered at all because the target light distribution angle is narrow. In Patent Documents 2 and 3, the total reflection on the surface of the light distribution lens is taken into consideration, and the main objective is to prevent the total reflection from occurring. It cannot be said that has been obtained.
Japanese Patent Laid-Open No. 51-42551 JP 2002-182126 A Japanese Patent No. 3020074

  Accordingly, the present invention has been made in view of the above problems, and provides an illumination optical system that is easy to assemble and process, and that can reduce the loss of light amount and widen the illumination range. For the purpose.

  In the illumination optical system according to the present invention, a first lens having a positive refractive power and a second lens group having a positive refractive power as a whole are arranged in order from the emission end side of the surface-emitting light source. The first lens has a first surface and a second surface in order from the emission end side, and a part of parallel light rays parallel to the optical axis of the first lens emitted from the emission end are provided on the second surface. Then, the light is totally reflected again by the first surface, and is then totally reflected again by the first surface, passes through the second lens group, and is emitted toward the object side.

  The first lens preferably allows the other part of the parallel rays to pass through the first and second surfaces and further the second lens group to be emitted toward the object side. Moreover, it is preferable that at least some of the parallel rays satisfying the condition of 0.3φ ≦ h ≦ 0.5φ satisfy the condition of the expression (1) described later. In this case, h is the distance from the position where the parallel light beam enters the second surface after passing through the first surface to the optical axis. Furthermore, the illumination optical system according to the present invention preferably satisfies the condition of the expression (2) described later, and more preferably satisfies the condition of the expression (3).

  Moreover, it is preferable that the illumination optical system according to the present invention satisfies the condition of the formula (4) described later. Furthermore, it is preferable that the illumination optical system according to the present invention satisfies the condition of the following formula (5). The second lens group is preferably composed of a single lens whose object side is a plane. Further, the surface emitting light source is preferably a light guide.

  An endoscope according to the present invention includes a surface emitting light source that emits light from a flat emission end, a first lens having positive refractive power in order from the emission end side, and a second lens having positive refractive power as a whole. A lens group, and the first lens has a first surface and a second surface in order from the emission end side, and is parallel to the optical axis of the first lens emitted from the emission end. A part of the light beam is totally reflected on the second surface, then totally reflected again on the first surface, passed through the second lens group and emitted to the object side, and emitted to the object side. And an observation means for observing the irradiated observation object.

  The illumination optical system according to the present invention reduces the light amount loss of illumination light by emitting a part of the light beam emitted from the emission end to the object side after being totally reflected twice by the first lens, The range can be widened.

  Embodiments according to the present invention will be described below with reference to FIGS. FIG. 1 schematically shows the endoscope of the present embodiment. FIG. 2 is a cross-sectional view in a plane including an optical axis X described later, and shows the light guide 10 and the illumination optical system 20 according to the present embodiment. As shown in FIG. 1, the endoscope 40 includes an insertion unit 30 that is inserted into a body cavity, and an operation unit 31 that is used to operate the endoscope 10 by gripping the endoscope 40. The light guide 10 (see FIG. 2) is inserted through the insertion portion 30, a light source 32 is optically connected to one end (not shown) of the light guide 10, and the other end is the light source. It becomes the radiation | emission end 11 (refer FIG. 2) for radiating | emitting 32 illumination light. As shown in FIG. 2, the illumination optical system 20 is disposed at a position facing the emission end 11, and the emission end 11 and the illumination optical system 20 are provided at the distal end portion 33 of the endoscope.

  Illumination light from the light source passes through the light guide 10 and is sent to the emission end 11. The illumination light sent to the emission end 11 is condensed and diffused by the illumination optical system 20 and then irradiated to an observation object (internal organ officer) (not shown). The illumination light is reflected by the observation object, and the reflected light is captured by the observation means (imaging device (CCD)), and the observation object is output as an image to a monitor or the like (not shown) according to the captured reflected light. Is done. The observation means may be, for example, a fiber scope as long as it observes the observation object by capturing the reflected light of the observation object.

