JPH09159908A - Combined lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently correct chromatic aberration and Petzval's sum by constituting a lens of a homogeneous lens having negative refractive power and a specified radial type refractive index distribution lens which has positive refractive power and in which a refractive index is distributed in a radial direction from an optical axis, bringing the plane shaped parts of both lenses into contact with each other and satisfying a specified condition. SOLUTION: This lens is constituted of the homogeneous lens having the negative refractive power and one radial type refractive index distribution lens which has the positive refractive power and in which the refractive index is distributed in the radial direction from the optical axis, and is expressed by an expression N(r)=N00 +N10 r<2> +N20 r<4> ; and both surfaces of refractive index distribution lens are plane and at least one-side surface of the homogenous lens is plane, and the plane shaped parts of both lenses are brought into contact or stuck to each other and they satisfy a condition: 1/V10 <1/νh . Provided (r) expresses a distance from the optical axis in the radial direction, N(r) expresses the refractive index distribution at a point being the distance (r), N10 expresses the coefficient of 2i-order refractive index distribution, and νh expresses the Abbe number of the homogeneous lens, and V10 expresses dispersion corresponding to the coefficient of the 2i-order refractive index distribution of the refractive index distribution lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination lens (a lens composed of a plurality of lenses and used as one lens) using a radial type gradient index lens.

[0002]

2. Description of the Related Art For example, an optical system used under a white light source such as a camera for silver halide photography, a microscope, a video camera or an endoscope usually has a plurality of aberrations in order to satisfactorily correct various aberrations such as chromatic aberration and Petzval sum. Needs one lens. Further, in addition to correction of various aberrations, it is required to reduce the number of lenses or to simplify the lens frame structure in order to reduce the cost. As a means for solving this, it has been conventionally known to use a radial type gradient index lens element in an optical system. The radial type gradient index lens element is excellent in correction of chromatic aberration and Petzval sum among various aberrations, and thus is particularly effective in reducing the number of lenses in a lens system used under a white light source. For example, as a conventional example in which a radial type gradient index lens is used in a camera for silver salt photography, Japanese Patent Laid-Open No. 60-
The one described in Japanese Patent No. 218614 is known. This conventional example is a lens system in which a Gauss type optical system, which conventionally requires the number of lenses of about 6 to 7, is composed of two lenses by using a radial type gradient index lens. Further, as a conventional example in which a radial type gradient index lens is used as an objective lens for an endoscope, JP-A-5-10 is known.
A lens system described in Japanese Patent No. 7471 is known.
This conventional example is a lens system in which a retro-focus type optical system, which has conventionally required about 6 lenses, is composed of 2 to 4 lenses by using a radial type gradient index lens. However, in all of these conventional examples, since the surface shape of the radial type gradient index lens element is spherical, it is possible to easily match the optical axis of the surface and the optical axis of the medium with high accuracy in the actual processing scene. It is not preferable in terms of realizing a difficult and high-performance lens system or in terms of realizing a lens system that is inexpensive to manufacture.

In view of the above problems, it may be possible to use the radial type gradient index lens element as it is without being spherically processed, but the Petzval sum is particularly insufficiently corrected as compared with the case of spherically processing. Therefore, it is not preferable.

Further, in order to increase the degree of freedom of aberration correction, a radial type gradient index lens having a biplanar shape and a homogeneous lens having a flat surface on one side and a spherical surface on the other surface are joined at a flat portion. The example used as described above is, for example, JP-A-58-5.
It is known from Japanese Patent No. 9420, Japanese Patent Laid-Open No. 4-114112, and the like. However, these conventional examples relate to pickup lenses used under a monochromatic light source, and the publications of these conventional examples do not describe correction of chromatic aberration. Further, Japanese Patent Laid-Open No. 1-2-2, which is a conventional example of this type.
Similarly, Japanese Patent Laid-Open No. 8514 and Japanese Patent Laid-Open No. 2-284107 do not describe correction of chromatic aberration.

Further, as a conventional example in which a radial type gradient index lens and a homogeneous spherical lens are cemented at a flat portion and applied to a lens system used under a white light source, European Patent (Application Publication No. 6)
The specification of 09093 and JP-A-58-184113 are known. These conventional examples are examples in which a radial type gradient index lens is used in the relay lens part of a rigid endoscope, but the value of Petzval sum is large, and the lens length is very long with respect to the diameter, so the angle of view is narrow. It can only be used for lens systems for special applications such as relay lenses for rigid endoscopes.

[0006]

The present invention provides a combination lens which is excellent in workability and can be applied to various optical systems used under a white light source, in which various aberrations, particularly chromatic aberration and Petzval sum, are well corrected. The purpose is to provide.

[0007]

A combination lens of the present invention has at least one homogeneous lens having a negative refractive power and a refractive index distributed in a radial direction from an optical axis having a positive refractive power as described below. And one radial type gradient index lens element represented by the formula (a), the radial type gradient index lens element has a shape of both planes, and at least one surface of at least one side of the homogeneous lens is partially or entirely The planar shape of the homogeneous lens and the planar shape of the radial type gradient index lens are adhered or brought into close contact with each other, and the following condition (1) is satisfied.

N (r) = N ₀₀ + N ₁₀ r ² + N ₂₀ r ⁴ (a) (1) 1 / V ₁₀ <1 / ν _h where r is the distance from the optical axis in the radial direction, N (r) is the refractive index distribution at the distance r, N _i0 is the 2i th order refractive index distribution coefficient, ν _h is the Abbe number of the homogeneous lens, V _i0 is the 2 i th order refractive index distribution of the radial type gradient index lens It represents the variance corresponding to the coefficient and is given by the following equations (b) and (c).

V ₀₀ = (N _00d −1) / (N _00F −N _00C ) (i = 0) (b) V _i0 = N _i0d / (N _i0F −N _i0C ) (i = 1,2,3 ·)・) (C) where N _00d , N _00F and N _00C are d line and F, respectively.
The refractive indices of the lines C and C on the optical axis, N _i0d , N _i0F and N _i0C are the 2i-th order refractive index distribution coefficients of the d line, F line and C line, respectively.

In the present invention, in order to solve the above problems, the following combined lens unit applicable to a part of an optical system used under a white light source was considered. It is a combination lens in which a homogeneous lens having a flat surface on at least one surface and a radial type gradient index lens on both surfaces are adhered or in close contact, and the refractive power and Abbe number of both lenses are set to appropriate values. . If the radial type gradient index lens has a shape of both planes, it is possible to prevent decentering of the surface and the medium, which is a problem in the actual processing scene, and if a homogeneous lens is adhered or adhered, Various aberrations can be corrected well. Further, if the homogeneous lens has a flat surface portion and is bonded or adhered to the radial type gradient index lens element at this flat surface portion, the optical axes of the homogeneous lens element and the radial type gradient index lens element can be relatively easily and accurately matched. be able to. Further, at this time, chromatic aberration and Petzval sum can be satisfactorily corrected by setting parameters such as refractive power and Abbe number of the homogeneous lens and the radial type gradient index lens element to appropriate values. Hereinafter, these corrections will be described in detail.

The axial chromatic aberration PAC of the radial type gradient index lens unit is expressed by an approximate expression of the expression (d).

