JP3996685B2 - Achromatic lens - Google Patents

Description

【００２３】
これらの式（ｅ），（ｉ）からθ_1gF は次のようになる。

【００２４】
この式より、ラジアル型ＧＲＩＮレンズの媒質の部分分散比も、ここでの前提の範囲では、異常分散性を持たない通常のガラスと同様であることがわかる。
【００２５】
以上の内容と前記条件（３）とからラジアル型ＧＲＩＮレンズが異常分散性が少ない場合には、その媒質のアッベ数が次の条件（４）を満足することが望ましい。
（４） ６７＜Ｖ₁ ＜３７０
【００２６】
上記の条件（４）の上限、下限のいずれを超えても、対象とする３波長での色収差が大になり、可視領域全域での残存２次スペクトルを良好に補正することが困難になるか、ラジアル型ＧＲＩＮレンズの素材に、通常の素材とは大きく異なる異常分散性を有する素材が必要になり、素材の作製が困難になる。
【００２７】
また、本発明の色消しレンズにおいて、ラジアル型ＧＲＩＮレンズが異常分散性の極めて少ない場合、又は色消しレンズを厳密な２次スペクトル補正を行なう場合には、条件（４）の代りに次の条件（４−１）を満足することが望ましい。
（４−１） ８４＜Ｖ₁ ＜３１０
【００２８】
この条件（４−１）の上限、下限のいずれを超えても残存２次スペクトルの量が大きくなるか、厳密な２次スペクトル補正を行なうためには、通常とは異なる異常分散性を有する素材のＧＲＩＮレンズにせざるを得なくなり素材の作製上好ましくない。
以上の条件（３），（３−１），（４），（４−１）を満足させて色収差の補正を行なうとφ_m 、φ_D は同符号となる。
【００２９】
次に、本発明の色消しレンズにおいて、例えば図２に示すような、面に曲率のついたラジアル型ＧＲＩＮレンズと回折型レンズを組合わせた構成にした場合、ラジアル型ＧＲＩＮレンズの面にて発生する屈折力φ_S を考慮する必要がある。
【００３０】
ラジアル型ＧＲＩＮレンズが面に曲率を有する場合の色収差は、式（ｆ），（ｇ）の代りに次の式（ｍ），（ｎ）が用いられる。
ＰＡＣ＝Ｋ［（φ_S ／Ｖ₀ ）＋（φ_m ／Ｖ₁ ）＋（φ_D ／Ｖ_D ）］ （ｍ）
ＰＡＣ＝Ｋ［（φ_S ／Ｖ₀ ）θ_0gF ＋（φ_m ／Ｖ₁ ）θ_1gF
＋（φ_D ／Ｖ_D ）θ_D ］ （ｎ）
ここでＶ₀ ，θ_0gF は夫々ラジアル型ＧＲＩＮレンズの軸上のアッベ数および軸上の部分分散比である。θ_0gF は以下の式にて表される。
θ_0gF ＝（Ｎ_0g−Ｎ_0F）／（Ｎ_0F−Ｎ_0C）
ここでＮ_0gはｇ線における屈折率分布を表わす係数Ｎ₀ である。
【００３１】
この場合、取扱いが複雑になるが、条件（３），（３−１），（４），（４−１）は、次の式（ｏ），（ｐ），（ｑ）から求められる等価部分分散比θ_e1gFおよび等価アッベ数Ｖ_e1を夫々θ_1gF およびＶ₁ の代りに用いればラジアル型ＧＲＩＮレンズが曲率を有する場合まで拡張して扱うことができる。
φ＝φ_S ＋φ_m （ｏ）
φ／Ｖ_e1＝（φ_s ／Ｖ₀ ）＋（φ_m ／Ｖ₁ ） （ｐ）
（φ／Ｖ_e1）θ_e1gF＝（φ_S ／Ｖ₀ ）θ_0gF ＋（φ_m ／Ｖ₁ ）θ_1gF （ｑ）
ここで、φはラジアル型ＧＲＩＮレンズの全体の屈折力である。
【００３２】
これにより面に曲率を有するラジアル型ＧＲＩＮレンズと回折型レンズとを組合わせた構成の本発明の色消しレンズは、次の条件（１），（２）を満足することが望ましい。
（１） ０．１＜θ_e1gF＜０．５
（２） ６７＜Ｖ_e1＜３７０
【００３３】
更に条件（１），（２）の代りに下記条件（１−１），（２−１）を満足することが一層好ましく、例えば厳密な２次スペクトルの補正された色消しレンズを得ることができる。
（１−１） ０．２＜θ_e1gF＜０．４
（２−１） ８４＜Ｖ_e1＜３１０
【００３４】
尚、両面共に平面であるラジアル型ＧＲＩＮレンズの面のパワーφ_S は０である。φ_S ＝０である場合はこれら式は夫々下記のようになる。
θ_e1gF＝θ_1gF
Ｖ_e1＝Ｖ₁
【００３５】
つまり、前記条件（３）、（４）は条件（１）、（２）においてＶ_e1の代わりにＶ₁ を、θ_e1gFの代わりにθ_1gF とすればよい。したがって、面が曲面、平面のいずれのＧＲＩＮレンズにおいても条件（１）、（２）を満足することが望ましい。