The illumination optical system 20 is formed by arranging a first lens 21 having a positive refractive power and a second lens group 22 having a positive refractive power as a whole from the emission end 11 side. The first lens 21 and the second lens group 22 are disposed on the same optical axis X. The first lens 21 has a first surface R ₁ and a second surface R ₂ from the emission end 11 side, and the first and second surfaces R ₁ and R ₂ are formed as convex surfaces. Since the first lens 21 is a spherical lens, the first and second surfaces R ₁ and R ₂ are spherical.

The second lens group 22 is composed of one or more lenses, and preferably is composed of one lens. Therefore, the second lens group 22 has at least two or more surfaces, and has at least a third surface R ₃ positioned closest to the light guide 10 and a fourth surface R ₄ positioned closest to the object side.

  The light guide 10 is formed in a cylindrical shape by bundling a large number of optical fibers, and its emission end 11 has a flat surface. That is, the light guide 10 is a surface emitting light source having a flat emission end. The central axis of the light guide 10 in the vicinity of the emission end 11 coincides with the optical axis X of the first lens 21 and the second lens group 22. Here, the rays of illumination light emitted from the emission end 11 are a set of diffused rays, parallel rays parallel to the optical axis X, and the like. However, since the intensity of parallel rays is high from the exit end, it is necessary to consider mainly only the emission angle (light distribution angle) of parallel rays. In the following description, only parallel rays will be described.

As shown in FIG. 3, most of the parallel rays emitted from the emission end 11 pass through the first and second surfaces R ₁ and R _2, and the second lens group 22 from the third surface R ₃ . (Hereinafter, this incident ray is referred to as a direct incident ray). However, part of the parallel light passes through the first surface R _1, the incident angle of the second surface R ₂ exceeds the critical angle, it is totally reflected by the second surface R _2, the first surface R ₁ Return to. Its back light rays are incident angle on the first surface R ₁ because again exceeds the critical angle, it is totally reflected again by the first surface R _1. The light beam that has been totally reflected twice passes through the second surface R ₂ and is incident on the second lens group 22 from the third surface R ₃ (hereinafter, this incident light beam is referred to as a two-time total reflection light beam). Both the direct incident light and the two-time totally reflected light incident on the second lens group 22 are emitted from the fourth surface R ₄ and emitted to the observation object side (that is, the object side).

  In FIG. 3, light rays L <b> 1 to L <b> 5 emitted at equal intervals from the center portion of the emission end 11 to the outer edge portion are shown. Here, among these light rays, a light ray relatively emitted from the outside, that is, an outermost edge ray L5 emitted from the outermost edge of the emission end 11, for example, is a total reflection ray twice, and the other rays L1 to L4 are directly incident rays It becomes.

  That is, in the present embodiment, the twice total reflected light beam is a light beam emitted from the vicinity of the outermost edge of the emission end 11 like the outermost edge light beam L5, for example. That is, the two-time total reflection light beam is not totally reflected by the first lens 21, for example, by the lens holding frame of the second lens group 22, or totally reflected by the second lens group 22. It is a light beam that is not irradiated on the observation object. However, in the present embodiment, even such a light beam can be emitted to the object side, so that a light amount loss of illumination light can be reduced.

Further, since the twice total reflected light beam (for example, the outermost edge light beam L5) passes near the outer edge portion of the second lens group 22, it directly passes through the incident light beam (for example, the light beams L1 to L4) and the second lens group 22. Different areas. Therefore, by changing the curvature of the third surface R ₃ of the second lens group 22, the light distribution of the totally reflected light beam can be easily controlled twice without largely changing the light distribution of the directly incident light beam.

