JP2010101973A - Imaging lens system and imaging optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens system that is telecentric on an object side, short in the entire length of a lens system, and effective in cost reduction. <P>SOLUTION: The imaging lens system includes, in the order starting from the object side to the imaging side, first to fifth lenses L1 to L5. A diaphragm S is disposed in between the third lens L3 and fourth lens L4, and a half mirror is disposed between the third lens L3 and diaphragm S. Illuminating light enters the third lens L3 via the half mirror HM. The object is illuminated via the second and first lens L2 and L1. In the imaging lens system configured as is described, the diaphragm S is disposed in the back focus position of the first to third lenses, thereby obtaining the imaging lens that is telecentric on the object side and satisfies expressions: (1) D6>2×ED6 and (2) D6>2×ED7, where ED6 represents the effective diameter of a light beam on the imaging-side face of the third lens, ED7 represents the aperture diameter of the diaphragm, and D6 represents the distance on the optical axis, between the imaging-side face of the third lens and the diaphragm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging lens system and an imaging optical apparatus.

  When performing assembly work between optical substrates, mounting optical elements on an optical substrate, or mounting electronic components on an electronic substrate, the assembly position and mounting position are accurately positioned at a predetermined position. Therefore, an area in which work is performed (hereinafter referred to as “work area”) is imaged with an imaging optical device.

  The imaging lens system used in such an imaging optical apparatus is configured so that the “size of the captured image” does not change even when the distance between the object to be worked and the objective lens changes when observing the work area. It is common to provide telecentricity on the object side.

As such an imaging lens system, those described in Patent Documents 1 to 3 are known.
The imaging lens systems described in Patent Documents 1 and 2 include two cemented lenses in the lens system, and the total number of lenses is as large as 7 to 8, leaving room for improvement in terms of material costs and manufacturing costs. ing.

  Although the imaging lens system described in Patent Document 3 has a total number of lenses as small as five, two of them are joined, and high precision is required for processing. There is room for improvement.

  Furthermore, since the imaging lens systems described in Patent Documents 1 to 3 need to provide “related parts such as illumination” near the lens barrel, a working distance (an object in the work area and an objective lens located closest to the object side) For example) is set as long as 80 mm or more.

  By the way, if the imaging lens system is “telecentric on the object side” and the working distance is long, the total length of the imaging lens system must be increased, and it is difficult to reduce the size of the imaging optical apparatus.

JP 2006-30495 A JP 2006-65141 A JP2007-65524

  The present invention has been made in view of the above-described circumstances, and realizes an imaging lens system that is telecentric on the object side, has a short overall lens system, and is advantageous for cost reduction. An object of the present invention is to realize an imaging optical device using an imaging lens system.

  The imaging lens system according to the present invention has "a first to a fifth lens are sequentially arranged from the object side to the image side, and has a diaphragm between the third lens and the fourth lens. An imaging lens system in which a half mirror is arranged between them, illumination light is incident on the third lens via the half mirror, and is irradiated onto the object via the second lens and the first lens.

  The first lens is a biconvex lens, the second lens is a “positive meniscus lens with the convex surface facing the object side”, the third lens is “a negative lens having a concave surface on the image side”, and the fourth lens is “the convex surface is on the object side” The negative meniscus lens toward the lens ”and the fifth lens are“ biconvex lenses ”separated from the fourth lens.

Further, the diaphragm is disposed at the “back focus position of the first to third lenses”, thereby being telecentric on the object side.
Light effective diameter on the image side surface of the third lens: ED6, aperture diameter of the stop: ED7, distance on the optical axis between the image side surface of the third lens and the stop: D6 is a condition:
(1) D6> 2 × ED6
(2) D6> 2 × ED7
(Claim 1).

