JP5020536B2 - Reading lens - Google Patents

Description

  The present invention relates to a reading lens applied to a scanner or the like that reads a sentence or an image using an imaging element such as a CCD (charged coupled device).

Conventionally, a double Gauss type lens has been used as a reading lens suitable for a scanner for reading texts and images. Double Gauss lenses have good image flatness, small distortion, and can be brightened.
The double Gaussian reading lens includes, in order from the object side, a meniscus first lens having a positive refractive power with a convex surface facing the object side, and a meniscus having a positive refractive power with a convex surface facing the object side. A second lens having a shape, a third meniscus lens having a negative refractive power which is cemented to the second lens and has a convex surface facing the object side, an aperture stop, and has a negative refractive power having a concave surface facing the object side A fourth meniscus lens, a fifth meniscus lens that is cemented to the fourth lens and has a positive refractive power with the concave surface facing the object side, and a meniscus shape having a positive refractive power with the concave surface facing the object side A lens having the sixth lens is known (see, for example, Patent Document 1 and Patent Document 2).
However, in these reading lenses, the total angle of view 2ω is about 36 ° to 40 °, and at a wider angle of view, the astigmatic difference becomes large, and the distortion aberration increases, so that text and images are increased. It is difficult to use for reading.

Further, as another double Gauss type reading lens, in order from the object side, a meniscus first lens having a positive refractive power with the convex surface facing the object side, and a positive refractive power with the convex surface facing the object side A second meniscus lens having a negative refractive power with a convex surface facing the object side, an aperture stop, and a fourth meniscus shape having a negative refractive power with a concave surface facing the object side A meniscus fifth lens having a positive refractive power which is cemented to the lens and the fourth lens and has a concave surface facing the object side, and a meniscus sixth lens having a positive refractive power which has the concave surface facing the object side What was provided is known (for example, refer patent document 3).
However, this reading lens is used for general photographic purposes, and although the distortion is not so severe as compared with the above-mentioned reading lens, the total field angle 2ω is used up to about 46 °. It is difficult to use for reading characters and images with a wider angle of view.

JP 2005-292353 A JP-A-11-271612 JP 2001-281535 A

Therefore, in order to cope with the limitation of such a double Gauss type reading lens, a retrofocus type lens in which a concave lens is arranged on the object side can be considered as a countermeasure 1. However, in this embodiment, although it is possible to widen the angle of view, the distortion aberration is inclined to the minus side, which is not suitable for reading applications.
As a countermeasure 2, a configuration in which concave meniscus lenses are arranged on both the object side and the image side is conceivable. In this mode, the angle of view can be widened and distortion can be kept small, but it is difficult to increase the aperture.As a result, a bright lens cannot be obtained, and illumination is limited. It is not suitable for reading applications.

  The present invention has been made in view of the circumstances of the above-described prior art, and an object of the present invention is to satisfy a large angle of view (about 2ω = 55 °) that cannot be covered by a double Gauss type lens arrangement, and various aberrations. In particular, it is an object of the present invention to provide a bright reading lens that can correct distortion well and has an F value (F number) of about 3.5.

