JPH0933802A - Wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve chromatic aberration performance and aberrations and distortion of the most circumferential part of a picture plane by composing a front lens group of a specific concave plastic lens and a rear lens group of a specific convex plastic lens and a convex-concave glass cemented glass lens. SOLUTION: This wide-angle lens consists of four lenses which are a 1st meniscus lens 1 having its concave surface on an image plane side, a 2nd meniscus lens having its concave surface on the object side, a 3rd biconvex lens 3, and a 4th meniscus lens 4 having its concave surface on the object side in order from the object side. Further, the 1st lens 1 is provided with an aspherical surface on its object side, the 2nd lens 2 is provided with an aspherical surface on its image plane side, and the 3rd lens 3 and 4th lens 4 are cemented into a glass lens. Consequently, a large aperture ratio is obtained, the lens is simplified into 4-lens-element constitution, and the chromatic aberration performance and the aberrations and distortion of the most circumferential part of the picture plane can be improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a wide-angle lens.

[0002]

2. Description of the Related Art Conventionally, a photographic lens having a comparatively wide angle of view often adopts a so-called retrofocus type in which two lens groups, a front lens group having a negative refractive power and a rear lens group having a positive refractive power, are arranged. . The retrofocus type taking lens has an advantage that it can take a long back focus, and since it adopts a lens configuration that converges the light flux diverged in the front group in the rear group, off-axis aberrations such as spherical aberration, astigmatism, and distortion. There is a large amount of. In general, it is very difficult to satisfactorily correct these various aberrations as compared with a Gauss type taking lens, which is nearly symmetrical, because the lens configuration is asymmetric.

In particular, when an attempt is made to reduce the F number to achieve a large aperture ratio, a large amount of high-order spherical aberration occurs, the curvature of field increases, the flatness of the image surface of the entire screen is lost, and the distortion aberration becomes negative. To increase significantly.

In order to obtain good optical performance while keeping the brightness and the photographing angle of view constant, for example, there is a method of increasing the number of lenses or weakening the refractive power of both the front group and the rear group. However, in all of these methods, the total lens length becomes long and the entire lens system becomes large. Further, in order to obtain a sufficiently long back focus, it is sufficient to increase the distance between the front group and the rear group, but if it is increased too much, the total lens length becomes long and it becomes difficult to miniaturize the taking lens.

An example of a retrofocus type photographic lens composed of five lenses having an F number of 2.8, a photographic field angle of 37 to 38 degrees, and a relatively small number of lenses is disclosed in, for example, Japanese Patent Laid-Open No. 54-12723.
JP-A-57-163212.

However, in the taking lenses proposed in these publications, chromatic coma and astigmatism remain in the middle of the screen because the number of lenses is reduced, and chromatic aberration of magnification increases as the angle of view increases. Is increasing.

In order to solve these problems, a wide-angle lens using an aspherical surface is described in JP-A-62-78520. However, this Japanese Patent Laid-Open No. 62-78520
The wide-angle lens having an aspheric surface proposed in Japanese Patent Publication No.
The number of lenses is still as large as 5, and reduction of the number of lenses and downsizing have not been achieved.

On the other hand, a retrofocus type photographing lens having three lenses is described in JP-A-6-34878, JP-A-6-34879 and JP-A-6-82690. However, in JP-A-6-34878 and JP-A-6-34879, the F
The number was as large as 4 to 5, and the increase in diameter was not achieved. Further, in Japanese Patent Laid-Open No. 6-82690, although the F number is 1.4, the aspherical glass lens ball is 3
Since it uses a single sheet, it cannot be considered that the cost reduction has been achieved.

[0009]

The applicant has achieved an F-number of 1.8 by defining the focal lengths of the front and rear groups and introducing an aspherical plastic lens.
A 9-degree wide-angle lens is proposed in Japanese Patent Laid-Open No. 2-208617. Among these, the front group of concave lenses and the convex lens
An example in which the number of lenses is four, which is composed of a concave lens group and a convex lens rear group, and a concave lens front group and a convex lens (Abbe number 7
0) An example with three lenses, which is composed of a rear group of convex lenses, is shown.

