JP2003232998A - Wide angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide angle lens applicable to a compact photographing machine such as a CCD camera having high image quality, made small in size and light in weight, produced at a low cost, made bright and having a long exit pupil. <P>SOLUTION: The wide angle lens 100 is constituted of a 1st group lens 10 having negative power and a 2nd group lens 20 having positive power arranged in order from an object side, the 2nd group lens is equipped with a front group lens 30 on the object side and a rear group lens 40 on an image surface side while putting a diaphragm 5 in between. Three lenses 12, 2 and 4 are plastics lenses, and their four lens surfaces are aspherical, and a part of the rear group lens is an achromatic glass lens 50. When it is defined that the focal distance of the 1st group lens is F1, the focal distance of the 2nd group lens is F2, the focal distance of the front group lens is fM, the focal distance of the rear group lens is fR, the focal distance of the achromatic glass lens group is fR1, the focal distance of the lens group 60 is fR2 and the Abbe number of the front group lens is νdM, they satisfy following conditional expressions. (1) 1.6<fR1/fR2<3.7, (2) 1.2<fM/fR<2.2, (3) 0.5<|F1/F2|<1.2 and (4) νdM≤45. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to CCDs and CMOSs.
The present invention relates to a compact and lightweight wide-angle lens having a long rear focal length, which is compatible with high image quality and is used for a vehicle-mounted camera, a camera mounted with a mobile phone, etc.

[0002]

2. Description of the Related Art Recently, there is a demand for an ultra-wide-angle lens which is compact and has an image capturing angle of more than 100 degrees in the horizontal direction in a rear view confirmation camera or a surveillance camera of an automobile or the like. CCDs and CMOSs are mostly used for the light receiving elements of small cameras using such wide-angle lenses. A feature of these light receiving elements is that there is a restriction on the angle of light rays that can be captured by each pixel. A camera incorporating an optical system that ignores this property sharply reduces the amount of peripheral light, resulting in a so-called dark peripheral camera.

In order to correct such a phenomenon, a method of incorporating an electrical correction circuit (shading correction circuit) is generally adopted. However, in this method, the circuit board becomes large and does not meet the demand for miniaturization and compactness. As a method other than the electrical correction, a method of arranging a microlens forming a pair with the light receiving element to expand the light receiving angle to the element surface has also been proposed. However, this method causes a significant increase in cost and is not practical.

Therefore, in recent years, attempts have generally been made to solve the above problems by using a lens system. For example, the performance is adjusted by using a large number of spherical lenses to realize a lens with a long exit pupil. Further, for the purpose of downsizing and weight reduction, a proposal using two aspherical lenses including a concave aspherical lens and a convex aspherical lens arranged in order from the object side has been made.

[0005]

However, in order to realize a high-performance wide-angle lens with a long exit pupil by using a large number of spherical lenses, not only the total cost of the lens optical system becomes extremely high, but also the size of the lens becomes large. It will not be put to practical use because it will become.

Further, in a method using two aspherical lenses, a concave lens and a convex lens, for the purpose of downsizing and weight reduction, not only is it difficult to obtain a long exit pupil, but it is also difficult to suppress chromatic aberration of magnification. As a result, there are naturally limits to their use.

As described above, in any of these types of wide-angle lenses, it is possible to realize a reduction in size and weight and a reduction in cost, suppress chromatic aberration of magnification, and simultaneously satisfy the requirements for obtaining a long exit pupil. It's extremely difficult.

Therefore, an object of the present invention is to propose a super-wide-angle lens which can realize reduction in size and weight and cost, can sufficiently correct aberrations in a high wavelength band, and has a long exit pupil. Especially.

[0009]

In order to solve the above-mentioned problems, the wide-angle lens of the present invention comprises a first lens group having negative power and a second lens group having positive power, which are arranged in order from the object side. And the second group lens sandwiches a diaphragm,
It comprises a front lens group arranged on the object side and a rear lens group arranged on the image side, wherein the rear lens group is
A glass lens group including at least one glass lens for achromatism arranged on the diaphragm side is provided.

At least three lenses of the lens group constituting the entire lens system are preferably plastic lenses.

Further, among the lens surfaces of these three lenses, at least four surfaces are aspherical surfaces, a lens having a small Abbe number is used as the front lens group, and achromatic correction is performed by the glass lens group. There is.

