JPH0727117B2 - Lighting lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention relates to an exposure apparatus for a circuit pattern of a printed circuit board, an IC, etc., or a contact printing apparatus for plate making, an intaglio machine, and other various illumination systems such as a copying machine. The present invention relates to an illumination lens which can be applied to, and particularly improved so as to illuminate the entire surface uniformly or without increasing the illuminance of the peripheral portion on the irradiated surface, or by increasing the illuminance of the peripheral portion as necessary. Is.

<< Prior Art >> An illumination lens of this type is arranged between a surface light source LS and an illuminated surface OG as shown in FIG. 15, and is constituted by a single lens L as shown in FIG. 16, for example. There is.

By the way, specific examples are as shown in Table 1.

Table 1 a = 50, b = 100, y = 10, f = 1 r 1 = 0.5, r 2 = -0.5, d = 1.5, n = 1.5 where, f is the focal length of the single lens L, other code Is the
This is shown in FIGS. 15 and 16. Then, as shown in FIG. 15, this type of illumination lens forms a real image of the light source LS arranged in the front by the first surface r ₁ at a point P in the vicinity of the second surface r ₂ , and the entrance pupil A By projecting a real image of the object on the illuminated surface OG arranged behind the lens by the second surface r ₂ , the illuminated surface OG
Are illuminated as uniformly as possible. Such an illumination lens is known as a relay condenser type lens.

<< Problems to be Solved by the Invention >> In the case of the above-described conventional illumination optical system, the illuminance distribution on the illuminated surface OG decreases toward the peripheral portion as shown in FIG.

For example, under the setting conditions shown in Table 1, when the central part (θ = 0 °) on the irradiated surface OG is 100%, the calculated illuminance distribution is 90% or more when the irradiation height is H = The area is only up to 18 (corresponding to the exit angle θ = 10 °), and the illuminance distribution is 58 in the region where the irradiation height is H = 40 (corresponding to θ = 22 °).
%, The illuminance distribution drops to 41% in the region where the irradiation height is H = 50 (corresponding to θ = 27 °).

This is because the conventional illuminating lens described above does not consider the improvement of the illuminance distribution.

On the other hand, the illuminance distribution on the illuminated surface OG can be considered as follows.

In FIG. 15, if the light source LS is on the optical axis Z, and the light beam b ₁ from the center of the light source LS is incident on the entrance pupil A of the lens L at an incident height h, then this light beam b ₁ travels inside the lens L. After that, the light exits from the exit pupil B and reaches the irradiation height H on the irradiation target surface OG.

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

In this case, assuming that there is no light amount loss at the time of transmission through the lens, at the entrance pupil A, the entrance height h is the inner diameter and the width is Δh.
The light flux that has passed through the ring-shaped minute area ΔS ₁ reaches a ring-shaped minute area ΔS ₂ having the irradiation height H on the surface OG to be 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, if the illuminance at the entrance height h on the entrance pupil A is e, The illuminance E at the irradiation height H on the irradiation surface OG is proportional to the ratio (ΔS ₁ / ΔS ₂ ) of the minute areas and is therefore expressed by the following equation.

E = e (△ S ₁ / △ S ₂ ) = e (2h △ h + △ h ² ) / (2H △ H + △ H ² ) = e (△ h / △ H) {(2h + △ h) / (2H + △ H)} Here, if ΔH is brought close to 0 as much as possible, and, And E is expressed by the following equation.

E = ef (H) However, f (H) = (dh / dH) (d / 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 OG with respect to the above illuminance is shown.

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

Next, the reason why the peripheral illuminance of the illuminated surface of the lens satisfying the sine condition is lowered will be described. For a lens satisfying the sine condition, the following expression is established between the entrance height h and the exit angle θ.

h = fsin θ (where f is the focal length of the lens), and the relationship between the sine condition and the reduction in illuminance in the surroundings will be described below with reference to FIG.

