JP3020074B2 - Illumination optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applicable to endoscopes and the like.
The present invention relates to a simple illumination optical system.

[0002]

2. Description of the Related Art In recent years, as the optical system of an endoscope has been widened, a wide-angle illumination system has been required.
There is also an increasing demand for an illumination optical system that provides an appropriate illuminance distribution to an observation target.

In response to the above requirements, an optical system described in Japanese Patent Application Laid-Open No. 56-20428 is known as an example of a wide-angle endoscope illumination optical system. As shown in FIG. 20, a positive lens system 2 is disposed in front of a light guide 1 made of an optical fiber bundle, and the light from the light guide 1 is once condensed by the lens system 2 and then diverged to wide angle. It is the one that made the lighting possible.

In this conventional example, the relationship between the incident height h of a ray emitted from the light guide in parallel with the optical axis to the lens system and the exit angle θ from the illumination optical system with respect to the incident ray height h is as follows.
Almost h = fsinθ. Where f is the illumination optical system
The focal length.

The phase on a planar object according to this conventional example
The opposite illuminance distribution is obtained as follows.

The relative illuminance distribution around the center of a planar object having a perfect diffusion surface is generally expressed by the following equation (1). F (θ) = (β / β _M × β / β _S ) ⁻¹ (1) where β is a paraxial magnification with respect to the object plane, and β _M and β _S are magnifications in the meridional direction and the sagittal direction with respect to the object plane, respectively. .

When the object distance is sufficiently far from the exit pupil position of the lens system, β _M and β _{S in the} above equations are given by the following equations (2) and (3), respectively. β _M = βcos ² θ ｛dA (θ) / dθ｝ (2) β _S = β ｛A (θ) / tan θ｝ (3) where A (θ) = h / f.

From the above equations (2) and (3), the relative illuminance distribution when illuminating the planar object having the perfect diffusion surface in the above-mentioned conventional example is F (θ) = cos ⁴ θ, and FIG. To
As shown from the center to the periphery, cos ⁴ θ
Darkens in proportion to

The relative illuminance distribution when illuminating a spherical or tube-shaped object according to this conventional example can be obtained as follows.

Generally, the relative illuminance distribution of a spherical object having a perfect diffusion surface and the relative illuminance distribution of a tube-shaped object are given by the following equations (5) and (6), respectively. G (θ) = F (θ) × 1 / cos ³ θ (5) H (θ) = F (θ) × tan ³ θ (6) where G (θ) and H (θ) are perfect diffusion surfaces, respectively. 3 is a relative illuminance distribution of a spherical object and a tube-shaped object.

From the above equations (5) and (6), the relative illuminance distributions of the perfectly diffuse spherical object and tube-like object in the conventional example are G (θ) = cos θ and H (θ), respectively. =
cos θ · sin ³ θ, as shown in FIG .

As is apparent from FIG. 19, in the case of a spherical object, cos θ increases from the center to the periphery.
, The illuminance distribution is practically satisfactory. In addition, the illuminance distribution of the tubular hollow object does not suddenly become bright around the visual field, and an appropriate illuminance distribution is obtained.

However, as in the above conventional example, h = fsi
The illumination optical system satisfying the relationship of nθ has a viewing angle of 110 °.
When applied to the above-described wide-angle observation optical system, the power of the second and third surfaces counted from the object side becomes too strong with the increase in the angle of view, and h and sin θ are not proportional to each other. High rays are totally reflected on the first or third surface, counted from the object side. Also, the higher the incident ray height, the more easily total reflection occurs. Therefore, the illuminance in a wide angle range of 110 ° or more does not increase so much, and only the light amount sharply decreases. Further, as an example of an illumination optical system applicable to a wide-angle observation optical system having a viewing angle of 110 ° or more, there is an optical system described in JP-A-58-95706. The configuration shown in FIG. 21 is disadvantageous in that the number of lenses is large and the cost is high as compared with the conventional example shown in FIG.

Further, as an illumination optical system which provides a uniform illuminance distribution at the time of illuminating a planar object, the distance h between the incident height h and the exit angle θ
And an optical system in which tan θ is approximately proportional is known. This is described in Japanese Patent Application Laid-Open No. 62-178207 shown in FIG.

