JP2866035B2 - Wide-angle lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a single focus wide angle lens,
In particular, the present invention relates to a retrofocus wide-angle lens.

[0002]

2. Description of the Related Art As a wide-angle lens used for various video cameras (for example, a home video camera and a security camera), generally, the wide-angle lens and a CCD as an image sensor are used.
Since it is necessary to insert an optical element such as a low-pass filter between them, a retrofocus type lens having a long back focus is used.

A retrofocus type lens is roughly divided into a front group having a negative refractive power and a rear group having a positive refractive power. In general, the front group has a single meniscus having a negative refractive power. The rear group is composed of four lenses arranged in order of a convex lens, a concave lens, a convex lens, and a convex lens from the object side. Incidentally, the rear group has a lens configuration necessary for obtaining a large exit angle of light rays from the final lens toward the periphery of the light receiving surface corresponding to the large light receiving surface of the image sensor while obtaining good aberration characteristics.

[0004]

It is generally said that such a retrofocus type lens has an asymmetric lens arrangement between the front group and the rear group, so that it is generally difficult to correct aberrations. Therefore, when the number of lenses is increased, the size of the lens system is increased, which causes a problem of increasing costs. In addition, if an aspheric lens is used for aberration correction while avoiding an increase in the number of lenses, high processing accuracy is required, and there is a problem that the cost is increased.

[0005] With recent technological advances, the light receiving area of the image sensor has been reduced, and it has become unnecessary to make the exit angle of the light beam from the final lens toward the periphery of the light receiving surface so large as described above. There is a demand for a new lens configuration that has good aberration characteristics and meets various circumstances.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a wide-angle lens capable of realizing cost reduction and excellent aberration correction.

Another object of the present invention is to provide a wide-angle lens having good aberration characteristics without increasing the number of lenses and without using an aspherical lens.

Another object of the present invention is to provide a new type of retrofocus wide-angle lens having a long back focus and suitable for video cameras, security cameras, microfilm cameras, and the like.

[0009]

According to the present invention, there is provided a single-focus wide-angle lens comprising a front unit and a rear unit, wherein the front unit is arranged in order from the object side. A bi-convex first lens having a positive refractive power, and a meniscus-shaped second lens having a negative refractive power and a concave surface facing the image surface side, wherein the rear group is arranged from the object side. A biconvex third lens having a positive refractive power, a fourth lens having a negative refractive power, and a biconvex fifth lens having a positive refractive power, which are arranged in this order; Each of the lenses is a spherical lens.

That is, as described above, since the light receiving area of the image pickup device is reduced, it is not necessary to make the emission angle of the light beam from the final lens toward the periphery of the light receiving surface so large. Against the background,
In the present invention, the front group is composed of two lenses, and the rear group is composed of three lenses. That is, the number of lenses in the rear group is reduced by one and the number of lenses in the front group is increased by one in comparison with the conventional retrofocus wide-angle lens. The objective is to improve the aberration characteristics without increasing the number of lenses in the entire lens system. Further, in the present invention, since all lenses are constituted by spherical lenses and no aspherical lenses are used, the manufacturing cost can be reduced and the cost of the product can be reduced.

Here, in a preferred embodiment of the present invention, the following conditions are satisfied in the above five-lens configuration.

(1) 0.21f ≦ d6 ≦ 0.51f (2) 0 ≦ d8 ≦ 0.28f (3) -4.10f ≦ r6 ≦ −1.87f (4) −1.62f ≦ r7 ≦ − 1.01f (5) −2.36f ≦ r10 ≦ −1.27f where f is the combined focal length of the entire system, dk is the kth lens thickness or the distance between lens surfaces from the object side,
rj is the radius of curvature of the j-th lens surface from the object side. In addition, the unit of all lengths is mm, and the lens thickness and the distance between lens surfaces (air gap) are on the optical axis.

In a preferred aspect of the present invention, the fourth aspect
The lens is formed of a biconcave lens or a meniscus lens having a concave surface facing the object side. Further, in a preferred aspect of the present invention, the fourth lens and the fifth lens are cemented, or the fourth lens and the fifth lens are arranged close to each other without contact.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

First, common features of the embodiments shown in the drawings will be described, and then the specific contents of each embodiment will be shown.