The focal length (f = 1) of the illumination lens L is the light source.
It is sufficiently small with respect to the distance (a = 50) between the LS and the lens L, and the light from the center of the light source LS enters the entrance pupil A at an entrance height h, converges at the point P, and then exits at the exit angle θ. , The point R on the surface OG to be the irradiation height H is reached.

From FIG. 15, the irradiation height H is expressed by the following equation.

H = btan θ ...... At this time, the illuminance on the irradiated surface OG is defined by (dh / dH) (h / H) as in the above equation.

Meanwhile, the, from the formula, (dh / dθ) = fcosθ , (dH / dθ) = b / cos 2 θ (h / H) = (f / b) cosθ , and the illuminance is expressed by the following equation.

(Dh / dH) (h / H) = (f ² / b ² ) cos ⁴ θ …… The formula shows that if a lens that satisfies the sine condition is used, the illuminance on the illuminated surface is the cosine of the exit angle θ raised to the fourth power. Proportionally
It shows that it will decrease.

By the way, in the conventional lens shown in Table 1, when the ray tracing calculation was actually performed, it was confirmed that the above formula was not satisfied when the incident height h became large, and h <f · sin θ. In other words, in the formula, (dh / dH) (h / H) <(f ² / b ² ) cos ⁴ θ, which means that the ambient illuminance will be lower than that of a lens satisfying the sine condition.

For this reason, in the conventional illumination system, if the uniform illuminance distribution of about ± 5% is to be secured, the emission angle θ can be used only up to about 10 °. Therefore, in order to secure the required irradiation area, from the light source to the illuminated surface. The length of the optical path up to is increased, and the size of the entire device is increased.

Further, 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 an imaging lens, the projected image is the cosine fourth law of the imaging lens or the like. Due to the influence, the illuminance is further reduced in the peripheral area. Conventionally, it has not been possible to positively correct the decrease in peripheral illuminance due to such an imaging lens by the illumination lens.

The present invention has been made in view of the above circumstances, and evenly corrects the entire surface without reducing the illuminance at the peripheral portion on the irradiated surface, or corrects the peripheral illuminance reduction due to the imaging lens as described above. It is an object of the present invention to provide an illuminating lens that can be illuminated with light.

<< Means for Solving the Problems >> The present invention has been made to achieve the above object, and such an illumination lens is configured as follows.

That is, an illumination lens which is arranged between a light source and a surface to be illuminated and which is composed of two lenses in two groups, wherein the first lens is a positive lens whose rear surface is a convex surface and the second lens is a double lens in order from the light source side. Is composed of a positive lens having a convex surface and is configured to satisfy the following conditional expression.

−3.0 ≦ (d ₃ / r ₄ ) ≦ −0.3 …… 1.0f ≦ f ₂ ≦ 1.55f …… However, f is the combined focal length f ₂ of this entire illumination lens, and the focal length d ₃ of the second lens is The thickness r ₄ of the second lens is the radius of curvature of the rear surface of the second lens.

<< Operation >> The operation of the illumination lens having the above-described configuration will be described below with reference to FIGS. 2, 3, and 15.

First, the illuminating lens according to the present invention is a two-lens configuration lens. The distance a between the light source LS and the illuminating lens L and the illuminating lens L and the specific irradiation surface are compared with the combined focal length f (hereinafter simply referred to as the focal length of the illuminating lens) f formed by these two lenses L ₁ and L _2. The distance b'with OG is set large enough,
Moreover, the first lens L ₁ is a positive lens having a convex surface on the rear surface, and the second lens
Lens is a positive lens having a convex surface, thereby forming an image of the light source in the vicinity of the O connexion second lens L ₂ to the first lens L _1, the entrance pupil, which is set in front of the first lens L ₁ A
Is projected onto the illuminated surface OG by the second lens L ₂ .

Next, regarding the illumination lens L of the present application, the entrance height h and the exit angle θ
It is explained that the irradiated surface OG is uniformly irradiated if the property of h = ftan θ is brought between and.