By the way, the basic of chromatic aberration correction is to use a concave-convex lens having a different Abbe number for each lens group.
When the front group is a single lens, axial chromatic aberration and lateral chromatic aberration cannot be corrected independently. For example, in the third embodiment of Japanese Patent Laid-Open No. 2-208617, the axial chromatic aberration is 0.040 mm, the lateral chromatic aberration is 0.017 mm (image height 2.0 m).
m). Further, generally, the distortion of a wide-angle lens tends to be large, but even in the example of Japanese Patent Laid-Open No. 2-208617, the value is twice or more that of a normal video camera lens.

On the other hand, in fields such as built-in personal computers and workstations, for which demand is greatly increasing, important issues are color, resolution of the entire screen and low distortion.
For the lens applied to this, improvement of chromatic aberration performance, aberration at the outermost peripheral portion of the screen, and distortion is a problem. further,
In order to reduce the cost, it is a subject to provide an aspherical surface only on the plastic lens ball and realize aberration correction by the aspherical surface.

[0012]

In order to solve the above problems, the present invention uses a concave plastic lens having an aspherical surface on the object side as the front lens group structure, and a concave surface on the object side as the rear lens group structure. That is, a meniscus-shaped convex plastic lens having an aspherical surface on the image-side facing side and a convex / concave laminated glass lens. Further, based on the bending coefficient B defined by the formula 1, the shape of the second lens is calculated by the formula 3
That is, it was specified to satisfy the condition of.

[0013]

## EQU00002 ## B = (Rb + Ra) / (Rb-Ra)
(Formula 2) where Ra is the radius of curvature of the lens side on the object side, and Rb is the radius of curvature on the image side.

[0014]

[Equation 3] -4 <B ₂ <-2
(Equation 3) Other features of the present invention are described in operation.

[0015]

The operation of the present invention will be described with reference to FIG.

FIG. 1 is an explanatory view showing the lens structure of a wide-angle lens to which the present invention is applied.

In the figure, 1 is a plastic lens which is a first lens having a negative focal length, 2 is a plastic lens which is a second lens having a positive focal length, and 3 is a glass lens which is a third lens which has a positive focal length. Reference numeral 4 denotes a glass lens, which is a fourth lens having a negative focal length, 5 denotes a diaphragm (or a fixed open diaphragm), and 6 denotes a parallel plane plate in which a filter face plate and the like are integrated. In order from the object side, a meniscus lens-shaped first lens 1 having a concave surface facing the image side, a large meniscus lens-shaped second lens 2 having a concave surface facing the object side, and a biconvex third lens Lens 3, fourth meniscus lens shape concave on the object side
The lens configuration of the lens 4 is four. Further, an aspherical surface is provided on the object side of the first lens 1, an aspherical surface is provided on the image surface side of the second lens 2, and the third lens 3 and the fourth lens 4 are laminated to form a glass lens.

According to the present invention, by constructing the wide-angle lens with the above-mentioned lens configuration and satisfying the above-mentioned conditions, the simplification of a large aperture ratio and the number of lenses is 4, and further, the chromatic aberration performance and the peripheral portion of the screen are reduced. We have achieved a wide-angle lens with improved aberration and distortion.

Numerical values are shown in the embodiment, but the focal length is 3.3.
In the case of a wide-angle lens as small as ~ 4.4 mm, it is necessary to use a retrofocus type photographing lens in order to secure the back focus. In the retrofocus type photographing lens, the ray height of the axial ray is small in the negative first lens group arranged far away in front of the diaphragm, and conversely, the ray height of the principal ray is large. . The ray height of the axial ray in the second lens group disposed immediately behind the stop at the rear is large, and conversely, the ray height of the principal ray is small.
Therefore, axial chromatic aberration mainly occurs in the second lens group in which the ray height of the axial ray is large, and the ray height of the principal ray is large in the first lens group.
Lateral chromatic aberration mainly occurs in the lens group. That is, in order to correct axial chromatic aberration and lateral chromatic aberration at the same time, it is necessary to use a concave lens and a convex lens in combination in the first lens group and the second lens group. However, as the number of lenses increases, the entire lens becomes larger and longer. Usually, the first lens group is composed of one concave lens, and the axial chromatic aberration and the lateral chromatic aberration are balanced on this. For example, a first lens group of concave lenses, a convex lens, a concave lens,
Japanese Unexamined Patent Publication (Kokai) No. 2-208 composed of a second lens group of convex lenses
In Example 3 of Japanese Patent No. 617, the axial chromatic aberration is 0.040.
mm, chromatic aberration of magnification 0.017 mm (image height 2.0 mm).