The wide-angle lens according to the present invention is composed of five lenses, that is, the front group is composed of two lenses, and the rear group is composed of three lenses. Here, all of the five lenses are spherical lenses. For the following description, the first to fifth lenses will be defined in order from the object side.

The first lens (L1) is formed of a biconvex lens having a weak positive refractive power (power) common to the embodiments. The first lens mainly relates to correction of distortion and horizontal chromatic aberration caused by the second lens. The second lens (L2) is disposed close to the first lens (non-contact to prevent interference fringes), and has a strong negative refraction with the concave surface facing the image plane side in order to obtain a sufficient angle of view. It is composed of a meniscus lens having power. These first
The front group is constituted by the lens and the second lens, and the refractive power of the entire front group is negative.

The third lens (L3) is composed of a biconvex lens having a positive refractive power, and exhibits a main positive power. The distance d4 between the second lens and the third lens (the distance between the front group and the rear group) is separated to some extent in order to shorten the focal length. The fourth lens (L4) is composed of a biconcave lens or a meniscus lens having a negative refractive power, and the radius of curvature r7 of the object-side lens surface is related to correction of spherical aberration caused by the third lens and the like. The distance d6 between the third lens and the fourth lens mainly relates to correction of longitudinal chromatic aberration. The last fifth lens (L5) is a lens composed of a biconvex lens having a weak positive refractive power and mainly having a function of adjusting the focal length. Fourth lens and fifth lens
The lenses may be cemented or non-contact closely placed. A rear group is constituted by the third lens, the fourth lens and the fifth lens, and thereafter the entire group has a positive refractive power.

The lens configuration in each embodiment satisfies the following conditions, whereby satisfactory aberration correction is obtained as shown in each embodiment described later.

(1) 0.21f ≦ d6 ≦ 0.51f (2) 0 ≦ d8 ≦ 0.28f (3) -4.10f ≦ r6 ≦ −1.87f (4) −1.62f ≦ r7 ≦ − 1.01f (5) −2.36f ≦ r10 ≦ −1.27f where f is the combined focal length of the entire system, dk is the kth lens thickness or the distance between lens surfaces from the object side,
rj is the radius of curvature of the j-th lens surface from the object side.

The above condition (1) relates to the distance d6 between the third lens and the fourth lens, and is an important factor for obtaining good optical performance. When d6 exceeds the upper limit of 0.51f, the g-line of spherical aberration has an image height of 50%.
From the vicinity, it largely deviates to the minus side, and the g-line of the lateral chromatic aberration expands from the vicinity on the axis to the plus side. Further, with respect to the lateral aberration, the jump of the peripheral portion is increased, and the optical performance as a whole is greatly deteriorated. On the other hand, when d6 falls below the lower limit of 0.21f, the entire g-line shifts to the minus side with respect to the image plane (longitudinal chromatic aberration worsens) with respect to spherical aberration, and the bulge increases near the image height of 70%. . In addition, the g-line of the lateral chromatic aberration swells from the vicinity of the axis to the minus side, and the lateral aberration increases greatly in the periphery of the meridional, thereby deteriorating the optical performance of the aberration as a whole.

The above condition (2) relates to the distance d8 between the fourth lens and the fifth lens. If d8 exceeds the upper limit of 0.28f, the entire g line shifts to the minus side with respect to the image plane with respect to spherical aberration (longitudinal chromatic aberration worsens),
Further, the g-line of the lateral chromatic aberration expands in the negative direction from near the axis. Regarding the transverse aberration, the jump around the periphery of the meridional increases, and the optical performance as a whole aberration deteriorates. Therefore, it is desirable that d8 is as small as possible, and the fourth lens and the fifth lens can be joined.

The above condition (3) relates to the radius of curvature r6 of the lens surface on the image plane side of the third lens. That r
If 6 exceeds the upper limit of -1.87f, the entire g line shifts to the minus side with respect to the image plane with respect to spherical aberration (longitudinal chromatic aberration worsens). Inflate. Regarding the lateral aberration, the jump of the periphery of the meridional increases, and the optical performance as a whole aberration deteriorates. On the other hand, r6 is the lower limit of -4.10f.
When the spherical aberration is below the range, the entire g line largely shifts to the minus side with respect to the image plane with respect to the spherical aberration (longitudinal chromatic aberration worsens), and the aberration curve near the periphery falls to the minus side to lose its shape. Also,
Regarding the lateral aberration, the jump of the peripheral portion becomes large, and the optical performance as a whole aberration deteriorates.