Here, the first lens 21 is a light ray that is emitted from the vicinity of the outermost edge of the emission end 11, such as the outermost edge ray L5, and is at least a parallel ray that satisfies the condition of 0.3φ ≦ h ≦ 0.5φ. some of the light rays so as to be totally reflected by the second surface R _2, is set so as to satisfy the expression (1) shown below. Where φ is the diameter (= width) of the light guide 10, N is the refractive index of the first lens 21, r ₁ is the radius of curvature on the first surface R ₁ side of the first lens 21, and r ₂ is the first radius. The radius of curvature on the second surface R ₂ side of the lens 21, h is the distance from the position where the parallel rays pass through the first surface R ₁ and then enter the second surface R ₂ to the optical axis.

Incidentally, A conditional formula (1), the lower limit, does not occur total reflection at the second surface R _2. Further, if A exceeds the upper limit in the conditional expression (1), the light beam totally reflected by the second surface R ₂ does not hit the first surface R ₁ , so that it is not emitted from the first lens, resulting in a light amount loss. . That is, if the refractive index N and the radii of curvature r ₁ and r ₂ are set so that at least a part of light rays satisfying the condition of 0.3φ ≦ h ≦ 0.5φ satisfies the conditional expression (1), the light rays Can totally reflect on the second surface R ₂ and reach the first surface R ₁ , so that most of the light beam emitted from the light guide can be used effectively.

The first lens 21 satisfies the following conditional expression (2). Where φ is the diameter (= width) of the light guide 10, N is the refractive index of the first lens 21, r ₁ is the radius of curvature on the first surface R ₁ side of the first lens 21, and r ₂ is the first radius. The radius of curvature on the second surface R ₂ side of the lens 21, h ₂ is the distance from the position where the parallel rays emitted from the outermost edge of the emission end 11 enter the second surface R ₂ to the optical axis.

By setting the refractive index N and the radii of curvature r ₁ and r ₂ so as to satisfy the conditional expression (2), in particular, parallel rays emitted from the outermost edge of the light guide are totally reflected by the second surface R ₂ , and The first surface R ₁ can be reached. If the refractive index N and the radii of curvature r ₁ and r ₂ are set so that the light beam at the outermost edge can be totally reflected, it is possible to effectively use the greater part of the light beam emitted from the light guide.

The first lens 21 satisfies the following conditional expression (3). However, the outermost edge light L5 emitted from the outermost edge of the exit end 11 of the parallel light emitted from the exit end 11 is totally reflected at a position distance h ₂ distant from the optical axis X in the second surface R _2, Further, it is assumed that the first surface R ₁ reaches a position away from the optical axis X by a distance h ₁ . In the present embodiment, the distance h mentioned above is equal to the distance h _2. Furthermore, the outermost edge refers to the outermost part of the emission end 11 and refers to the part whose distance from the central axis of the light guide is φ / 2.

When B is below the lower limit of conditional expression (3), the light beam totally reflected by the second surface R ₂ is not totally reflected by the first surface R ₁ . When B exceeds the upper limit of the conditional expression (3), total reflection occurs on the first surface R ₁ , but the totally reflected light beam becomes divergent light, and is therefore broken by the lens holding frame of the first lens 21. Or, since the diameter of the second lens is increased, it is not suitable for downsizing the distal end portion of the endoscope.

Further, in order for the second lens group 22 to irradiate the object to be observed with a light beam incident from the first lens 21 without loss and with a wide orientation angle, the focal length f ₂ of the second lens group 22 is as follows. It is desirable to satisfy the conditional expressions (4) and (5). Note that f is the focal length of the entire illumination optical system 20.
1.5 <f ₂ /f<2.3 (4)
0.7 <f ₂ /φ<1.2 (5)

Here, if the focal length f ₂ exceeds the upper limit of the expressions (4) and (5), the orientation angle becomes narrow and the illumination range of the illumination light cannot be sufficiently widened. On the other hand, if the focal length f ₂ becomes too small beyond the lower limits of the equations (4) and (5), total reflection is likely to occur on the fourth surface R ₄ of the second lens group 22 and it does not exit to the object side. The amount of light loss increases.