However, observation by an endoscope is not limited to a planar object, and various objects such as a spherical object and a luminal object are used as described above.

For example, in the case of a medical endoscope, the inner surface of the stomach is substantially spherical, and the inner surface of the esophagus and trachea is substantially tubular.

When a spherical object is illuminated by an illumination optical system in which h is proportional to tan θ, the illuminance distribution becomes 1 / from the center to the periphery as shown in FIG. 23 according to equations (1) and (5). It becomes bright in proportion to cos ³ θ.
Further, in the peripheral portion, the light passing through the lens diffusely reflects on the inner surface of the lens outer peripheral portion and disappears, or is totally reflected, so that the light rapidly becomes dark as shown by a curve b in FIG .
Illuminance distribution when illuminating the spherical object so, ring
Irradiance distribution becomes uneven. Note that FIG.
And the curve a. b. c is a planar object, a spherical object,
It represents the illuminance distribution when illuminating a luminal object.
You.

When a tubular object is illuminated by this conventional illumination optical system, the illuminance distribution sharply increases in proportion to tan ³ θ as approaching the visual field according to equations (1) and (6). In addition, the range that can be observed with appropriate brightness becomes very narrow, and illumination is difficult to observe, which is not preferable.

[0019]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional illumination optical system, and can be used for a wide-angle endoscope of 110 ° or more, and is applicable to a spherical object. It is an object of the present invention to provide an inexpensive illumination optical system which provides a substantially uniform illuminance distribution, provides a good illuminance distribution even to a planar object or a luminal object, and has a small light amount loss.

[0020]

The illumination optical system according to the present invention comprises:
In an illumination optical system including at least one positive lens,
The focal length of the illumination optical system is f, the incident light height of light rays incident on the optical system parallel to the optical axis is h, and the emission angle when a light ray with a light height h exits from the optical system is θ. When
It is characterized in that the relationship of h = fθ is almost satisfied.

As described above, the observation with an endoscope or the like is not limited to a planar object, but may be various objects such as a spherical object or a luminal object. When illuminating such various objects, it is not sufficient to provide a uniform illuminance distribution only for a planar object. Therefore, in order to obtain an illumination optical system that gives a substantially uniform light distribution to a spherical object and an appropriate illuminance distribution even to a planar object or a luminal object, as described above, the relationship of h = fθ is used. Needs to be satisfied.

When the relationship of h = fθ is satisfied, the above formulas (1), (5), and (6) show that the relative relationship between a planar object, a spherical object, and a luminal object having a perfect diffusion surface is obtained. Illuminance distribution is
F (θ) = θcos ³ θ / sinθ, G (θ) = θ, respectively
/ Sin θ, H (θ) = θ cos ² θ · tan ² θ. This is illustrated in FIG.

That is, the illuminance distribution of the spherical object increases in accordance with θ / sin θ from the center to the periphery. However, in practice, the light beam illuminating the periphery of the visual field is irregularly reflected by the inner surface of the lens outer peripheral portion and disappears, or the amount of light is rapidly reduced at the periphery by total reflection. Therefore, FIG.
It becomes as shown in. Curve A ₁ in this figure spherical object, curve A ₂ is luminal object, curve A ₃ is for planar objects. Therefore, when illuminating a spherical object,
As in the conventional example that almost satisfies the relationship of h = ftan θ, the illumination has a ring-shaped illumination distribution unevenness.
You. However, the intensity of uneven illuminance is small, so there is a problem in practical use.
Give an illuminance distribution that can be considered almost uniform
become.

If a substantially uniform illuminance distribution can be obtained for a spherical object, h =
Although the range that can be observed with an appropriate illuminance distribution is somewhat narrower than an illumination optical system that almost satisfies the relationship of fsin θ, there is no practical problem.

Further, for a planar object, h = fsin
A better illuminance distribution is provided than an illumination optical system that almost satisfies the relationship of θ.