The reading lens of the present invention has a meniscus first lens having a positive refractive power and a convex surface facing the object side, which are arranged in order from the object side to the image plane side, and a negative refractive power. A second lens having a meniscus shape having a convex surface facing the object side, a third lens having a positive refractive power and a convex surface facing the object side, and a negative refractive power that is cemented to the third lens. A fourth lens having a concave surface facing the image surface, an aperture stop having a predetermined aperture, a fifth lens having a positive refractive power and a convex surface facing the image surface, and a fifth lens. a sixth lens having a concave surface on the object side has a negative refractive power, a seventh lens of a meniscus shape having a concave surface facing the positive object side has a refractive power, and a, as characterized by Yes.
According to this configuration, the first lens to the fourth lens mainly play a role for obtaining a wide angle of view, and the fifth lens to the seventh lens mainly have a strong refractive power and have spherical aberration, distortion, etc. It has a role to correct various aberrations well.
That is, a wide angle of view is secured by disposing a meniscus second lens behind the first lens, the positive refractive power is weakened by the first lens and the second lens, and the third lens and the fourth lens are By joining and strengthening the positive refractive power, it is possible to prevent the focal length from shifting negatively and increasing distortion aberration to the negative side. In addition, the fifth lens and the sixth lens are joined to increase the positive refractive power of the seventh lens, while reducing spherical aberration and the like generated in the seventh lens.
In this way, the first lens (first lens to fourth lens) has a lens group with weak positive refractive power covering a wide angle of view, and the second lens (fifth lens to seventh lens) has Although a lens group having a strong positive refractive power is arranged and the lens form approximates to a double Gaussian type, it is functionally similar to the retrofocus type. By taking advantage of the wide angle of view, which is a feature of the focus type, it is possible to satisfy a large angle of view (2ω = 55 °), correct various aberrations, particularly distortion, and an F value (F number) of about 3.5. A bright reading lens can be obtained.

In the above configuration, the third lens is a plano-convex lens having a convex surface on the object side and a plane on the image surface side, and the fourth lens is a plano-concave lens having a plane on the object side and a concave surface on the image surface side. A configuration can be employed.
According to this configuration, since the third lens and the fourth lens are cemented with each other, the surface processing becomes easy, the processing cost can be reduced, and the optical axis can be easily aligned.

In the above configuration, the fifth lens may be a plano-convex lens having a plane on the object side and a convex surface on the image plane side.
According to this configuration, the object side surface of the fifth lens can be easily processed, and the processing cost can be reduced.

In the above configuration, the sixth lens can 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, it is easy to process the image side surface of the sixth lens, and the processing cost can be reduced.

In the above configuration, a configuration in which the first lens, the third lens, the fifth lens, and the seventh lens are all formed of the same glass material can be employed.
According to this configuration, the material cost can be reduced by using a common glass material for the four lenses.

In the above configuration, the fourth lens and the sixth lens may be formed of the same glass material.
According to this configuration, the material cost can be reduced by using a common glass material for the two lenses.

  According to the reading lens having the above-described configuration, a large angle of view (about 2ω = 55 °) that cannot be covered by a double Gauss type lens can be secured, and various aberrations, particularly distortion aberrations, can be favorably corrected. Thus, a bright reading lens having an F value (F number) of about 3.5 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 a reading lens according to the present invention. FIG. 1 is a lens configuration diagram, FIG. 2 is an optical path diagram, and FIG. 3 is a lens barrel incorporating a reading lens. It is a partial sectional view shown.

As shown in FIG. 1, the reading lens includes a meniscus first lens 1 having a positive refractive power and a convex surface facing the object side in order from the object side to the image plane side. A second lens 2 having a meniscus shape having a convex surface facing the object side, a third lens 3 having a positive refractive power and a convex surface facing the object side, and a negative refractive power A fourth lens 4 having a concave surface on the image surface side, an aperture stop SD having a predetermined aperture, a fifth lens 5 having a positive refractive power and a convex surface facing the image surface side, and a fifth lens 5 A sixth lens 6 that is cemented and has negative refractive power and has a concave surface facing the object side, and a meniscus seventh lens 7 that has positive refractive power and has the concave surface facing the object side are provided. An image plane P is disposed behind the seventh lens 7.
Although this reading lens approximates a double Gauss type lens arrangement, it is a new form in which the advantages of the double Gauss type and the retrofocus type are combined.

  In addition, when the reading lens is formed as a lens barrel, as shown in FIG. 3, the fourth lens 4 → the lens presser 13 → the second lens from the front (object side) of the cylinder 10 that defines the aperture stop SD. The third lens 3 → the lens presser 12 → the first lens 1 → the lens presser 11 is fitted and fixed in the order, and the sixth lens from the rear (image plane side) of the cylindrical portion 10 that defines the aperture stop SD. 6 → Lens presser 14 → Seventh lens 7 → Lens presser 15 are fitted and fixed in this order.

