JPH0734056B2 - Lighting lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention is applied to a circuit pattern exposure device such as a printed circuit board or an IC, a printing apparatus for plate making, a plate-making machine, and other various lighting devices such as copying machines. Illuminating lens.

<< Prior Art >> As an illumination lens of this type, for example, the 14th
A relay capacitor type as shown in the figure is well known.

This optical system includes a condenser lens C and a field lens F.
And a real image S ′ of the light source S arranged in front of the condenser lens C is formed in the vicinity of the field lens F,
By projecting the real image of the entrance pupil A of the condenser lens C onto the irradiated surface OP arranged behind the field lens F, an object (for example, a transmission original plate for printing) placed on the irradiated surface P can be as much as possible. It is configured to uniformly illuminate.

<< Problems to be Solved by the Invention >> In the case of the above-mentioned conventional illumination lens, the illuminance distribution on the illuminated surface is as shown in FIG. descend. By the way, lens F
According to a simple calculation, the illuminance on the irradiated surface P corresponding to the degree of emission θ = 27 ° from is reduced to 37% in the peripheral portion with respect to the central portion (θ = 0 °). In addition, the cause of the decrease in illuminance at the peripheral portion is not only the above cosine fourth law, but also the lens vignetting (vignetting) and the uneven illuminance at the entrance pupil A. Illuminance decreases.

Therefore, when a transparent original plate or the like placed on the surface to be illuminated is illuminated by such an illumination system and an image of the original plate is projected by the imaging optical system, the projected image is the cosine 4 of the imaging lens. Due to the effect of the power law, the illuminance is further reduced in the peripheral area.

Therefore, conventionally, in order to improve such a decrease in illuminance at the peripheral portion, a gradient filter (a filter having a low light transmittance in the central portion) is interposed in the illumination optical system, or the illuminated surface and the illumination are This has been dealt with by setting a sufficiently large distance from the lens and reducing the angle of view of the imaging lens. However, in the former case, the gradient filter suppresses the amount of light transmitted through the central portion, resulting in a large loss of light amount as a whole. Not only does it occur, but it is not possible to positively correct the reduction in peripheral illuminance due to the projection lens.

Further, conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-267722, there is known an illuminance distribution variable condenser lens for increasing the illuminance of the peripheral portion over the illuminance of the central portion on the illuminated surface. . According to this lens, since it is not necessary to interpose a gradient filter, it is possible to suppress the loss of light quantity.

However, in the conventional illuminance distribution variable condenser lens described above, since all the light emitted from the lens (the principal ray) is parallel to the optical axis, it is necessary to make the diameter of the illuminated surface and the effective diameter of the lens substantially equal. Therefore, it is necessary to increase the size of the lens having a large effective diameter, that is, the device, as the irradiation surface is enlarged.

The present invention has been made in view of the above circumstances, and is for illumination that irradiates a surface to be irradiated that is sufficiently larger than the effective diameter and that increases the illuminance of the peripheral portion of the surface to be irradiated from the illuminance of the central portion. The purpose is to provide a lens.

<< Means for Solving Problems >> The present invention is configured as follows to achieve the above object.

First, the entrance pupil A of the illumination lens arranged between the light source S and the illuminated surface P and the illuminated surface P are conjugated, the focal length of the lens is f, and the distance between the lens and the light source S is a. When the distance between the lens and the irradiated surface P is b, the relations f << a and f << b are satisfied. Further, as shown in FIG. ₁ , the incident height of the light ray b ₁ incident on the entrance pupil A from the light source S to the lens is set to h, and the light ray b ₁ on the illuminated surface when it reaches the illuminated surface P. When the irradiation height at H is H, a function f including the incident height h, the irradiation height H, and the change rates (dh / dH) of these is calculated.
(H) is defined by f (H) = (h / H) (dh / dH), and this function f (H) should satisfy f (o) <f (H) at the periphery of the irradiated surface. It is characterized by being configured in.

<< Operation >> The illumination lens according to the present invention is configured as described above, and the illuminance distribution on the irradiated surface P can be considered as follows.

In FIG. 1, the light source S is on the optical axis Z, and the light beam b ₁ from the center (So) of the light source S enters the entrance pupil A of the lens L at an incident height h.
Suppose that the light beam b ₁ is incident on the irradiation surface P, then the light beam b ₁ reaches the irradiation height H on the irradiation surface P.

Here, since the entrance pupil A of the lens L and the illuminated surface P are conjugate, when the incident height h on the entrance pupil A is determined, the illuminated surface P
The upper irradiation height H is determined.