With this structure, it is possible to realize a super wide-angle lens with a long exit pupil for high image quality, which can correct chromatic aberration of magnification including the near-infrared region, which is originally difficult to correct, and can realize various excellent aberration corrections. it can.

More specifically, in the wide-angle lens of the present invention, the focal length of the first lens group is F1, the focal length of the second lens group is F2, and the front lens group on the front side of the second lens group through a diaphragm. The focal length of the lens is fM, the focal length of the rear group lens is fR, the focal length of the glass lens group for achromatism arranged on the diaphragm side of the rear group lens is fR1,
The focal length of the image side lens unit of the rear lens unit is fR
2. When the Abbe number of the front lens group is νdM, the following conditional expressions (1), (2), (3) and (4) are satisfied. 1.6 <fR1 / fR2 <3.7 (1) 1.2 <fM / fR <2.2 (2) 0.5 <| F1 / F2 | <1.2 (3) νdM ≦ 45 (4)

The conditional expression (1) relates to the chromatic aberration and the exit pupil, and if the upper limit of 3.7 is exceeded, the exit pupil can be lengthened, but the power of the final lens group on the image side of the rear lens group. Becomes stronger, and it becomes difficult to correct each aberration, and at the same time, it becomes impossible to keep the on-axis and off-axis chromatic aberration excellent. If the lower limit value of 1.6 is not reached, the distance of the exit pupil becomes short, the angle at which the image plane is taken into the peripheral portion with respect to the light receiving element increases, and the amount of peripheral light decreases. As a result, even if the electric correction circuit (shading correction circuit) is adjusted to correct such a phenomenon, the circuit board becomes large, which does not meet the demand for compactness. It will be a factor of up. In addition, it is difficult to correct off-axis chromatic aberration and astigmatism, and it is difficult to stabilize the performance of the entire lens system.

Conditional expression (2) relates to on-axis and off-axis chromatic aberrations. If the upper limit value of 2.2 is exceeded, the power of the front lens group becomes weak and it is difficult to correct chromatic aberration of off-axis magnification. In addition, in order to keep the chromatic aberration on the axis good at the same time, it is necessary to reduce the chromatic aberration correction value of the achromatic lens arranged immediately after the aperture. Therefore, for each wavelength (λ = 4
(00 to 900 nm) becomes difficult to match the ideal image plane position. If the lower limit value of 1.2 is not reached, the power of the front lens group becomes strong, which makes it difficult to correct each aberration, and at the same time, the radius of curvature of each lens becomes extremely small, which causes processing restrictions. It cannot keep good performance. In addition, each wavelength (400
(To 900 nm) to an ideal image plane position, and it is difficult to satisfy axial chromatic aberration and lateral chromatic aberration at the same time.

Conditional expression (3) shows the degree of influence of the size of the lens system on the lens performance. When the upper limit of 1.2 is exceeded, the power of each lens group becomes weak, and the lens production Although the performance is improved, the size of the entire lens system becomes large, and at the same time, of the off-axis aberrations, the performance in the sagittal direction deteriorates. If the lower limit value of 0.5 is not reached, the power of each lens group becomes strong, and the lens system itself can be downsized, but in order to secure the lens performance, high precision workability is required and cost is increased. It becomes a factor of.

Conditional expression (4) is particularly for stabilizing lateral chromatic aberration among the off-axis chromatic aberrations. If this condition is exceeded, axial chromatic aberration can be reduced, but off-axis lateral aberration can be reduced. Chromatic aberration expands, and the original performance cannot be satisfied.

According to the wide-angle lens of the present invention, the angle of incidence on the CCD or the like can be suppressed to a small value, satisfactory aberration correction can be performed by sufficient achromatization, and a super-wide-angle lens that is compact, lightweight and inexpensive for high image quality. Can be provided.

Here, the first group lens can be composed of one lens having a negative power or a plurality of lenses having a negative power.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a wide-angle lens to which the present invention is applied will be described below with reference to the drawings.

Prior to the description of each embodiment, a typical configuration of the wide-angle lens according to the present invention will be described with reference to FIG.