  Here, in the first lens 1 to the seventh lens 7, as shown in FIG. 1, each surface is Si (i = 1 to 13), and the curvature radius of each surface Si is Ri (i = 1 to 13). ), The refractive index of the first lens 1 to the seventh lens 7 with respect to the d-line is represented by Ni (i = 1 to 7) and the Abbe number is represented by νi (i = 1 to 7). A distance (thickness, air interval) on the optical axis L from the first lens 1 to the image plane P is represented by Di (i = 1 to 13).

The first lens 1 is a meniscus lens having a positive refractive power, which is formed of a glass material and has a convex surface on the object side surface S1 and a concave surface on the image surface side S2 as shown in FIG. The object-side surface S1 and the image-side surface S2 are both formed into spherical surfaces.
As shown in FIG. 1, the second lens 2 is a meniscus lens having negative refractive power in which the object-side surface S3 is convex and the image-side surface S2 is concave. The object-side surface S3 and the image-side surface S4 are both formed as spherical surfaces.

The third lens 3 is made of a glass material, and as shown in FIG. 1, a biconvex lens having a positive refractive power in which the object-side surface S5 is a convex surface and the image-side surface S6 is a convex surface or a flat surface. It is a plano-convex lens. The object-side surface S5 and the image-side surface S6 are both formed into spherical surfaces.
The fourth lens 4 is formed of a glass material, and as shown in FIG. 1, the object side surface S6 is a concave surface or a flat surface and the image surface side surface S7 is a concave surface. It is a plano-concave lens. The object-side surface S6 and the image-side surface S7 are both formed into spherical surfaces. In the fourth lens 4, the object-side surface S <b> 6 is joined to the image-side surface S <b> 6 of the third lens 3.
Here, the image surface side surface S6 of the third lens 3 and the object side surface S6 of the fourth lens 4 are preferably formed to be flat surfaces. In this case, since the third lens 3 and the fourth lens 4 are cemented with each other, the surface can be easily processed, the processing cost can be reduced, and the optical axis can be easily aligned.

The fifth lens 5 is made of a glass material, and as shown in FIG. 1, a meniscus lens having a positive refractive power in which the object-side surface S9 is a concave surface or a flat surface and the image surface-side surface S10 is a convex surface. It is a plano-convex lens. The object-side surface S9 and the image-side surface S10 are both formed as spherical surfaces.
The sixth lens 6 is made of a glass material, and as shown in FIG. 1, a biconcave lens having negative refractive power in which the object-side surface S10 is a concave surface and the image-side surface S11 is a concave surface or a flat surface. It is a plano-concave lens. The object-side surface S10 and the image-side surface S11 are both formed as spherical surfaces. In the sixth lens 6, the object-side surface S <b> 10 is bonded to the image-side surface S <b> 10 of the fifth lens 5.
Here, the object side surface S9 of the fifth lens 5 or the image surface side surface S11 of the sixth lens 6 is preferably formed in a plane. In this case, processing of the object side surface S9 of the fifth lens 5 or the image surface side surface S11 of the sixth lens 6 is facilitated, and processing costs can be reduced.

  The seventh lens 7 is a meniscus lens having a positive refractive power, which is made of a glass material and has a surface S12 on the object side that is concave and a surface S13 on the image side that is convex as shown in FIG. The object-side surface S12 and the image-side surface S13 are both formed into spherical surfaces.

Here, the first lens 1, the third lens 3, the fifth lens 5, and the seventh lens 7 are preferably all made of the same glass material (glass material). In this case, the material cost can be reduced by using a common glass material for the four lenses.
The fourth lens 4 and the sixth lens 6 are preferably formed of the same glass material (glass material). In this case, the material cost can be reduced by using a common glass material for the two lenses.

