JP2008058387A - Superwide-angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact superwide-angle lens which has a large angle of view, is bright and is suitable for a 1/4 CCD. <P>SOLUTION: The superwide-angle lens having a five-group six-lens configuration comprises, in order from an object side to an image surface side: a meniscus-shaped first lens 1 which has a negative refractive power and whose convex faces the object side; a meniscus-shaped second lens 2 which has a negative refractive power and whose convex faces the object side; a third lens 3 which has a positive refractive power; an aperture diaphragm SD which has a predetermined aperture; a fourth lens 4 which has a positive refractive power and whose both surfaces are convex; a meniscus-shaped fifth lens which has a negative refractive power, whose concave faces the object side and which is cemented to the fourth lens 4; and a meniscus-shaped sixth lens 6 which has a negative refractive power and whose convex faces the object side. Thus, the superwide-angle lens which has an angle of view of about 220 degrees and is bright because the F-number is about 2.0, short because the lens entire length is about 20 mm, compact, high in optical performance, and suitable for the 1/4 CCD, etc. is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a small super-wide-angle lens used in an electronic imaging system such as a digital camera using a solid-state imaging device such as a CCD, and in particular, a lens system such as an in-vehicle camera and a surveillance camera using a 1/4 CCD. The present invention relates to a retrofocus type super-wide-angle lens having a wide angle of 220 ° or more applied to the diagonal.

In recent years, with the widespread use of digital cameras, there is an increasing demand for high performance, low cost, and compactness regarding lenses used in electronic photographing apparatuses. For example, many lens configurations that satisfy a wide angle, high performance, low cost, and compactness adopt a retrofocus type in which an emission angle is reduced while sufficiently ensuring a back focus.
In general, lenses used for surveillance cameras and in-vehicle cameras are required to be lightweight, compact and have a large angle of view. Especially for applications such as in-vehicle cameras, in order to cover a wide field of view. It is desired to be a super wide angle lens having a large angle of view.

As a conventional super-wide-angle lens, a first meniscus lens having a concave surface facing the image surface side, a second meniscus lens having a concave surface facing the image surface side, and a biconcave lens array arranged in order from the object side A third lens, a biconvex fourth lens, a plano-concave fifth lens having a concave surface facing the image surface side, a biconvex sixth lens cemented to the fifth lens, and a convex surface facing the object side A lens having a plano-convex seventh lens and having an angle of view of 230 degrees is known (for example, see Patent Document 1).
However, this super wide-angle lens has a wide field of view, but the back focus is very short. As an imaging medium that is applied together with this super wide-angle lens, a special image sensor that can handle short back focus is used. In addition, since it is composed of seven lenses, it cannot sufficiently meet the demand for downsizing (thinning).

As another ultra-wide-angle lens, a meniscus first lens arranged in order from the object side and having a concave surface facing the image surface side, a biconcave shape near the center of the optical axis and an image near the outer peripheral edge Bonded to a second lens having an aspherical surface with a concave surface facing the surface, a third lens with a meniscus shape with a concave surface facing the object side, a fourth lens with a concave surface facing the image surface side, and a fourth lens A biconvex fifth lens, a meniscus sixth lens having a concave surface facing the image plane, and a biconvex seventh lens cemented to the sixth lens, and an angle of view of 120 to 140 degrees. Is known (see, for example, Patent Document 2).
However, in this super-wide-angle lens, an aspherical surface is provided for a resin lens formed using a resin material, so the cost can be reduced by using a resin, but it can be used in a high-temperature environment such as an in-vehicle camera. In this case, stable optical characteristics cannot be ensured due to the influence of temperature. In addition, this super wide-angle lens also has a seven-lens configuration and cannot sufficiently meet the demand for downsizing (thinning).