On the other hand, on the entrance pupil A, a light ray incident on a position separated by a minute height Δh from h reaches a position on the irradiated surface P separated by a minute height ΔH from H.

In this case, assuming that there is no light amount loss during transmission through the lens, the entrance pupil A has an entrance height h as an inner diameter and a width Δh.
The light flux that has passed through the ring-shaped minute area ΔS ₁ simultaneously reaches the ring-shaped minute area ΔS ₂ having the irradiation height H on the irradiated surface P as the inner diameter and the width ΔH.

Here, ΔS ₁ and ΔS ₂ are expressed by the following equations.

ΔS ₁ = π {(h + Δh) ² −h ² } ΔS ₂ = π {(H + ΔH) ² −H ² } Therefore, assuming that the illuminance at the incident height h on the entrance pupil A is e, the irradiation on the irradiated surface P is The illuminance E at high H is proportional to the ratio (ΔS ₁ / ΔS ₂ ) of the minute areas and is represented by the following equation.

E = e (ΔS ₁ / ΔS ₂ ) = e (2hΔh + Δh ² ) / (2HΔH + ΔH ² ) = e (Δh / ΔH) {(2h + Δh) / (2H + ΔH)} Here, if ΔH approaches 0 as much as possible, and And E is expressed by the following equation.

E = ef (H) However, f (H) = (dh / dH) (h / H).

Here, when the illuminance e on the entrance pupil A is considered to be constant irrespective of the entrance height h (when the illuminance distribution on the entrance pupil A is uniform), the function f (H) is calculated as follows. The relative illuminance itself on the irradiated surface P with respect to the above illuminance is shown.

That is, the relative illuminance of the central portion where the irradiation height H = 0 on the surface to be illuminated P is represented by f (0), and other than the central portion (H ≠ 0)
The relative illuminance of is represented by f (H).

Therefore, in the illumination lens according to the present invention, h, H and (dh / d
When the function f (H) including H) is defined as above,
Since the peripheral portion of the irradiated surface P is configured to satisfy f (0) <f (H), the illuminance around the irradiated surface P increases from the center toward the peripheral portion.

Further, in the present invention, since the light source S is arranged far from the lens with respect to the focal length of the lens (f << a), substantially parallel light is incident on the lens. The light emitted from the lens is once condensed at the focal point and then spreads. At this time, the irradiated surface P is arranged far away from the lens with respect to the focal length of the lens (f << b).
As a result, even when the effective diameter of the lens is small,
A large irradiation surface can be irradiated.

In the paraxial region, H =-{(a'-f) / fa '} b'h, so f (0)
Is represented as f (0) = [fa '/ {(a'-f) b'}] ² . Here, a'is the distance between the light source and the front principal point of the illumination lens, and b'is the distance between the real image of the light source and the illuminated surface.

<< Examples >> Hereinafter, first to sixth examples according to the present invention will be described. In any of the embodiments, the positional relationship shown in FIG. 1 is set to have the following values.

Focal length of lens L f = 1.0 Distance between light source S and lens a = 50 Size of light source S 2a · tan ω Distance between lens L and illuminated surface b = 100 That is, in each embodiment, f << a and f <
The relationship of <b is satisfied.

Then, in the first to third embodiments, all each lens G ₁ ~G ₄ of the lens L is a spherical lens, the fourth to sixth embodiments, a lens including an aspherical surface Is.

The aspherical surface of the lens is defined by the coordinate Z in the optical axis direction and the height Y from the optical axis, and Z is represented by the following equation with Y as a variable.

^{Z = CY 2 / [1+ {} 1- (K + 1) C 2 Y 2} 1/2] + A 1 Y 4 + A 2 Y 6 + A 3 Y 8
+ A ₄ Y ¹⁰ However, C = 1 / r (r is a radius of curvature) K is a conic constant A ₁ , A ₂ , ... Is a coefficient.

First Embodiment A first embodiment according to the present invention is shown in FIG. In this embodiment, the lenses G _{1 to} G _{3 of the three} lenses in the third group, which form the lens L, are all formed of spherical lenses as described above. The data of the lens corresponding to FIG. 2 are as follows.

r d n 1 12.8443 0.599 1.64294 2 −1.5549 0.248 3 1.1351 0.338 1.83139 4 −2.8552 0.301 5 −1.2607 0.631 1.73621 6 −0.7708 In this embodiment, the effective diameter of the entrance pupil A is 1.2, and the light source S faces from the center of the entrance pupil A. The effective angle of view is 2ω = 43.6 °.

