JP2007286372A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small imaging lens suitable for a monitor camera used in a mounting machine. <P>SOLUTION: This imaging lens has a first lens 1 having a negative refractivity with its concave surface facing the object side, a second lens 2 of a meniscus shape having a positive refractivity with its concave surface facing the object side, an aperture diaphragm SD of a predetermined diameter, a third lens 3 having a positive refractivity, and a 4th meniscus lens 4 having a negative refractivity with its concave surface facing the object side, all arranged in this order from the object side. In this configuration, the front group lenses consisting of the first lens 1 and the second lens 2 mainly spread the input light to lengthen the back focusing, and the rear group lenses consisting of the third lens 3 and the 4th lens 4 mainly converge the light to focus. Thus, it is possible to obtain an imaging lens which can secure a sufficient back focusing and is miniaturized by providing a reflector mirror but can secure the required imaging magnification, conjugate length, and visual field with excellent optical characteristics, and sufficiently corrected distortions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens used in a camera having an imaging element such as a CCD, and more particularly to a retrofocus imaging lens used in a camera that recognizes an electronic component or the like in a mounting machine that mounts the electronic component or the like on a substrate. .

In the process of mounting electronic components on the board, in order to accurately determine each electronic component at a predetermined position, the electronic component picked up by the pick-up nozzle of the mounting machine is imaged by a recognition camera and the obtained image data is calculated. By processing and finely adjusting the position of the suction nozzle, a slight positional deviation of the electronic component is also corrected.
As an imaging lens applied to this recognition imaging camera, in order to reduce image distortion, it is conceivable to use a symmetric type or a symmetric type triplet, tesser, double Gauss type lens or the like. By the way, since the recognition camera is arranged in a limited space of the mounting machine, there is a possibility that it may interfere with other members when an imaging lens as described above is arranged or close to the symmetrical type. It is conceivable to adopt a method of bending the optical path by disposing a reflecting mirror between the lens and the lens or between the lens and the image plane.
However, if the lens is arranged so as to satisfy a predetermined imaging magnification, the distance between the lens and the image plane, that is, the back focus is small, and it is difficult to arrange the reflecting mirror without interfering with other members.

In view of this, it is conceivable to replace a lens that is symmetric or close to symmetric with a retrofocus lens that can ensure a large back focus compared to the focal length.
Conventional retrofocus lenses include a meniscus first lens having negative refractive power toward the object-side convex surface, an aperture stop, a biconvex second lens, a biconcave third lens, A lens including a convex fourth lens, having a wide angle, a long back focus, excellent telecentricity, and applied to a digital still camera or the like is known (for example, see Patent Document 1).
In addition, a meniscus first lens having a negative refractive power with a convex surface facing the object side, a biconvex second lens, an aperture stop, a light shielding plate, a biconcave third lens, and a positive refractive power A lens including a fourth lens and a biconvex fifth lens, having a wide angle, a long back focus, excellent telecentricity, and applied to a digital camera or the like is known (for example, see Patent Document 2).
Furthermore, a meniscus first lens having negative refractive power with a convex surface facing the object side, a biconvex second lens, an aperture stop, a biconcave third lens, and a fourth lens having positive refractive power. A lens including a lens and a biconvex fifth lens that has a long back focus and is suitable for a digital camera or the like is known (for example, see Patent Document 3).

JP 2003-195163 A JP 2002-228925 A JP-A-10-293246

  However, the conventional retrofocus lenses are mainly aimed at improving the telecentricity of the image side and ensuring a wide angle of view. When applied to the lens, the outer diameter of the lens becomes unnecessarily large and the thickness of the lens becomes too thick, which is not preferable as an imaging lens disposed in a limited space.

  The present invention has been made in view of the circumstances of the prior art described above, and its object is to provide the required imaging magnification (0.42 to 0.46), conjugate length (210 mm to 220 mm), and While ensuring a field of view (approximately φ12mm), various aberrations, especially distortion, are sufficiently corrected, sufficient back focus can be secured to insert a reflector, low cost, small size, high optical performance, electronic components, etc. An object of the present invention is to provide a retrofocus imaging lens suitable for a mounting process or the like.