As described above, the illumination optical system including at least one positive lens substantially satisfies the relationship of h = fθ, and can be applied to a wide-angle observation optical system exceeding 110 °. In order to reduce the curvature, it is sufficient to configure at least one surface of the lens with a curved surface whose curvature becomes weaker than the approximate curvature as the distance from the optical axis increases.

For example, as shown in FIG. 18, even with a single lens whose surface on the object side is flat and whose surface on the incident side is aspherical, an illumination optical system that satisfies the above relationship and has a small loss of light amount can be constructed.

In the lens shown in FIG. 18, h = fθ
The aspherical surface that satisfies the relationship is obtained as follows.

In FIG. 18, the optical axis direction is the x axis, the direction perpendicular to the optical axis is the h axis, the function of the surface to be obtained is F (h), and the coordinate value (h, x) = (h, F (h)). ) At the position F (h)
Is the inclination angle of the tangent to the h-axis, and the coordinates (h, F
(H)) The angle of refraction of an incident light beam at that height with respect to the normal 1 at the position (a) is α, the angle of incidence of this light beam on the object-side surface of the illumination optical system is β, and the exit angle is θ, Assuming that the refractive index of the glass of the lens is n and the focal length of the illumination optical system is f, the relationship between the incident light height h and the light emission angle θ is given by the following equation when h is proportional to θ. . h = f · θ
(7) Expression x = indicating the shape of the aspherical surface that satisfies the above expression (7)
_Find F _θ (h) . The conditions for that are the following five equations. α + β = ω (9) nsin α = sin ω (10) nsin β = sin θ (11) h = f · θ (7) tan ω = dF _θ (h) / dh (12) Equations (7), (9), and (10) , (11) leads to the following relationship.

From the equations (12) and (13), the following equation (1) is obtained.
4) is required.

F _θ (h ) obtained from the equation (14) is as shown in the following equation (15).

Assuming that h is proportional to sin θ, an expression representing the shape of the aspheric surface is as shown in the following expression (16).

As shown in FIG. 25, the aspheric surface having the shape represented by the equations (14) and (16) has a smaller increase in the inclination than the spherical surface having the same focal length. In the figure, the vertical axis represents the amount of inclination, the horizontal axis represents h, and the curves (14) and (16) represent equations (14) and (14), respectively.
The slope of the aspheric surface given by (16), S is the slope of the spherical surface
Is shown.

In the case of a single-lens illumination lens having a flat surface on the object side, the relationship between the incident ray height h and the exit angle θ is determined by the inclination of the aspheric surface, so that h = f · θ is satisfied. The illumination lens has an aspheric surface satisfying the expression (14).
Will be.

When the relationship between the incident light height h and the exit angle θ from the illumination optical system with respect to the incident light height h is approximately h = f · θ, the aspheric shape used in the present invention satisfies the following conditions. It is preferable to satisfy.

[0036] However 0 ≦ h ≦ D where D is the maximum incident light height, f ₁ is the focal length of time representing the aspherical lens including an aspheric surface of the present invention the approximate curvature.

If the aspherical surface used in the illumination optical system of the present invention exceeds the lower limit of the condition (17), if the lens surface other than the aspherical surface has power, the power on that surface becomes too strong, and the loss of the light amount is large. At the same time, the illuminance distribution on the spherical surface tends to cause ring-shaped uneven illuminance. Also, if the upper limit is exceeded, the approximate curvature of the aspheric surface becomes stronger when there is power on a surface other than the aspheric surface, and when an aspheric lens is made by press molding, the workability of the molding die deteriorates and the Therefore, it is difficult to provide a substantially uniform light distribution. Further, in the illumination optical system of the present invention, the size of the light source changes because the shape of the aspheric surface is a convex surface in which the curvature of the curved surface becomes weaker than the approximate curvature as going from the optical axis to the direction perpendicular to the optical axis. Even if only the amount of light going to the periphery of the field of view changes,
The illuminance distribution from the periphery of the visual field to the center hardly changes, and only the illuminance distribution around the visual field changes. Therefore, in the illumination optical system of the present invention, it is possible to cope with different observation viewing angles simply by changing the size of the light source without changing the illumination lens, and it is used as an illumination optical system common to various types of endoscopes. This has an even greater effect on reducing the cost of the illumination lens.