FIG. 3 is a diagram showing the illuminance distribution on the irradiated surface P according to this embodiment, and D ₀ , D ₁ , and D ₂ are graphs showing the illuminance distribution under the following setting conditions in an axisymmetric manner. In these figures, the horizontal axis represents the height from the optical axis on the illuminated surface, and the vertical axis represents the illuminance ratio (%) with the light amount in the central portion as 100.

In the figure, D ₀ is the distribution due to the light beam (b ₁ ) from the center (S ₀ ) of the light source S, and D ₁ is the ring at the position (S ₁ ) 70% of the height from the center to the end of the light source S. The distribution of the rays from the strip is D ₂
Indicates the distribution of light rays from the annular portion at the end (S ₂ ) of the light source S, and this relationship is the same in other embodiments described later.

As is clear from these graphs, in the effective irradiation area 90φ on the irradiation surface P, the illuminance gradually increases from the center to the peripheral portion. As a result, it is possible to effectively eliminate the above-mentioned problems.

This embodiment is advantageous in that the effective angle of view 2ω can be made sufficiently large while the lens L is composed of spherical lenses G _{1 to} G ₃ .

Second Embodiment A second embodiment according to the present invention is shown in FIG. In this embodiment, the lenses G ₁ and G _{2 of the two} lenses in the second group, which form the lens L, are both spherical lenses as described above. This 4th
The data of the lens corresponding to the figure is as follows.

r d n 1 5.8058 0.702 1.94359 2 −1.5459 0.278 3 0.8281 1.256 1.49028 4 −0.7142 In this embodiment, the effective diameter of the entrance pupil A is 1.06, and the effective angle of view from the center of the entrance pupil A to the light source S is 2ω = 27.0 °. is there.

FIG. 5 shows the illuminance distribution on the irradiated surface P according to this embodiment, and as is clear from this figure, the illuminance gradually increases in the peripheral portion within the effective irradiation area 90φ. Further, even though the lens is two spherical lenses, it has a property of increasing the illuminance in the periphery, which is very advantageous in terms of manufacturing cost.

Third Embodiment A third embodiment according to the present invention is shown in FIG. In this embodiment, the lenses G _{1 to} G _{4 of the four} lenses in the four groups which compose the lens L are all formed of spherical lenses as described above. This 6th
The data of the lens corresponding to the figure is as follows.

rd n 1 1.2970 0.3643 1.67470 2 −2.1677 0.1079 3 −9.6551 0.2889 1.70011 4 −1.7124 0.1473 5 0.8925 0.3064 1.66258 6 1.2785 0.1641 7 −1.8578 0.3579 1.68473 8 0.5743 In this embodiment, the effective diameter of the entrance pupil A is 1.04, and that of the entrance pupil A is 1.04. The effective angle of view of the light source S from the center is 2ω = 40.2 °.

FIG. 7 shows the irradiation distribution on the irradiated surface P according to this embodiment, and it can be seen that the illuminance gradually increases in the peripheral area within the effective irradiation area 90φ.

In this example, the refractive index n has a relatively small value, which is advantageous in that a general-purpose optical glass material can be used.

Fourth Embodiment A fourth embodiment according to the present invention is shown in FIG. In this embodiment, the second group is composed of _two lenses G ₁ and G ₂ , and the second surface is an aspherical surface when viewed from the light source side (left side in the figure). The data of the lens corresponding to FIG. 8 are as follows.

r d n 1 1.2713 0.467 1.55649 2 −0.8983 0.249 3 1.4294 1.526 1.52216 4 −1.4859 Aspheric coefficient K A ₁ A ₂ A ₃ A ₄ 2 −1.409 0.630 0.044 0.112 0.086 In this embodiment, the effective diameter of the entrance pupil A is 1.24. The effective angle of view of the light source S from the center of the entrance pupil A is 2ω = 37.6 °.

FIG. 9 shows the illuminance distribution on the irradiated surface P according to this example, and shows that the illuminance gradually increases in the peripheral portion within the effective irradiation area 90φ. From this graph, it can be seen that the peripheral illuminance is 150% or more when the light source is at the center of the optical axis, and the correction factor of the illuminance distribution is very high.

This embodiment is also advantageous in that the value of the refractive index n is small and a general optical glass material can be used.