Furthermore, the focal length f ₁ of the first lens 21 is preferably adjusted so as to satisfy the following conditional expression (6).
1.4 <f ₁ / f <2 (6)

When the focal length f ₁ exceeds the upper limit in the expression (6) as compared with the focal length f of the entire illumination optical system 20, the orientation angle of the emitted illumination light is not sufficiently increased. On the other hand, when the focal length f ₁ exceeds the lower limit in the expression (6), the directly incident light beam easily causes total reflection in the second lens group 22 (fourth surface R ₄ ), and the light amount loss increases. Further, the twice total reflected light does not sufficiently enter the second lens group 22.

Further, the focal length f of the entire system is preferably adjusted to the following conditional expression with respect to the diameter φ of the light guide.
1.8 <φ / f <2.3 (7)

  If the focal length f with respect to the diameter φ of the light guide becomes too large and exceeds the lower limit of the expression (7), the light distribution angle of the emitted illumination light will not be sufficiently large. On the other hand, if the upper limit of the expression (7) is exceeded, the light beam is directed to the lens holding frame or the like, and total reflection occurs in the second lens group 22, resulting in a large light loss.

The directly incident light beam and the twice total reflected light beam emitted from the emission end 11 are once condensed by the illumination optical system 20 and then diffused again to irradiate the observation object. Here, the condensing points of the directly incident light and the twice total reflected light are different. The condensing point of the directly incident light beam is preferably located closer to the light guide 10 than the fourth surface R ₄ of the second lens group 22, and more preferably located within the second lens group 22. This is because if the condensing point is on the object side from the fourth surface R _4, the light is condensed on the observation target and may become high temperature.

When the condensing point of the direct incident light is on the light guide 10 side from the fourth surface R ₄ , the fourth surface R ₄ has non-power or negative power, that is, the fourth surface R ₄ is a flat surface or a concave surface. Preferably there is. This is because when the fourth surface R ₄ has positive power, the orientation angle of the emitted light beam becomes narrow. Furthermore, the fourth surface R ₄ is preferably a flat surface. This is because, when the fourth surface R ₄ exposed to the outside is a flat surface when used in an endoscope, cleaning is easy even if the lens is very small. Therefore, when the second lens group 22 is constituted by one lens, for example, the third surface R ₃ is formed as a spherical surface and a convex surface, and the fourth surface R ₄ is formed as a flat surface.

  FIG. 5 schematically shows the light distribution of the light beam emitted from each region when the emission end 11 of the light guide 10 is concentrically divided into regions 1 to 4 as shown in FIG. If the light beam emitted from the region 4 is not totally reflected twice by the first lens 21, it is totally reflected by the second lens group 22, and as shown in FIG. Is not irradiated. However, in the present embodiment, the light emitted from the region 4 is totally reflected twice by the first lens 21 and then becomes a twice total reflected light incident on the second lens group 22. As shown in FIG. 5, the observation object is sufficiently irradiated. In addition, since the twice totally reflected light beam is emitted with a relatively large light distribution angle, the illumination light is uniformly irradiated over a wide range as shown in FIG. Therefore, the illumination optical system of the present embodiment is particularly effective when a very wide illumination range (for example, 100 to 150 °) is required.

In the present embodiment, the case where both the first and second surfaces R ₁ and R ₂ are spherical has been described, but either one or both of the first and second surfaces R ₁ and R ₂ are described. May be an aspherical surface. For example, if only the second surface R ₂ is an aspherical surface, a second surface R ₂ of the first lens 21, in order to totally reflect a portion of the parallel light emitted from the exit end 11 is below Conditional expression (8) shown must be satisfied.

When both the first and second surfaces R ₁ and R ₂ are aspherical surfaces, the second surface R ₂ of the first lens 21 totally reflects a part of the parallel rays emitted from the emission end 11. For this purpose, the following conditional expression (9) must be satisfied.

ただし、Ｓ₁（ｙ）は第１面Ｒ₁の高さｙでのサグ、Ｓ₂（ｙ）は第２面Ｒ₂の高さｙでのサグである。

However, S ₁ (y) is a sag at the height y of the first surface R ₁ , and S ₂ (y) is a sag at the height y of the second surface R ₂ .