From the equation, (dh / dθ) = f / cos ² θ and (dH / dθ) = b / cos ² θ, h / H = f / b. Therefore, substituting both equations into the above equation gives (dh / dH ) (H / H) = f ² / b ² ... The expression shows that the illuminance on the illuminated surface is constant regardless of the emission angle θ, that is, the illumination height H.

Furthermore, when θ becomes large and h> f · tan θ, it is easily inferred that the illuminated surface OG is more peripheral and the illuminance is higher than the center.

The present illumination lens is configured so as to satisfy the conditions (1) to (3) in order to have the property of this or the formula.

That is, irrespective of the size of the light source, the output angle θ of a light beam having a large incident height h emitted from the second lens L ₂ is set not to be too large, and the light beam having a small incident height h is set to the second lens L ₂ By increasing the angle of emission from, the reduction in illuminance at the peripheral portion of the illuminated surface is eliminated.

For example, in FIG. 2, a ray parallel to the optical axis Z is refracted by the rear surface r ₂ of the first lens L ₁ having a strong refractive power,
Due to the large spherical aberration of the first lens L _1, a light ray having a large incident height h is strongly refracted. Therefore, the position P ₁ that cuts the optical axis Z of the light ray Q _{1 with} a large incident height h is a light ray with a small incident height h.
It is located ahead of the position P ₂ that cuts the optical axis Z of Q ₂ .

However, as defined by the conditional expression described later, the rear surface r ₄ of the second lens L ₂ has a large refracting power behind the image points P _{1 to} P ₂ of the light rays, and as described above. For the ray Q ₁ which has a large incident height h and intersects the optical axis Z at the position of P ₁ , the refracting power of the surface r ₄ does not act so much, and rather the incident height h is small and the optical axis at the position of P ₂ is small. It has a divergent effect on the optical axis Q ₂ intersecting with Z. That is, the emission angle of a light beam having a relatively large incident height h is suppressed to be small to prevent a decrease in illuminance in the peripheral portion of the illuminated surface.

The rear surface r ₂ of the first lens L ₁ produces positive coma. This is, for example, as shown in FIG. _3, a light beam Q ₃ emitted from the lower end of the light source and incident on the lower end of the first lens front surface r _1.
This means that the rear surface r ₂ is defined so that the incident height on the rear surface r ₄ of the second lens does not become too large. That is, the second
If the incident height on the rear surface r _{4 of the} lens becomes too large, that surface
This is because the output angle θ becomes too small on the contrary due to the strong refractive power of r ₄ , and the effective irradiation area becomes narrow.

The present illumination lens is constructed so as to satisfy the following conditional expression.

_{-3.0 ≦ (d 3 / r 4} ) ≦ -0.3 ...... The expression is intended to define the refractive power of the rear surface r ₄ of the second lens L _2, a thickness d ₃ of the lens L _2, said first 1 lens L ₁
Rays refracted by the rear surface r ₂ of the lens barrel vignet (vign
The upper limit and the lower limit are defined so that the emission angle does not become too small.

That is, when (d ₃ / r ₄ ) becomes smaller than the lower limit value, the radius of curvature r ₄ of the rear surface of the second lens is negative, so that the refracting power of that surface becomes large and the incident light enters from on-axis and off-axis. For rays Q ₁ and Q ₃ with a high height h, the exit angle θ becomes too small,
The effective irradiation area on the irradiated surface becomes smaller. Further, the thickness d ₃ of the second lens L ₂ becomes relatively thick, vignetting due to the lens barrel occurs, and light energy is lost.

Conversely, when the (d ₃ / r ₄₎ is greater than the upper limit value, the refractive power of the second lens L ₂ to maintain to some extent, the radius of curvature r ₃ of the second lens front surface (third surface) of Figure 3 As shown by the phantom line, it must be small and the lens interval d ₂ must be increased to some extent. As a result, the ray Q _{3 which} is an off-axis ray and is incident on the lower end portion of the first lens L ₁ is the _third ray as much as the lens interval d ₂ is increased.
The height of incidence on the surface increases. Therefore, the refracting power on the third surface is large, and the emission angle θ becomes too small. Therefore, the effective irradiation area on the irradiated surface becomes narrow. In order to prevent such inconvenience from occurring, the above equation should be applied to the second lens rear surface r ₄
It defines d ₃ .

