JP2876097B2 - Wide-angle bifocal lens using aspherical surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle bifocal lens used for a video camera or the like, and more particularly to a wide-angle bifocal lens having an ultra-wide angle range of 80.degree.

[0002]

2. Description of the Related Art As a lens used in a video camera or the like, a bifocal lens including an ultra wide angle range of 80 ° in view has been conventionally used.

[0003]

However, the conventional bifocal lens of the related art generally has a drawback that an extremely large distortion is generated particularly on the wide-angle side.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and includes a super-wide-angle region having an angle of view of 80 °, a small distortion, and excellent correction of various aberrations. It is intended to obtain a wide-angle bifocal lens.

In summary, a wide-angle bifocal lens using an aspheric surface according to the present invention includes, in order from the object side: a single concave lens having at least one aspheric surface, and a cemented lens of a convex lens and a concave lens. A first lens group having a negative refractive power as follows: a second lens group having a variable power function by moving in the optical axis direction and having a cemented lens of a concave lens and a convex lens, and having a positive refractive power as a whole: A third lens group including a single concave lens and a cemented lens of a convex lens and a concave lens, and having a positive refractive power as a whole:
Satisfies the condition defined by Equation (3).

[0006]

[Equation 1] ν1N> ν1P, ν2N <ν2P, ν3N <ν3P

[0007]

[Equation 2] N1N <N1P, N2N> N2P, N3N> N3P

[0008]

## EQU3 ## R21 <R22 <2R21

In the equations (1) and (2), νiN: Abbe number of the concave lens of the cemented lens of the ith lens group νiP: Abbe number of the convex lens of the cemented lens of the ith lens group NiN: of the cemented lens of the ith lens group Refractive index of concave lens NiP: Refractive index of convex lens of cemented lens of ith lens group R21: Curvature radius of object side surface of cemented lens of second lens group R22: Image plane side of cemented lens of second lens group Radius of curvature

[0010]

In the wide-angle bifocal lens according to the present invention, distortion on the wide side is corrected by forming at least one aspheric surface on the single concave lens constituting the first lens group.

The conditions of equations (1) and (2) relate to the correction of chromatic aberration. If these conditions are not satisfied, chromatic aberration will increase, making it difficult to satisfactorily correct chromatic aberration on both the wide side and the tele side. become.

The condition of equation (3) relates to spherical aberration and coma, and if these conditions are not satisfied, it becomes difficult to correct the coma of the lower ray, especially on the telephoto side.

[0013]

【Example】

An embodiment of the present invention will be described below with reference to the drawings. As shown in the optical axis sectional view of the first embodiment shown in FIG. 1 and the optical axis sectional view of the second embodiment shown in FIG. 6, the wide-angle bifocal lens using the aspheric surface of the present invention is arranged in order from the object side. : A first lens group A having a single concave lens 1 having at least one aspheric surface and a cemented lens of a convex lens 2 and a concave lens 3 and having a negative refractive power as a whole: changing by moving in the optical axis direction With a double function, concave lens 4 and convex lens 5
A second lens group B having a positive refractive power as a whole, and a third lens group having a single concave lens 6 and a cemented lens of a convex lens 7 and a concave lens 8 and having a positive refractive power as a whole. C: Satisfies the conditions defined in Expressions 1 to 3. Incidentally, 9 constituting the fourth lens group D is, for example, a glass material such as a face plate.

Table 1 shows specific numerical values of the first embodiment.
Table 2 shows specific numerical values of the second embodiment. In Tables 1 and 2, and FIGS. 1 and 6, r1 to r16 indicate the radius of curvature of each surface of the lens sequentially from the object side. In Tables 1 and 2, d1 to d15 denote the wall pressure of each lens or the air gap between the surfaces of the lenses sequentially from the object side, n1 to n9 denote the refractive index of each lens sequentially from the object side, and ν1 to ν9 denote the The Abbe number of each lens is shown sequentially from the object side.

In the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 6, r9 denotes a stop, and the stop r9 moves in the optical axis direction together with the second lens unit B which performs a zooming action. However, the amount of movement is different from that of the second lens group B,
Accordingly, the air gap d5 between the first lens group A and the second lens group B, and the air gap between the second lens group B and the aperture stop r9 are caused by the zooming effect due to the movement of the second lens group B. d8
The air gap d9 between the stop r9 and the third lens unit C changes as shown in Tables 1 and 2, respectively.