PAC = K (φ _s / V ₀₀ + φ _m / V ₁₀ ) (d) where K is a constant depending on the ray height of the axial ray and the final paraxial ray angle, and φ _S and φ _m are radials. The refractive power of the surface of the type gradient index lens and the thin thickness of the medium.

The refractive power of the medium is approximated by the equation (e).

Φ _m ≈−2N ₁₀ t _G (e) where t _G is the lens thickness of the radial type gradient index lens.

Here, in the present invention, since the radial type gradient index lens element has the shape of both planes in order to improve the manufacturability, φ _S ≈0, and the equation (d) is only the second term. Further, since the homogeneous lens is adhered or closely attached, the axial chromatic aberration of the combined lens of the present invention is represented by the following formula (f).

PAC = K (φ _h / ν _h + φ _m / V ₁₀ ) (f) where φ _h and ν _h are the thin-walled refractive power of the homogeneous lens adhered or closely attached to the radial type gradient index lens and Abbe number.

From equation (f), it can be seen that the amount of axial chromatic aberration generated can be controlled by changing the value of V ₁₀ . Therefore, the same refracting power φ as the combined lens of the present invention is used.
Considering the case where the axial chromatic aberration is made smaller than that of a homogeneous lens having an Abbe number of ν _h, it is necessary to satisfy the following equation.

K (φ _h / ν _h + φ _m / V ₁₀ ) <K (φ / ν _h ) However, if φ = φ _m + φ _h is expanded, φ _m / V ₁₀ <φ _m / ν _h From this, the above condition (1) is derived.

As described above, when the Abbe number ν _h of the homogeneous lens of the combination lens and the medium Abbe number V ₁₀ of the radial type gradient index lens element satisfy the condition (1), the axial chromatic aberration is satisfactorily corrected. It becomes possible. That is, the condition (1) is a necessary condition for favorably correcting the axial chromatic aberration with the combined lens of the present invention, and if the condition (1) is not satisfied, the axial chromatic aberration of the combined lens is insufficiently corrected. Therefore, it is not preferable.

Further, in order to satisfactorily correct the axial chromatic aberration, in addition to the condition (1), it is necessary to set the refractive power arrangements of the homogeneous lens and the radial type gradient index lens element to appropriate values. However, when setting the refractive power arrangement, it is necessary to sufficiently consider the Petzval sum correction in addition to the chromatic aberration. This is because the Petzval sum is an aberration whose generation amount is substantially determined by the refractive power arrangement of the lens system, like chromatic aberration, and it is difficult to correct it by pending etc. once the arrangement is determined.

The Petzval sum PTZ of the radial type gradient index lens unit is expressed by an approximate expression of the following expression (g).

PTZ = φ _S / N ₀₀ + φ _m / N ₀₀ ² (g) Further, in the present invention, since both surfaces are formed to improve manufacturability, φ _S ≈0, and the equation (g) is There are only two terms. Further, since a homogeneous lens is adhered or closely attached, the Petzval sum of the combination lens of the present invention is represented by the following formula (h).

PTZ = φ _h / n _h + φ _m / N ₀₀ ² (h) where n _h is the refractive index of the homogeneous lens.

From the equation (h), the denominator of the second term is squared, so that, for example, the value of the Petzval sum generated in the combination lens compared to a homogeneous lens having the same refractive power and having a refractive index n _h. Can be made smaller.

Next, from the equations (f) and (h), consider the arrangement of appropriate refractive power for simultaneously correcting the axial chromatic aberration and Petzval sum of the combined lens.

First, for easy understanding, the parameter of the refractive power ratio a of the medium given by the following equation (i) is given by the equation (f),
When introduced into formula (h), formula (f ') and formula (h'), respectively
Is obtained.

A = φ _m / φ (φ = φ _m + φ _h ) (i) PAC = Kφ {(ν _h −V ₁₀ ) a + V ₁₀ } / (ν _h V ₁₀ ) (f ′) PTZ = φ {( n _h −N ₀₀ ² ) a + N ₀₀ ² } / (n _h N ₀₀ ² ) (h ′) Here, in order to make it easy to understand the relationship between the refractive power ratio a of the medium and the axial chromatic aberration and Petzval sum, the expression (f FIG. 17 is a graph of ') and equation (h'). In FIG. 17, the horizontal axis represents the refractive power ratio a of the medium, and the vertical axis represents the axial chromatic aberration PAC and Petzval sum PTZ of the combined lens. Also,
In the figure, a _PAC is the value of the refractive power ratio a of the medium when the axial chromatic aberration PAC = 0 of the combined lens, and a _PTZ is the refractive power ratio a of the medium when the Petzval sum PTZ = 0 of the combined lens. Values, which are given by equation (j) and equation (k) below.

A _PAC = V ₁₀ / (V ₁₀ −ν _h ) (j) a _PTZ = N ₀₀ ² / (N ₀₀ ² −n _h ) (k) From FIG. 17, axial chromatic aberration and Petzval sum are simultaneously corrected. To realize this, first, it is necessary that a _PAC and a _PTZ have close values. For example, if the signs of a _PAC and a _PTZ are different, it becomes impossible to correct axial chromatic aberration and Petzval sum at the same time with the combination lens. In addition to this, if the value of the refractive power ratio a of the medium also has a value close to these values, it is possible to achieve a combined lens in which axial chromatic aberration and Petzval sum are extremely well corrected.

However, since the refractive index N ₀₀ on the optical axis does not greatly differ from the refractive index of the existing homogeneous glass in manufacturing the gradient index material, N ₀₀ is a value of about 1.5 to 1.9. have. Also, the refractive index n _h of the homogeneous glass is 1.5 to 1.9.
Since it is a value of the degree, the expression (k) is the following relational expression (k ').
To be satisfied.

A _PTZ = N ₀₀ ² / (N ₀₀ ² −n _h )> 1 (k ′) Since the combination lens of the present invention satisfies the condition (1), the expression (j) is expressed by the following relation. Expression (j ') is satisfied.

A _PAC = V ₁₀ / (V ₁₀ −ν _h )> 0 (j ′) From this, the values of a _PAC and a _PTZ when the axial chromatic aberration and Petzval sum values are well corrected are It is necessary to be 0 or more, and the value of the refractive power ratio a of the medium must be 0 or more. Further, from (k ′), it is more desirable that the value of the refractive power ratio a of the medium is 1 or more. That is, it is desirable that the refractive power of the medium of the radial type gradient index lens and the refractive power arrangement of the homogeneous lens satisfy the relationship of the following expression (i ′).

Φ _m / (φ _m + φ _h )> 1 (i ′) If the refractive powers of the radial type gradient index lens component and the homogeneous lens forming the combination lens satisfy the expression (h ′), the axial chromatic aberration is obtained. It is possible to satisfactorily correct the Petzval sum.

Further, since it is desirable for the combined lens of the present invention to have a positive refracting power, it is necessary to satisfy φ _m > 0 and φ _h <0 for the expression (h ′) to hold. . That is, it is necessary that the refractive power of the medium of the radial type gradient index lens has a positive value and the refractive power of the homogeneous lens has a negative value. If the homogeneous lens has a positive value, it becomes difficult to satisfactorily correct Petzval sum and axial chromatic aberration.