JP 2005-345577 A JP-A-10-115778

By the way, in order to secure a large angle of view of about 220 °, it is necessary to arrange a strong divergence system on the object side, which tends to cause performance deterioration due to image plane distortion and astigmatism. In addition, the retrofocus type generally tends to increase the outer diameter of the negative lens in the front group, leading to an increase in size and weight of the super wide-angle lens.
In addition, in order to shorten the overall length of the lens and reduce the size, it is necessary to bend the light beam by reducing the radius of curvature (increasing the curvature) and bringing it closer to a hemispherical shape. As a result, the cost increases.
Furthermore, in an environment where a temperature change is severe as a place where an ultra-wide angle lens is used, a plastic lens formed using a resin material is not preferable because the optical characteristics are not stable.

  The present invention has been made in view of the above circumstances, and its object is to have an angle of view (2ω) of 220 degrees or more, an F-number as bright as about 2.0, and a total lens length of about 20 mm. Another object of the present invention is to provide an ultra-wide-angle lens that is small and has high optical performance and is suitable for use in a 1/4 CCD.

The super wide-angle lens of the present invention includes a first meniscus lens having a negative refractive power and a convex surface facing the object side, which is arranged in order from the object side to the image plane side, and has a negative refractive power. A second meniscus lens having a convex surface facing the object side, a third lens having a positive refractive power, an aperture stop having a predetermined aperture, and a fourth lens having a positive refractive power on both sides. A fifth meniscus lens having negative refractive power and having a concave surface directed toward the object side and bonded to the fourth lens, and a sixth meniscus shape having negative refractive power and having a convex surface directed toward the object side It is characterized by the lens.
According to this configuration, by making the first lens and the second lens into a meniscus shape, it is possible to suddenly bend a light beam and capture a light beam having an angle of view of about 220 °. In addition, by using a negative, negative, positive, positive, negative, and negative six-lens configuration, the F-number is as bright as about 2.0, the total lens length is as short as about 20 mm, and it has a small size and high optical performance. Therefore, it is possible to obtain a super wide angle lens suitable for a 1/4 CCD.

In the above configuration, when the refractive index of the first lens is N1 and the refractive index of the second lens is N2, the following conditional expressions (1), (2),
(1) N1> 1.8
(2) N2> 1.8
A configuration that satisfies the above can be adopted.
According to this configuration, when the first lens and the second lens satisfy the conditional expressions (1) and (2), a high refractive index can be set. As a result, the radius of curvature of the lens surface can be relaxed, It is possible to prevent problems such as manufacturing yield or processing defects.

In the above configuration, when the refractive index of the fourth lens is N4 and the Abbe number is ν4, the refractive index of the fifth lens is N5 and the Abbe number is ν5, the following conditional expressions (3), (4),
(3) N4 <N5
(4) ν4> ν5
A configuration that satisfies the above can be adopted.
According to this configuration, the fourth lens and the fifth lens are in the relations of the conditional expressions (3) and (4), that is, the refractive index of the fourth lens is smaller than the refractive index of the fifth lens. By satisfying the relationship in which the number is larger than the Abbe number of the fifth lens, chromatic aberration can be corrected well, and high optical performance can be obtained.

In the above configuration, the first lens to the sixth lens can be formed of a glass material, and all surfaces can be formed as spherical surfaces.
According to this configuration, stable optical performance can be obtained even when used in severe temperature environments that reach high temperatures such as in-vehicle cameras, and the cost can be reduced by using only spherical surfaces. Can do.

In the above configuration, when the radius of curvature of the image side surface of the first lens is R2 and the focal length is f, the following conditional expression (5):
(5) R2 / f <3.4
A configuration that satisfies the above can be adopted.
According to this configuration, the first meniscus lens having the concave surface facing the image surface side satisfies the conditional expression (5), thereby ensuring a large field angle of about 220 degrees and a large outer diameter of the lens. As a whole, downsizing can be achieved.