【００３６】
以上述べた本発明の色消しレンズは、望遠鏡、顕微鏡の光学系の他、これと撮像素子とを組合わせた撮像装置を構成することが出来る。
【００３７】
【発明の実施の形態】
次に、本発明の色消しレンズの実施の形態を各実施例をもとに説明する。
【００３８】
実施例１は、図３に示す通りで両平面のラジアル型ＧＲＩＮレンズの像側の面上に回折型レンズを構成したものである。この実施例１のスペックおよびレンズデータは次の通りである。
ｆ＝10，Ｆ／4.0 ，最大像高 1.85
ｒ₁ ＝∞（絞り） ｄ₁ ＝6.9489 ｎ₁ （屈折率分布レンズ）
ｒ₂ ＝∞ ｄ₂ ＝0 ｎ₂ ＝1001 ν₂ ＝-3.45 ( 回折型レンズ）
ｒ₃ ＝-2.496×10⁵
屈折率分布レンズ
Ｎ₀ ＝1.6640，Ｎ₁ ＝-7.5000 ×10^-3，Ｖ₀ ＝38.2，Ｖ₁ ＝104
θ_1dC ＝0.30
θ_1gF ＝0.34，θ_e1gF＝0.34，Ｖ_e1＝104
【００３９】
実施例２は、図４に示すように物体側より両平面のラジアル型ＧＲＩＮレンズと平板ガラス上に作製された回折型レンズとより構成されている。このレンズのスペックおよびレンズデータは下記の通りである。
ｆ＝10，Ｆ／4.0 ，最大像高 1.85
ｒ₁ ＝∞（絞り）ｄ₁ ＝6.7176 ｎ₁ （屈折率分布レンズ）
ｒ₂ ＝∞ ｄ₂ ＝3.0000
ｒ₃ ＝∞ ｄ₃ ＝2.0000 ｎ₂ ＝1.51633 ν₂ ＝64.15
ｒ₄ ＝∞ ｄ₄ ＝ 0.0000 ｎ₃ ＝1001 ν₃ ＝-3.45 ( 回折型レンズ）
ｒ₅ ＝-6.696×10⁴
屈折率分布レンズ
Ｎ₀ ＝1.6640，Ｎ₁ ＝-7.5000 ×10^-3，Ｖ₀ ＝38.2，Ｖ₁ ＝101
θ_1dC ＝0.30
θ_1gF ＝0.35，θ_e1gF＝0.35，Ｖ_e1＝101
【００４０】
実施例３は、図５に示す通りの構成で、物体側が凹面で像側が平面のラジアル型ＧＲＩＮレンズとその側面の面上に回折型レンズを構成したものである。このレンズのスペックおよびレンズデータは下記の通りである。
ｆ＝10，Ｆ／4.0 ，最大像高 1.85
ｒ₁ ＝-10.000 （絞り）ｄ₁ ＝7.7588ｎ₁ （屈折率分布レンズ）
ｒ₂ ＝∞ ｄ₂ ＝0 ｎ₂ ＝1001 ν₂ ＝-3.45 （回折型レンズ）
ｒ₃ ＝-3.804×10⁵
屈折率分布レンズ
Ｎ₀ ＝1.60000 ，Ｎ₁ ＝-1.0000 ×10^-2，Ｖ₀ ＝45.00 ，Ｖ₁ ＝78
θ_1dC ＝0.30
θ_1gF ＝0.34，θ_e1gF＝0.21，Ｖ_e1＝184
本発明の実施例１〜３のデータ中で設計基準波長はｄラインであり、回折型レンズはいわゆる高屈折率近似を用い、基準波長ｄラインの屈折率が１００１となる形で示している。
【００４１】
図６は本発明の色消しレンズと同じスペックのレンズを通常の接合レンズ構成した色消しレンズで、下記データを有する接合レンズである。
ｆ＝10，Ｆ／4.0 ，最大像高 1.85
ｒ₁ ＝4.0230（絞り） ｄ₁ ＝3.0000 ｎ₁ ＝1.51633 ν₂ ＝64.15
ｒ₂ ＝-2.9157 ｄ₂ ＝1.0000 ｎ₂ ＝1.62004 ν₂ ＝36.26
ｒ₃ ＝234.6664
【００４２】
前記本発明の実施例１，２，３および図６に示す色消し接合レンズの軸上色収差は、次の通りである。

【００４３】
本発明の色消しレンズの特徴は以上述べた通りであり、特許請求の範囲の各請求項に記載する構成のものの他、次の各項に記載するものも本発明の目的を達成し得る。
【００４４】
（１）特許請求の範囲の請求項１に記載された色消しレンズで、条件（１）の代りに下記条件（１−１）を満足することを特徴とする色消しレンズ。
（１−１） ０．２＜θ_e1gF＜０．４
【００４５】
（２）特許請求の範囲の請求項２に記載された色消しレンズで、条件（２）の代りに下記条件（２−１）を満足することを特徴とする色消しレンズ。
（２−１） ８４＜Ｖ_e1＜３１０
【００４６】
（３）特許請求の範囲の請求項１または２あるいは前記（１）又は（２）の項に記載された色消しレンズで、ラジアル型ＧＲＩＮレンズが両面平面であることを特徴とする色消しレンズ。
