JPH10333026A - Lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a high-performance optical system of a small number of lenses by allowing medium to have specified refractive index distribution and making both surfaces thereof specified diffraction optical surfaces. SOLUTION: The medium has the refractive index distribution expressed by an expression I and both surfaces thereof are the diffraction optical surfaces expressed by an expression II. In the expression I, H means height in a direction perpendicular to an optical axis, N0 means a refractive index on the optical axis, N1 means a quadratic refractive index distribution coefficient, N2 means a forth-order refractive index distribution coefficient, N3 means a sixth-order refractive index distribution coefficient and N4 means an eighth-order refractive index distribution coefficient. In the expression II, ϕ(H) means a phase function, H means height in the direction perpendicular to the optical axis, Ri is the i-order phase function and λ0 means design wavelength. Thus, the direction of the dispersion distribution of a refractive index distribution type lens becomes a direction where production is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens, and more particularly to a high-performance lens suitable for a photographic camera or a video camera.

[0002]

2. Description of the Related Art Hitherto, various types of lenses such as photographic cameras and video cameras using a gradient index lens have been proposed. Since the refractive index distribution type lens has a refraction function based on the refractive index distribution of the medium in addition to the power based on the refraction function of the lens surface, it adds a new degree of freedom when designing an optical system. And aberration can be corrected favorably.

The dispersion distribution of such a gradient index lens has a positive dispersion direction and a negative dispersion direction. When trying to correct chromatic aberration using a gradient index lens,
As described in Yamamoto and Tsuchida, “Photo Lens-Camera Lens Using Heterogeneous Lens”, OPTRONICS, (1992), No. 1, 171-175, a gradient index lens having a distribution in the negative dispersion direction is effective. It is known that there is. However, the medium in the negative dispersion direction has a problem that it is extremely difficult to manufacture.

On the other hand, there have been proposed various optical systems using a diffractive lens in which a fine step-like or saw-tooth pattern is added to a lens surface at a predetermined pitch and light rays incident on the lens surface are deflected by diffraction. I have. When such a diffractive lens is used, the large negative dispersion characteristic of the diffractive optical surface of the diffractive lens can be used, so that aberration correction, particularly correction of chromatic aberration, can be performed well.

[0005] However, when a diffractive lens is used, the negative dispersion of the diffractive optical surface alone often has too strong a characteristic, and when the power of the diffractive optical surface is too large, a strong negative dispersion characteristic results. There is a problem that chromatic aberration is excessively corrected and negative chromatic aberration occurs.

To solve such a problem, Japanese Patent Application Laid-Open No. 4-181908 proposes an optical system including both the above-mentioned refractive index type lens and diffraction type lens.
The optical system described in this publication has a refractive index distribution in a positive dispersion direction that can be manufactured by combining a radial type refractive index distribution lens and a diffraction type lens having a refractive index distribution in a direction perpendicular to the optical axis. Meanwhile, an optical system capable of performing chromatic aberration correction has been proposed.

[0007]

However, in the optical system described in the above publication, since the diffractive optical surface is provided on a spherical surface or a flat surface, aberration correction is insufficient and optical performance cannot be said to be sufficient. There was a problem. Further, at least two lenses are required as the number of lenses constituting the optical system, and there is a problem that a sufficient angle of view cannot be obtained when the optical system is constituted by one lens.

An object of the present invention is to provide a lens suitable for forming an extremely high-performance optical system with a small number of optical systems.

[0009]

In order to achieve the above object, in a lens according to the present invention, a medium has a refractive index distribution represented by the following formula [a], and both surfaces have the following It is a diffractive optical surface represented by the formula [b].

[0010]

(Equation 7)

Where H: height in a direction perpendicular to the optical axis, N ₀ : refractive index on the optical axis, N ₁ : second-order refractive index distribution coefficient, N ₂ : fourth-order refractive index distribution Coefficient, N ₃ : sixth-order refractive index distribution coefficient, N ₄ : eighth-order refractive index distribution coefficient.