Further, in order to satisfactorily correct the axial chromatic aberration and Petzval sum in the combination lens of the present invention, it is desirable that the homogeneous lens has a certain large negative refractive power.
As described above, the refractive power of the medium of the radial type gradient index lens has a positive value, and the refractive power of the homogeneous lens has a negative value, which is necessary for good correction of axial chromatic aberration and Petzval sum. This is a condition, but if the refractive power of the homogeneous lens is extremely small at this time, it becomes difficult to satisfactorily correct the Petzval sum in particular. Therefore, it is desirable to satisfy the following condition (2).

[0035] _{(2) -2 <f c /} f h <-0.05 However, f _c is the focal length of the focal length, f _h is homogeneous lens combination lenses.

If the combined lens of the present invention satisfies the condition (2), it is possible to satisfactorily correct the Petzval sum. If the upper limit of -0.05 of the condition (2) is exceeded, the Petzval sum will be undercorrected and the image plane will tilt toward the object side, which is not preferable. If the lower limit of -2 is exceeded, the Petzval sum will be overcorrected and the image plane will tilt away from the object, which is not preferable.

When the combined lens of the present invention is applied to a white optical system, it is desirable that the combined lens has a large refracting power φ. This is because even if the axial chromatic aberration and Petzval sum are satisfactorily corrected, these effects cannot be effectively used if the refractive power is weak. Therefore, it was considered to increase the refracting power φ (= φ _m + φ _h ) while considering the correction of axial chromatic aberration and Petzval sum. In order to increase the refractive power φ, there is a method of increasing the positive refractive power of the radial type gradient index lens or weakening the negative refractive power of the homogeneous lens. However, weakening the negative refracting power of the homogeneous lens as described above is not preferable in terms of Petzval sum correction. Therefore, we considered increasing the positive refractive power of the medium of the radial type gradient index lens. From the equation (e), it is necessary to increase N ₁₀ or increase t _G in order to increase the refractive power of the medium. However, it is difficult to manufacture a material having an extremely large N ₁₀ in terms of manufacturing a material having a refractive index distribution. In the present invention, considering that the lens thickness of the radial type gradient index lens element is set to an appropriate thickness so as to obtain a sufficient refractive power without making N ₁₀ extremely large, the following condition (3) is considered.
It is desirable to satisfy

(3) 0.1 <t _G / f _T <7 where f _T is the focal length of the optical system to which the combination lens is applied, and in the case of a zoom lens, it is the focal length at the wide-angle end.

If the condition (3) is satisfied, it becomes possible to effectively use the effect of correcting axial chromatic aberration and Petzval sum when the combined lens of the present invention is applied to an optical system. If the lower limit of 0.1 is exceeded, the refractive power of the combined lens will be weakened, and it will be difficult to effectively use the effect of correcting axial chromatic aberration and Petzval sum. On the other hand, if the upper limit of 7 is exceeded, the lens becomes thick and the manufacturing cost of the radial type gradient index lens element becomes high, which is not preferable.

Further, when the combined lens of the present invention is applied to a lens system which requires higher performance of image formation, it is desirable to further satisfy the condition (4).

(4) 0.25 <t _G / f _T <5.5 If the lower limit of 0.25 is exceeded, the refracting power of the combination lens will be weakened, and the effect of correcting axial chromatic aberration and Petzval sum will be reduced. It becomes difficult to effectively use it in a lens system that requires high-performance imaging performance. On the other hand, if the upper limit of 5.5 is exceeded, the lens becomes thick and the transmittance and flare deteriorate, so that it becomes difficult to achieve high-performance imaging performance.

Further, when the axial chromatic aberration of the optical system is better corrected by using the combination lens of the present invention, it is desirable to satisfy the following condition (5).

(5) −0.05 <1 / V ₁₀ <0.012 If the radial type gradient index lens element satisfies the condition (5), it may be possible to correct axial chromatic aberration better. If the upper limit of 0.012 is exceeded, axial chromatic aberration will be undercorrected, which is not preferable. If the lower limit value of -0.05 is exceeded, the axial chromatic aberration will be overcorrected, which is not preferable.

Further, when the combined lens of the present invention is applied to an optical system in which correction of chromatic aberration is particularly important, such as a microscope objective lens, it is desirable to satisfy the condition (6).

(6) −0.03 <1 / V ₁₀ <0.008 If the radial type gradient index lens element satisfies the condition (6), it is applied to an optical system in which correction of axial chromatic aberration is particularly important. can do. If the upper limit of 0.008 is exceeded, axial chromatic aberration will be undercorrected, which is not preferable.
If the lower limit value of -0.03 is exceeded, axial chromatic aberration will be overcorrected, which is not preferable.

Further, the radial type gradient index lens element can control the amount of spherical aberration generated by changing the value of the fourth-order term N ₂₀ of the refractive index distribution. In order to satisfactorily correct spherical aberration in the combined lens of the present invention, it is desirable to satisfy the condition (7).

(7) −0.6 <N ₂₀ × f _T ⁴ <0.6 If the radial type gradient index lens element satisfies the condition (7), it becomes possible to excellently correct spherical aberration. If the upper limit of 0.6 is exceeded, spherical aberration will be overcorrected, which is not preferable. If the lower limit of -0.6 is exceeded, spherical aberration will be undercorrected, which is not preferable.

Further, when the combined lens of the present invention is applied to a lens system which requires higher performance of image formation, it is desirable to satisfy the following condition (8).

(8) −0.4 <N ₂₀ × f _T ⁴ <0.4 If the radial type gradient index lens element satisfies the condition (8), spherical aberration can be corrected more favorably. .
If the upper limit of 0.4 is exceeded, spherical aberration will be overcorrected and high-performance imaging performance cannot be achieved, which is not preferable. On the other hand, if the lower limit value of -0.4 is exceeded, spherical aberration will be undercorrected and high-performance imaging performance cannot be achieved, which is not preferable.

Further, in the combination lens of the present invention,
By satisfying the condition (1), it is possible to reduce the generation amount of the axial chromatic aberration. However, in the case where the lateral chromatic aberration as well as the lateral chromatic aberration is corrected well, the following condition (9) is satisfied. Is desirable.

(9) 1 / ν _h <0.025 Since the ray heights of the off-axis rays passing through the homogenous lens and the radial type gradient index lens element constituting the combination lens of the present invention are different, chromatic aberration is generated in any lens. It is desirable that the generation amount of is small. Therefore, the homogeneous lens condition is (9)
If the above condition is satisfied, it is possible to excellently correct lateral chromatic aberration as well as lateral chromatic aberration. If the condition (9) is not satisfied, lateral chromatic aberration will be undercorrected.

Further, in the lens system of the present invention, it is desirable to satisfy the following condition (10) in order to correct the Petzval sum better.

(10) N _00d > 1.55 If the condition (10) is satisfied, the value of the second term of the formula (h) becomes smaller, and the Petzval sum generated in the medium of the radial type gradient index lens element is sufficiently small. It can be made very small. If the condition (10) is not satisfied, the Petzval sum generated in the medium will be undercorrected, which is not preferable.

Further, in the combination lens system of the present invention, a homogenous lens or a radial type gradient index lens element is constructed by an optical element which has an effect of, for example, a low pass filter or a band cut filter for cutting a specific wavelength component. It is also possible to realize a functional combination lens.