【００４７】
（４）特許請求の範囲の請求項１又は２あるいは前記の（１）又は（２）の項に記載された色消しレンズで、ラジアル型ＧＲＩＮレンズの少なくとも１面が曲面であることを特徴とする色消しレンズ。
【００４８】
（５）前記の（４）の項に記載された色消しレンズで、ラジアル型ＧＲＩＮレンズの物体側の面が凹面であることを特徴とする色消しレンズ。
【００４９】
（６）前記（１），（２），（３），（４）又は（５）に記載された色消しレンズを備えたことを特徴とする撮像装置。
【図面の簡単な説明】
【図１】本発明の色消しレンズの基本構成を示す図
【図２】本発明の色消しレンズの他の構成を示す図
【図３】本発明の実施例１の構成を示す図
【図４】本発明の実施例２の構成を示す図
【図５】本発明の実施例３の構成を示す図
【図６】従来の色消しレンズの構成を示す図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an achromatic lens used in an optical system such as a telescope, a microscope, a camera, and a video camera, an imaging lens provided with an achromatic lens, and an imaging device provided with the achromatic lens.
[0002]
[Prior art]
In general, an optical system used in a telescope, a microscope, a camera, a video camera, or the like has a configuration in which a large number of lenses are combined in order to improve optical performance. In particular, in order to correct chromatic aberration of an optical system, a cemented achromatic lens called achromatic is often used. In this achromat, chromatic aberration is normally corrected for light of two wavelengths such as C-line and F-line, but chromatic aberration is strictly corrected for light of other wavelengths such as g-line. In other words, so-called secondary spectrum chromatic aberration remains. In particular, this residual chromatic aberration is often a problem for telescopes, microscope objective lenses, camera telephoto lenses, etc., and in order to correct this, a lens system in which achromaticity called apochromat is achromatic. Is used.
[0003]
However, in order to obtain an apollochromate, it is necessary to use glasses having anomalous dispersion such as fluorite and special low-dispersion glass. Since these glass materials are expensive and difficult to process, the optical system is expensive. .