In the reading lens configured as described above, the first lens 1 to the fourth lens 4 in the first half mainly serve to obtain a wide angle of view, and the fifth lens 5 to the seventh lens 7 in the second half mainly have a strong refractive power. And has a function of satisfactorily correcting various aberrations such as spherical aberration and distortion.
That is, the second lens 2 having a meniscus shape is disposed behind the first lens 1 to ensure a wide angle of view, the first lens 1 and the second lens 2 have a weak positive refractive power, and the third lens 3 In addition, the fourth lens 4 is joined to increase the positive refractive power, thereby preventing the focal length from shifting negatively and increasing distortion aberration to the negative side.
Further, the fifth lens 5 and the sixth lens 6 are joined to increase the positive refractive power of the seventh lens 7 while reducing the spherical aberration generated in the seventh lens 7.

As described above, a lens group having a weak positive refractive power covering a wide angle of view is arranged in the first half lens (first lens 1 to fourth lens 4), and the latter half lens (fifth lens 5th to fifth lens). 7 lens 7), a lens group having a strong positive refractive power is arranged, so that the lens form is similar to a double Gauss type, but is functionally similar to a retrofocus type, and a double Gauss type It is formed so as to take advantage of the symmetry that is the feature of the lens and the wide angle of view that is the feature of the retrofocus type.
As a result, a large angle of view (approximately 2ω = 55 °) that cannot be covered by conventional double Gauss lenses can be secured, and various aberrations such as spherical aberration, astigmatism, distortion, and particularly distortion can be corrected well. In addition, a bright reading lens having an F value (F number) of about 3.5 can be obtained.

  Next, specific numerical examples of the reading lens will be described below as Example 1, Example 2, and Example 3.

  The main specification specifications and values of various numerical data (setting values) in Example 1 are as follows. In addition, the aberration diagrams relating to spherical aberration, astigmatism, and distortion in Example 1 are the results shown in FIG. In the astigmatism in FIG. 4, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.

<Specification specifications>
Use wavelength 1 (main wavelength) = 546.1 nm, use wavelength 2 = 656.3 nm, use wavelength 3 = 435.8 nm, focal length = 25.0 mm, angle of view (2ω) = 55 °, outside the first lens 1 Diameter dimension φ1 = 17 mm, second lens 2 outer diameter dimension φ2 = 15 mm, third lens 3 outer diameter dimension φ3 = 11 mm, fourth lens 4 outer diameter dimension φ4 = 11 mm, fifth lens 5 outer diameter dimension φ5 = 9.5 mm, outer diameter size of the sixth lens 6 φ6 = 10 mm, outer diameter size of the seventh lens 7 φ7 = 15 mm, aperture diameter φ = 5.7 mm, F value (F number) = 3.3, conjugate Length = 204 mm, shooting magnification = 0.1652

<Curvature radius Ri of first lens 1 to seventh lens 7>
R1 = 16.880 mm, R2 = 31.190 mm, R3 = 16.900 mm, R4 = 6.977 mm, R5 = 8.711 mm, R6 = -123.800 mm, R7 = 7.923 mm, R8 = ∞ (aperture stop) , R9 = −254.700 mm, R10 = −6.693 mm, R11 = 159.700 mm, R12 = −41.610 mm, R13 = −15.020 mm

<Surface spacing on the optical axis>
D1 = 1.96 mm, D2 = 0.15 mm, D3 = 1.00 mm, D4 = 0.90 mm, D5 = 3.00 mm, D6 = 1.00 mm, D7 = 2.25 mm, D8 = 2.25 mm, D9 = 3.00 mm, D10 = 1.00 mm, D11 = 2.62 mm, D12 = 2.28 mm, D13 = 20.93 mm

<Refractive index Ni (d line) of the first lens 1 to the seventh lens 7>
N1 = 1.77250, N2 = 1.51633, N3 = 1.77250, N4 = 1.62004, N5 = 1.77250, N6 = 1.62004, N7 = 1.77250
<Abbe number νi of the first lens 7 to the seventh lens 7>
ν1 = 49.6, ν2 = 64.1, ν3 = 49.6, ν4 = 36.3, ν5 = 49.6, ν6 = 36.3, ν7 = 49.6

  In the first embodiment, the angle of view 2ω is 55 °, the F number (F number) is 3.3, and various aberrations, particularly distortion, are corrected well as shown in FIG. A lens was obtained.