[0012]

(Equation 8)

Where φ (H): phase function, H: height in the direction perpendicular to the optical axis, Ri: i-th phase coefficient, and λ ₀ : design wavelength.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lens according to an embodiment of the present invention will be described. The lens according to the embodiment of the present invention includes:
The medium has a refractive index distribution represented by the following formula [1], and both surfaces are diffractive optical surfaces represented by the following formula [2].

[0015]

(Equation 9)

H: height in the direction perpendicular to the optical axis, N ₀ : refractive index on the optical axis, N ₁ : second-order refractive index distribution coefficient, N ₂ : fourth-order refractive index distribution Coefficient, N ₃ : sixth-order refractive index distribution coefficient, N ₄ : eighth-order refractive index distribution coefficient.

[0017]

(Equation 10)

Here, φ (H): phase function, H: height in a direction perpendicular to the optical axis, Ri: i-th phase coefficient, λ ₀ : design wavelength.

In the case where an optical system is constituted only by a medium having a uniform refractive index as in the prior art, even if an aspherical surface is added to the refracting surface of the lens, the ability of the aspherical surface to correct chromatic aberration and Petzval sum correction. Therefore, at least two lenses (one positive lens and one negative lens) are required for the optical system.

Further, as disclosed in the prior art, when the single focus optical system is constituted by a spherical or flat refractive index distribution type lens, the degree of freedom for the third-order aberration correction is insufficient. Therefore, it is impossible to configure a single-focal optical system with one sheet (LGAtokinson et.al., “Des
ign of a gradient-index photographic objective ”,
See Appl. Opt., Vol. 21, 1982, 993-998. ). The same applies to a zoom optical system, and a single lens group cannot be formed.

However, since the gradient index lens has both chromatic aberration correction and Petzval sum correction capabilities,
By combining a refractive index distribution type lens with an aspherical surface, it becomes possible to form a single-focal-length optical system with one piece, or to form one group in a zoom optical system. In this case, since the dispersion of the medium glass itself is in the positive direction, the dispersion direction of the refractive index distribution needs to be negative in order to correct the positive dispersion of the medium glass by one sheet. However,
A medium having such a negative dispersion characteristic is very difficult to manufacture.

On the other hand, the diffractive optical surface has a great feature that it has a negative dispersion as represented by the following equation.

[0023]

[Equation 11]

Here, λ _d : the wavelength of the d-line λ _F : the wavelength of the F-line λ _C : the wavelength of the C-line From this equation, when correcting the chromatic aberration by combining the refractive optical surface and the diffractive optical surface, It can be seen that since the diffractive optical surface has a negative dispersion, the signs of the powers of the refractive optical surface and the diffractive optical surface may be the same. Therefore, chromatic aberration can be corrected by forming a diffractive optical surface on one of the surfaces of one refraction lens. However, although the combination of a refractive optical surface and a diffractive optical surface is very effective for correcting chromatic aberration, the negative chromatic value of the diffractive optical surface is so large that the correction of chromatic aberration becomes overcorrected and the negative There is also a problem that chromatic aberration is generated.

Therefore, by making the medium of the lens a refractive index distribution material having a positive dispersion, the chromatic aberration due to the negative dispersion, which has been overcorrected by the diffractive optical surface, is corrected by the refraction effect by the refractive index distribution of the medium. Can be very favorable. In this case, the direction of the dispersion distribution of the refractive index distribution is the direction in which positive chromatic aberration occurs (the direction in which ν ₁ > 0) or the direction of the weak negative dispersion distribution (the direction in which ν ₁ has a large negative value). Therefore, unlike the case where the color correction is performed only with the gradient index lens (the direction in which ν ₁ becomes a small negative value), the manufacture of the gradient index lens is facilitated. Note that ν ₁ is defined by the following equation.