By using an aspherical surface as the homogeneous spherical lens, it is possible to satisfactorily correct various aberrations.

Further, considering that the combination lens of the present invention is manufactured at a low cost, it is desirable that the homogeneous lens has a concave surface and a plane shape. If the surface on one side is flat, polishing is extremely easy and processing can be performed at low cost.

Further, in the combined lens of the present invention, if homogeneous lenses are adhered or adhered to both surfaces of the radial type gradient index lens element, various aberrations, particularly chromatic aberration and Petzval sum can be corrected well. Is. Further, in order to easily match the optical axes of the homogeneous lens and the radial type gradient index lens element with high accuracy, at least one surface of at least one side of the homogeneous lens has a planar shape, and the radial type refractive index at the plane portion. Adhesion or close contact with a distributed lens is desirable. For example, if the outer diameters of a homogeneous lens and a radial type gradient index lens are made equal, and both lenses are adhered or adhered to each other on a flat surface with the outer diameters as a boundary, it is easy and highly accurate. It is possible to match the optical axes of both lenses. Also,
As another method, measure the optical axis position of one or both of the homogeneous lens and the radial type gradient index lens, and adjust the lens position so that the optical axes of both lenses match, and bond or adhere both lenses. It is also possible. At this time, if both lenses have a flat surface portion and both lenses are in contact with each other, the adjustment becomes extremely easy. In addition, the adhesion or close contact between the two lenses has an advantage that the lens frame structure can be simplified. In addition, even if a ring (spacer) for adjusting the lens interval or a thin plate for the diaphragm is inserted between the homogeneous lens and the radial type gradient index lens element, almost the same effect can be obtained with respect to the above-mentioned workability and aberration correction. Can be obtained.

[0058]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the combination lens of the present invention will be described based on each example. The combination lens of the present invention is applied to various optical systems, for example, a wide-angle endoscope objective lens as in Example 3, a microscope objective lens as in Example 5, or a zoom as in Example 6. It is applied to various optical systems such as lenses. It is also possible to use two sets of combination lenses as in the fourth embodiment.

Examples of the compound lens of the present invention will be shown below. Example 1 f _T = 4.2, F number 2.0, 2ω = 42 ° r ₁ = -10.4898 d ₁ = 1.0000 n ₁ = 1.48749 ν ₁ = 70.21 r ₂ = ∞ d ₂ = 8.0000 n ₂ (refractive index distribution lens) r ₃ = ∞ d ₃ = 1.0000 n ₃ = 1.51633 ν ₃ = 64.15 r ₄ = ∞ Gradient distribution lens N ₀₀ N ₁₀ N ₂₀ d line 1.75000, -0.9934 x 10 ^-1 , -0.28601 x 10 ^-4 C line 1.74500, -0.19904 x 10 ^-1 , -0.28557 x 10 ^-4 F wire 1.76167, -0.20005 x 10 ^-1 , -0.28703 x 10 ^-4 1 / V ₁₀ = 0.005, 1 / ν _h = 0.014, f _C / f _h = -0.195 t _G / f _T = 1.905, N ₂₀ × f _T ⁴ = -0.009

Example 2 f _T = 4.88, F number 3.5, 2ω = 28.6 ° r ₁ = 10.11312 d ₁ = 1.8000 n ₁ = 1.84666 ν ₁ = 23.78 r ₂ = 4.3922 (aspherical surface) d ₂ = 0.5000 r ₃ = ∞ d ₃ = 8.0000 n ₂ (refractive index distribution lens) r ₄ = ∞ d ₄ = 1.0000 n ₃ = 1.51633 ν ₃ = 64.15 r ₅ = ∞ aspherical coefficient P = 1, A ₄ = -0.63278 × 10 ^-2 , A ₆ = 0.38524 × 10 ^-2 A ₈ = -0.12709 × 10 ^-2 Refractive index distribution lens N ₀₀ N ₁₀ N ₂₀ d line 1.75000, -0.19934 × 10 ^-1 , -0.28601 × 10 ^-4 C line 1.74500, -0.19904 × 10 ^-1 , 、 0.28557 × 10 ^-4 F line 1.76167 、 -0.20005 × 10 ^-1 , -0.28703 × 10 ^-4 1 / V ₁₀ = 0.005, 1 / ν _h = 0.042 、 f _C / f _h = 0.456 t _G / f _T = 1.641, N ₂₀ × f _T ⁴ = -0.016

Example 3 f _T = 0.844, NA = 0.011, 2ω = 129.2 °, object point distance 11 mm r ₁ = ∞ d ₁ = 0.3600 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 0.6800 d ₂ = 0.8000 r ₃ = ∞ d ₃ = 3.8000 n ₂ (refractive index distribution lens) r ₄ = ∞ d ₄ = 2.8000 n ₃ = 1.51633 ν ₃ = 64.15 r ₅ = ∞ refractive index distribution lens N ₀₀ N ₁₀ N ₂₀ N ₃₀ d line 1.70000, -0.12580, 0.78000 x 10 ^-2 , -0.47000 x 10 ^-3 C line 1.69475, -0.12567, 0.77922 x 10 ^-2 , -0.46953 x 10 ^-3 F line 1.71225, -0.12609, 0.78182 x 10 ^-2 , -0.47110 x 10 ^-3 1 / V ₁₀ = 0.003, 1 / ν _h = 0.025, f _C / f _h = -1.096 t _G / f _T = 4.502, N ₂₀ × f _T ⁴ = 0.004

Example 4 Magnification 10 ×, image height 13.25 mm, NA = 0.3, WD = 8.2368 mm r ₁ = -15.1221 d ₁ = 2.1659 n ₁ = 1.48749 ν ₁ = 70.21 r ₂ = ∞ d ₂ = 1.4031 n ₂ (Refractive index distribution lens 1) r ₃ = ∞ d ₃ = 14.6902 r ₄ = -15.1221 d ₄ = 2.1659 n ₃ = 1.48749 ν ₃ = 70.21 r ₅ = ∞ d ₅ = 6.2606 n ₄ (Refractive index distribution lens 2) r ₆ = ∞ Gradient distribution lens 1 N ₀₀ N ₁₀ N ₂₀ N ₃₀ d line 1.74320, -0.44065 x 10 ^-2 , 0.15976 x 10 ^-5 , -0.10847 x 10 ^-8 C line 1.73865, -0.44012 x 10 ^-2 , 0.15955 × 10 ^-5 , -0.10826 × 10 ^-8 F line 1.75372, -0.44190 × 10 ^-2 , 0.16028 × 10 ^-5 , -0.10880 × 10 ^-8 Gradient index lens 2 N ₀₀ N ₁₀ N ₂₀ N ₃₀ d line 1.74320, -0.27110 x 10 ^-2 , 0.41329 x 10 ^-5 , 0.33007 x 10 ^-8 C line 1.73865, -0.27005 x 10 ^-2 , 0.41183 x 10 ^-5 , 0.32896 x 10 ^-8 F line 1.75372, -0.27356 x 10 ^{-2, 0.41669 × 10 -5, 0.33284} × 10 -8 combination lens 1 1 / V ₁₀ = 0.004, _{/ Ν h = 0.014, f C} / f h = -0.449 t G / f T = 0.723, N 20 × f T 4 = 0.099 combination lens _{2 1 / V 10 = 0.013,} 1 / ν h = 0.014, f C / f _h = -7.118 t _G / f _T = 0.397, N ₂₀ × f _T ⁴ = 0.256