  The main specifications and the values of various numerical data (setting values) in Example 2 are as follows. In addition, FIG. 5 shows aberration diagrams regarding spherical aberration, astigmatism, and distortion in Example 2. In the astigmatism shown in FIG. 5, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.

<Specification specifications>
Use wavelength 1 (main wavelength) = 546.1 nm, use wavelength 2 = 656.3 nm, use wavelength 3 = 435.8 nm, focal length = 25.1 mm, angle of view (2ω) = 55 °, outside the first lens 1 Diameter dimension φ1 = 17 mm, second lens 2 outer diameter dimension φ2 = 15 mm, third lens 3 outer diameter dimension φ3 = 11 mm, fourth lens 4 outer diameter dimension φ4 = 11 mm, fifth lens 5 outer diameter dimension φ5 = 9.5 mm, outer diameter size of the sixth lens 6 φ6 = 10 mm, outer diameter size of the seventh lens 7 φ15 = 15 mm, aperture diameter φ = 5.6 mm, F value (F number) = 3.4, conjugate Length = 204.6 mm, shooting magnification = 0.1652

<Curvature radius Ri of first lens 1 to seventh lens 7>
R1 = 16.980 mm, R2 = 34.130 mm, R3 = 18.780 mm, R4 = 6.956 mm, R5 = 8.601 mm, R6 = -151.400 mm, R7 = 7.955 mm, R8 = ∞ (aperture stop) , R9 = ∞ (plane), R10 = −6.579 mm, R11 = 77.880 mm, R12 = −53.800 mm, R13 = −15.730 mm

<Surface spacing on the optical axis (mm)>
D1 = 2.14 mm, D2 = 0.15 mm, D3 = 1.00 mm, D4 = 0.76 mm, D5 = 3.07 mm, D6 = 1.00 mm, D7 = 2.11 mm, D8 = 2.11 mm, D9 = 3.16 mm, D10 = 1.00 mm, D11 = 2.27 mm, D12 = 2.65 mm, D13 = 2.36 mm

<Refractive index Ni (d line) of the first lens 1 to the seventh lens 7>
N1 = 1.77250, N2 = 1.51633, N3 = 1.77250, N4 = 1.62004, N5 = 1.77250, N6 = 1.62004, N7 = 1.77250
<Abbe number νi of the first lens 7 to the seventh lens 7>
ν1 = 49.6, ν2 = 64.1, ν3 = 49.6, ν4 = 36.3, ν5 = 49.6, ν6 = 36.3, ν7 = 49.6

  In the second embodiment, the angle of view 2ω is 55 °, the F number (F number) is 3.4, and various aberrations, particularly distortion, are corrected well as shown in FIG. A lens was obtained.

  The main specification specifications and values of various numerical data (setting values) in Example 3 are as follows. In addition, aberration diagrams relating to spherical aberration, astigmatism, and distortion in Example 3 are the results shown in FIG. In the astigmatism 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) = 546.1 nm, use wavelength 2 = 656.3 nm, use wavelength 3 = 435.8 nm, focal length = 25.0 mm, angle of view (2ω) = 55 °, outside the first lens 1 Diameter dimension φ1 = 17 mm, second lens 2 outer diameter dimension φ2 = 15 mm, third lens 3 outer diameter dimension φ3 = 11 mm, fourth lens 4 outer diameter dimension φ4 = 11 mm, fifth lens 5 outer diameter dimension φ5 = 9.5 mm, outer diameter dimension of the sixth lens 6 φ6 = 10 mm, outer diameter dimension of the seventh lens 7 φ7 = 15 mm, aperture diameter φ = 5.6 mm, F value (F number) = 3.3, conjugate Length = 204.6 mm, shooting magnification = 0.1652