[0026]

(Equation 12)

Here, N ₁ d: a secondary refractive index distribution coefficient for the d line N ₁ F: a secondary refractive index distribution coefficient for the F line N ₁ C: a secondary refractive index distribution coefficient for the C line

Hereinafter, other conditions which should be satisfied by the lens of the present invention will be described. In the following conditions, it is desirable to satisfy all conditions at the same time, but it is not always necessary to satisfy the entire condition at the same time, and they may be satisfied independently. It is desirable that the lens of the present embodiment satisfies the following condition [5].

[0029]

(Equation 13)

However, N ₁ : second order refractive index distribution coefficient, νd (H): Abbe number at a height H from the optical axis, νd (0): Abbe number on the optical axis, wherein νd (H) and νd (0) is represented by the following equation,

[0031]

[Equation 14]

N _d (H): refractive index for d-line at height H from the optical axis, N _F (H): refractive index for F-line at height H from the optical axis, N _C (H) : Refractive index for C-line at a height H from the optical axis.

The condition [5] relates to the dispersion distribution of the refractive index distribution medium, and is a condition for correcting chromatic aberration generated on the diffractive optical surface. Exceeding this range is undesirable because the chromatic aberration overcorrected by the diffractive optical element is further deteriorated by the refraction effect of the refractive index distribution. In addition, the production of a gradient index lens is also difficult, which is undesirable.

In the lens of the embodiment, the diffractive optical surface preferably satisfies the following condition [7].

[0035]

(Equation 15)

Where φd = −2 mR ₂ R ₂ : second-order phase coefficient, m: diffraction order, φ = φr + φd φ: combined power of the entire lens φr: combined power of the entire lens due to refraction The sum of the power due to the refraction of the surface and the power due to the refraction based on the refractive index distribution of the medium, assuming a homogeneous lens), φd: the power due to the diffraction.

Condition [7] regulates the power of the diffractive optical surface. If the upper limit of conditional expression [7] is exceeded, the power of the diffractive optical surface with respect to the entire lens becomes too strong, and the chromatic aberration of the diffractive optical surface is excessively corrected. Conversely, if the lower limit of the expression [7] is exceeded, the power of the diffractive optical surface in the group becomes too weak, and chromatic aberration correction becomes insufficient.

It is desirable that the lens of the embodiment satisfies the following condition [8].

[0039]

(Equation 16)

Where φ1d: power due to the diffraction effect of the first surface, φ2d: power due to the diffraction effect of the second surface, φd = −2 mR ₂ R ₂ : second-order phase coefficient, m: diffraction order.

The condition [8] is a condition that defines the power due to the diffractive action of each surface when diffractive optical surfaces are provided on both surfaces of the lens. When the value exceeds the range defined by the condition [8], the diffractive action of one surface becomes too strong, and it becomes difficult to manufacture the diffractive optical surface, which is not desirable.

It is desirable that the lens of the embodiment satisfies the following condition [9].

[0043]

[Equation 17]

However, N ₁ : second-order refractive index distribution coefficient, φ: combined power of the entire lens.

Condition [9] is for correcting the Petzval sum using a gradient index lens. When the value exceeds the range of the condition [9], the Petzval sum based on the refraction effect due to the refractive index distribution of the medium becomes large, which is not desirable. If the ratio is outside this range, the curvature of the lens must be increased.

It is desirable that the lens of the embodiment satisfies the following conditions [10] and [11].

[0047]

(Equation 18)

Where N ₁ d: the second-order refractive index distribution coefficient for the d-line N ₂ d: the fourth-order refractive index distribution coefficient for the d-line φ: combined power of the entire lens Conditions [10] and [11] are as follows: This is related to the refractive index distribution of the lens. If the refractive index distribution exceeds this range, it becomes difficult to correct high-order aberrations, and the refractive index distribution becomes too large.