The present illumination lens is further configured to satisfy the following conditional expression.

1.0f ≦ f ₂ ≦ 1.55f ...... The formula defines the focal length f ₂ of the second lens L ₂ .

The focal length f ₂ of the second lens L ₂ is smaller than the lower limit value, too strong refractive power for light Q ₃ incident on the lower portion of the lens, the exit angle θ becomes small, on the surface to be illuminated The effective irradiation area becomes smaller.

On the other hand, when the focal length f ₂ becomes larger than the upper limit value, the magnification is almost inversely proportional to f _{2 due} to the conjugate relationship between the entrance pupil plane due to L ₂ and the illuminated surface, so the conjugate image of the entrance pupil becomes small. Become. That is, the effective irradiation area becomes narrow. Also, since the power of L ₂ is small, it is not possible to reduce the exit angle for a light beam having a large incident height, regardless of the size of the light source, and on the irradiated surface, from the middle part to the peripheral part, This will cause a sharp decrease in illuminance.

The second formula is the second lens so that such inconvenience does not occur.
It defines the focal length of L ₂ .

<< Examples >> Examples of the illumination lens according to the present invention will be described below.

Each of the illumination lenses L of the respective examples has two lenses L ₁
-It is composed of L ₂ . Further, in any of the embodiments, the following set values are assumed under the optical arrangement shown in FIG.

Light source size 2y = 17.64φ (maximum incident angle ωmax = 10 °) Distance from light source to lens entrance pupil A a = 50 Distance from second lens rear surface to illuminated surface b ′ = 100 Effective illuminated surface size Hmax = 90φ (Maximum output angle θmax = 24.
2 °) Effective diameter of lens D = 1.0φ Focal length of illumination lens f = 1.0 And the entrance pupil A is set in front of the first lens L ₁ , and its image is projected on the illuminated surface OG. Is set to. All the following illumination lenses have the same arrangement and configuration with the same reference numerals as shown in FIG.

First Example FIG. 1 shows a first example of the illumination lens according to the present invention, and its lens data is as shown in Table 2 below.

The first embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

(D ₃ / r ₄ ) ＝-1.541, f ₂ = 1.526 The illuminance distribution on the illuminated surface is ±±
It is within 4%.

The first embodiment exemplifies a case where the focal length f ₂ of the second lens L ₂ is close to the maximum. The first embodiment shows a standard arrangement of lenses.

Second Example FIG. 5 shows a second example of the illumination lens according to the present invention, and its lens data is as shown in Table 3 below.

The second embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

(D ₃ / r ₄ ) = − 3.0, f ₂ = 1.07 Further, the illuminance distribution on the irradiated surface is ± as shown in FIG.
It is paid within 4%.

The second embodiment exemplifies a case where the value (d ₃ / r ₄ ) of the conditional expression becomes the minimum value.

Third Embodiment FIG. 7 shows a third embodiment of the illumination lens according to the present invention, and its lens data is as shown in Table 4 below.

The third embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

(D ₃ / r ₄ ) = − 0.3, f ₂ = 1.207 In addition, the illuminance distribution on the irradiated surface shows only a few% reduction in the illuminance in the middle part and the illuminance in the peripheral part as shown in FIG. Is a few percent higher.

The third embodiment exemplifies another case where the value (d ₃ / r ₄ ) of the conditional expression becomes the maximum value.

Fourth Embodiment FIG. 9 shows a fourth embodiment of the illumination lens according to the present invention, and its lens data is as shown in Table 5 below.

The fourth embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

_{(D 3 / r 4) =} - 1.524, f 2 = 1.022 Also, the illuminance distribution on the illuminated surface is sufficiently illuminance is higher at the peripheral portion as shown in Figure 10.

In the fourth embodiment, the focal length f ₂ of the second lens L ₂ is the shortest as compared with the other embodiments.