Example 5 Magnification 20 ×, image height 10.5 mm, NA = 0.4, WD = 1.06 mm r ₁ = ∞ d ₁ = 21.6063 n ₁ (refractive index distribution lens) r ₂ = ∞ d ₂ = 1.5278 n ₂ = 1.48749 ν ₂ = 70.21 r ₃ = 5.3752 d ₃ = 1.9921 r ₄ = -3.7704 d ₄ = 5.7047 n ₃ = 1.54814 ν ₃ = 45.78 r ₅ = -6.7479 d ₅ = 0.1000 r ₆ = -15.9975 d ₆ = 11.3836 n ₄ = 1.88300 ν ₄ = 40.78 r ₇ = -20.0917 Refractive index distribution lens N ₀₀ N ₁₀ N ₂₀ N ₃₀ d line 1.67000, -0.73239 x 10 ^-2 , 0.13526 x 10 ^-4 , -0.10734 x 10 ^-7 C line 1.66521, -0.73091 x 10 ^-2 , 0.13499 x 10 ^-4 , -0.10712 x 10 ^-7 F wire 1.68117, -0.73583 x 10 ^-2 , 0.13590 x 10 ^-4 , -0.10785 x 10 ^-7 1 / V ₁₀ = 0.007, 1 / Ν _h = 0.014, f _C / f _h = -0.469 t _G / f _T = 2.303, N ₂₀ × f _T ⁴ = 0.105

Example 6 f _T = 8.99 to 23.54 to 72.01, F number 2.0 to 2.0 to 2.0 2ω = 51 ° to 20 ° to 6.4 ° r ₁ = 56.9216 d ₁ = 1.8000 n ₁ = 1.84666 ν ₁ = 23.78 r ₂ ＝ 37.1745 d ₂ ＝ 5.5000 n ₂ ＝ 1.61800 ν ₂ ＝ 63.39 r ₃ ＝ 411.4915 d ₃ ＝ 0.2000 r ₄ ＝ 35.4817 d ₄ ＝ 4.2000 n ₃ ＝ 1.49700 ν ₃ ＝ 81.61 r ₅ ＝ 70.4018 d ₅ ＝ D ₁ (variable) _{r 6 = 78.8955 d 6 = 1.0000} n 4 = 1.61800 ν 4 = 63.39 r 7 = 10.1490 d 7 = 5.4000 r 8 = -39.8780 d 8 = 1.0000 n 5 = 1.61800 ν 5 = 63.39 r 9 = 50.0629 d 9 = 0.2000 r _{10 = 18.0611 d 10 = 2.8700 n} 6 = 1.83350 ν 6 = 21.00 r 11 = 32.1135 d 11 = D 2 ( variable) r ₁₂ = ∞ _{(stop) d 12 = 6.0000 r 13 =} 43.3128 d 13 = 4.4001 n 7 = 1.74100 _{ν 7 = 52.65 r 14 = -124.7618} d 14 = 1.0000 r 15 = -88.9910 d 15 = 3.3028 n 8 = 1.69895 ν 8 = 30.12 r 16 = ∞ d 16 = 2.5105 n 9 ( gradient index lens) r ₁₇ = d ₁₇ = D _{3 (variable) r 18 = 42.7284 d 18 =} 1.8000 n 10 = 1.78472 ν 10 = 25.71 r 19 = 15.7567 d 19 = 7.8648 n 11 = 1.72916 ν 11 = 54.68 r 20 = -45.1076 d 20 = D 4 _{(variable) r 21 = ∞ d 21 =} 5.0000 n 12 = 1.51633 ν 12 = 64.15 r 22 = ∞ gradient index lens _{n 00 n 10 n 20 n 30} d line ^{1.70000, -0.26527 × 10 -2, 0.39061} × 10 - ^5, 0.59043 × 10 ^-8 C line ^{1.69618, -0.26649 × 10 -2, 0.39061} × 10 -5, 0.59043 × 10 -8 F line ^{1.70891, -0.26242 × 10 -2, 0.39061} × 10 -5, 0.59043 × 10 - ⁸ f 8.99 23.54 72.01 D ₁ 1.5 23.327 39.68 D ₂ 40.187 18.356 2.0 D ₃ 8.242 5.421 9.347 D ₄ 3.195 6.018 2.092 1 / V ₁₀ = -0.015, 1 / ν _h = 0.033, f _C / f _h = -1.378 t _G / F _T = 0.279, N ₂₀ × f _T ⁴ = 0.026

Example 7 f _T = 1.18, NA = 0.01, 2ω = 74.8 °, object distance 15 mm r ₁ = ∞ d ₁ = 0.3000 n ₁ = 1.51633 ν ₁ = 64.15 r ₂ = 1.1693 d ₂ = 0.3000 r ₃ = ∞ d ₃ = 1.5926 n ₂ (refractive index distribution lens) r ₄ d ₄ = 0.8325 n ₃ = 1.51633 ν ₃ = 64.15 r ₅ = -0.9417 (aspherical surface) aspherical coefficient P = 1, A ₄ = 0.38208, A _{6 = -0.87563, A 8 = 0.10053} × 10 index lens _{N 00 N 10 N 20 N 30} d line 1.62000, -0.17530, -0.18627,0.74637 C line 1.61628, -0.17530, -0.18627,0.74638 F line 1.62868, - 0.17529, -0.18626, 0.74635 1 / V ₁₀ = 0.000, 1 / ν _h = 0.016, f _C / f _h = -1.764 t _G / f _T = 1.353, N ₂₀ × f _T ⁴ = -0.358 where r ₁ , r ₂ , ... is the radius of curvature of each surface of the lens, d
₁ , d ₂ , ... Is the thickness of each lens and the lens interval, n
₁ , n ₂ , ... Are refractive indices of d-line of each lens, ν ₁ , ν
₂ , ... Is the Abbe number of each lens.

An embodiment of the present invention is shown in FIG.
That is, it is a combination lens in which a first lens that is a negative lens and a second lens that is a positive lens are arranged in order from the object side, and the second lens is a radial type gradient index lens element having both planes. The negative first lens has a concave surface on the object side and a flat surface on the image side, and is adhered or adhered to the radial type gradient index lens element at this flat surface portion. Further, by providing the diaphragm S between the homogeneous lens L _h and the radial type gradient index lens L _g , the ray height of off-axis rays passing through the lens system is lowered, which helps to reduce the lens diameter. There is.

The combination lens of this embodiment can be used as a part of an optical system used under a white light source such as a silver halide camera or a microscope objective lens, but a CCD is provided at the image plane position.
By arranging a solid-state image pickup device such as a CMD or a CMD, it can be used as an image pickup system used for a videophone or an intercom, for example. Example 1 is an example used in such an image pickup system. A filter F for cutting a specific wavelength component is adhered or adhered to the image side surface of the radial type gradient index lens element, and the image plane position is A solid-state image sensor E is arranged.

If the radial type gradient index lens element or the homogeneous lens element has a filter function for cutting a specific wavelength component, the filter F in FIG. 1 can be omitted.