Therefore, when used in combination with a high pixel count sensor, it is necessary to improve chromatic aberration performance. However, if the chromatic aberration correction is performed by the second lens group configuration of the convex lens, the concave lens, and the convex lens, the refracting power of each lens ball of the second lens group becomes too strong, and the monochromatic aberration itself deteriorates.
Even if the axial chromatic aberration can be reduced, the chromatic aberration of magnification cannot be easily reduced in the second lens group having a small chief ray height. Therefore, it is necessary to make the lens configuration of the second lens group a convex lens / convex lens / concave lens in order to make the lens away from the aperture stop which has a ray height of the principal ray as large as possible in the second lens group. Become. At this time, on the contrary,
Since the ray height of the axial ray at this concave lens becomes small, the effect of correcting axial chromatic aberration becomes small. Therefore, it is necessary to increase the refracting power of each lens in the second lens group in order to correct chromatic aberration. At this time, by using a glass-bonded lens for the convex lens and the concave lens,
It is necessary to prevent total reflection of light rays by this convex lens.

Specifically, the convex lens (third lens) is used with the lens data shown in Examples 1, 2, 3, and 4 below.
If an air layer with a space of 0 is inserted between the lens) and the concave lens (fourth lens), a light beam that causes total reflection on the image-side lens surface of the convex lens is generated by the light flux traveling toward the periphery. In this state, the peripheral light amount ratio is significantly deteriorated, and the target specification value cannot be satisfied. Therefore, in order to secure a target peripheral light amount ratio, it is essential to use a convex lens (third lens) and a concave lens (fourth lens) as a cemented lens.

Further, since the lens diameter of the small-sized wide-angle lens is small, it becomes difficult to polish the glass lens and the cost increases. The original purpose was to reduce the number of lenses themselves by making these glass lens balls with a small lens diameter into plastics, reducing the cost and aspherical effect on the plastic lens surface. In particular, the first purpose was to plasticize the first lens 1 having a small radius of curvature.

However, when a plastic lens is used, temperature compensation using a combination of a concave and a convex plastic lens is required, so the remaining second lens 2 is determined as a plastic lens.

The above is the description of the basic lens structure of the present invention. Next, the shape of the second lens 2 which is a plastic lens will be described.

In order to perform temperature compensation by the first lens 1 and the second lens 2, the first lens 1 having a small axial ray height is used.
Second, which increases the refracting power of the beam and increases the axial ray height
It is necessary to reduce the refractive power of the lens 2. However, if the refracting power of the first lens 1 is increased, the ray height of the axial ray in the second lens 2 is inevitably increased, and conversely, the refracting power of the first lens 1 is increased for temperature compensation. It is desirable to make it small. On the other hand, the refractive power of the first lens 1 cannot be made too small in order to secure a certain amount of back focus. Therefore, it is necessary to reduce the refractive power of the second lens 2 to perform temperature compensation.

Since the second lens group apparently has a basic structure of two convex lenses, it is desirable to divide the refractive power of the second lens group into two equal parts in terms of aberration correction. Further, taking the third embodiment of JP-A-2-208617 as an example,
Since the lateral magnification of the second lens group is 0.8, the second lens 2
It is necessary that the shape is a meniscus convex lens with a concave surface facing the object side. Specifically, by defining the bending coefficient B ₂ of the second lens 2 so as to satisfy the condition of Expression 3, excellent aberration correction can be performed.

In particular, the lens of the present invention is aimed at making the distortion aberration equivalent to that of a video camera, so that it is necessary to make the bending coefficient B ₂ a significantly negative value. First, the peripheral light amount ratio when the distortion is improved will be described, and then the bending coefficient B ₂ will be described.

The peripheral light amount ratio R (θ) is defined by Equation 5 using the aperture efficiency V (θ) of Equation 3.

[0029]

V (θ) = S (θ) / S (0) × 100 (Equation 4)

[0030]

[Equation 5] R (θ) = V (θ) f ² · sin θ · cos θ / [y (dy / dθ)] (Equation 5) where S (θ) is a parallel light beam passing through the lens at the incident inclination angle θ. The cross-sectional area perpendicular to the optical axis of the bundle, S (0) is the cross-sectional area perpendicular to the optical axis of the parallel ray bundle that is incident parallel to the optical axis and passes through the lens, f is the focal length of the lens, and y is the incident tilt angle θ. Is the image height corresponding to.