[0004]
In addition to lenses that use ordinary refraction, there are lenses called diffractive lenses that use diffraction phenomena. This diffractive lens has chromatic dispersion characteristics different from those of ordinary lenses. As an example of using this diffractive lens for correcting the secondary spectrum of chromatic aberration, there is an optical system as shown in Applied Optics, Vol. 27, pages 2960-2971, which is a combination of a cemented lens and a diffractive lens. Is.
[0005]
Another example of a lens system in which chromatic aberration is corrected by using a diffractive lens is a lens system in which a diffractive lens and a radial GRIN lens are combined as disclosed in Japanese Patent Laid-Open No. 4-181908.
[0006]
[Problems to be solved by the invention]
An optical system combining a cemented lens and a diffractive lens as shown in the above-mentioned document (Applied Optics) has three optical elements, resulting in a large number of optical elements and high cost. In addition, the lens system combining the radial GRIN lens and the diffractive lens described in the above publication focuses only on the correction of the primary chromatic aberration, and does not describe the secondary spectrum.
[0007]
The present invention provides a lens system in which the secondary spectrum of chromatic aberration is highly corrected with few optical elements.
[0008]
[Means for Solving the Problems]
The achromatic lens of the present invention includes a radial type gradient index lens (radial type GRIN lens) whose refractive index changes in a direction perpendicular to the optical axis, and a diffractive optical element (diffractive type lens). (1) is satisfied.
(1) 0.1 <θ _e1gF <0.5
However, θ _e1gF is an equivalent partial dispersion ratio of the radial GRIN lens.
[0009]
The radial GRIN lens has a refractive index distribution in a direction perpendicular to the optical axis of the medium, and the refractive index distribution N (r) is expressed by the following formula (a).
N (r) = N ₀ + N ₁ r ² + N ₂ r ⁴ + N ₃ r ⁶ + (a)
In the above formula (a), N ₀ is the refractive index on the optical axis, N _i (i = 1, 2, 3...) Is a coefficient representing the refractive index distribution, and r is the distance in the vertical direction from the optical axis. is there.
[0010]
The Abbe number of the radial GRIN lens is given by the following equations (b) and (c).
_{V 0 = (N 0d -1)} / (N 0F -N 0C) (b)
V _i = N _id / (N _iF −N _iC ) (i = 1, 2, 3...) (C)
Here, N _iL (i = 0, 1, 2, 3,...) Is a coefficient representing the refractive index distribution at the wavelength L, and N _0d , N _0F , and N _0C are d-line, F-line, and C-line, respectively. Refractive indexes on the optical axis, N _id , N _iF , and N _iC are coefficients representing refractive index distributions on the d-line, F-line, and C-line, respectively.
[0011]
Further, the partial dispersion ratios θ _1dC and θ _1gF of the medium of the radial GRIN lens are given by the following equations (d) and (e).
θ _1dC = (N _1d −N _1C ) / (N _1F −N _1C ) (d)
θ _1gF = (N _1g −N _1F ) / (N _1F −N _1C ) (e)
Here, N _1g is a coefficient N ₁ representing the refractive index distribution in the g-line.
[0012]
A diffractive lens has a concentric pattern and acts as a lens due to light diffraction, and has a unique color dispersion compared to ordinary glass such as an Abbe number of -3.45. Has characteristics.
[0013]
As described above, the achromatic lens of the present invention is a lens in which the residual secondary spectrum of chromatic aberration is highly corrected by combining the radial GRIN lens and the diffractive lens.
[0014]
First, for example, as shown in FIG. 1, consider a lens system in which a dual-plane radial GRIN lens G and a diffractive lens D are combined. Here, assuming that the power of the medium of the radial GRIN lens G is φ _m , the power of the diffractive lens D is φ _D, and both lenses are arranged close to each other as shown in the figure, the thin-wall approximation uses this lens system. The C-line and F-line chromatic aberrations generated in this way are given by the following equation (f).
PAC = K {(φ _m / V ₁ ) + (φ _D / V _D )} (f)
Where V ₁ is the Abbe number of the medium of the radial GRIN lens, V _D is the Abbe number of the diffractive lens, and K is a constant.
[0015]
Further, the chromatic aberration of the g line with respect to the F line is given by the following equation (g).
PAC = K {(φ _m / V ₁ ) · θ _1gF + (φ _D / V _D ) · θ _D } (g)
Here, θ _1gF is a partial dispersion ratio of the medium of the radial GRIN lens, and θ _D is a partial dispersion ratio of the diffractive lens with respect to g-line and F-line.