The above condition (4) relates to the radius of curvature r7 of the object-side lens surface of the fourth lens. That r
When 7 exceeds the upper limit of -1.01f, the g-line of the spherical aberration is largely inclined to the minus side from the vicinity of the image height of 50%. Regarding the transverse aberration, the jump around the periphery of the meridional increases, and the optical performance as a whole aberration deteriorates. on the other hand,
When r7 is lower than the lower limit of -1.62f, the entire g line shifts to the minus side with respect to the image plane (longitudinal chromatic aberration worsens) with respect to spherical aberration, and the swelling near the image height of 70% increases. Further, the g-line of the lateral chromatic aberration expands in the negative direction from near the axis. Regarding the transverse aberration, the jump around the periphery of the meridional increases, and the optical performance deteriorates as a whole.

The above condition (5) relates to the radius of curvature r10 of the lens surface on the object side of the fifth lens. When the value r10 exceeds the upper limit of −1.27f, the g-line of the spherical aberration is greatly inclined to the minus side from the vicinity of the image height of 50%, and the g-line of the lateral chromatic aberration expands to the plus side from the vicinity of the axis. Regarding the lateral aberration, the jump of the peripheral portion becomes large, and the optical performance as a whole aberration deteriorates. When the value of r10 is smaller than the lower limit of -2.36f, the entire g-line shifts to the minus side with respect to the image plane (longitudinal chromatic aberration is deteriorated) with respect to spherical aberration, and the bulge around 70% image height is large. Become. In addition, the g-line of the lateral chromatic aberration expands in the negative direction from near the axis. Regarding the transverse aberration, the jump around the periphery of the meridional increases, and the optical performance as a whole aberration deteriorates.

[0026]

Next, the configuration of each embodiment will be described with reference to the drawings.

[First Embodiment] FIG. 1 shows the configuration of the first embodiment. In each figure, F indicates a front group consisting of a first lens L1 and a second lens L2, and R indicates a third lens L
The rear group consisting of the third, fourth, and fourth lenses L4, L5 is shown. The following table shows each numerical value of this example.

[0028]

[Table 5] Here, f is the combined focal length of the entire system, FNo is the aperture ratio, horizontal 2ω is the horizontal angle of view, rj is the radius of curvature of the j-th lens surface from the object side, and dk is the object The kth lens thickness or lens surface distance from the side,
Ni is the refractive index for the d-line of the i-th lens from the object side, and νi is the Abbe number of the i-th lens from the object side.

FIG. 2 shows aberration characteristics in this embodiment, that is, (A) spherical aberration, (B) astigmatism,
And (C) distortion. Here, H indicates the height of the incident light, and Y 'indicates the height of the image plane. The d line corresponds to yellow, the g line corresponds to blue, and the c line corresponds to red, and SC indicates a sine condition. DS indicates the sagittal plane direction, and DT
Indicates the meridional plane direction.

In each of the embodiments, the first aperture stop is disposed slightly toward the third lens from the center between the second lens and the third lens, and the second aperture stop is disposed between the third lens and the fourth lens. Aperture stops are arranged. Of course, the location of the stop can be changed as appropriate. In the first, second, and fourth embodiments, a biconcave lens is used as the fourth lens, and the fourth lens and the fifth lens are bonded with an optical lens adhesive.

[Second Embodiment] FIG. 3 shows a configuration of a second embodiment. FIG. 4 shows aberration characteristics in this embodiment. The following table shows each numerical value of this example.

[0032]

[Table 6] Third Embodiment FIG. 5 shows the structure of a third embodiment. FIG. 6 shows the aberration characteristics in this embodiment. The following table shows each numerical value of this example.

[0033]

[Table 7] In this embodiment, unlike the other embodiments, the fourth lens is constituted by a meniscus lens, and the fourth lens and the fifth lens are connected to each other.
The lens is non-contact.

Fourth Embodiment FIG. 7 shows the configuration of a fourth embodiment. FIG. 8 shows aberration characteristics in this embodiment. The following table shows each numerical value of this example.