Further, in the first and second embodiments, the object side surface r of the single concave lens 1 constituting the first lens unit A is described.
1 is formed into an aspherical shape, and the aspherical shape is
Is defined by

[0018]

(Equation 4)

In the formula (4), Z: the distance from the tangent plane to the aspherical vertex of the point on the aspheric surface having a height y from the optical axis y: the height from the optical axis C: the curvature of the aspherical vertex (= 1 / r) ε: conical constants D, E, F, G: aspherical surface coefficients, respectively, and are the conic constant ε and aspherical surface coefficients D, E, F, G in the first and second embodiments. Are shown in the corresponding Tables 1 and 2, respectively.

FIG. 2 shows the spherical aberration and astigmatism on the wide side of the first embodiment, FIG. 3 shows the distortion and chromatic aberration of magnification of the first embodiment on the wide side, and FIG. 4 shows the first embodiment. 5 shows the spherical aberration and astigmatism on the telephoto side, and FIG. 5 shows the distortion and chromatic aberration of magnification on the telephoto side of the first embodiment.
7 shows the spherical aberration and astigmatism on the wide side of the second embodiment, FIG. 8 shows the distortion and chromatic aberration of magnification on the wide side of the second embodiment, and FIG. 9 shows the telephoto side of the second embodiment. FIG. 10 shows spherical aberration and astigmatism, and FIG. 10 shows distortion and lateral chromatic aberration on the telephoto side of the second embodiment, respectively. In these characteristic curves, d indicates the d line, F indicates the F line, C indicates the C line, and SC indicates the sine condition. Furthermore,
In FIGS. 2, 4, 7, and 9, DS indicates the sagittal direction, and DT indicates the meridional direction.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

As described above, according to the present invention, as shown in the above embodiment and the aberration curve, it includes a super wide-angle region with an angle of view of 80 ° and has a high magnification close to three times. ,
A wide-angle bifocal lens with little distortion on the wide side and excellent correction of various aberrations was obtained.

[Brief description of the drawings]

FIG. 1 is an optical axis sectional view of a wide-angle bifocal lens according to a first example of the present invention.

FIG. 2 is a diagram illustrating spherical aberration and astigmatism on the wide side according to the first embodiment.

FIG. 3 is a diagram illustrating distortion and chromatic aberration of magnification on the wide side according to the first embodiment.

FIG. 4 is a diagram illustrating spherical aberration and astigmatism on the telephoto side according to the first embodiment.

FIG. 5 is a diagram illustrating distortion and chromatic aberration of magnification on the tele side in the first embodiment.

FIG. 6 is an optical axis cross-sectional view of a wide-angle bifocal lens according to Example 2 of the present invention.

FIG. 7 is a diagram illustrating spherical aberration and astigmatism on the wide side according to the second embodiment.

FIG. 8 is a diagram showing distortion and chromatic aberration of magnification on the wide side according to the second embodiment.

FIG. 9 is a diagram illustrating spherical aberration and astigmatism on the telephoto side according to a second embodiment.

FIG. 10 is a diagram showing distortion and chromatic aberration of magnification on the telephoto side according to the second embodiment.

[Explanation of symbols]

 A first lens group B second lens group C third lens group 1 single concave lens 2 convex lens 3 concave lens 4 concave lens 5 convex lens 5 6 single concave lens 7 convex lens 8 concave lens 8

Claims (1)

(57) [Claims] 1. A first lens group having a negative refractive power as a whole, comprising, in order from the object side, a single concave lens having at least one aspheric surface, a cemented lens of a convex lens and a concave lens, and an optical axis direction. The second lens group having a positive refractive power as a whole, having a cemented lens of a concave lens and a convex lens,
It has a third lens group composed of a cemented lens of a convex lens and a concave lens, and having a positive refractive power as a whole.
A wide-angle bifocal lens using an aspheric surface, which satisfies the conditions defined in (2) and (3). (1) ν1N> ν1P, ν2N <ν2P, ν3N <ν3P (2) N1N <N1P, N2N> N2P, N3N> N3P (3) R21 <R22 <2R21, where νiN is the concave lens of the cemented lens of the ith lens group. Abbe number νiP: Abbe number of the convex lens of the cemented lens of the ith lens group NiN: refractive index of the concave lens of the cemented lens of the ith lens group NiP: refractive index of the convex lens of the cemented lens of the ith lens group R21: second lens group R22: radius of curvature of the image-side surface of the cemented lens in the second lens group