The wide-angle lens 100 shown in this figure is in Example 1 described later, and the wide-angle lens 100 is
It has a first group lens 10 having negative power and a second group lens 20 having positive power, which are arranged in order from the object side. The second group lens 20 includes a front group lens 30 arranged on the object side and a rear group lens 40 arranged on the opposite side (image surface side) with the diaphragm 5 interposed therebetween. The rear group lens 40 includes a glass lens group 50 arranged on the diaphragm 5 side and a lens 60 arranged on the image plane side.

The first group lens 10 of this example is composed of two concave lenses 11 and 12, and at least the concave lens 1
2 is a plastic lens. The front lens group 30 of the second lens group 20 is composed of a convex aspherical lens 2 made of a plastic lens, and the glass lens group 50 of the rear lens group 40.
Is composed of glass lenses 31 and 32, and the lens 60 is composed of a convex aspherical lens 4 made of a plastic lens.

In the illustrated construction, the glass lens group 50 is a cemented lens consisting of a concave lens 31 and a convex lens 32, but it is also possible to separate the concave and convex lenses.

A low-pass filter 6 and a cover glass 7 are arranged between the convex aspherical lens 4 forming the rear lens group 40 and the image forming surface 8 (light receiving surface of the light receiving element). . The low pass filter 6 and the cover glass 7 may be omitted.

In addition, as a matter of course, even if all or a part of the above-mentioned at least three aspherical lenses made of plastics are replaced with aspherical lenses made of glass mold, the same effect can be obtained. Needless to say.

Here, in the lens that constitutes the wide-angle lens, the respective surfaces are ordered from the object side as shown by the numbers in parentheses in the figure, and the radius of curvature of the i-th surface is Ri, i-th And the distance between the (i + 1) th surface is di, the refractive index of the ith surface is Ndi, and i
The Abbe number of the second surface is νdi. Further, the aspherical shape has the following formula (5), where X is the axis of the optical axis direction, H is the height direction perpendicular to the optical axis, k is the cone coefficient, and A, B, C, and D are the aspherical coefficients. Is represented by

[0028]

[Equation 1]

[0029]

(Example) (Example 1) In the lens system according to Example 1,
As shown in FIG. 1 described above, the first group lens 10 is composed of two negative lenses, and a glass lens is used for the first negative lens 11 from the object side. Further, one surface of the second negative lens 12 in the first group lens 10 is an aspherical surface, and both surfaces of the front group lens 30 of the second group lens 20 and both surfaces of the lens 4 on the image side of the rear group lens 40 are respectively formed. It is aspherical. Data of the lens system of this example are shown in Tables 1 and 2, and an aberration diagram thereof is shown in FIG. 3, where SA is spherical aberration, OSC is sine condition, AS is astigmatism, and DIST is distortion. Also, astigmatism AS
In the figure, T represents the tangential and S represents the sagittal image plane. The performance of the wide-angle lens according to Example 1 is as follows. Brightness FNo. : 1.8 Focal length f = 1.45 mm Horizontal angle of view W = 125 ° Exit pupil ep = 157.48 mm

[0030]

[Table 1]

[0031]

[Table 2]

Example 2 The configuration of the lens system according to Example 2 is as shown in FIG. 1 similarly to Example 1, but the first negative lens of the first lens group 10 from the object side. 11 is a glass lens, and one surface of the second negative lens 12 and 2
Both surfaces of the front lens group 30 of the group lens 20 and one surface of the lens 4 on the image side of the rear lens group are aspherical. Data of the lens system of this example are shown in Tables 3 and 4, and FIG. 4 is an aberration diagram thereof.

[0033]

[Table 3]

[0034]

[Table 4]

Example 3 The configuration of the lens system according to Example 3 is the same as that of FIG. 1, but the aberration correction of this lens system is such that good correction can be obtained in the wavelength range λ = 400 to 900 nm. In consideration of the above, as in Examples 1 and 2,
The first negative lens 11 from the object side of the first group lens 10 is a glass lens, and one surface of the second negative lens 12 of the first group lens 10 and the front group lens 30 and the rear group of the second group lens 20. Aspherical surface correction was performed on both surfaces of the lens 4 on the image plane side of the lens 40. Data of the lens system of this example are shown in Tables 5 and 6, and FIG. 5 is an aberration diagram thereof.