  According to the super wide-angle lens having the above-described configuration, the F-number has a brightness of about (FNo =) 2.0 while securing a field angle of about 220 degrees, and the number of lenses is reduced without using an aspherical surface. Therefore, it is possible to achieve a reduction in cost and to obtain a small super-wide-angle lens with high optical performance.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 and 2 show an embodiment of an ultra-wide angle lens according to the present invention. FIG. 1 is a configuration diagram of the lens, and FIG. 2 is an optical path diagram of the ultra-wide angle lens shown in FIG.
This super wide-angle lens is a meniscus first lens 1 having a negative refractive power and a convex surface facing the object side, arranged in order from the object side to the image plane side, and an object having a negative refractive power. A meniscus second lens 2 with a convex surface facing side, a third lens 3 having a positive refractive power, an aperture stop SD having a predetermined aperture, and a fourth lens 4 having a positive refractive power and convex on both sides. A fifth meniscus lens 5 having negative refractive power and having a concave surface facing the object side and being joined to the fourth lens 4, and a meniscus sixth lens having negative refractive power and having a convex surface facing the object side The lens is formed so as to form five groups and six elements.
A glass filter (not shown) such as an infrared cut filter or a low-pass filter is disposed behind the sixth lens, and an imaging plane P of an image sensor such as a CCD is disposed behind the glass filter.

  Here, in a configuration in which the first lens 1 to the third lens 3, the aperture stop SD, the fourth lens 4 to the sixth lens 6, and the image plane P are arranged in order from the object side along the optical axis L, FIG. As shown in FIG. 4, each surface is Si (i = 1 to 12), the radius of curvature of each surface Si is Ri (i = 1 to 12), the refractive index of the i-th lens with respect to the d-line is Ni and the Abbe number is It represents by νi (i = 1 to 6). Further, the distance (thickness, air distance) in the optical axis L direction from the first lens 1 to the image plane P is represented by Di (i = 1 to 12) as shown in FIG.

The first lens 1 is a meniscus lens that is formed of a glass material and has a negative refractive power, the object-side surface S1 is convex and the image-side surface S2 is concave. Here, both the surfaces S1 and S2 are formed into spherical surfaces.
The second lens 2 is a meniscus lens that is formed of a glass material and has a negative refractive power, the object-side surface S3 is convex and the image-side surface S4 is concave. Here, both surfaces S3 and S4 are formed into spherical surfaces.
As described above, the first lens 1 and the second lens 2 are formed in a meniscus shape having a convex surface facing the object side, thereby making it possible to suddenly bend the light beam and capture a light beam having an angle of view of about 220 °. ing.

The third lens 3 is made of a glass material and has a biconvex shape or meniscus shape in which the object-side surface S5 is convex and the image-side surface S6 is convex or concave so as to have positive refractive power. The lens. Here, both surfaces S5 and S6 are formed into spherical surfaces.
The fourth lens 4 is a biconvex lens that is formed of a glass material and has a convex surface on the object side S8 and a convex surface S9 on the image side so as to have a positive refractive power. Here, both surfaces S8 and S9 are formed into spherical surfaces.
The fifth lens 5 is a meniscus lens that is formed of a glass material and has a negative refractive power. The surface S9 on the object side is concave and the surface S10 on the image side is convex. It is joined to the lens 4. Here, both surfaces S9 and S10 are formed into spherical surfaces.
The sixth lens 6 is a meniscus lens that is formed of a glass material and has a negative refractive power, the object-side surface S11 is convex and the image-side surface S12 is concave. Here, both the surfaces S11 and S12 are formed into spherical surfaces.

  As described above, the meniscus first lens 1 and the second lens 2 having negative refractive power, the third lens 3 having positive refractive power, the biconvex fourth lens 4 having positive refractive power, The F-number is configured by a five-group six-lens configuration including a meniscus fifth lens having negative refractive power and cemented to a fourth lens, and a meniscus sixth lens having negative refractive power. Is as bright as about 2.0, the total length of the lens is as short as about 20 mm, has a small and high optical performance, and can be obtained as a super wide-angle lens suitable for a 1/4 CCD or the like.