Since the distortion of a retrofocus lens generally has a large negative value, the image height y does not increase so much even if the incident tilt angle θ increases. That is, dy /
dθ has a small value, and the peripheral light amount ratio R (θ) can be increased. On the other hand, when the distortion is small, y = tan θ, and thus the peripheral light amount ratio R (θ) is given by the formula 6.

[0032]

[Equation 6] R (θ) = V (θ) · cos ⁴ θ
(Equation 6) Assuming that a horizontal angle of view of 60 degrees is obtained, the focal length f of the lens is 4.2 mm (= 2.
4 mm / tan 30 °). At this time, cos ⁴ θ = 0.43 because θ = 36 ° at the outermost part (3.0 mm) of the sensor.
Becomes Therefore, in order to obtain the peripheral light amount ratio R (θ) ≈60%, the aperture efficiency V (θ) ≈140% is required. That is,
About 1.4 times as many marginal rays as the on-axis rays will pass.

By the way, since the light beam diverges from the first lens 1 and then passes through the second lens 2 and becomes substantially parallel, the cross-sectional area of the light beam at the second lens 2 is larger than the value at the first lens 1. Become. Therefore, in order to correct the aberration, the second lens 2
It is necessary to make the shape of the optimum shape. In particular, since it is necessary to determine the shape of the light flux of the marginal rays for the sake of aperture efficiency, it is indispensable to set the bending coefficient B ₂ that further emphasizes the meniscus shape.

[0034]

EXAMPLES As examples of the present invention, numerical examples 1 and 2 for a 1/4 inch CCD sensor and a 1/3 inch CCD sensor with a wide-angle lens of F2.8 and a horizontal angle of view of 60 ° will be described below. Numerical Examples 3 and 4 are shown. In the numerical example, r (i) is the radius of curvature of the i-th lens surface S (i) in order from the object side, and d (i) is the lens surface S (i) to the lens surface S (i +).
The distance on the optical axis between 1), N (j) and ν (j) are the refractive index and the Abbe number of the j-th lens in order from the object side. The angle of view represents the diagonal angle of view with a real ray. Further, the aspherical shape is represented by the sag amount Z in the optical axis direction, and the height h from the optical axis, the paraxial radius of curvature r, the conic constant K, the fourth order, the sixth order, and the eighth order
It is defined by Equation 7 using the coefficients of the aspheric terms of the 10th and 10th orders.

[0035]

Z = (h ² / r) / {1 + √ [{1- (K + 1) h ² / r ² ]} + A ₄ h ⁴ + A ₆ h ⁶ + A ₈ h ⁸ + A ₁₀ h ¹⁰ (Equation 7) ) (Symbol: √ [] means to take the square root for the amount in []) [Numerical Example 1] f = 3.28 FNO. = 1: 2.91 2W = 73.0 ° S rd N ν 1 85.000 0.900 1.49200 57.9 2 2.325 1.770 3 (aperture) 1.715 4 −5.819 0 .610 1.49200 57.9 5 −2.523 0.200 6 8.100 2.210 1.71300 53.9 7 −3.150 0.500 1.846666 23.9 8 −10439 2. 015 9 ∞ 3.800 1.52307 58.5 10 ∞ The first surface is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 0.0 A ₄ = 3.469 / 10 ² A ₆ = -6.580 / 10 ³ A ₈ = 1.042 / 10 ³ A ₁₀ = -6.880 / 10 ⁵ The second surface also It is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 8.884 ÷ 10 ² A ₄ = 5.769 ÷ 10 ² A ₆ = 1.473 ÷ 10 ² A ₈ = -1.196 ÷ 10 ² A ₁₀ = 6.568 / 10 ^3rd 5th The surface is also an aspherical surface, and the coefficient of Equation 4 is as follows.

K = −0.2362 A ₄ = 1.572 ÷ 10 ⁴ A ₆ = 2.829 ÷ 10 ⁵ A ₈ = 1.087 ÷ 10 ⁵ A ₁₀ = −1.341 ÷ 10 ⁵ [Numerical Example 2] f = 3.26 FNO. = 1: 2.91 2W = 73.2 ° S rd N ν 1 27.000 0.900 1.49200 57.9 2 2.203 1.770 3 (aperture) 1.715 4 −4.4454 1 .630 1.49200 57.9 5 -2.430 0.200 6 7.265 2.340 1.71300 53.9 7 -3.200 0.500 1.846666 23.9 8 -10.96 2. 015 9 ∞ 3.800 1.52307 58.5 10 ∞ The first surface is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 0.0 A ₄ = 3.310 ÷ 10 ² A ₆ = −5.774 ÷ 10 ³ A ₈ = 7.178 ÷ 10 ⁴ A ₁₀ = −1.609 ÷ 10 ⁵ The second surface is also It is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 5.517 ÷ 10 ² A ₄ = 5.619 ÷ 10 ² A ₆ = 1.735 ÷ 10 ² A ₈ = −1.645 ÷ 10 ² A ₁₀ = 8.572 ÷ 10 ³ Fifth The surface is also an aspherical surface, and the coefficient of Equation 4 is as follows.