  Next, examples 1 to 6 will be described. In each example, the second lens group 22 was constituted by a single lens. In this embodiment, the light guide emission end is the 0th surface.

The optical data of Examples 1 to 6 are shown in Tables 1 to 6, respectively. In the table, R represents the radius of curvature of each lens surface, D represents the lens thickness or lens spacing, N represents the refractive index, and ν represents the Abbe number.

  In Example 1-6, the lens figure which showed the locus | trajectory of only the outermost edge light ray L5 is shown to FIG. 7, 9, 11, 13, 15, and 17, respectively. In Example 1-6, the lens figure which showed the locus | trajectory of the light rays L1-L5 is shown to FIG. 8, 10, 12, 14, 16, 18 respectively. Each lens diagram shows the light guide and the illumination optical system in a cross section including the optical axis X of the illumination optical system.

Table 7 shows the calculation results of conditional expressions (1) to (9) in Examples 1 to 6. In all of the examples, the first surface and the second surface were spherical surfaces, but conditional expressions (8) and (9) were also calculated for reference.

In Example 1, as shown in Table 7, it was sin ⁻¹ (1 / N) = 0.560. Here, the outermost edge ray L5 is a parallel ray satisfying the condition of 0.3φ ≦ h ≦ 0.5φ, and h = h ₂ , so A (or A ′) = 0.667, and the formula ( The conditions of 1) and formula (2) were satisfied. B = 0.663, which satisfied the conditions of the expression (3). At this time, as shown in FIG. 7, for example, the outermost edge light beam L5 was totally reflected on the second surface and then further totally reflected on the first surface. That is, in Example 1, a part of the parallel light beam emitted from the emission end was totally reflected twice by the first lens and then incident on the second lens group.

  In Example 1, the conditions of the formulas (4) to (7) were satisfied as shown in Table 7. At this time, as shown in FIG. 8, each light beam emitted from the light guide was emitted to the object side without being scattered and not totally reflected by the second lens group. In addition, since the light beam L5 emitted from the outermost edge is emitted with a relatively large orientation angle, the illumination light was uniformly irradiated over a wide range. As described above, the illumination optical system of Example 1 satisfied all the conditional expressions (1) to (7), and was able to irradiate light rays from the light guide in a wide range without loss.

  In the second to sixth embodiments, as in the first embodiment, each illumination optical system satisfies the conditional expressions (1) to (3). For example, the outermost light ray L5 is totally reflected on the second surface. Further, the light was totally reflected by the first surface and emitted to the object side through the second lens group. Further, similarly to the first embodiment, each illumination optical system satisfies the conditions of the conditional expressions (4) to (7), and the light beam emitted from the emission end is irradiated to the observation object in a wide range without loss. It was.

  The illumination optical systems in Examples 1 to 6 satisfied conditional expressions (8) and (9), respectively, as shown in Table 7.

It is the schematic diagram which showed the endoscope of this embodiment. It is sectional drawing which showed the illumination optical system of this embodiment, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of this embodiment, Comprising: It is the figure which showed the twice total reflected light beam and the direct incident light beam. It is the schematic diagram which divided and showed the output end of the light guide typically into four. It is the schematic diagram which showed the light distribution of the light beam of this embodiment. It is the schematic diagram which showed the light distribution of the light ray radiate | emitted from the outgoing end which does not have two total reflection light rays. It is sectional drawing which showed the illumination optical system of Example 1, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of Example 1, Comprising: It is the figure which showed the twice total reflected light and the direct incident light. It is sectional drawing which showed the illumination optical system of Example 2, Comprising: It is the figure which showed only 2 times total reflection light. It is sectional drawing which showed the illumination optical system of Example 2, Comprising: It is the figure which showed the twice total reflection light beam and the direct incident light beam. It is sectional drawing which showed the illumination optical system of Example 3, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of Example 3, Comprising: It is the figure which showed the twice total reflected light and the direct incident light. It is sectional drawing which showed the illumination optical system of Example 4, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of Example 4, Comprising: It is the figure which showed the twice total reflected light and the direct incident light. It is sectional drawing which showed the illumination optical system of Example 5, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of Example 5, Comprising: It is the figure which showed the twice total reflected light and the direct incident light. It is sectional drawing which showed the illumination optical system of Example 6, Comprising: It is the figure which showed only 2 times total reflected light. It is sectional drawing which showed the illumination optical system of Example 6, Comprising: It is the figure which showed the twice total reflected light beam and the direct incident light beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light guide 11 Output end 20 Illumination optical system 21 1st lens 22 2nd lens group