In the imaging lens system according to claim 1, the curvature radius of the object side surface of the third lens: R5, and the curvature radius of the object side surface of the fourth lens: R8 are:
(3) 0.05 ≧ 1 / R5 ≧ 0
(4) 40>R8> 0
It is preferable that the first lens and the second lens, or the first lens and the fifth lens are made of the same glass material.
The imaging optical device according to the present invention is an “imaging optical device using an imaging lens for forming an image of an observation surface on a light receiving surface of an image sensor and observing the observation surface”, and includes an imaging lens system and illumination It has an optical system and an image sensor (Claim 3).

  The “observation surface” is a surface to be imaged, and has been described as a work area earlier. The observation surface is an object surface in the imaging of the imaging lens system.

  As the “imaging lens system”, the imaging lens system according to claim 1 or 2 is used.

  The “image sensor” is provided so that its light receiving surface matches the image plane of the image sensor. As the imaging device, various devices such as a CCD area sensor and a CMOS can be used as appropriate.

  The “illumination optical system” causes the illumination light to enter the third lens via a half mirror disposed on the optical path between the third lens and the fourth lens in the imaging lens system, and the light from the light source is captured by the imaging lens. The light is condensed on the “image side focal position in the synthesis system of the first to third lenses” of the system.

  As a light source for the illumination optical system, a white light source or a monochromatic light source can be used as appropriate. However, if a monochromatic light source such as an LD or LED is used, it is inexpensive and the chromatic aberration of the imaging lens system is not problematic. There is an advantage that the imaging lens system can be easily designed.

  In the imaging optical device according to the third aspect, the first to fifth lenses of the imaging lens system are arranged on the “imaging optical path bent between the third lens and the fourth lens by reflection by a half mirror”. The illumination light passes through the half mirror and enters the third lens of the imaging lens system, and the imaging light from the observation surface exits from the fifth lens along the imaging optical path bent by the half mirror and takes an image. It can be the structure which injects into an element (Claim 4).

  In place of such a configuration, the first to fifth lenses of the imaging lens system are “arranged in one row with the half mirror in between”, and the illumination light is “reflected by the half mirror, and the third lens of the imaging lens system” The image forming light from the observation surface can be “transmitted through the half mirror and emitted from the fifth lens” and enter the imaging device. In this case, when a parallel flat plate half mirror is used, it is necessary to design the first to fifth lens systems in consideration of “astigmatism generated by the half mirror”.

  If the explanation is supplemented slightly, the above conditions (1) and (2) are conditions for sufficiently securing the space between the third lens and the fourth lens as a “space for arranging the half mirror”. When the distance on the optical axis between the image side surface of the third lens and the stop: D6 exceeds the lower limit of the conditions (1) and (2), the distance between the third lens and the stop becomes “half mirror arrangement”. On the other hand, if the half mirror is made small and forcibly arranged, the beam diameter between the third and fourth lenses has to be reduced, and the image on the observation surface becomes dark or aberration correction is difficult. It becomes.

  In addition, the fourth lens and the fifth lens are separate, and by not joining them, the shape of the four surfaces of these lenses can be used as design parameters, so a sufficient field of view is ensured while shortening the conjugate length. The telecentricity on the object side can be secured.

  In addition, as in claim 2, the radius of curvature of the object side surface of the third lens: R5 and the radius of curvature of the object side surface of the fourth lens: R8 satisfy the conditions (3) and (4), and the first lens By forming the first lens and the second lens or the first lens and the fifth lens with the same glass material, good imaging performance can be realized.

Satisfying the conditions (3) and (4) has the following significance.
That is, in the condition (3), “1 / R5 is 0 or more” means that the object side surface of the third lens is a flat surface or a convex surface.

  The imaging light beam transmitted through the first lens and the second lens is incident on the object plane of the third lens in a converged state by the action of the first lens and the second lens having positive power. At this time, when considering off-axis light in the convergent light beam, if the object surface of the third lens is concave, the incident angle to the surface increases, and astigmatism and coma tend to increase. By satisfying the lower limit side of the condition (3), it is possible to reduce the astigmatism and the coma.