The imaging lens of the present invention includes a first lens having a negative refractive index and a concave surface directed toward the object side, which is arranged in order from the object side to the image plane side, and a positive refractive index toward the object side. A second meniscus lens having a concave surface, an aperture stop having a predetermined aperture, a third lens having a positive refractive index, and a meniscus second lens having a negative refractive power and having a concave surface facing the object side. And 4 lenses.
According to this configuration, the front group lens composed of the first lens and the second lens mainly plays a role of extending the incident light rays and lengthening the back focus, and the rear group lens composed of the third lens and the fourth lens. It mainly plays a role of converging the light beam emitted from the second lens to form an image at the focal point.
As described above, the front group lens (first lens and second lens) and the rear group lens (third lens and fourth lens) can sufficiently secure the back focus, and the required imaging magnification and conjugate. An imaging lens having good optical characteristics in which a long length and a field of view can be secured and distortion and the like are sufficiently corrected can be obtained.

The imaging lens of the present invention includes a first lens having a negative refractive index and a concave surface facing the object side, which are arranged in order from the object side to the image plane side, and an object having a positive refractive index. A second lens having a meniscus shape having a concave surface facing the side, a third lens having a positive refractive index, a fourth lens having a negative refractive power and a concave surface facing the object side, and a predetermined aperture And an aperture stop having the following.
According to this configuration, the front group lens composed of the first lens and the second lens mainly plays a role of extending the incident light rays and lengthening the back focus, and the rear group lens composed of the third lens and the fourth lens. It mainly plays a role of converging the light beam emitted from the second lens to form an image at the focal point.
As described above, the front group lens (first lens and second lens) and the rear group lens (third lens and fourth lens) can sufficiently secure the back focus, and the required imaging magnification and conjugate. An imaging lens having good optical characteristics in which long and visual fields can be secured and distortion is sufficiently corrected can be obtained.
Furthermore, here, since the aperture stop is disposed behind the fourth lens, the aperture stop can be easily replaced and changed.

In the imaging lens having the above configuration, the first lens may be a plano-concave lens having a concave surface on the object side and a flat surface on the image surface side.
According to this configuration, the processing of the first lens is simplified, the manufacturing cost can be reduced, and the cost of the imaging lens as a whole can be reduced.

In the imaging lens having the above-described configuration, a configuration in which at least one reflecting mirror is disposed between the fourth lens and the image plane can be employed.
According to this configuration, the recognition camera including the imaging lens can be easily arranged in a limited space such as a mounting machine.

  According to the imaging lens having the above configuration, the back focus can be sufficiently secured, is small, low cost, has high optical performance, and is suitable for a camera for recognition mounted on a mounting machine such as an electronic component. An imaging lens can be obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 to 3 show an embodiment of an imaging lens according to the present invention. FIG. 1 is a lens configuration diagram, FIG. 2 is an optical path diagram, and FIG. 3 is an aberration diagram.

As shown in FIG. 1, the imaging lens includes a first lens 1 and a positive refractive index, which are arranged in order from the object side to the image plane side and have a negative refractive index and a concave surface facing the object side. A front lens group (I) comprising a second meniscus lens 2 having a concave surface facing the object side, a third lens 3 having a positive refractive index, and a concave surface facing the object side having a negative refractive power And a rear lens group (II) comprising a fourth meniscus lens 4 and an aperture stop SD having a predetermined aperture between the second lens 2 and the third lens 3 and immediately before the third lens 3. It has a retrofocus type lens configuration of 4 elements in 2 groups.
Then, as shown in FIG. 2, an image is formed on the image plane P located on the optical axis L without reflecting mirror 5 behind the fourth lens 4, and reflected behind the fourth lens 4. By disposing the mirror 5, the light beam that has passed through the fourth lens 4 is bent to form an image on the image plane P '.

  In this imaging lens, as shown in FIG. 2, light rays emitted from the object OBJ pass through the first lens 1 and the second lens 2 (front group lens) having negative refractive power as a whole and diverge. The third lens 3 and the fourth lens having a positive refractive power as a whole as a result of the diverging light beam passing through the aperture stop SD and being narrowed down to a light beam in a predetermined angular range. 4 passes through the rear lens group 4 and converges in a direction approaching the optical axis L, and forms an image on the image plane P ′ via the image plane P or the reflecting mirror 5.