Further, in Example 1, since the homogeneous lens L _h has a negative refractive power, 1 / V ₁₀ of the radial type gradient index lens component L _g has a small positive value in order to satisfactorily correct axial chromatic aberration. I tried to have it.

Further, the combined lens of the present invention has an advantage that it is particularly excellent in correction of spherical aberration, as compared with a radial type gradient index lens L _g which is directly spherically processed. In other words, if the concave surface is directly processed, the refractive index of this surface gradually decreases from the optical axis to the periphery,
It has the effect of weakening the negative refracting power and reduces the value of positive spherical aberration generated on the surface. For this reason, negative spherical aberration occurs as a whole. However, in the combination lens of the present invention, since the surface shape of the radial type gradient index lens element L _g is biplanar, the spherical aberration generated on the surface is almost 0, and such a problem does not occur, and the whole system does not occur. It is possible to excellently correct spherical aberration.

In the first embodiment, the diaphragm S is replaced by the homogeneous lens L.
Since it is provided between _h and the radial type gradient index lens L _g , a low dispersion glass satisfying 1 / ν _h <0.02 is used for the homogeneous lens. Therefore, it is possible to correct not only the axial chromatic aberration but also the chromatic aberration of magnification.

Further, the combined lens of the present invention has an excellent feature in correction of chromatic aberration as compared with a lens directly subjected to spherical surface processing. FIG. 18 is a glass map in which the vertical axis is the refractive index and the horizontal axis is the Abbe number. The area surrounded by the thick line is the approximate range of existing glass, and the arrows show the refractive index and Abbe number of the radial type gradient index lens. , The black circles represent the refractive index and Abbe number on the optical axis. For example, the values of the refractive index and the Abbe number distributed from the optical axis to the periphery of the radial type gradient index lens material manufactured by the ion exchange method or the sol-gel method are indicated by the arrow A in FIG. As shown in the figure, it is within the range of the existing glass. For example, as shown by the arrow B in FIG. 18, the refractive index on the optical axis and the Abbe number are within the range of the existing glass. It is extremely difficult to manufacture a radial type gradient index lens material whose Abbe number is out of the range of existing glass. However, there are cases where such a material is desired to correct various aberrations. For example, the material represented by the arrow B is a material that is advantageous for correcting chromatic aberration because it has a small dispersion.

By using the combination lens of the present invention, even if the radial type gradient index lens element is a material within the range of the existing glass, it is almost the same as a material having a refractive index distribution outside the range of the above existing glass. It is possible to obtain the same effect. This point will be specifically described with reference to the first embodiment. An arrow A represents the radial type gradient index lens of the first embodiment, N ₀₀ = 1.75, V ₀₀ = 45, V ₁₀ ≈20.
The axial chromatic aberration PAC _A having a value of 0 is represented by the following formula.

PAC _A = K (φ _S / 45 + φ _m / 200) Further, the axial chromatic aberration PAC _B of the arrow _B is expressed by the following formula.

PAC _B = K (φ _S /70.21+φ _m / 200) In the present Example 1, n _h = 1.48749, ν _h = 70.2
It is composed of a homogenous lens No. 1 and a radial type gradient index lens, and the axial chromatic aberration PAC _C of this combined lens is given by the following formula.

[0076] _{PAC C = K (φ h /70.21+φ} m / 200) Therefore, if you choose the refractive power of the homogeneous lens such that φ _h ≒ φ _s, table by an arrow B is practically difficult to produce the It is possible to achieve a combined lens having a chromatic aberration correction effect that is substantially the same as that of the material described above.

As described above, in the combination lens of the present invention,
By selecting a desired homogeneous lens, there is an advantage that the degree of freedom in aberration correction is increased.

The aberrations of Example 1 are as shown in FIG.
It can be seen that various aberrations are well corrected even though the number of lenses is two.

The second embodiment of the present invention is shown in FIG. In other words, it is a combination lens in which the first lens that is a negative lens and the second lens that is a positive lens are arranged in order from the object side, and the second lens is a radial type gradient index lens element having both planes. Further, the first lens has a meniscus shape with a concave surface facing the image side, and has a flat surface portion 1 on the outer peripheral portion with respect to the effective diameter of the image surface side surface, and this flat surface portion 1 forms a radial type gradient index lens element. Adhered or adhered.

In Example 2, the homogeneous lens of the combination lens used in Example 1 was replaced with a meniscus-shaped homogeneous lens L _h , and the radial type gradient index lens L _g was common, but This is an example of realizing a combination lens having different focal lengths. That is, the combination lens of the present invention has a radial type gradient index lens component L _{g as} shown in FIG.
Is a common type, and by combining homogeneous lenses of various shapes with different r, d, and n, for example, L _h1 , L _h2 , and L _h3 , the radial type gradient index lens L _g is one type, but the focal length is It is possible to achieve the combined lenses L _C1 , L _C2 , and L _{C3 in} which the amounts of various aberrations are different. Since the radial type gradient index lens can be used as a common component, it is possible to realize an inexpensive lens system in spite of being compatible with various lens systems used under a white light source.

Further, by providing the diaphragm S on the object side of the homogeneous lens at L _h , it is possible to particularly favorably correct off-axis aberrations.

Further, since the focal length is long as compared with the first embodiment and correction of axial chromatic aberration is particularly difficult, in this embodiment, the Abbe number of the homogeneous lens should satisfy 1 / ν _h > 0.03. did.

Further, various aberrations are well corrected by using an aspherical surface for the image side of the homogeneous lens. The shape of the aspherical surface used in the examples is represented by the following formula.

However, the above equation takes the x-axis in the optical axis direction,
The y axis is taken in the direction perpendicular to the optical axis, r is the radius of curvature on the optical axis, P is the conical constant, and A _2i is the aspherical coefficient.

When the homogenous lens and the radial type gradient index lens of the combination lens of the present invention are adhered, an adhesive may be applied to the plane portion indicated by 1 in FIG. 2 for assembly. 2 is an enlarged view of the portion indicated by B in the sectional view of FIG. 2 [A of FIG. 2]. As shown by reference numeral 3 in FIG. Is also possible.

The aberrations of Example 2 are as shown in FIG.
It can be seen that various aberrations are well corrected even though the number of lenses is two.

The third embodiment of the present invention is shown in FIG. That is, from the object side in order, the first lens of the negative lens,
This is a combination lens in which the second lens is a positive lens and the second lens is a radial type gradient index lens element of both planes. Further, the first lens is a plano-concave lens, and has a flat surface portion 1 on the outer peripheral portion with respect to the effective diameter of the image side surface, and the flat surface portion 1 is adhered or adhered to the radial type gradient index lens L _g . . Further, the diaphragm S is provided at a position of 1 mm from the object side surface of the radial type gradient index lens L _g toward the image side. Further, a filter F for cutting a specific wavelength component is used on the image side of the radial type gradient index lens.

The third embodiment is an example in which a wide angle of the lens system is achieved by increasing the negative refractive power of the homogeneous lens.
For example, it can be used for an objective lens of an endoscope.
When the combined lens of the present invention is applied to a wide-angle lens system as in Example 3, it is desirable to satisfy the following condition (11).

(11) -2 <f _C / f _h <-0.6 If the upper limit of condition (11) -0.6 is exceeded, it will be difficult to achieve a wide angle of view. If the lower limit of -2 is exceeded, the Petzval sum will be overcorrected and the image plane will tilt away from the object.