Here, it is considered to perform achromatic processing regarding the three colors of C line, F line, and g line. For this purpose, the equations (f) and (g) must be simultaneously set to 0, and θ _1gF and θ _D must have the same value.
[0016]
Here, as described in the previous document, θ _D is 0.2956. Therefore, as a condition for three colors to be _erased , θ _1gF needs to take the following values.
θ _1gF = 0.2956 (h)
[0017]
The present invention is based on the conditions derived here, considering that the actual optical system is thick and that it is necessary to balance each wavelength in the visible region other than the three colors, In order to satisfactorily correct the secondary spectrum, the following condition (3) was satisfied.
(3) 0.1 <θ _1gF <0.5
[0018]
If either the upper limit or the lower limit of the condition (3) is exceeded, the secondary spectrum cannot be corrected well.
[0019]
In the achromatic lens of the present invention, it is desirable to satisfy the following condition (3-1) instead of the condition (3) in order to reduce chromatic aberration strictly at three wavelengths.
(3-1) 0.2 <θ 1 _gF <0.4
[0020]
Next, consider the partial dispersion ratio θ 1 _gF of the radial GRIN lens. The refractive index of optical glass is expressed by the following formula (i) according to Herzberger's dispersion formula (published by the Japan Opto-Mechatronics Association, “Optical I-Optics: Basics and Design of Optical Systems” on page 395). It is expressed as
n (L) = 1 + (n _d −1) {1 + B (L) + A (L) τ _d } (i)
Here, A (L) and B (L) are coefficients that depend only on the wavelength L, and τ _d is the dispersion factor and the inverse of the Abbe number.
[0021]
From the above equation (i), the following equation (j) is derived.
δn (L) = {1 + B (L) + A (L) τ _d } δn _d +
A (L) (n _d −1) δτ _d (j)
[0022]
Now, assuming that the characteristics of the glass in each minute region of the radial GRIN lens satisfy Hertzberger's relational expression, considering the vicinity of the optical axis, assuming that the higher-order coefficient of N ₂ or higher representing the distribution is small,
N _1L = δn _L / δr ² (k)
Therefore, the Abbe number V _{1 of the} medium is given by the following equation (1).

[0023]
From these equations (e) and (i), θ _1gF is as follows.

[0024]
From this equation, it can be seen that the partial dispersion ratio of the medium of the radial GRIN lens is the same as that of ordinary glass having no anomalous dispersion within the range of the premise here.
[0025]
From the above contents and the condition (3), when the radial GRIN lens has a small anomalous dispersion, it is desirable that the Abbe number of the medium satisfies the following condition (4).
(4) 67 <V ₁ <370
[0026]
Whether the upper limit or the lower limit of the above condition (4) is exceeded, does the chromatic aberration at the three wavelengths of interest increase and makes it difficult to satisfactorily correct the remaining secondary spectrum over the entire visible range? In addition, the material of the radial GRIN lens requires a material having anomalous dispersion that is significantly different from that of a normal material, which makes it difficult to produce the material.
[0027]
Further, in the achromatic lens of the present invention, when the radial GRIN lens has extremely low anomalous dispersion, or when the achromatic lens is subjected to strict secondary spectral correction, the following condition is used instead of the condition (4). It is desirable to satisfy (4-1).
(4-1) 84 <V ₁ <310
[0028]
In order to carry out strict secondary spectrum correction, whether the amount of the remaining secondary spectrum becomes large even if either the upper limit or the lower limit of this condition (4-1) is exceeded, a material having anomalous dispersion different from usual Therefore, it is necessary to use a GRIN lens.
When the above conditions (3), (3-1), (4), and (4-1) are satisfied and chromatic aberration is corrected, φ _m and φ _D have the same sign.
[0029]
Next, in the achromatic lens of the present invention, for example, as shown in FIG. 2, when a radial GRIN lens having a curved surface and a diffractive lens are combined, the surface of the radial GRIN lens is used. It is necessary to consider the generated refractive power φ _S.
[0030]
For the chromatic aberration when the radial GRIN lens has a curvature on the surface, the following equations (m) and (n) are used instead of the equations (f) and (g).