That is, the front lens group (I) composed of the first lens 1 and the second lens 2 mainly plays a role of extending the incident light beam and lengthening the back focus, and the rear lens composed of the third lens 3 and the fourth lens 4. The group lens (II) mainly plays a role of converging light rays to form an image at a focal point.
As described above, the front group lens (I) (the first lens 1 and the second lens 2) and the rear group lens (II) (the third lens 3 and the fourth lens 4) can sufficiently secure the back focus. .
Therefore, as shown in FIG. 2, by arranging the reflecting mirror 5 to be inclined at a predetermined angle behind the fourth lens 4, an image can be formed on the image plane P ′ at a position away from the optical axis L.
Further, since the distortion aberration is canceled or reduced inside each of the front lens group (I) and the rear lens group (II), the distortion aberration of the entire lens can be suppressed to an extremely small amount.

  Here, in the first lens 1 to the aperture stop SD to the fourth lens, as shown in FIG. 1, each surface is Si (i = 1 to 9), and the curvature radius of each surface Si is Ri (i = 1 to 9), the refractive index of the first lens 1 to the fourth lens 4 with respect to the d-line is represented by Ni (i = 1 to 4), and the Abbe number is represented by νi (i = 1 to 4). The distance (thickness, air interval) on the optical axis L from the first lens 1 to the image plane P is Di (i = 1 to 8), and the air is converted from the rear surface S9 to the image plane P of the fourth lens 4. The distance, that is, the back focus is represented by BF.

The first lens 1 is a lens having a negative refractive power of a meniscus formed of a glass material or a resin material and having a concave surface on the object side and a convex surface on the image surface side. Here, both the concave surface and the convex surface are formed into spherical surfaces.
The second lens 2 is a lens formed of a glass material or a resin material and having a meniscus positive refractive power having a concave surface on the object side and a convex surface on the image surface side. Here, both the concave surface and the convex surface are formed into spherical surfaces.
The first lens 1 and the second lens 2 form a front group lens having negative refractive power as a whole.

The third lens 3 is a lens having a positive refractive power of a biconvex shape that is formed of a glass material or a resin material and has a convex surface on the object side and a convex surface on the image surface side. Here, both convex surfaces are formed into spherical surfaces.
The fourth lens 4 is formed of a glass material or a resin material, and has a meniscus negative refractive power with a concave surface on the object side and a convex surface on the image surface side. Here, both the concave surface and the convex surface are formed into spherical surfaces.
The third lens 3 and the fourth lens 4 form a rear lens group having a positive refractive power as a whole.

  According to the imaging lens having the above configuration, it is required by the front group lens (I) (the first lens 1 and the second lens 2) and the rear group lens (II) (the third lens 3 and the fourth lens 4). An imaging magnification, a conjugate length, and a field of view can be ensured, a good optical characteristic in which distortion is sufficiently corrected can be secured, and a sufficient back focus BF for arranging the reflecting mirror 5 can be secured. Can do. As a result, an imaging lens suitable for a recognition camera capable of imaging components with high accuracy in a mounting machine such as an electronic component while achieving downsizing and cost reduction can be obtained.

  Specific Example 1 of the imaging lens having the above-described configuration is shown below. Here, the main specification specifications and various numerical data (setting values) in the first embodiment are as follows. Further, spherical aberration, astigmatism, and distortion are as shown in FIG. In the astigmatism in FIG. 3, S indicates an aberration on the sagittal plane, and M indicates an aberration on the meridional plane.

<Specification specifications>
Use wavelength 1 (main wavelength) = 587.6 nm, use wavelength 2 = 656.3 nm, use wavelength 3 = 486.1 nm, focal length = 41.82 mm, field of view = φ12.0 mm, aperture aperture SD aperture = φ12.0 mm , Brightness (F number) = 5.6, conjugate length (object to image plane) = 220 mm, imaging magnification = 0.4292, outer diameter dimension of the first lens 1 = φ12 mm, outer diameter dimension of the second lens 2 = φ12 mm, third lens 3 outer diameter dimension = φ14 mm, fourth lens 4 outer diameter dimension = φ16 mm, back focus (BF) = 80.00 mm