[0035]

[Table 8]

[0036]

As described above, according to the present invention, it is possible to construct a wide-angle lens having good aberration characteristics without increasing the number of lenses and without using an aspherical lens. And a wide-angle lens that can realize good aberration correction.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens system according to a first embodiment.

FIG. 2 is a diagram illustrating aberration characteristics of the lens system according to the first embodiment.

FIG. 3 is a diagram illustrating a lens system according to a second embodiment.

FIG. 4 is a diagram illustrating aberration characteristics of the lens system according to the second embodiment.

FIG. 5 is a diagram illustrating a lens system according to a third embodiment.

FIG. 6 is a diagram illustrating aberration characteristics of the lens system according to the third embodiment.

FIG. 7 is a diagram illustrating a lens system according to a fourth embodiment.

FIG. 8 is a diagram illustrating aberration characteristics of the lens system according to the fourth embodiment.

[Explanation of symbols]

L1 first lens, L2 second lens, L3 third lens, L4 fourth lens, L5 fifth lens, F front group,
R Rear group.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (10)

(57) [Claims] 1. A single-focus wide-angle lens comprising a front group and a rear group, wherein the front group is a biconvex first lens having a positive refractive power and arranged in order from the object side; And a meniscus-shaped second lens having a concave surface facing the image plane side. The rear unit is a biconvex second lens having a positive refractive power, arranged in order from the object side. and third lens, a fourth lens having negative refractive power, a fifth lens of biconvex having a positive refractive power, in the configuration, either the respective lens Ri spherical lens der the following conditions
Wide-angle lens characterized by satisfying . (1) 0.21f≤d6≤0.51f (2) 0≤d8≤0.28f (3) -4.10f≤r6≤-1.87f (4) -1.62f≤r7≤-1.01f Here, f is the combined focal length of the entire system, and dk is the object side.
Is the kth lens thickness or distance between lens surfaces,
rj is the radius of curvature of the j-th lens surface from the object side
You. 2. The wide-angle lens according to claim 1 , wherein the following condition is further satisfied. (5) -2.36f ≦ r10 ≦ −1.27f 3. The wide-angle lens according to claim 2 , wherein said fourth lens is a biconcave lens. 4. The wide-angle lens according to claim 3 , wherein the fourth lens and the fifth lens are cemented. 5. The wide-angle lens according to claim 2 , wherein the fourth lens is a meniscus lens having a concave surface facing the object side. 6. The wide-angle lens according to claim 5 , wherein the fourth lens and the fifth lens are arranged in close proximity in a non-contact manner. 7. The wide-angle lens according to claim 1, having the following numerical values. [Table 1] Here, f is the combined focal length of the entire system, FNo is the aperture ratio, horizontal 2ω is the horizontal angle of view, rj is the radius of curvature of the j-th lens surface from the object side, and dk is the object The kth lens thickness or lens surface distance from the side,
Ni is the refractive index for the d-line of the i-th lens from the object side, and νi is the Abbe number of the i-th lens from the object side. 8. The wide-angle lens according to claim 1, having the following numerical values. [Table 2] Here, f is the combined focal length of the entire system, FNo is the aperture ratio, horizontal 2ω is the horizontal angle of view, rj is the radius of curvature of the j-th lens surface from the object side, and dk is the object The kth lens thickness or lens surface distance from the side,
Ni is the refractive index for the d-line of the i-th lens from the object side, and νi is the Abbe number of the i-th lens from the object side. 9. The wide-angle lens according to claim 1, having the following numerical values. [Table 3] Here, f is the combined focal length of the entire system, FNo is the aperture ratio, horizontal 2ω is the horizontal angle of view, rj is the radius of curvature of the j-th lens surface from the object side, and dk is the object The kth lens thickness or lens surface distance from the side,
Ni is the refractive index for the d-line of the i-th lens from the object side, and νi is the Abbe number of the i-th lens from the object side. 10. The wide-angle lens according to claim 1, having the following numerical values. [Table 4] Here, f is the combined focal length of the entire system, FNo is the aperture ratio, horizontal 2ω is the horizontal angle of view, rj is the radius of curvature of the j-th lens surface from the object side, and dk is the object Is the thickness of the k-th lens from the side or the distance between the lens surfaces, Ni is the refractive index for the d-line of the i-th lens from the object side, and νi is the Abbe number of the i-th lens from the object side. .