[0036]

[Table 5]

[0037]

[Table 6]

(Examples 4 and 5) As shown in FIG. 2, the lens system according to Examples 4 and 5 has a first-group lens 10
Is formed of one lens 1, and both surfaces of one surface of this lens 1 and the image side lens 4 of the front lens group 30 and the rear lens group 40 of the second lens group 20 are aspherical. Since the lens configuration other than this is the same as that in the case of FIG. 1, corresponding portions are denoted by the same reference numerals, and description thereof will be omitted.

Data of the lens system of Example 4 are shown in Tables 7 and 8 and aberration diagrams thereof are shown in FIG. Data of the lens system of Example 5 are shown in Tables 9 and 10, and aberration diagrams thereof are shown in FIG.

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

[Table 9]

[0043]

[Table 10]

[0044]

As described above, in the wide-angle lens according to the present invention, the two-group lens has the one-group lens having negative power and the second-group lens having positive power, which are arranged in order from the object side. Includes a front group lens disposed on the object side and a rear group lens disposed on the image side with the diaphragm interposed therebetween. The rear group lens is disposed on the diaphragm side for achromatism. It has a glass lens group. In addition, at least four of the lens surfaces of at least three lenses of the lens groups that form the entire lens system are aspherical surfaces,
A lens with a small Abbe number is used as the front lens group, and achromatic correction is performed by the glass lens group. As a result, it is possible to realize a super wide-angle lens with a long exit pupil for high image quality, which can correct chromatic aberration of magnification including the near-infrared region, which is originally difficult to correct, and can realize various excellent aberration corrections.

The wide-angle lens according to the present invention is small and lightweight,
It was confirmed that it was possible to manufacture at low cost, the chromatic aberration of magnification was well corrected, and the exit pupil was sufficiently long. Therefore, according to the present invention, it is possible to inexpensively realize a super-wide-angle lens having a long exit pupil, which is compact and lightweight, and can cope with high image quality.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a typical configuration of a wide-angle lens to which the present invention has been applied.

FIG. 2 is a configuration diagram of Examples 4 and 5 of a wide-angle lens to which the present invention has been applied.

FIG. 3 is a graph showing various aberrations of the lens optical system according to the first example of the present invention.

FIG. 4 is a graph showing various aberrations of the lens optical system according to Example 2 of the present invention.

FIG. 5 is a graph showing various aberrations of the lens optical system according to Example 3 of the present invention.

FIG. 6 is a graph showing various aberrations of the lens optical system according to Example 4 of the present invention.

FIG. 7 is a graph showing various aberrations of the lens optical system according to Example 5 of the present invention.

[Explanation of symbols]

100 Wide-angle lens optical system 10 First group lens 1, 11, 12 Lenses constituting the first-group lens 20 second group lens 30, 2 front group lens 40 rear lens group 50 Glass group in front of rear group lens 31 concave glass lens 32 convex glass lens 60,4 Lens behind the rear lens group 6 low pass filter 7 cover glass 8 Image forming surface (light receiving surface of light receiving element)

Claims (2)

[Claims] 1. A first group lens having a negative power and a second group lens having a positive power, which are arranged in order from the object side. The second group lens is arranged on the object side with a diaphragm interposed therebetween. Front lens group and a rear lens group arranged on the image side, wherein the rear lens group is a glass lens group composed of at least one glass lens for achromatism arranged on the diaphragm side. Of the lens groups constituting the entire lens system, at least four of the lens surfaces of at least three lenses are aspherical surfaces, and the focal length of the first group lens is F1, and the second group is The focal length of the lens is F2, the focal length of the front group lens on the front side of the second group lens is fM, the focal length of the rear group lens is fR, and the focus of the glass lens group in the rear group lens is F2. Distance fR1 fR2 the focal length of the lens group on the image side in the rear lens group, when the νdM the Abbe number of the front lens group, the following conditional expression (1),
A wide-angle lens characterized by satisfying (2), (3) and (4). 1.6 <fR1 / fR2 <3.7 (1) 1.2 <fM / fR <2.2 (2) 0.5 <| F1 / F2 | <1.2 (3) νdM ≦ 45 (4) 2. The lens according to claim 1, wherein the first group lens is one lens having negative power,
Alternatively, a wide-angle lens characterized by being composed of a plurality of lenses having negative power.