In addition, as described above, the first lens 1 to the sixth lens 6 are all made of glass material, and all surfaces are formed into spherical surfaces. Even when used in the above, stable optical performance can be obtained, and the cost can be reduced by using only a spherical surface.
In addition, if it is not used under such a severe temperature environment and cost reduction is not required so much, a resin material is used as the first lens 1 to the sixth lens 6, and an aspherical surface is appropriately adopted to further optically The performance may be improved.

In the above configuration, the refractive index N1 of the first lens 1 and the refractive index N2 of the second lens 2 are preferably the following conditional expressions (1), (2),
(1) N1> 1.8
(2) N2> 1.8
It is formed so as to satisfy.
Conditional expressions (1) and (2) define the refractive indexes of the first lens 1 and the second lens 2, and are set to a high refractive index by satisfying the conditional expressions (1) and (2). As a result, the radius of curvature of the lens surface can be relaxed, and problems such as manufacturing yield or processing defects can be prevented from occurring.

In the above configuration, the refractive index N4 and Abbe number ν4 of the fourth lens 4 and the refractive index N5 and Abbe number ν5 of the fifth lens 5 are preferably the following conditional expressions (3), (4),
(3) N4 <N5
(4) ν4> ν5
It is formed so as to satisfy.
Conditional expression (4) defines the relationship between the refractive indexes of the fourth lens 4 and the fifth lens 5, and conditional expression (5) defines the relationship between the Abbe numbers of the fourth lens 4 and the fifth lens 5. It is.
That is, the relationship between the fourth lens 4 and the fifth lens 5 in the conditional expressions (3) and (4), that is, the refractive index N4 of the fourth lens 4 is smaller than the refractive index N5 of the fifth lens 5, and the fourth lens. By satisfying the relationship that the Abbe number ν4 of 4 is larger than the Abbe number ν5 of the fifth lens 5, chromatic aberration can be corrected well, and high optical performance can be obtained.

Furthermore, in the above configuration, the curvature radius R2 and the focal length f of the surface S2 on the image plane side of the first lens 1 are preferably set to the following conditional expression (5):
(5) R2 / f <3.4
It is formed so as to satisfy.
Conditional expression (5) defines the ratio of the radius of curvature of the image plane side surface of the first lens to the focal length of the lens system, and the meniscus-shaped first lens 1 with the concave surface S2 facing the image plane side is defined as follows. By satisfying conditional expression (5), while ensuring a large angle of view (2ω) of about 220 degrees, it is possible to suppress the increase in the outer diameter of the first lens 1 and reduce the overall size. can do.
Next, specific numerical examples of the super wide-angle lens will be described below.

Numerical data of conditional expressions (1) to (5) in the examples, main specifications of the first lens 6 to the sixth lens 6, and various numerical data (setting values) are as follows.
<Value of conditional expression>
(1) N1> 1.8 = 1.83400> 1.8
(2) N2> 1.8 = 1.83400> 1.8
(3) N4 <N5 = 1.77250 <1.84666
(4) ν4> ν5 = 49.6> 23.8
(5) R2 / f <3.4 = 5.5000 / 1.63 <3.4 → 3.37 <3.4

<Specification specifications>
Use wavelength = 436 nm, 486 nm, 546 nm, 588 nm, 656 nm, focal length of lens system = 1.63 mm, imaging range = φ4.6 mm, aperture aperture SD aperture = φ2.14 mm, F number (FNo) = 2.0, Conjugate length (object to image plane) = ∞, angle of view (2ω) = 220 °, back focus = 2.50 mm, total lens length = 20.05 mm, outer diameter of first lens 1 = φ16 mm, second lens 2 Outer diameter dimension = φ10 mm, third lens 3 outer diameter dimension = φ5 mm, fourth lens 4 outer diameter dimension = φ4 mm, fifth lens 5 outer diameter dimension = φ4 mm, sixth lens 6 outer diameter dimension = φ5 mm