The lens according to the embodiment has the following condition [12].
It is desirable to satisfy

[0050]

[Equation 19]

Where φ _{sd is} the power of the lens surface (sum of the power due to the refraction of the surface and the power due to the diffraction of the lens when the lens is a homogeneous lens), and φ _m is the power of the refractive index distribution of the lens ( Power due to the refraction effect based on the refractive index distribution of the medium), and more specifically, φ _sd and φ _m are:
Assuming that the combined power of the entire lens is φ, φ = φ _s + φ _d + φ _m [13] φ _sd = φ _s + φ _d [14] φ _m = −2 · N ₁ d · T [15] , Φ _s : power due to refraction of the surface when the lens is a homogeneous lens (the refractive index is the refractive index on the optical axis of the lens) φ _d : power of the diffractive optical surface T: core thickness of the lens N ₁ d: d-line Is represented by the second-order refractive index distribution coefficient

Conditional expression [12] is a condition that the refractive index distribution of the lens should be satisfied. If the upper limit of this condition is exceeded, the refractive index distribution becomes too large, making the production difficult and causing higher-order aberrations. It is not desirable. If the lower limit is exceeded, Petzval correction becomes difficult, and correction of each aberration, particularly correction of higher-order aberrations, becomes difficult.

In the lens according to the embodiment, in order to provide a degree of freedom for correcting the third-order aberration, at least one surface of the refractive index distribution type lens combined with the diffractive optical surface has a refracting action equivalent to an aspheric surface. It is desirable to have a diffractive optical surface that also has With this configuration, 3
The degree of freedom for the next-order aberration correction is greatly increased, so it is possible to achieve a high-performance optical system in which a single-focus optical system is composed of one lens, and each lens group of the zoom optical system is composed of one lens. Becomes

When the diffractive optical surface has a refraction function equivalent to an aspherical surface, the lens of the embodiment preferably satisfies the following condition [16].

[0055]

(Equation 20)

Where φa: power due to local surface refraction of the refractive optical surface equivalent to the aspherical surface, φ0a: power due to refraction to the reference curvature of the refractive optical surface equivalent to the aspherical surface, φ: overall power of the lens _Where φ _a and φ _0a are φ _a = C _alo (N (H) ′ − N (H)) [17] φ _0a = C ₀ (N ₀ ′ −N ₀ ) [18] C _alo : Local curvature of the refractive optical surface equivalent to the aspherical surface, C0: Reference curvature of the refractive optical surface equivalent to the aspherical surface, N (H) ': Light of the incident side medium of the refractive optical surface equivalent to the aspherical surface Refractive index at height H from axis, N (H): Refractive index at height H from optical axis of exit side medium of refractive optical surface equivalent to aspherical surface, N ₀ ': Equivalent to aspherical surface The refractive index on the optical axis of the medium on the incident side of the refractive optical surface, N ₀ : the refractive index on the optical axis of the medium on the exit side of the refractive optical surface equivalent to an aspheric surface.

The condition [16] is a condition relating to a refracting action equivalent to the aspherical surface of the lens. If the upper limit is exceeded, various aberrations occurring on other spherical surfaces of the lens are further deteriorated by the effect of the aspherical surface. It is not desirable. If the lower limit is exceeded, the aspheric effect is excessively corrected, and even when both surfaces of the lens are surfaces having a refraction effect substantially equivalent to the aspheric surface, the excessive correction is caused by the refraction effect of another aspheric surface. It is difficult to counteract, which is undesirable.

Further, an optical system using the lens of the embodiment will be described with reference to the drawings. FIG. 1 to FIG.
FIG. 6 is a configuration diagram illustrating a configuration of a lens according to first to fourth embodiments.

Each of the embodiments is a single focus optical system composed of one gradient index lens, and both sides of the lens are diffractive optical surfaces. The first embodiment is a single-focus optical system composed of one lens G, which is a biconvex shape and has a refraction function equivalent to an aspheric surface on both sides and a diffraction function.

The second embodiment has a shape in which a strong concave surface is directed toward the image side, and has a single focal point G1 which is a surface having a diffractive effect and a diffractive effect equivalent to an aspheric surface on both sides. It is an optical system.

The third embodiment is a single-focus optical system having one lens G1 having a shape with a concave surface facing the object side and having a refraction function equivalent to an aspheric surface on both sides and a surface having a diffraction function. System.