Fifth Embodiment FIG. 11 shows a fifth embodiment of the illumination lens according to the present invention, and its lens data is as shown in Table 6 below.

The fifth embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

(D ₃ / r ₄ ) = − 2.258, f ₂ = 1.319 Further, the illuminance distribution on the irradiated surface is sufficiently high in the peripheral portion as shown in FIG. 12, and for example, the original plate placed on the irradiated surface is
It can be applied when printing on a desired photosensitive material through an imaging lens.

Sixth Embodiment FIG. 13 shows a sixth embodiment of the illuminating lens according to the present invention, and its lens data is as shown in Table 7 below.

The sixth embodiment has the following numerical values and is constructed so as to satisfy the conditional expression.

(D ₃ / r ₄ ) ＝ − 1.899, f ₂ = 1.434 In addition, the illuminance distribution on the irradiated surface shows a slight decrease in illuminance at the middle part as shown in FIG. ing.

<Effects of the Invention> As can be seen from the above examples, according to the illumination lens of the present invention, the area of the surface 80 to be illuminated on the rear surface 100 of the lens having a diameter of 80 to 100 is illuminated uniformly or brighter toward the periphery. . This corresponds to an exit angle from the lens of 22 ° to 27 °. With the conventional lens, if we try to secure the illuminance distribution of about ± 5%, we can only use the emission angle up to about 10 °, whereas with this illumination lens, the illumination area of the same area is illuminated with the same illuminance distribution. When doing so, the distance from the illumination lens to the illuminated surface can be shortened to 1/2 to 1/3.

Furthermore, since the edge of the illuminated surface can be illuminated brighter as necessary, even if there is an optical element that reduces the edge illuminance between the illumination lens and the illuminated surface, for example, a uniform illumination distribution is finally obtained. realizable.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of an illuminating lens based on the present invention, FIGS. 2 and 3 are ray tracing diagrams of the illuminating lens, and FIG. 4 is a diagram showing the illuminating lens. Illuminance distribution diagram, FIG. 5, FIG. 7, FIG. 9, FIG. 11 and FIG. 13 are lens configuration diagrams showing another embodiment, and FIG.
FIG. 8, FIG. 10, FIG. 10, FIG. 12 and FIG. 14 are illuminance distribution diagrams corresponding to other examples, respectively. FIG. 15 is a principle diagram of an illumination optical system using an illumination lens, and FIG. Is a configuration diagram of an illuminating lens showing a conventional example, and FIG. 17 is an illuminance distribution diagram by the illuminating lens. LS ... light source, L ... illumination lens, L ₁ ... first lens,
L ₂ …… Second lens, OG …… Irradiation surface, h …… Incident height, H
...... Irradiation height, f …… Composite focal length, f ₂ …… Focal length of the second lens, r ₁ …… Curve radius of the front surface of the first lens, r ₂ …… Curve radius of the rear surface of the first lens, r ₃ … ... radius of curvature of front surface of second lens, r ₄ ... radius of curvature of rear surface of second lens, d ₁ ... thickness of first lens, d ₂ ... distance between first lens and second lens, d ₃
...... Thickness of second lens, n ₁ …… Refractive index of first lens, n ₃
The refractive index of the second lens.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-52-76048 (JP, A) JP-A-51-53830 (JP, A) Actual development-Sho-49-34738 (JP, U) JP-B-37- 10291 (JP, B1)

Claims (1)

[Claims] 1. Two groups 2 arranged between a light source and a surface to be illuminated.
An illuminating lens including a plurality of lenses, wherein the first lens is a positive lens having a convex rear surface and the second lens is a positive lens having both convex surfaces in order from the light source side, and the following conditional expressions are satisfied. Illumination lens characterized by being configured as follows: −3.0 ≦ (d ₃ / r ₄ ) ≦ −0.3 …… 1.0f ≦ f ₂ ≦ 1.55f …… where f is the composite focal length of the entire illumination lens. f ₂ is the focal length of the second lens d ₃ is the thickness of the second lens r ₄ is the radius of curvature of the rear surface of the second lens