Further, in this embodiment, since the combined lens of the present invention is used in a lens system having a wide angle of view, it is particularly difficult to correct Petzval sum, but the radial type gradient index lens element has N _00d > 1.6. This is satisfactorily corrected by satisfying.

Further, by providing the diaphragm inside the radial type gradient index lens element, it is possible to reduce the diameter of the lens and to particularly favorably correct the off-axis aberration.

The aberration diagram of Example 3 is as shown in FIG.
It can be seen that various aberrations are well corrected even though the number of lenses is two.

The fourth embodiment of the present invention is shown in FIG. That is, it is composed of a combination lens L _{C1 including} a negative first lens and a positive second lens in order from the object side, and a combination lens L _{C2 including} a negative lens and a positive lens,
Each of the positive lenses is a radial type gradient index lens having both planes, and each of the negative lenses is a concave plane homogeneous lens. Example 4 is an example of achieving a high-performance microscope objective lens with a small number of lenses by using two sets of the combination lenses of the present invention.

By applying the combination lens of the present invention to the optical system used under the white light source as in Example 4, it is possible to achieve a high-performance lens system with a small number of lenses.

Further, as the homogeneous lens, lenses having the same r, d, and n are used, and as in the case described in Embodiment 2 with reference to FIG. 17, some of the lenses are common. Achieved cost reduction.

The aberrations of Example 4 are as shown in FIG. 11, and it can be seen that the various aberrations are well corrected.

The fifth embodiment of the present invention is shown in FIG. That is, the combination lens L _{C1 including} the first lens of the radial type gradient index lens element L _g and the second lens of the homogeneous lens element L _h having a negative refractive power in the form of a plane in order from the object side, and the homogeneous lens element with a negative refractive power. This is a microscope objective lens with a magnification of 20 times, which is composed of a third lens of the lens L _{h2 and} a fourth lens of the homogeneous lens L _h3 having a positive refractive power. The second lens is a plano-concave lens, and is cemented or adhered to the radial type gradient index lens on the object side surface. In the present embodiment, by using the combination lens, a lens system in which various aberrations are well corrected is achieved although the number of lenses is as small as four.

Further, the Petzval sum is satisfactorily corrected by using a homogeneous lens having a low refractive index and a negative refractive power as the combination lens. When the Petzval sum correction is particularly problematic in a microscope objective lens or an optical system having a wide angle of view as in this embodiment, it is desirable that the refractive index of the homogeneous lens constituting the combination lens is 1.6 or less. .

When the combination lens is applied to an optical system in which the transmittance or flare of the lens is a problem, such as a rigid endoscope or an objective lens of a microscope, the total length of the radial type gradient index lens element is about 40 mm or less. Is desirable.
Further, as in the present embodiment, the radial type gradient index lens element is
If it is about 5 mm or less, a lens system having a better imaging performance can be achieved.

Further, when the combination lens of the present invention is applied to a lens system having a relatively narrow angle of view such as a microscope objective lens, it is not preferable that a homogeneous lens having a negative refractive power has a large value, and the condition ( It is good to satisfy 12).

(12) −0.6 <f _C / f _h <−0.1 If the lower limit value of condition (11) −0.6 is exceeded, the Petzval sum is overcorrected and the image surface moves away from the object. Falls in the direction. If the upper limit of -0.1 is exceeded, the Petzval sum will be undercorrected and the image plane will tilt toward the object side.

The aberration diagram of the fifth embodiment is shown in FIG. 12, and it can be seen that various aberrations are well corrected.

The sixth embodiment of the present invention is shown in FIG. That is, in order from the object side, the first lens unit G ₁ having a fixed positive refractive power at the time of zooming and the second lens group G ₂ having a negative refractive power having a zooming action by moving back and forth on the optical axis at the time of zooming. And a zoom lens composed of a third lens unit G ₃ having a positive refractive power which is fixed at the time of zooming, and a fourth lens unit G ₄ having a positive refractive power which is movable at the time of zooming and has a function of correcting the shift of the focal position. . The first group G ₁ is composed of a cemented lens of a negative lens and a positive lens and a positive lens, and the second group G ₂
Is composed of a negative lens, a negative lens and a positive lens, and the third lens group G ₃
Is a combination lens L _c composed of a positive lens, a negative lens, and a positive radial type gradient index lens L _g , and the fourth group is a cemented lens of a negative lens and a positive lens. Third group G
_In the combination lens of No. _3, a concave flat homogeneous lens L _h and a radial type gradient index lens L _g having a shape of both planes are bonded or adhered. Especially in the combination lens, the third lens group G ₃
The axial chromatic aberration of is well corrected. Also, the third group G ₃
In particular, in order to satisfactorily correct spherical aberration in particular, one positive lens is used in addition to the combination lens, and it is particularly difficult to correct axial chromatic aberration. So, one of the combination lenses
This is satisfactorily corrected by making the value of / V ₁₀ have a negative value. Aberration diagrams of Example 6 are shown in FIGS. 13, 14 and 15.
It can be seen that various aberrations are well corrected.

The seventh embodiment of the present invention is shown in FIG. That is, it is a three-lens structure of a first lens of a negative lens, a second lens of a positive lens, and a third lens of a positive lens in order from the object side, and the second lens is composed of a radial type gradient index lens L _g of both planes It is a combined lens. Also, the first
The lens is a plano-concave lens, and has a flat surface portion 1 on the outer peripheral portion with respect to the effective diameter of the image-side surface, and the flat surface portion 1 is bonded or adhered to the radial type gradient index lens L _g . The third lens is a plano-convex lens, and is adhered or adhered to the radial type gradient index lens element on the object side surface. Example 7 is an example in which another lens is bonded or adhered to the combination lens of the present invention. The seventh embodiment is an example in which a lens system having a wide angle of view is realized by using a combination lens including the first lens and the second lens and a positive homogeneous lens. For example, an objective lens of an endoscope or a surveillance camera or It can be used as an optical system for board cameras.

Further, by making the diameter of the radial type gradient index lens constituting the combination lens different from the diameter of the homogeneous lens, the lens frame or the part 2 of the lens frame can be efficiently arranged, and the lens system Achieved miniaturization.

When the combination lens of the present invention is held by the lens frame, the homogenous lens and the radial type gradient index lens need not necessarily be bonded.

The aberrations of Example 7 are as shown in FIG. 16, and it can be seen that various aberrations are well corrected despite the fact that the number of lenses is two.

Next, the case where the compound lens of the present invention is manufactured will be described in detail in comparison with the conventional example.

FIG. 20 shows a conventional example, which is an example of the case where the radial type gradient index lens element L _g is directly subjected to spherical surface processing. FIG. 20A is a diagram showing a cylindrical radial type gradient index lens and a refractive index distribution before spherical surface processing,
In the figure, L _g is a radial type gradient index lens, n (r) is the refractive index at a point of radius r, and the optical axis 5 of the medium coincides with the central axis of the outer peripheral portion 6. FIG. 20B is an ideal example in which one surface R ₁ is processed into a spherical surface, and the optical axes of the surface and the medium coincide with each other. However, in the actual processing scene,
It is difficult to easily process the surface R ₁ with high precision as in the case of 0 (B), and as shown in FIG.
And the optical axis 7 of the plane R ₁ is δ in the direction 8 perpendicular to the optical axis of the medium,
The tilt angle ε may be eccentric. In the case of a homogeneous lens, even if such eccentricity occurs, decentering is not a problem because centering can be performed by cutting the lens outer periphery with the optical axis of the polished surface as a collision, but in the case of a radial type gradient index lens the medium is used. Since the optical axis of is eccentric with respect to the outer peripheral portion, centering cannot be performed.