<Curvature radius Ri (mm) of first lens 1 to aperture stop SD to fourth lens 4>
R1 = −7.2888 mm, R2 = −209.0900 mm, R3 = −14.2260 mm, R4 = −8.1419 mm, R5 = ∞ (aperture stop SD), R6 = 33.5650 mm, R7 = −16.6220 mm, R8 = -14.7720mm, R9 = -30.9520mm

<Surface spacing (mm)>
D1 = 1.00 mm, D2 = 1.00 mm, D3 = 2.50 mm, D4 = 14.25 mm, D5 = 0.10 mm, D6 = 4.00 mm, D7 = 1.62 mm, D8 = 1.50 mm, BF = 80.00mm,

<Refractive index Ni (d line) of the first lens 1 to the fourth lens 4>
N1 = 1.51680, N2 = 1.58913, N3 = 1.58913, N4 = 1.75520
<Abbe number νi of the first lens 1 to the fourth lens 4>
ν1 = 64.2, ν2 = 61.2, ν3 = 61.2, ν4 = 27.5

  In Example 1, the imaging magnification is 0.4292, the conjugate length is 220 mm, the field of view is 12.0 mm, the back focus BF is 80.00 mm, and spherical aberration, astigmatism, distortion, etc. are sufficiently corrected. As a result, an imaging lens suitable for the recognition camera of the mounting machine was obtained.

4 to 6 show another embodiment of the imaging lens according to the present invention. FIG. 4 is a lens configuration diagram, FIG. 5 is an optical path diagram, and FIG. 6 is an aberration diagram. The description of the same configuration as that of the above-described embodiment is omitted.
As shown in FIG. 1, the imaging lens includes a first lens 1 ′ having a negative refractive index and a concave surface facing the object side, and a positive refractive index, which are arranged in order from the object side to the image plane side. A front lens group (I) comprising a second meniscus lens 2 having a concave surface facing the object side, a third lens 3 having a positive refractive index and a concave surface facing the object side having a negative refractive power. 2 groups of 4 retrofocus lenses having a rear lens group (II) composed of a fourth meniscus lens 4 directed toward the rear and an aperture stop SD having a predetermined aperture in the vicinity of the rear of the fourth lens 4 It has a configuration.
Then, as shown in FIG. 5, the image is formed on the image plane P located on the optical axis L without reflecting the mirror 5 behind the fourth lens 4, and reflected behind the fourth lens 4. By disposing the mirror 5, the light beam that has passed through the fourth lens 4 is bent to form an image on the image plane P '.

  In this imaging lens, as shown in FIG. 5, the light emitted from the object OBJ passes through the first lens 1 ′ and the second lens 2 (front group lens) having negative refractive power as a whole and diverges. And the divergent light beam passes through the third lens 3 and the fourth lens 4 (rear group lens) having a positive refractive power as a whole and is converged in a direction approaching the optical axis L, and is thereby aperture stop. By passing through the SD, the light is narrowed down to a light beam in a predetermined angle range and formed on the image plane P ′ through the image plane P or the reflecting mirror 5.

That is, back focus is achieved by the front group lens (I) (first lens 1 ′ and second lens 2) and rear group lens (II) (third lens 3 and fourth lens 4), as in the previous embodiment. As shown in FIG. 5, an image is formed on the image plane P ′ at a position away from the optical axis L by disposing the reflecting mirror 5 at a predetermined angle behind the fourth lens 4 as shown in FIG. Can be made.
Further, as in the above-described embodiment, the distortion aberration is canceled or reduced in each of the front lens group (I) and the rear lens group (II), so that the distortion aberration of the entire lens is extremely small. The amount can be suppressed.
The first lens 1 ′ is a plano-concave lens that is formed of a glass material or a resin material and has a negative refractive power in a plano-concave shape with a concave surface on the object side and a plane on the image surface side. Here, the concave surface is formed into a spherical surface.

  According to the imaging lens having the above configuration, it is required by the front group lens (I) (first lens 1 ′ and second lens 2) and the rear group lens (II) (third lens 3 and fourth lens 4). Imaging magnification, conjugate length, and field of view can be secured, good optical characteristics in which distortion is sufficiently corrected can be secured, and sufficient back focus BF for arranging the reflecting mirror 5 can be secured. be able to. As a result, an imaging lens suitable for a recognition camera capable of imaging components with high accuracy in a mounting machine such as an electronic component while achieving downsizing and cost reduction can be obtained.