  When “1 / R5” increases in the condition (3), the convex curvature of the object plane of the third lens increases. Since the third lens is a negative lens having a concave surface on the image side, in order to ensure the function required as a negative lens, the larger the convex curvature of the object surface of the third lens, the more concave the image side surface. Therefore, it is difficult to manufacture the third lens. Accordingly, an upper limit of “1 / R5” is suitably about 0.05.

  Further, as in the case of the embodiments described later, when the third lens uses “a material having a higher refractive index and higher dispersion than the first and second lenses”, the chromatic aberration of the entire imaging lens system is corrected favorably. It is extremely important to satisfy the condition (3).

  The condition (4) for regulating the range of the radius of curvature R5 and the radius of curvature of the object side surface of the fourth lens: R8 will be described below. It is close.

  The “object side surface of the fourth lens” satisfying the condition (4) is a convex surface, and by placing the convex surface satisfying the condition (4) at the image side position near the stop, “coma aberration and The effect of astigmatism can be reduced. The range in which such an effect can be effectively realized is the range of condition (4).

  In particular, as in the example, when using a “glass material having a higher refractive index and higher dispersion than the material of the fifth lens” as the material of the fourth lens, by using the convex surface in the range of the condition (4), The occurrence of spherical aberration on the convex surface is less than that of the fifth lens, and the power of the entire imaging lens system can be increased while suppressing spherical aberration and chromatic aberration as “the entire synthetic system of the fourth and fifth lenses”. .

  As described above, according to the present invention, a novel imaging lens system and imaging optical device can be realized.

In the imaging lens system of the present invention, since the illumination of the observation surface is performed through the half mirror disposed in the lens system, “the illumination can be performed through the first to third lenses of the imaging lens system”, and the lens barrel Since there is no need to provide “related parts such as lighting” in the vicinity, it is not necessary to take a long working distance.
Therefore, the imaging lens system of the present invention can be realized with a small overall length and a conjugate length while being telecentric on the object side, and can achieve extremely good performance as shown in a specific example described later. An imaging optical device using the can also be realized with small size and high performance.

Hereinafter, embodiments will be described.
FIG. 1 shows a main part of the imaging optical device.

  In FIG. 1, the symbol OBA is an “observation plane”, which is an object plane in imaging of the imaging lens system. The imageable range on the observation surface OBA is the “working area” described above.

  Reference numeral L1 indicates a “first lens”, reference numeral L2 indicates a “second lens”, reference numeral L3 indicates a “third lens”, and reference numeral HM indicates a “half mirror”. The half mirror HM has a parallel plate shape, and the surface on the third lens L3 side is a “half mirror surface”.

  Reference sign S indicates “aperture”, reference sign L4 indicates “fourth lens”, reference sign L5 indicates “fifth lens”, and reference sign ML indicates “mirror for bending the optical path”. The symbol IMA is “image plane by the imaging lens system”, and the imaging element is arranged with its light receiving surface matched to this image plane. The mirror ML is not necessary depending on the layout of the optical system.

Reference numeral LS denotes a “light source” of the illumination optical system. The light source LS is an LED in this example. Reference numeral LC denotes a condensing lens and constitutes an illumination optical system together with the light source LS.
The illumination optical system including the light source LS and the condensing lens LC collects the monochromatic light from the light source LS at the image-side focal position P of the “synthetic system” by the first to third lenses L1 to L3 as shown in the figure. Set to Note that the image-side focal position P is slightly deviated from the optical axis of the synthesis system due to refraction by the transparent parallel flat plate constituting the half mirror HM.

  In other words, the imaging optical apparatus whose embodiment is shown in FIG. 1 is an imaging optical apparatus that uses an imaging lens system for forming an image of the observation surface OBA on the light receiving surface of the image sensor and observing the observation surface OBA. And an imaging lens system, an illumination optical system, and an imaging device (not shown). The imaging device is provided such that its light receiving surface coincides with the image plane IMA of the imaging lens system. The systems LS and LC are for “illuminating light to enter the third lens L3 via the half mirror HM disposed on the optical path between the third lens L3 and the fourth lens L4 in the imaging lens system”. , The light from the light source LS is condensed at the image-side focal position P in the “synthesis system of the first to third lenses L1 to L3 of the imaging lens system”.