Therefore, in the lens system of the present invention, as in the model shown in FIG. 21, a radial type gradient index lens L _g having a shape of both planes and a homogeneous spherical lens L _h having a plane portion P are used by adhering or adhering. I did it. FIG. 21A shows a radial type gradient index lens L _g whose both surfaces are processed into a flat surface and a homogeneous lens L _h having a flat surface P on one side. The optical axis 5 of the medium of the radial type gradient index lens L _g coincides with the central axis of the outer peripheral portion 6, and since the homogeneous lens L _h can be centered, the optical axis 5 of the surface R ₁ is the outer periphery. The central axis of the portion 6 can be easily matched with high accuracy. FIG. 21B shows a radial type gradient index lens L.
_g and the homogenous lens L _h with their respective planes P ₁ and P
₂ shows the figure that is adhered or adhered. At this time, for example, if the outer peripheral portion 6 of the radial type gradient index lens L _{g and} the outer peripheral portion 6 of the homogeneous lens L _h are aligned with each other, the optical axis of the medium of the radial type gradient index lens and the light of the homogeneous lens are matched. The axis can be easily matched.

Further, in the conventional method of manufacturing a radial type gradient index lens element shown in FIG. 20, if decentering occurs during spherical surface processing, the radial type gradient index lens element L _g cannot be used, resulting in poor yield and high cost. However, in the manufacturing method shown in FIG. 19 for the combined lens of the present invention, as described above, the eccentricity at the time of spherical surface processing does not pose any problem, so that the yield can be increased and processing can be performed at extremely low cost. Further, since the radial type gradient index lens has flat surfaces on both sides, it can be processed with high accuracy and at low cost.

In the present invention, the lens system described in the following items also achieves the object.

(1) A lens according to the first aspect of the invention, which is a combination lens satisfying the following condition (2).

(2) -2 <f _C / f _h <-0.05 (2) The first aspect of the claims or the above (1).
The lens described in the item (1), which is a combination lens satisfying the following condition (3).

(3) 0.1 <t _G / f _T <7 (3) The first aspect of the claims or the above (1).
Alternatively, in the lens described in the item (2), a combination lens satisfying the following condition (4).

(4) 0.25 <t _G / f _T <5.5 (4) As described in the first item of the claims or the above (1), (2) or (3). A combination lens that satisfies the following condition (5).

(5) −0.05 <1 / V ₁₀ <0.012 (5) As described in the first item of the claims or the above (1), (2) or (3). A combination lens that satisfies the following condition (6).

(6) −0.03 <1 / V ₁₀ <0.008 (6) The first aspect of the claims or the above (1), (2), (3), (4) or ( A lens combination described in the item 5), which satisfies the following condition (7).

(7) −0.6 <N ₂₀ × f _T ⁴ <0.6 (7) Claim 1 or the above (1), (2), (3), (4) A lens according to item (5) or (6), which satisfies the following condition (8).

(8) −0.4 <N ₂₀ × f _T <0.4 (8) Claim 1 or the above (1), (2), (3), (4), A lens combination described in the item (5), (6) or (7), which satisfies the following condition (9).

(9) 1 / ν _h <0.025 (9) Claim 1 or the above (1), (2), (3), (4), (5), (6) ),
A lens according to item (7) or (8), which satisfies the following condition (10):

(10) N _00d > 1.55 (10) The first item of the claims or the above (1), (2), (3), (4), (5), (6),
The lens described in (7), (8) or (9),
A combination lens in which at least one surface of the homogeneous lens is aspherical.

(11) The first item of the claims or the above (2), (3), (4), (5), (6),
The lens described in (7), (8), (9) or (10), which is a combination lens satisfying the following condition (11).

(11) −2 <f _C / f _h <−0.6 (12) The first item of the claims or the above (2), (3), (4), (5), ( 6), (7),
The lens described in (8), (9) or (10), which is a combination lens satisfying the following condition (12).

(11) −0.6 <f _C / f _h <−0.1

[0126]

According to the present invention, as is apparent from each of the embodiments, a combination lens having excellent workability and various aberrations, in particular axial chromatic aberration and Petzval sum, corrected satisfactorily is achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a fifth embodiment of the present invention.

FIG. 6 is a sectional view of a sixth embodiment of the present invention.

FIG. 7 is a sectional view of a seventh embodiment of the present invention.

8 is an aberration curve diagram of Example 1. FIG.

9 is an aberration curve diagram of Example 2. FIG.

FIG. 10 is an aberration curve diagram of Example 3

FIG. 11 is an aberration curve diagram of Example 4.

FIG. 12 is an aberration curve diagram of Example 5.

FIG. 13 is an aberration curve diagram for Example 6 at the wide-angle end.

FIG. 14 is a diagram of aberration curves at the intermediate focal length of Example 6.

FIG. 15 is an aberration curve diagram for Example 6 at the telephoto end.

16 is an aberration curve diagram for Example 7. FIG.

FIG. 17 is a graph showing the relationship between the refractive power ratio a of the medium, the axial chromatic aberration, and the Petzval sum.

FIG. 18 is a diagram showing a distribution of refractive index-Abbe number of a glass material.

FIG. 19 is a diagram showing an example of a combination of a radial type gradient index lens and a homogeneous lens.

FIG. 20 is a view showing an example in which a radial type gradient index lens, which is a conventional manufacturing example, is directly subjected to spherical surface processing.

FIG. 21 is a view showing an example of manufacturing the combined lens of the present invention.

Claims (1)

[Claims] 1. A radial type refraction represented by the following formula (a) in which at least one homogeneous lens having a negative refracting power and a refractive index distributed in a radial direction from an optical axis having a positive refracting power. The radial type gradient index lens has a shape of both planes, and at least one surface of at least one side of the homogeneous lens has a substantially planar shape. The shape portion and the flat shape portion of the radial type gradient index lens are bonded or adhered to each other,
A combination lens characterized by satisfying the condition (1). N (r) = N ₀₀ + N ₁₀ r ² + N ₂₀ r ⁴ (a) (1) 1 / V ₁₀ <1 / ν _h where r is the distance from the optical axis in the radial direction, N (r) Is the refractive index distribution at the distance r, N _i0 is the 2i th order refractive index distribution coefficient, ν _h is the Abbe number of the homogeneous lens, and V _i0 is the 2 i th order refractive index distribution coefficient of the radial type gradient index lens. It is expressed by the following equations (b) and (c). _{V 00 = (N 00d -1)} / (N 00F -N 00C) (i = 0) (b) V i0 = N i0d / (N i0F -N i0C) (i = 1,2,3 ··) ( c) Here, N _00d , N _00F and N _00C are d line and F, respectively.
The refractive indices of the lines C and C on the optical axis, N _i0d , N _i0F and N _i0C are the 2i-th order refractive index distribution coefficients of the d line, F line and C line, respectively.