PAC = K [(φ _S / V ₀ ) + (φ _m / V ₁ ) + (φ _D / V _D )] (m)
PAC = K [(φ _S / V ₀ ) θ _0gF + (φ _m / V ₁ ) θ _1gF
+ (Φ _D / V _D ) θ _D ] (n)
Here, V ₀ and θ _0gF are the Abbe number on the axis of the radial GRIN lens and the partial dispersion ratio on the axis, respectively. θ _0gF is expressed by the following equation.
θ _0gF = (N _0g −N _0F ) / (N _0F −N _0C )
Here, N _0g is a coefficient N ₀ representing the refractive index distribution in the g-line.
[0031]
In this case, the handling becomes complicated, but the conditions (3), (3-1), (4), and (4-1) are equivalents obtained from the following equations (o), (p), and (q). If the partial dispersion ratio θ _e1gF and the equivalent Abbe number V _e1 are used in place of θ _1gF and V ₁ , respectively, the radial GRIN lens can be extended and handled.
φ = φ _S + φ _m (o)
φ / V _e1 = (φ _s / V ₀ ) + (φ _m / V ₁ ) (p)
(Φ / V _e1 ) θ _e1gF = (φ _S / V ₀ ) θ _0gF + (φ _m / V ₁ ) θ _1gF (q)
Here, φ is the overall refractive power of the radial GRIN lens.
[0032]
Accordingly, it is desirable that the achromatic lens of the present invention having a configuration in which the radial GRIN lens having a curvature on the surface and the diffractive lens are combined satisfy the following conditions (1) and (2).
(1) 0.1 <θ _e1gF <0.5
(2) 67 <V _e1 <370
[0033]
Furthermore, it is more preferable to satisfy the following conditions (1-1) and (2-1) instead of the conditions (1) and (2). For example, an achromatic lens with a strict secondary spectrum corrected can be obtained. it can.
(1-1) 0.2 <θ _e1gF <0.4
(2-1) 84 <V _e1 <310
[0034]
Note that the power φ _S of the surface of the radial GRIN lens, which is flat on both sides, is zero. When φ _S = 0, these equations are as follows.
θ _e1gF = θ _1gF
V _e1 = V ₁
[0035]
That is, in the conditions (3) and (4), V ₁ may be set instead of V _e1 and θ _1gF instead of θ _{e1gF in the} conditions (1) and (2). Therefore, it is desirable that the conditions (1) and (2) be satisfied for any GRIN lens having a curved surface or a flat surface.
[0036]
The achromatic lens of the present invention described above can constitute an imaging device that combines an optical system of a telescope and a microscope as well as an imaging element.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the achromatic lens of the present invention will be described based on each example.
[0038]
In Example 1, as shown in FIG. 3, a diffractive lens is formed on the image side surface of a radial GRIN lens of both planes. The specifications and lens data of Example 1 are as follows.
f = 10, F / 4.0, maximum image height 1.85
r ₁ = ∞ (aperture) d ₁ = 6.99489 n ₁ (refractive index distribution lens)
r ₂ = ∞ d ₂ = 0 n ₂ = 1001 ν ₂ = -3.45 (diffractive lens)
r ₃ = -2.496 × 10 ⁵
Refractive index distribution lens N ₀ = 1.6640, N ₁ = -7.5000 × 10 ⁻³ , V ₀ = 38.2, V ₁ = 104
θ _1dC = 0.30
θ _1gF = 0.34, θ _e1gF = 0.34, V _e1 = 104
[0039]
As shown in FIG. 4, the second embodiment includes a radial GRIN lens that is flat on both sides from the object side, and a diffractive lens that is manufactured on a flat glass. The specifications and lens data of this lens are as follows.
f = 10, F / 4.0, maximum image height 1.85
r ₁ = ∞ (aperture) d ₁ = 6.7176 n ₁ (refractive index distribution lens)
r ₂ = ∞ d ₂ = 3.0000
r ₃ = ∞ d ₃ = 2.0000 n ₂ = 1.51633 ν ₂ = 64.15
r ₄ = ∞ d ₄ = 0.0000 n ₃ = 1001 ν ₃ = -3.45 (diffractive lens)
r ₅ = -6.696 × 10 ⁴
Refractive index distribution lens N ₀ = 1.6640, N ₁ = -7.5000 × 10 ⁻³ , V ₀ = 38.2, V ₁ = 101
θ _1dC = 0.30
θ _1gF = 0.35, θ _e1gF = 0.35, V _e1 = 101
[0040]
In Example 3, a radial GRIN lens having a concave surface on the object side and a flat surface on the image side and a diffractive lens on the side surface are configured as shown in FIG. The specifications and lens data of this lens are as follows.