  The imaging lens system includes first, second, third, fourth, and fifth lenses L1 to L5 sequentially from the object side to the image side, and between the third lens L3 and the fourth lens L4. A half mirror HM is disposed between the third lens L3 and the diaphragm S, and the illumination light is incident on the third lens L3 via the half mirror HM, and has the second lens L2 and the first lens L1. The first lens L1 is a “biconvex lens”, the second lens L2 is a “positive meniscus lens with the convex surface facing the object side”, and the third lens L3 is “concave on the image side”. , A fourth lens L4 is a “negative meniscus lens having a convex surface facing the object side”, a fifth lens L5 is a “biconvex lens separated from the fourth lens L4”, and the aperture S is the first lens. ~ Back focus position of the third lens L1 ~ L3 By being arranged in a telecentric on the object side.

Further, as shown in a specific example described later, the imaging lens system includes an effective light beam diameter ED6 on the image side surface of the third lens L3, an aperture diameter of the aperture S: ED7, an image side surface of the third lens L3 and the aperture. The distance on the optical axis: D6 is the condition:
(1) D6> 2 × ED6
(2) D6> 2 × ED7
The radius of curvature of the object side surface of the third lens L3 is R5, and the radius of curvature of the object side surface of the fourth lens L4 is R8.
(3) 0.05 ≧ 1 / R5 ≧ 0
(4) 40>R8> 0
The first lens L1 and the second lens L2 or the first lens L1 and the fifth lens L5 are made of the same glass material.

  In addition, the first to fifth lenses L1 to L5 of the imaging lens system are disposed on the “imaging optical path bent between the third lens L3 and the fourth lens L4” by reflection by the half mirror HM, and are illuminated. The light passes through the half mirror HM and enters the third lens L3 of the imaging lens system, and the imaging light from the observation surface OBA passes from the fifth lens L5 along the imaging optical path bent by the half mirror HM. It exits and enters the image sensor.

  That is, in the imaging optical device shown in FIG. 1, when the light source LS emits light, the emitted illumination light (monochromatic light) is condensed at the point P by the condenser lens LC and transmitted through the half mirror HM while diverging. Then, the light enters the third lens L3 and irradiates the observation surface OBA via the second lens L2 and the first lens L1.

  Since the condensed light P of the illumination light coincides with the “image side focal position of the composite system of the first to third lenses L1 to L3”, the illumination light condensed at the point P diverges and passes through the half mirror HM. Transmits, travels in the direction of the optical axis of the third lens L3, passes through the third to first lenses L3 to L1, and is converted into a parallel beam by the action of these lenses L1 to L3 so as to be orthogonal to the observation plane OBA. Is done.

The reflected light from the observation surface OBA becomes image forming light and enters the first lens L1, passes through the first to third lenses L1 to L3, and enters the half mirror HM. The effective beam diameter of the imaging light emitted from the image side surface of the third lens L3 is “ED6” in the condition (1).
The imaging light reflected by the half mirror HM passes through the stop S, passes through the fourth lens L4 and the fifth lens L5, is reflected by the mirror ML, and forms an image of the observation surface OBA on the image plane IMA. To do. The formed image is received by an “imaging device in which the light receiving surface coincides with the image plane IMA”, converted into imaging data, converted into image data, and processed by a data processing device (not shown).

  The aperture stop S is disposed at the back focus position of the synthesis system of the first to third lenses L1 to L3, so that the imaging lens system is telecentric on the object side.

  The aperture diameter of the diaphragm S is “ED7” in the condition (2).

  Hereinafter, two specific examples of the imaging lens system used in such an imaging optical apparatus will be described.