K = -0.3515 A ₄ = -7.586 / 10 ⁴ A ₆ = -1.408 / 10 ⁴ A ₈ = 2.672 / 10 ⁵ A ₁₀ = -1.997 / 10 ⁵ [Numerical value Example 3] f = 4.35 FNO. = 1: 2.91 2W = 73.2 ° S rd N ν 1 64.885 0.980 1.49200 57.9 2 3.377 2.700 3 (aperture) 1.900 4 −5.5342 .100 1.49200 57.9 5 -3.161 0.200 6 9.095 3.000 1.71300 53.9 7 -4.120 1.000 1.846666 23.9 8 -14.624 2. 500 9 ∞ 4.500 1.52307 58.5 10 ∞ The first surface is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 317.8 A ₄ = 1.892 ÷ 10 ² A ₆ = −2.091 ÷ 10 ³ A ₈ = 1.840 / 10 ⁴ A ₁₀ = −5.836 ÷ 10 ⁶ The second surface is also It is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 0.8639 A ₄ = 2.625 / 10 ² A ₆ = 4.075 / 10 ³ A ₈ = -2.295 / 10 ³ A ₁₀ = 6.163 / 10 ⁴ The fifth surface is also non- It is a spherical surface, and the coefficient of Equation 4 is as follows.

K = -1.600 / 10 ² A ₄ = 8.866 / 10 ⁴ A ₆ = 1.573 / 10 ⁴ A ₈ = -1.351 / 10 ⁵ A ₁₀ = 1.734 / 10 ⁶ [ Numerical Example 4] f = 4.36 FNO. = 1: 2.91 2W = 73.3 ° S rd N ν 1 4.438 0.980 1.49200 57.9 2 1.796 2.849 3 (aperture) 1.950 4-6.128 2 .200 1.49200 57.9 5 -3.216 0.200 6 9.263 3.260 1.71300 53.97 -4.335 0.500 1.846666 23.9 8-15.150 3. 000 9 ∞ 4.500 1.52307 58.5 10 ∞ The first surface is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 1.827 A ₄ = 5.002 ÷ 10 ⁴ A ₆ = −3.620 ÷ 10 ⁴ A ₈ = 8.720 / 10 ⁵ A ₁₀ = −1.656 ÷ 10 ^{5 Also on} the fifth surface It is an aspherical surface, and the coefficient of Equation 4 is as follows.

K = 1.542 ÷ 10 ² A ₄ = 1.146 ÷ 10 ³ A ₆ = 1.159 ÷ 10 ⁴ A ₈ = −7.620 ÷ 10 ⁶ A ₁₀ = 2.194 ÷ 10 ⁶ The relationship between the numerical example of the present invention and the condition of Expression 3 is as follows.

[0047] On the other hand, the values of the focal length f ₂ of the _second lens and the focal length f ₃₄ of the third and fourth cemented lenses in each numerical example are as follows, but the refracting power of the second lens group is about 2 or the like. You can see that you are sharing.

[0048] The results of chromatic aberration correction, which is an improvement of the present invention, are also shown below.