Fifth Embodiment A fifth embodiment according to the present invention is shown in FIG. In this embodiment, the second group consists of _two lenses G ₁ and G ₂ , and the second surface and the third surface are aspherical surfaces when viewed from the light source side (left side in the figure). The data of the lens corresponding to FIG. 10 are as follows.

r d n 1 0.9371 0.547 1.47653 2 −1.0495 0.327 3 0.8904 1.079 1.50661 4 −0.9141 Aspheric coefficient K A ₁ A ₂ A ₃ A ₄ 2 −15.133 0.271 0.555 0.522 2.048 3 −1.036 0.047 −1.756 −0.619 −1.637 In the example, the effective diameter of the entrance pupil A is 1.12, and the effective angle of view of the light source S from the center of the entrance pupil A is 2ω = 43.6 °.

FIG. 11 shows the illuminance distribution on the irradiated surface P according to this embodiment, and the illuminance gradually increases in the peripheral portion within the effective irradiation area 90φ. Further, this embodiment has a wide angle of view even though it has a two-piece construction, and can be said to be an extremely high-performance type.

Sixth Embodiment A sixth embodiment according to the present invention is shown in FIG.

In this embodiment, a single lens is used, and both the first surface and the second surface are aspherical surfaces. The data of the lens corresponding to FIG. 12 are as follows.

r d n 1 0.5770 2.124 1.77585 2 −1.3693 Aspherical coefficient K A ₁ A ₂ A ₃ A ₄ 1 −1.629 −0.010 −0.615 −0.843 −1.011 2 0.582 0.0 0.016 −0.100 −0.219 In this embodiment, Effective diameter is 1.02, entrance pupil A
The effective angle of view of the light source S from the center is 2ω = 39.6 °, and the effective irradiation area is 2H = 80φ.

FIG. 13 shows the illuminance distribution on the irradiated surface P according to this example, and shows that the illuminance gradually increases in the peripheral portion within the effective irradiation area 80φ.

According to this embodiment, it is possible to form a single lens. For example, when manufactured by press working, it is not necessary to adjust the lens interval, which is very advantageous in mass production.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications are possible.

<< Effects of the Invention >> The illumination lens according to the present invention can increase the illuminance at the peripheral portion of the illuminated surface more than at the central portion, and even if the effective diameter of the lens is small, a large amount of illumination can be obtained. The illuminated surface can be illuminated. Therefore, it is possible to improve the illuminance distribution on a large illuminated surface while preventing the loss of light amount and the increase in size of the device.

[Brief description of drawings]

FIG. 1 is a layout view of an illumination optical system for defining an illumination lens according to the present invention, FIG. 2 is a layout view showing a configuration of an illumination lens according to a first embodiment of the present invention, and FIG. The illuminance distribution on the illuminated surface corresponding to the first embodiment is shown. In these figures, D ₀ , D ₁ , and D ₂ are graphs of the illuminance distribution under different setting conditions, respectively, and FIG. FIG. 6, FIG. 8, FIG. 10 and FIG. 12 respectively show another embodiment, which is equivalent to FIG.
FIG. 7, FIG. 9, FIG. 11, FIG. 11 and FIG. 13 respectively correspond to FIG. 3 corresponding to other embodiments, and FIG. 14 is a layout view of a conventional illumination optical system, FIG. FIG. 8 is a diagram showing a decrease in the illuminance distribution according to the cosine fourth law in the periphery of the illuminated surface in the optical system. A: entrance pupil of lens, a: distance between lens and light source,
b: distance between lens and illuminated surface, b ₁ ... incident ray, f
…… Lens focal length, h …… incident height, H …… irradiation height,
f (H) ... function, (dh / dH) ... irradiation height H at incident height h
Change rate, L ... Illumination lens, P ... Irradiated surface, S ... Light source.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruo Uemura Inventor Harukawa-dori Teranouchi, Kamigyo-ku, Kyoto, Kyoto Prefecture 1 Daiichi Screen Manufacturing Co., Ltd., 1-chome Tenjin Kitamachi 1-chome (56) References 61-267722 (JP, A)

Claims (1)

[Claims] 1. An illumination lens arranged between a light source S and a surface to be illuminated P, wherein an entrance pupil A of the lens and the surface to be illuminated P are conjugated, and the focal length of the lens is f and the lens is When the distance between the lens and the light source S is a and the distance between the lens and the surface P to be illuminated is b, the relations f << a and f << b are satisfied, and the light source S enters the entrance pupil A of the lens. When the incident height of the light beam b ₁ is h, and the irradiation height on the irradiated surface P when the light beam b ₁ reaches the irradiated surface P is H, the incident height h, the irradiation height H, and their changes The function f (H) including the ratio (dh / dH) is defined by f (H) = (h / H) (dh / dH), and this function f (H) is the peripheral part on the irradiated surface P. And a lens for illumination, characterized in that f (0) <f (H) is satisfied.