Claims (11)

  A first lens having a positive refractive power and a second lens group having a positive refractive power as a whole are arranged in order from the emission end side of the surface emitting light source, and the first lens is arranged at the emission end. A first surface and a second surface in order from the side, and a part of a parallel light beam parallel to the optical axis of the first lens emitted from the emission end is totally reflected by the second surface. After that, the illumination optical system is characterized in that it is totally reflected again by the first surface, passes through the second lens group, and is emitted toward the object side.   2. The first lens according to claim 1, wherein another part of the parallel rays passes through the first and second surfaces and further the second lens group, and is emitted to the object side. The illumination optical system described. 3. The illumination optical system according to claim 1, wherein at least a part of the parallel rays satisfying a condition of 0.3φ ≦ h ≦ 0.5φ satisfies the following expression (1). system.

Is the width of the surface-emitting light source, N is the refractive index of the first lens, r ₁ is the radius of curvature of the first lens on the first surface side, and r ₂ is the radius of the first lens. The radius of curvature on the second surface side, h is the distance from the position where the parallel light rays enter the second surface after passing through the first surface to the optical axis. The illumination optical system according to any one of claims 1 to 3, wherein the condition of the following expression (2) is satisfied.

Where φ is the width of the surface-emitting light source, N is the refractive index of the first lens, r ₁ is the radius of curvature of the first lens on the first surface side, and r ₂ is the radius of the first lens. The radius of curvature on the second surface side, h _2, is the position from which the outermost edge ray emitted from the outermost edge of the surface-emitting light source among the parallel rays enters the second surface after passing through the first surface. Distance to the optical axis. The illumination optical system according to claim 4, wherein the condition of the following expression (3) is satisfied.

However, the distance h ₁ after the outermost light beam is totally reflected by the second surface, from a position incident on the first surface to the optical axis. The illumination optical system according to any one of claims 1 to 5, wherein a condition of the following expression (4) is satisfied.
1.5 <f ₂ /f<2.3 (4)
Where f is the focal length of the entire illumination optical system, and f ₂ is the focal length of the second lens group. The illumination optical system according to claim 1, wherein the condition of the following expression (5) is satisfied.
0.7 <f ₂ /φ<1.2 (5)
Here, f ₂ is the focal length of the second lens group, and φ is the width of the surface-emitting light source.   The illumination optical system according to claim 1, wherein the second lens group includes a single lens having a plane on the object side.   9. The illumination optical system according to claim 1, wherein the surface-emitting light source is a light guide.   An illumination optical system according to any one of claims 1 to 9, and observation means for irradiating an observation object with a light beam emitted from the illumination optical system toward the object side and observing the irradiated observation object Endoscope equipped. A surface emitting light source that emits a light beam from a plane exit end;
A first lens having a positive refractive power in order from the emission end side and a second lens group having a positive refractive power as a whole are arranged, and the first lens is arranged in order from the emission end side. A first surface and a second surface, and a part of a parallel light beam parallel to the optical axis of the first lens emitted from the emission end is totally reflected by the second surface; An illumination optical system that causes total reflection again at the first surface, passes through the second lens group, and emits the light toward the object side;
An endoscope comprising: observation means for irradiating an observation object with a light beam emitted toward the object side, and observing the irradiated observation object.

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