Further, by applying a coating of MgF ₂ , SiO ₂ or the like to the object side surface of the illumination lens of the present invention, the Fresnel reflection of the light beam emitted from the illumination lens is reduced, and the amount of light emitted from the illumination lens is reduced. You can increase it.

During observation with an endoscope, water droplets often get on the object-side surface of the illumination lens, and the illuminance distribution often deteriorates. However, by applying a coating to the object-side surface of the illumination lens, an effect of easily removing water droplets due to the water repellency of the coating can be obtained.

When a fiber bundle is used as the light source on the incident side, the exit end of the fiber bundle does not illuminate all parts uniformly, but only the core of each fiber shines. When illuminating with a positive lens, the end face of this fiber bundle is projected onto the object plane as it is, so only the core is brightly illuminated, and is illuminated just as if it were covered with a net on the object plane. May be difficult to observe. In such a case, each fiber 1 in the fiber bundle
A fusion fiber in which the density of the optical fiber is increased by fusing one of the fibers may be used. Further, a cylindrical reflecting mirror may be inserted between the fiber bundle and the illumination optical system of the present invention.
A single fiber may be inserted instead of the cylindrical reflecting mirror.

The reticulated illuminance unevenness is most noticeable when the image of the end face of the fiber bundle is formed to infinity. Therefore, when a single fiber is inserted, it is desirable to satisfy the following conditions. F _B <0 where F _B is the rear focal position of the entire illumination optical system when the aspheric surface is represented by the approximate curvature,
Measured from the final surface of the entire system (for example, r _{4 in} the case of Example 2 described later), the light source side is plus, and the object side (surface r ₁ side)
To minus.

The aspherical glass lens is usually produced by press molding, and the molding die used at that time is a concave type in the case of an aspherical convex lens. Therefore, molds for small lenses, such as those for endoscopes, cannot be polished because the grindstone for mold polishing interferes with the inner surface of the mold, and can cause burn-in of the lens or sinkage of the lens in the center during press molding. is there.

The power of the aspherical surface is reduced by forming a convex or concave surface on the object side of the illumination lens of the present invention, or the surface curvature is reduced by increasing the refractive index of the glass material of the aspherical lens. Workability may be improved. At this time, the refractive index n of the glass material preferably satisfies the following condition. n> 1.6 Further, a convex lens is inserted between the aspheric lens and the light source of the optical system of the present invention to reduce the power of the aspheric surface,
The workability of the aspheric lens may be improved. by the way,
In the case of the conventional example shown in FIG. 20 , when r ₁ , r ₂ , r ₃ , and r ₄ are set in this order from the object-side surface, the power of the surface r ₂ and the surface r
₃ is almost equal to the power. This is because the amount of total reflection of light rays on the surface r ₁ and the surface r ₃ is reduced in the spherical lens system, and an even wider illuminance distribution is obtained. In the case of a spherical lens, the power of the surface increases sharply toward the periphery of the lens. Therefore in order to reduce the amount of total reflection of the incident ray height high beam, it can not be very strong power of the surface r _3. In order to obtain a wide illuminance distribution, it is necessary to strengthen the power of the surface r _2. However, since the amount of total reflection on the power of the strongly too and surface r ₁ of the surface r ₂ becomes large, it is not possible to strongly too much of the surface r ₂ power. Therefore are they equal the power of the substantially flush r ₂ and the surface r ₃ for balancing the illuminance distribution and the light intensity.

However, in the present invention, when a convex lens is inserted between an illumination lens having an aspheric surface and a light source,
R ₁ , r ₂ (aspheric surface), r ₃ , r _{4 in} order from the surface on the object side
Then, the power of the surface r ₂ is not so strong as compared with the approximate curvature as it goes to the periphery of the lens. Therefore, even if the power of the surface r ₂ is increased to obtain a wide illuminance distribution,
The amount of total reflection of light at the surface r ₁ is not much increased. Therefore there is no need to be very strong the power of the surface r _3,
The amount of total reflection at the surface r ₃ can be reduced.