The fourth embodiment is a single-focus optical system composed of a single lens G1 formed by adding a diffraction pattern using resin as a material by composite molding on both surfaces of a flat refractive index distribution type lens. It is.

As described above, the single focus optical system of each embodiment achieves the configuration of the optical system with a minimum number of one, and succeeds in greatly reducing the number of lenses.

The lenses of the above-described first to third embodiments can be manufactured by directly molding a gradient index material, or a resin can be formed on the surface of a gradient index lens formed in a predetermined shape in advance. Can be manufactured by various manufacturing methods such as so-called composite molding in which a resin is applied to form a diffraction pattern.

The lens of the fourth embodiment may be directly molded. However, after cutting a rod lens formed of a refractive index distribution material into a predetermined core thickness, a resin having a diffraction pattern on a contact section is obtained. Can be easily manufactured by compound molding.

[0066]

EXAMPLES Examples of the present invention will be described below with reference to construction data, aberration diagrams and the like.

The following Examples 1 to 4 correspond to the above-described embodiments, respectively. The lens arrangement diagrams representing the embodiments respectively show the corresponding lens configurations of Examples 1 to 4.

In each embodiment, ri (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the object side, and di (i = 1, 2,
3, ...) indicates the i-th axial top surface distance counted from the object side, Ni (i = 1,2,3, ...), νi (i = 1,2,3, ...) Denotes the refractive index and Abbe number of the i-th lens counted from the object side with respect to the d-line. F is the focal length of the entire system, 2ω is the angle of view, Fn
o represents an F number. In addition, the letter E attached to the data in the example represents the exponent part of the corresponding numerical value.
If 1.0E−2, it indicates 1.0 × 10 ⁻² .

Further, in each embodiment, the surface marked with * for the radius of curvature ri indicates that the surface is an aspherical refracting optical surface or a surface having a refracting action equivalent to an aspherical surface. Is defined by the following equation.

[0070]

(Equation 21)

Here, H: height in the direction perpendicular to the optical axis, x (H): displacement amount in the optical axis direction at the height H (based on surface vertex) c: paraxial curvature ε: 2 Second-order surface parameter Ai: The i-th order aspheric coefficient.

Further, in each embodiment, the surface with the radius of curvature ri with a plus sign indicates a diffractive optical surface, which is defined by the following expression representing the surface shape of the diffractive optical surface.

[0073]

(Equation 22)

Here, φ (H): phase function, H: height in a direction perpendicular to the optical axis, Ri: i-th phase coefficient, λ ₀ : design wavelength.

In each example, GRINi in the column of refractive index Ni was used.
(i = 1, 2, 3,...) indicates the i-th refractive index distribution medium counted from the object side, and the refractive index distribution is defined by the following equation.

[0076]

(Equation 23)

Where H: height in the direction perpendicular to the optical axis, N ₀ : refractive index on the optical axis, N ₁ : second-order refractive index distribution coefficient, N ₂ : fourth-order refractive index distribution Coefficient, N ₃ : sixth-order refractive index distribution coefficient, N ₄ : eighth-order refractive index distribution coefficient.