<Curvature radius Ri of first lens 1 to seventh lens 7>
R1 = 18.270 mm, R2 = 37.450 mm, R3 = 18.630 mm, R4 = 7.230 mm, R5 = 8.754 mm, R6 = ∞ (plane), R7 = 8.269 mm, R8 = ∞ (aperture stop) , R9 = −179.200 mm, R10 = −7.874 mm, R11 = ∞ (plane), R12 = −34.020 mm, R13 = −14.580 mm

<Surface spacing on the optical axis>
D1 = 2.20 mm, D2 = 0.15 mm, D3 = 1.00 mm, D4 = 0.77 mm, D5 = 3.19 mm, D6 = 1.00 mm, D7 = 2.52 mm, D8 = 2.52 mm, D9 = 3.67 mm, D10 = 1.00 mm, D11 = 1.39 mm, D12 = 2.20 mm, D13 = 20.72 mm

<Refractive index Ni (d line) of the first lens 1 to the seventh lens 7>
N1 = 1.80400, N2 = 1.51742, N3 = 1.80400, N4 = 1.66680, N5 = 1.80400, N6 = 1.64769, N7 = 1.80400
<Abbe number νi of the first lens 7 to the seventh lens 7>
ν1 = 46.6, ν2 = 52.4, ν3 = 46.6, ν4 = 33.0, ν5 = 46.6, ν6 = 33.8, ν7 = 46.6

  In the third embodiment, the angle of view 2ω is 55 °, the F number (F number) is 3.3, and various aberrations, particularly distortion, are corrected well as shown in FIG. A lens was obtained.

  As described above, the reading lens of the present invention secures a large angle of view (about 2ω = 55 °) that cannot be covered by a double Gauss type lens, corrects various aberrations, particularly distortion aberration, etc., and provides an F value ( (F number) is as bright as about 3.5, so it can be applied as a reading lens for scanners that read texts and images, and it is necessary to read characters and images under limited lighting conditions. It is also useful in lens optical equipment.

It is a block diagram which shows one Embodiment of the reading lens which concerns on this invention. FIG. 2 is an optical path diagram of the reading lens shown in FIG. 1. It is a partial cross section figure which shows the lens barrel incorporating the reading lens shown in FIG. FIG. 6 is an aberration diagram showing various aberrations of spherical aberration, astigmatism, and distortion in the reading lens in Example 1. FIG. 6 is an aberration diagram showing various aberrations of spherical aberration, astigmatism, and distortion in the reading lens in Example 2. FIG. 6 is an aberration diagram showing various aberrations of spherical aberration, astigmatism, and distortion in the reading lens in Example 3.

Explanation of symbols

L Optical axis P Image surface SD Aperture stop 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 7th lens

Claims (6)

Are arranged in order from the object side to the image plane side,
A first meniscus lens having positive refractive power and having a convex surface facing the object side;
A meniscus second lens having negative refractive power and having a convex surface facing the object side;
A third lens having positive refractive power and having a convex surface facing the object side;
A fourth lens that is cemented to the third lens and has a negative refractive power and has a concave surface directed toward the image plane;
An aperture stop having a predetermined aperture;
A fifth lens having positive refractive power and having a convex surface facing the image surface side;
A sixth lens which is cemented to the fifth lens and has a negative refractive power and has a concave surface directed toward the object side;
A meniscus seventh lens having positive refractive power and having a concave surface facing the object side;
Constituted by a lens the reading, characterized in that. The third lens is a planoconvex lens having a convex surface on the object side and a flat surface on the image surface side,
The fourth lens is a plano-concave lens having a plane on the object side and a concave surface on the image side.
The reading lens according to claim 1. The fifth lens is a plano-convex lens having a plane on the object side and a convex surface on the image plane side.
The reading lens according to claim 1, wherein: The sixth lens is a plano-concave lens having a concave surface on the object side and a flat surface on the image surface side.
The reading lens according to claim 1, wherein the reading lens is a reading lens. The first lens, the third lens, the fifth lens, and the seventh lens are all formed of the same glass material.
The reading lens according to claim 1, wherein the lens is a reading lens. The fourth lens and the sixth lens are formed of the same glass material.
The reading lens according to claim 1, wherein the lens is a reading lens.

Images