"Example 1"
FIG. 2 shows the lens configuration of the imaging lens system of Example 1. The reference numerals in the figure are the same as those shown in FIG.
The first to fifth lenses L1 to L5 and the stop S are shown arranged on the same optical axis developed linearly. The half mirror HM disposed between the third lens L4 and the stop S, and the mirror ML disposed between the fifth lens L5 and the image plane IMA are not shown.
The “half mirror surface of the half mirror” faces the third lens L3 and the fourth lens L4, and has no influence on the imaging function of the first to fifth lenses L1 to L5.

  The data is shown below. Each surface from the observation surface OBA to the image surface IMA is represented by SO, S1 to S11, and SI. SO is the observation plane OBA, SI is the image plane IMA, and S1 to S11 represent each plane (lens plane and stop plane) counted from the object side of the first lens L1.

  “R” represents the radius of curvature of each surface, “D” represents the surface spacing, and “Nd and νd” represent the refractive index and Abbe number. The unit of the element having the length is “mm”.

Surface number R D Nd νd
OBA SO ∞ 13.4
L1 S1 23.0330 3.5 1.743320 49.3
S2-25.9650 0.24
L2 S3 7.4170 3.5 1.743320 49.3
S4 9.1542 0.9
L3 S5 78.7360 1.3 1.71736 29.5
S6 4.5053 12.0
S S7 ∞ 2.45
L4 S8 19.1102 1.1 1.805518 25.4
S9 9.4588 0.4
L5 S10 11.9224 2.5 1.60311 60.7
S11-9.8506 33.622
IMA SI ∞.

Field of view: φ = 9 mm, focal length of entire system: f = 39.9 mm, Fno = 8.0
Use wavelength: 530 nm (light emission wavelength of LED as a light source)
Since the effective beam diameter in S6 is ED6 = 5.10 mm, the aperture diameter of the diaphragm is ED7 = 3.48 mm, and the distance on the optical axis between the image side surface of the third lens L3 and the diaphragm S is D6 = 12.0 mm. D6> 2 × ED6, D6> 2 × ED7, satisfying the conditions (1) and (2), and securing a sufficient space to place a half mirror between the third lens L3 and the stop S is doing.

The imaging magnification is “equal magnification”, and an image sensor equivalent to “½ inch” can be used.
The working distance is 13.4 mm and the conjugate length is 71.41 mm. Both the working distance and the conjugate length are short. Field of view: φ is as wide as 9 mm.

"Example 2"
FIG. 3 shows the lens configuration of the imaging lens system of Example 2 following FIG.
The data of the second embodiment will be shown following the first embodiment.

Surface number R D Nd νd
OBA SO ∞ 18.6
L1 S1 46.4090 3.8 1.74320 49.3
S2-46.4090 0.1
L2 S3 8.5526 3.6 1.69700 48.5
S4 34.4980 3.05
L3 S5 ∞ 1.1 1.74077 27.7
S6 3.9808 12.3
S S7 ∞ 0.1
L4 S8 20.0900 2.6 1.800518 25.4
S9 6.2852 0.27
L5 S10 7.4170 3.95 1.74320 49.3
S11-9.4007 19.97
IMA SI ∞.

Field of view: φ = 9 mm, focal length of entire system: f = 43.5 mm, Fno = 4.0
Use wavelength: 530 nm (light emission wavelength of LED as a light source)
Since the effective beam diameter in S6 is ED6 = 4.71 mm, the aperture diameter of the stop is ED7 = 4.55 mm, and the distance on the optical axis between the image side surface of the third lens L3 and the stop S is D6 = 12.3 mm. D6> 2 × ED6, D6> 2 × ED7, satisfying the conditions (1) and (2), and securing a sufficient space to place a half mirror between the third lens L3 and the stop S is doing.

The imaging magnification is “0.5 times”, and an image sensor equivalent to “¼ inch” can be used. The working distance is 18.6 mm and the conjugate length is 69.44 mm, both of which are short. Field of view: φ is as wide as 9 mm.
Needless to say, both the first and second embodiments are “telecentric on the object side”. As described above, in both Examples 1 and 2, the working distance is 20 mm or less, the conjugate length is 75 mm or less, the imaging optical device can be made compact, and a wide field of view can be imaged.