  A specific example 2 of the imaging lens having the above configuration will be described below. Here, the main specification specifications and various numerical data (setting values) in the second embodiment are as follows. Further, spherical aberration, astigmatism, and distortion are as shown in FIG. In the astigmatism shown in FIG. 6, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.

<Specification specifications>
Use wavelength 1 (main wavelength) = 587.6 nm, use wavelength 2 = 656.3 nm, use wavelength 3 = 486.1 nm, focal length = 41.82 mm, field of view = φ12.0 mm, aperture aperture SD aperture = φ11.0 mm , Brightness (F number) = 5.1, conjugate length (object to image plane) = 210 mm, imaging magnification = 0.4550, outer diameter of the first lens 1 ′ = φ13 mm, outer diameter of the second lens 2 = Φ13 mm, outer diameter of third lens 3 = φ14 mm, outer diameter of fourth lens 4 = φ14 mm, back focus (BF) = 80.00 mm

<First lens 1 'to fourth lens 4, radius of curvature Ri (mm) of aperture stop SD>
R1 = −7.3338 mm, R2 = ∞, R3 = −23.6058 mm, R4 = −8.5209 mm, R5 = 31.2782, R6 = −15.3797 mm, R7 = −14.1394 mm, R8 = −25. 6847mm, R9 = ∞ (aperture stop SD)

<Surface spacing (mm)>
D1 = 1.00mm, D2 = 0.60mm, D3 = 3.30mm, D4 = 8.25mm, D5 = 3.50mm, D6 = 1.72mm, D7 = 1.20mm, D8 = 0.00mm, BF = 80.00mm,

<Refractive index Ni (d line) of first lens 1 'to fourth lens 4>
N1 = 1.51633, N2 = 1.51633, N3 = 1.51633, N4 = 1.75520
<Abbe number νi of first lens 1 ′ to fourth lens 4>
ν1 = 64.1, ν2 = 64.1, ν3 = 64.1, ν4 = 27.5

  In Example 2, the imaging magnification is 0.4555, the conjugate length is 210 mm, the field of view is 12.0 mm, the back focus BF is 80.00 mm, and spherical aberration, astigmatism, distortion, etc. are sufficiently corrected. As a result, an imaging lens suitable for the recognition camera of the mounting machine was obtained.

  As described above, the imaging lens of the present invention can sufficiently secure a back focus, can be disposed with a reflecting mirror, and can be mounted on an electronic component or the like because it can obtain high optical performance with a small size and low cost. Of course, the present invention is applicable not only to the mounting field but also to other lens optical systems that perform recognition or imaging.

It is a schematic block diagram which shows one Embodiment of the imaging lens which concerns on this invention. FIG. 2 is an optical path diagram of the imaging lens shown in FIG. 1. FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the embodiment of the imaging lens shown in FIG. 1. It is a schematic block diagram which shows other embodiment of the imaging lens which concerns on this invention. FIG. 5 is an optical path diagram of the imaging lens shown in FIG. 4. FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the embodiment of the imaging lens shown in FIG. 4.

Explanation of symbols

1, 1 '1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 Reflector L Optical axis BF Back focus

Claims (4)

Arranged in order from the object side to the image plane side,
A first lens having a negative refractive index and having a concave surface facing the object side;
A meniscus second lens having a positive refractive index and a concave surface facing the object side;
An aperture stop having a predetermined aperture;
A third lens having a positive refractive index;
A meniscus fourth lens having negative refractive power and having a concave surface facing the object side;
An imaging lens comprising: Arranged in order from the object side to the image plane side,
A first lens having a negative refractive index and having a concave surface facing the object side;
A meniscus second lens having a positive refractive index and a concave surface facing the object side;
A third lens having a positive refractive index;
A meniscus fourth lens having negative refractive power and having a concave surface facing the object side;
An aperture stop having a predetermined aperture;
An imaging lens comprising: The first lens is a plano-concave lens having a concave surface on the object side and a flat surface on the image surface side.
The imaging lens according to claim 1 or 2, wherein At least one reflecting mirror is disposed between the fourth lens and the image plane;
The imaging lens according to any one of claims 1 to 3.

Images