Example No. Axial chromatic aberration (mm) Magnification chromatic aberration (mm) 1 -0.009 0.008 (image height 1.8 mm) 2 -0.004 0.007 (image height 1.8 mm) 3 -0.013 0.010 ( Image height 2.3 mm) 4 0.013 0.011 (Image height 2.3 mm) Aberration diagrams for each numerical example at a shooting distance of 2 m are shown in FIG.
This is shown in FIGS. 4, 6 and 8. The two columns on the left side are coma aberration diagrams, and the relative image heights are 0, 0.3, 0.6, 0.9, 1 in order from the bottom.
Represents the coma aberration at each of 5 points. The rest is spherical aberration,
The sine condition, astigmatism, and distortion are shown respectively. The maximum value of the aberration diagram coordinate is ± 0.02m for coma.
m, spherical aberration, sine condition, astigmatism ± 0.05 mm, distortion ± 10%. Also, in the display of coma aberration,
Since the aperture efficiency of the peripheral portion exceeds 100%, the coma aberration is displayed by reducing the F number accordingly. Specifically, in the numerical example 1 of FIG. 2, the F number is 1.8, and in the numerical example 2 of FIG. 4, the F number is 1.8 and the numerical example 3
6 shows an F number of 2.2, and FIG. 8 of Numerical Example 4 shows an F number of 2.55, respectively. In addition, in spherical aberration and sine conditions,
Aberration diagrams are displayed using the F numbers as they are in each numerical example. As is clear from these aberration diagrams, it is understood that the lenses of each numerical example have an aperture efficiency of more than 100% and good performance.

In the embodiment, a numerical example of a wide-angle lens is shown with an F number of 2.8, but in the case where the peripheral light quantity ratio is equivalent to 30 to 40% at the wide end of the video camera, the aperture diameter is sufficient. It is also possible to increase the diameter to increase the diameter. For example, in Numerical Example 3, the peripheral light amount ratio is 40%.
A wide-angle lens with an F number of 2.2 can be obtained by increasing the diameter of the diaphragm until it becomes.

In each numerical example, the lens configuration diagram and the aberration diagram corresponding to the color video camera are shown, but it is natural that good performance can be realized even for the black and white video camera.

As described above, the plastic lens is the first lens 1
The present invention used for the second lens 2 has been described above.
It goes without saying that good performance can be obtained even if the plastic lens is a glass lens.

[0053]

According to the method of the present invention, the F number 2.
8. It is possible to achieve a wide-angle lens suitable for photographic use, video camera, etc., in which the aberration is satisfactorily corrected with an angle of view of about 69 °. In particular, since the chromatic aberration performance can also be improved, it is possible to achieve a wide-angle lens that is compatible with a high-resolution sensor with a high number of pixels.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a lens according to Numerical Example 1 of the present invention.

FIG. 2 is an explanatory diagram of aberrations representing a coma aberration, a spherical aberration, a sine condition, an astigmatism, and a distortion aberration with respect to a d-line in Numerical Example 1 of the present invention.

FIG. 3 is an explanatory diagram of a lens according to Numerical Example 2 of the present invention.

FIG. 4 is an explanatory diagram of aberrations representing a coma aberration, a spherical aberration, a sine condition, an astigmatism, and a distortion aberration with respect to a d-line according to Numerical Example 2 of the present invention.

FIG. 5 is an explanatory diagram of a lens according to Numerical Example 3 of the present invention.

FIG. 6 is an explanatory diagram of aberrations representing a coma aberration, a spherical aberration, a sine condition, an astigmatism, and a distortion for a d-line in Numerical Example 3 of the present invention.

FIG. 7 is an explanatory diagram of a lens according to Numerical Example 4 of the present invention.

FIG. 8 is an explanatory diagram of aberrations representing a coma aberration, a spherical aberration, a sine condition, an astigmatism, and a distortion aberration with respect to a d-line according to Numerical Example 4 of the present invention.

[Explanation of symbols]

1 ... 1st lens, 2 ... 2nd lens, 3 ... 3rd lens, 4
... 4th lens, 5 ... diaphragm, 6 ... plane parallel plate.

Claims (3)

[Claims] 1. A first lens having a negative focal length, a second lens having a positive focal length in a large air space, and a third lens having a positive focal length in order from the object side. In a lens system including a fourth lens having a negative focal length, the first lens is a plastic lens having an aspheric surface on the object side, and the second lens is a plastic lens having an aspheric surface on the image side. A wide-angle lens, wherein the third lens and the fourth lens are laminated glass lenses. 2. A lens having a meniscus lens-shaped negative focal length in which the first lens has a concave surface facing the image side, and a second lens has a meniscus lens-shaped positive focal length in which a concave surface faces the object side. The wide-angle lens according to claim 1, which is a lens having a. 3. The bending coefficient of the second lens is B ₂
The wide-angle lens according to claim 1, wherein the following condition is satisfied. [Equation 1] -4 <B ₂ <-2
(Equation 1) However, the bending coefficient B is B = (Rb + R) using the curvature radius Ra on the object side of the lens ball and the curvature radius Rb on the image side.
a) / (Rb-Ra).