<Curvature radius>
R1 = 13.7500 mm, R2 = 5.5000 mm, R3 = 18.8930 mm, R4 = 2.8390 mm, R5 = 5.7477 mm, R6 = 1633.6910 mm, R7 (aperture stop SD) = ∞, R8 = 5.4667 mm , R9 = −1.7345 mm, R10 = −12.0080 mm, R11 = 5.0175 mm, R12 = 9.9711 mm

<Spacing on the optical axis>
D1 = 1.03 mm, D2 = 2.50 mm, D3 = 1.02 mm, D4 = 3.50 mm, D5 = 2.29 mm, D6 = 2.47 mm, D7 = 0.20 mm, D8 = 1.79 mm, D9 = 1.00mm, D10 = 0.10mm, D11 = 1.64mm, D12 = 2.50mm

<Refractive index (Nd)>
N1 = 1.83400, N2 = 1.83400, N3 = 1.84666, N4 = 1.77250, N5 = 1.84666, N6 = 1.77250
<Abbe number (νd)>
ν1 = 37.2, ν2 = 37.2, ν3 = 23.8, ν4 = 49.6, ν5 = 23.8, ν6 = 49.6

The spherical aberration, astigmatism, and distortion in the above example 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.
According to this embodiment, the angle of view (2ω) is 220 °, the F-number is 2.0, the total lens length is 20.05 mm, the back focus is 2.50 mm, a large angle of view, a small size, and various aberrations are good. Thus, an ultra-wide-angle lens suitable for use in a 1/4 CCD or the like having a stable and high optical characteristic that is corrected by the above-mentioned and not affected by temperature can be obtained.

  As described above, the super wide-angle lens of the present invention has a field of view of about 220 degrees and has a brightness of F number (FNo =) of about 2.0, low cost, and stable high optics. Since it has performance, it can be applied as a lens system for a vehicle-mounted camera, a surveillance camera, and the like, and is also useful in other electronic imaging devices such as a digital still camera and a digital video camera.

It is a lens block diagram which shows one Embodiment of the super wide-angle lens which concerns on this invention. FIG. 2 is an optical path diagram of the super wide angle lens shown in FIG. 1. FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens P Image surface L Optical axis f Focal length N1 Refractive index N2 of 1st lens Refractive index N4 of 2nd lens 4th Refractive index of lens N5 Refractive index of fifth lens ν4 Abbe number of fourth lens ν5 Abbe number of second lens R2 Radius of curvature of image side surface of first lens

Claims (5)

Arranged in order from the object side to the image plane side,
A meniscus first lens having negative 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;
An aperture stop having a predetermined aperture;
A fourth lens having positive refractive power and convex on both sides;
A meniscus fifth lens having negative refractive power and having a concave surface directed toward the object side and joined to the fourth lens;
A sixth meniscus lens having negative refractive power and having a convex surface facing the object side;
An ultra-wide-angle lens characterized by comprising: When the refractive index of the first lens is N1 and the refractive index of the second lens is N2, the following conditional expressions (1), (2),
(1) N1> 1.8
(2) N2> 1.8
The super-wide-angle lens according to claim 1, wherein: When the refractive index of the fourth lens is N4 and the Abbe number is ν4, the refractive index of the fifth lens is N5 and the Abbe number is ν5, the following conditional expressions (3), (4),
(3) N4 <N5
(4) ν4> ν5
The super-wide-angle lens according to claim 1, wherein: The first lens to the sixth lens are all formed of a glass material, and all surfaces are formed into spherical surfaces.
The super-wide-angle lens according to any one of claims 1 to 3. When the radius of curvature of the image side surface of the first lens is R2 and the focal length is f, the following conditional expression (5):
(5) R2 / f <3.4
The super wide-angle lens according to claim 1, wherein:

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