Therefore, the present invention has an aspherical surface.
Of the convex lens provided between the illumination lens and the light source
Surface power φ₃, An aspherical illumination lens with an aspherical surface
Is the surface power at the approximate curvature of₂Then the following relationship
It is desirable to satisfy φ₃<Φ₂  In the present invention, an illumination lens having an aspheric surface and a light source
Illumination with an aspheric surface by providing a convex lens between them
Not only is the processability of the lens improved, but also the surface r₃Work of
With face r₂The ray that was out of the effective diameter at r₂Incident on
To increase the amount of light emitted from the illumination lens.
Rukoto can.

The shape of the aspherical surface at that time may be any aspherical surface having a curvature smaller than the approximate curvature as going from the optical axis to the direction perpendicular to the optical axis. The relationship between the ray height h and the exit angle θ from the illumination optical system with respect to the incident ray height h is substantially h = fθ.
It can be applied to a wide-angle observation optical system and has almost uniform light distribution for spherical objects, and is suitable for planar objects and luminal objects. It is possible to provide an illuminance distribution.

In the case of an illumination optical system using a convex lens, there is a place where the light beam having the highest intensity emitted from the light source at an emission angle of 0 ° is condensed to almost one point. For example, in the case of a medical endoscope, there is a possibility that a human body may be burned if the light converging point exists outside the most object side surface of the illumination lens. Further, in the case of an industrial endoscope, if there is a combustible material around the observation target, it may catch fire, and therefore, in the case of the illumination optical system of the present invention, the following conditions may be satisfied. desirable. f _F > 0 where f _F is the front focal position of the illumination optical system when the aspherical surface is represented by the approximate curvature.

Further, in the illumination optical system of the present invention, 11
In order to obtain a wide-angle illuminance distribution of 0 ° or more and reduce the light amount loss, the light beam having the highest light beam emitted from the light source in parallel with the optical axis is the most object-side surface of the illumination optical system. It is desirable not to totally reflect the light or to hit the outer periphery of the illumination lens.

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present inventionIllumination optical systemEach implementation of illumination lens
Here is an example. Example 1 r₁= ∞ ER₁= 1.09 d₁= 2.2 n₁= 1.80518 ν₁= 25.43 r₂= -0.8049 (aspherical surface) ER₂= 1.09 Aspherical surface coefficient P = -0.0161, E = -0.41668 × 10^-1  f = f₁= 1, D = 1.07, f_F= 0.219 Example 2 r₁= ∞ ER₁= 1.3 d₁= 2.94 n₁= 1.77842 ν₁= 25.71 r₂= -0.7849 (aspherical surface) ER₂= 1.3 d₂= 0 r₃= ∞ ER₃= 1.12 d₃= 4 n₃= 1.72825 ν₃= 28.46 (single fiber) r₄= ∞ ER₄= 1.12 Aspheric coefficientExample 3 r₁= ∞ ER₁= 1.47 d₁= 3.3 n₁= 1.77842 ν₁= 25.71 r₂= -1.4379 (aspherical surface) ER₂= 1.47 d₂= 0.13 r₃= 4.7059 ER₃= 1.27 d₃= 4.5 n₃= 1.72825 ν₃= 28.46 (single fiber) r₄= ∞ ER₄= 1.27 Aspheric coefficientExample 4 r₁= -4.635 ER₁= 1.3 d₁= 2.94 n₁= 1.77842 ν₁= 25.71 r₂= -0.8581 (aspherical surface) ER₂= 1.3 Aspheric coefficientExample 5 r₁= ∞ ER₁= 1.18 d₁= 2.66 n₁= 1.77842 ν₁= 25.71 r₂= -0.7847 (aspherical surface) ER₂= 1.18 Aspheric coefficientWhere r₁, R₂, ... radius of curvature of each lens surface, d₁, D
₂,... Are the thickness of each lens and the lens interval, n₁,
n₂, ... are the refractive indices of each lens, ν₁, Ν₂, ... are each Len
Abbe number, φ₂, Φ₃Are the faces r₂, R₃Power
ー, ER₁, ER₂… Is effective on each side of the lensradiusIt is.