  In the first embodiment, 1 / R5 = 0.127 and R8 = 19.1102. In the second embodiment, 1 / R5 = 0 and R8 = 20.0900. In the first embodiment, the first lens and the second lens are made of the same material, and in the second embodiment, the first lens and the fifth lens are made of the same material.

FIG. 4 shows aberration diagrams related to Example 1. In the figure of astigmatism, T is “tangential” and S is “sagittal”.
FIG. 5 is an aberration diagram related to Example 2 similar to FIG.
The performance of both Examples 1 and 2 is good, and the performance is also good in the visible range.

Since both the first and second embodiments do not include an “aspheric surface” in the imaging lens system, it is easy to manufacture each lens, which is advantageous in terms of cost.
In Examples 1 and 2, “LED having a light emission wavelength of 530 nm” is exemplified as a light source. However, the imaging lens systems of Examples 1 and 2 are designed so as to be well suited for color image capturing. Has been.

It is a figure showing one embodiment of an image pick-up optical element explanatory. 1 is a diagram illustrating a configuration of an imaging lens system according to Example 1. FIG. 6 is a diagram illustrating a configuration of an imaging lens system of Example 2. FIG. FIG. 6 is an aberration diagram for Example 1. FIG. 6 is an aberration diagram for Example 2.

Explanation of symbols

OBA observation surface
L1 1st lens L2 2nd lens L3 3rd lens HM Half mirror S Aperture L4 4th lens L5 5th lens
IMA image plane
LS light source
LC condenser lens

Claims (4)

The first, second, third, fourth, and fifth lenses are sequentially arranged from the object side to the image side, and there is a diaphragm between the third lens and the fourth lens. An imaging lens system in which a half mirror is arranged between the diaphragms, and illumination light is incident on the third lens through the half mirror and is irradiated onto the object through the second lens and the first lens. There,
The first lens is a biconvex lens, the second lens is a positive meniscus lens having a convex surface facing the object side, the third lens is a negative lens having a concave surface on the image side, the fourth lens is a negative meniscus lens having a convex surface facing the object side, The fifth lens is a biconvex lens separated from the fourth lens,
By disposing the diaphragm at the back focus position of the first to third lenses, it is telecentric on the object side,
Light effective diameter on the image side surface of the third lens: ED6, aperture diameter of the diaphragm: ED7, distance on the optical axis between the image side surface of the third lens and the diaphragm: D6, the conditions are:
(1) D6> 2 × ED6
(2) D6> 2 × ED7
An imaging lens system characterized by satisfying The imaging lens system according to claim 1,
The radius of curvature of the object side surface of the third lens is R5, and the radius of curvature of the object side surface of the fourth lens is R8.
(3) 0.05 ≧ 1 / R5 ≧ 0
(4) 40>R8> 0
And an imaging lens system, wherein the first lens and the second lens, or the first lens and the fifth lens are made of the same glass material. An imaging optical device using an imaging lens system for forming an image of an observation surface on a light receiving surface of an imaging element and observing the observation surface,
An imaging lens system, an illumination optical system, and an imaging device;
The imaging lens system according to claim 1 or 2 is used as the imaging lens system,
The imaging element is provided such that its light receiving surface matches the image plane of the imaging lens system,
The illumination optical system causes illumination light to enter the third lens via a half mirror disposed on the optical path between the third lens and the fourth lens in the imaging lens system, An imaging optical apparatus, wherein light is condensed at an image-side focal position in a synthesis system of the first to third lenses of the imaging lens system. The imaging optical device according to claim 3,
The first to fifth lenses of the imaging lens system are disposed on an imaging optical path bent between the third lens and the fourth lens by reflection by a half mirror,
The illumination light passes through the half mirror and enters the third lens of the imaging lens system,
The imaging optical device, wherein the imaging light from the observation surface exits from the fifth lens along the imaging optical path bent by the half mirror and enters the imaging device.

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