f = 10, F / 4.0, maximum image height 1.85
r ₁ = -10.000 (aperture) d ₁ = 7.7588 n ₁ (refractive index distribution lens)
r ₂ = ∞ d ₂ = 0 n ₂ = 1001 ν ₂ = -3.45 (diffractive lens)
r ₃ = -3.804 × 10 ⁵
Refractive index distribution lens N ₀ = 1.60000, N ₁ = -1.0000 × 10 ⁻² , V ₀ = 45.00, V ₁ = 78
θ _1dC = 0.30
θ _1gF = 0.34, θ _e1gF = 0.21, V _e1 = 184
In the data of Examples 1 to 3 of the present invention, the design reference wavelength is d-line, and the diffractive lens is shown in such a form that the so-called high refractive index approximation is used and the refractive index of the reference wavelength d-line is 1001.
[0041]
FIG. 6 is an achromatic lens in which a lens having the same specifications as the achromatic lens of the present invention is formed as a normal cemented lens, and is a cemented lens having the following data.
f = 10, F / 4.0, maximum image height 1.85
r ₁ = 4.0230 (aperture) d ₁ = 3.0000 n ₁ = 1.51633 ν ₂ = 64.15
r ₂ = -2.9157 d ₂ = 1.0000 n ₂ = 1.62004 ν ₂ = 36.26
r ₃ = 234.6664
[0042]
The longitudinal chromatic aberrations of the achromatic cemented lenses shown in Examples 1, 2, 3 and FIG. 6 of the present invention are as follows.

[0043]
The features of the achromatic lens of the present invention are as described above, and the structures described in the following claims as well as those described in the following claims can achieve the object of the present invention.
[0044]
(1) An achromatic lens according to claim 1, which satisfies the following condition (1-1) instead of condition (1):
(1-1) 0.2 <θ _e1gF <0.4
[0045]
(2) An achromatic lens according to claim 2, wherein the achromatic lens satisfies the following condition (2-1) instead of condition (2).
(2-1) 84 <V _e1 <310
[0046]
(3) The achromatic lens described in claim 1 or 2 or (1) or (2), wherein the radial GRIN lens is a double-sided plane. .
[0047]
(4) The achromatic lens described in claim 1 or 2 of claim or (1) or (2), wherein at least one surface of the radial type GRIN lens is a curved surface. Achromatic lens to be used.
[0048]
(5) An achromatic lens according to the item (4), wherein the object side surface of the radial GRIN lens is a concave surface.
[0049]
(6) An imaging device comprising the achromatic lens described in (1), (2), (3), (4) or (5).
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of an achromatic lens of the present invention. FIG. 2 is a diagram showing another configuration of the achromatic lens of the present invention. FIG. 3 is a diagram showing a configuration of Example 1 of the present invention. 4 is a diagram showing the configuration of Example 2 of the present invention. FIG. 5 is a diagram showing the configuration of Example 3 of the present invention. FIG. 6 is a diagram showing the configuration of a conventional achromatic lens.

Claims (6)

An achromatic lens having a radial GRIN lens whose refractive index changes in a direction perpendicular to the optical axis and a diffractive lens and satisfying the following condition (1).
(1) 0.1 < θ _e1gF <0.5
Here, θ _e1gF is an equivalent partial dispersion ratio of the radial GRIN lens. The achromatic lens according to claim 1, which satisfies the following condition (2).
(2) 67 < V _e1 <370
Where V _e1 is the equivalent Abbe number of the radial GRIN lens.   3. The achromatic lens according to claim 1, wherein the radial GRIN lens is a double-sided plane.   4. The achromatic lens according to claim 1, wherein at least one surface of the radial GRIN lens is a curved surface.   5. The achromatic lens according to claim 4, wherein the object side surface of the radial GRIN lens is a concave surface.   An imaging apparatus comprising the achromatic lens according to any one of claims 1 to 5.

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