The first embodiment satisfies the relationship h = f · θ as shown in FIG. 6 with the configuration shown in FIG. The illumination optical system of this embodiment has the illuminance distribution shown in FIG. 7 and can cope with an observation viewing angle up to about 150 °.

In the second embodiment, a single fiber is inserted between a lens having an aspheric surface and a light source in the configuration shown in FIG. In the second embodiment, the relationship between the height h of the incident light beam on the illumination optical system and the exit angle from the illumination optical system is set to substantially h = f · θ as shown in FIG. Illuminance distribution is shown in FIG.
As shown in the figure, it is possible to cope with an observation viewing angle of about 150 °.
Furthermore, this embodiment is characterized in that a single fiber is inserted between the light source and the aspherical lens, the mesh-like unevenness of the fiber bundle is not easily changed, and the illuminance distribution hardly changes even if the size of the light source is changed. Especially effective. In order that the illuminance distribution does not occur even when the size of the light source is changed, it is preferable to satisfy the following condition. 2d <L where d is the radius of the core of the single fiber and L is the length of the single fiber. In the third embodiment, a single fiber of a convex lens is inserted between a lens having an aspheric surface and a light source in the configuration shown in FIG. In the third embodiment, the relationship between the height h of the incident light source and the exit angle θ is as shown in FIG. 10, and approximately h = f · θ. However, in the third embodiment, the relationship between h and θ is h = f ·
Since it slightly deviates from θ to the h = ftan θ side, low-level ring-shaped illuminance unevenness occurs as shown in the illuminance distribution in FIG. 11 during illumination of a spherical object, but there is no problem in actual use.

This embodiment can correspond to an observation viewing angle of about 150 °. In this embodiment, a single fiber of a convex lens is inserted, and it is hardly affected by mesh irregularities of the fiber bundle, does not change the illuminance distribution even when the size of the light source is changed, and the workability of the aspherical lens is good. .

The fourth embodiment has the configuration shown in FIG. 4 and includes one aspherical lens having a concave surface on the object side as an illumination lens system. The relationship between h and theta is approximately h = f · theta as shown in Figure 12. In the fourth embodiment, the workability of the aspherical lens is better than when the object-side surface of the illumination lens is flat. Further, it is possible to correspond to an observation viewing angle of about 150 ° with the illuminance distribution as shown in FIG.

The fifth embodiment has the configuration shown in FIG. 7 and includes one aspherical lens. H and θ are substantially equal to h = f · θ as shown in FIG. However, in the fifth embodiment, the relationship between h and θ is slightly smaller than h = f · θ.
As shown in FIG. 15, the illuminance distribution on the spherical object is lower at the periphery than the illuminance distribution of the first embodiment shown in FIG. 7 due to the shift to the sin θ side, and gives a more uniform illuminance distribution. ing.

This illumination optical system has an observation viewing angle of about 150
Up to °.

By the way, the illumination optical system using the convex lens is
There is a place where the light beam having the highest intensity emitted from the light source at an emission angle of 0 ° is condensed to almost one point. If this focal point is located closer to the object than the illumination lens, there is a risk of burning the human body, for example, in the case of a medical endoscope, and in the case of an industrial endoscope, The object may catch fire.

Therefore, it is not preferable to make the illumination lens on the object side too thin. On the other hand, if the thickness of the illumination lens on the object side is increased, the amount of light rays hitting the side surface of the illumination lens on the object side increases, so that the amount of light emitted from the illumination optical system decreases and the illuminance around the visual field decreases. . Therefore, to avoid this, use a single fiber for the illumination lens on the object side and secure an appropriate thickness of the illumination lens, or place a single fiber in front of the illumination lens on the object side to reduce the focal point. It is also possible to secure the amount of light emitted from the illumination optical system and prevent the illuminance around the field of view from lowering while preventing the illumination optical system from going to the object side.

6, 8, 10, 12 , and 14 , a curve A is an example, a curve B is h = fsinθ , and a curve C is h = fsinθ .
fθ, and FIGS. 7, 9, 11, 13, 1
5, a curve a indicates a planar illuminance distribution, a curve b indicates a spherical illuminance distribution, and a curve c indicates an in-tube illuminance distribution.

The shape of the aspheric surface in the data of each of the above embodiments is represented by the following equation.

Where x and h are x-axis with the optical axis as the x-axis, the object side in the negative direction, and the h-axis as the origin at the intersection of the plane and the optical axis.
Coordinate values when taken in a direction perpendicular to the axis, C is the reciprocal of the radius of curvature (approximate curvature) of a circle in contact with the aspheric surface near the optical axis, p is the conic constant, and B, E, F, G. Secondary, 4 respectively
, 6th, 8th,... Aspherical coefficients.

[0061]

The illumination optical system according to the present invention has a viewing angle of 110.
° as it can be used over a wide angle endoscope, the spherical object
To provide a nearly uniform illuminance distribution for
It is an inexpensive device that gives a good illuminance distribution even to a hollow object and has little loss of light amount.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a fifth embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between h and θ in the first embodiment.

FIG. 7 is a diagram illustrating an illuminance distribution according to the first embodiment.

FIG. 8 is a diagram illustrating a relationship between h and θ in the second embodiment.

FIG. 9 is a diagram illustrating an illuminance distribution according to the second embodiment.

FIG. 10 is a diagram illustrating a relationship between h and θ in the third embodiment.

FIG. 11 is a diagram showing an illuminance distribution according to the third embodiment.

FIG. 12 is a diagram illustrating a relationship between h and θ in the fourth embodiment.

FIG. 13 is a diagram illustrating an illuminance distribution according to the fourth embodiment.

FIG. 14 is a diagram showing the relationship between h and θ in the fifth embodiment.

FIG. 15 is a diagram illustrating an illuminance distribution according to the fifth embodiment.

FIG. 16 is a diagram showing an illuminance distribution for each object.

FIG. 17 is a diagram showing an illuminance distribution when irregular reflection on the inner surface of the outer peripheral portion of the illumination lens is considered;

FIG. 18 is a diagram showing a state of incidence and emission of light rays in an illumination lens having an aspheric surface.

FIG. 19: Illuminance distribution for each object by a conventional illumination system

FIG. 20 is a diagram showing a configuration of a conventional illumination optical system.

FIG. 21 is a diagram showing a configuration of another conventional illumination optical system.

FIG. 22 is a diagram showing a configuration of a pair of illumination systems.

FIG. 23 is a diagram showing an illuminance distribution of the illumination system shown in FIG. 22;

FIG. 24 is a view showing an illuminance distribution in the illumination optical system shown in FIG. 22 when the influence of total reflection and the like is considered.

FIG. 25 is a diagram showing a relationship between h and inclination of a surface such as a spherical surface.

Claims (7)

(57) [Claims] 1. An illumination optical system including at least one positive lens, wherein a focal length of the illumination optical system is f, an incident ray height of a ray incident on the optical system parallel to an optical axis is h, and a ray height h is The exit angle at which a light ray exits from the optical system is θ
Where the illumination optical system substantially satisfies the relationship h = fθ. 2. The illumination optical system according to claim 1, wherein said positive lens has an aspheric surface, and said aspheric surface has a curved surface having a curvature smaller than an approximate curvature as the distance from the optical axis increases. 3. The illumination optical system according to claim 2, wherein said positive lens has an incident surface which is said aspherical surface. 4. The illumination optical system according to claim 3, wherein said aspheric surface has a shape satisfying the following conditions. However, the shape of the aspheric surface is such that the optical axis is the x axis and h is perpendicular to the optical axis.
Axis, at the intersection with the coordinate system of the aspheric surface and the x-axis at the origin is represented by x = F (h), f 1 is the focal length of the positive lens, n is a refractive index of the positive lens. 5. The apparatus according to claim 1, wherein a fiber bundle is provided as a light source, and light emitted from the fiber bundle is arranged so as to enter the illumination optical system.
Or the illumination optical system of 4. 6. The illumination optical system according to claim 5, wherein another positive lens is provided between said fiber bundle and said positive lens having an aspheric surface. 7. An illumination optical system according to claim 5, wherein a cylindrical reflecting member such as a cylindrical reflecting mirror or a single fiber is disposed between said fiber bundle and said positive lens having an aspheric surface. .