<< Example 1 >> f = 2.85 mm 2ω = 63.6 ° Fno = 4.6 [Radius of curvature] [Space between upper surfaces of the shaft] [Refractive index] r1 * + = 3.357 d1 = 4.722 N1 = GRIN1 r2 * + = -3.355 [ Aspheric surface data of the first surface (r1)] ε = 1.00000000 A4 = 6.9474377E-3 A6 = -1.0689611E-2 A8 = 3.7720502E-3 A10 = -4.5626730E-4 [Aspheric surface of the second surface (r2)] Data] ε = 1.00000000 A4 = 1.5701121E-1 A6 = -9.2570377E-2 A8 = 3.3071132E-2 A10 = -3.9399826E-3 [Diffractive optical surface data of the first surface (r1)] R2 = -5.1506442E- 3 R4 = 1.3873687E-2 R6 = -1.1896594E-2 R8 = 3.9458672E-3 R10 = -4.7100394E-4 [Diffractive optical surface data of the second surface (r2)] R2 = -2.0000000E-2 R4 = 7.0384875 E-2 R6 = 5.7223145E-2 R8 = -2.1253179E-2 R10 = 2.8538053E-3 [Refractive index distribution data of the first lens material (GRIN1)] 656.28 nm 587.56 nm 486.13 nm N0 1.62037 1.62588 1.63826 N1 -1.4950000 E-2 -1.5100000E-2 -1.5450000E-2 N2 -1.0250000E-3 -1.0300000E-3 -1.0380000E-3 N3 1.0000000E-4 1.0000000E-4 1.0000000E-4 << Example 2 >> f = 2.85 mm 2ω = 63.1 ° Fno = 4.6 [Radius of curvature] [Shaft upper surface interval] [Refraction Rate] r1 * + = 7.623 d1 = 4.779 N1 = GRIN1 r2 * + = -3.190 [Aspherical surface data of the first surface (r1)] ε = 1.00000000 A4 = -4.5606083E-2 [Non-surface of the second surface (r2) Spherical data] ε = 1.00000000 A4 = 2.6865812E-2 A6 = -4.6393386E-3 A8 = 2.2000634E-3 A10 = -3.2802513E-4 [Diffractive optical surface data of the first surface (r1)] R2 = -3.0408089E -3 R4 = -7.5413006E-3 [Diffractive optical surface data of the second surface (r2)] R2 = -2.7148712E-2 [Refractive index distribution data of the first lens material (GRIN1)] 656.28 nm 587.56 nm 486.13 nm N0 1.79610 1.80518 1.82776 N1 -5.1250000E-3 -5.1410000E-3 -5.1190000E-3 N2 -4.6060000E-3 -4.5830000E-3 -4.9250000E-3 << Example 3 >> f = 6.85mm 2ω = 61.8 ° Fno = 4.6 [Curvature radius] [Shaft upper surface interval] [Refractive index] r1 * + = -10.066 d1 = 1.809 N1 = GRIN1 r2 * + = ∞ [Aspherical surface data of first surface (r1)] ε = 1.00000000 A4 =- 5.4928018E-2 A6 = 1.4618570E-2 A8 = -3.9403615E-3 A10 = 1.3392053E-3 [Aspherical surface data of the second surface (r2)] ε = 1.00000000 A4 = 3.8613212E-2 A6 = 3.1206838E-3 A8 = -1.5660651E-2 A10 = -7.9921554E-3 [Diffractive optical surface data of first surface (r1) ] R2 = -1.4445769E-2 R4 = 1.7695005E-4 R6 = 1.1360398E-2 R8 = -5.2197156E-3 R10 = 1.0712798E-3 [Diffractive optical surface data of the second surface (r2)] R2 = -2.1316366 E-2 R4 = 1.2569456E-2 R6 = -1.5979725E-2 R8 = 3.8254788E-2 R10 = -2.0153958E-2 [Refractive index distribution data of the first lens material (GRIN1)] 656.28 nm 587.56 nm 486.13 nm N0 1.79610 1.80518 1.82776 N1 -4.0576079E-2 -4.3036818E-2 -4.6846937E-2 N2 -4.4355588E-2 -4.3880110E-2 -4.4093250E-3 N3 6.9471899E-3 7.7673720E-3 9.7926245E-3 N4 2.3588243E-3 2.1034788E-3 1.4122665E-3 << Example 4 >> f = 6.85mm 2ω = 61.8 ° Fno = 4.6 [Radius of curvature] [Shaft upper surface interval] [Refractive index] [Abbe number] r1 * + =- 7.544 d1 = 0.020 N1 = 1.51790 νd = 52.31 r2 = ∞ d2 = 1.607 N2 = GRIN1 r3 = ∞ d3 = 0.020 N3 = 1.51790 νd = 52.31 r4 * + = -16.203 [Aspherical data of the first surface (r1)] ε = 1.00000000 A4 = -6.9412435E-2 A6 = 1.5595209E-2 A8 = 1.4786093E-2 A10 = -8.2157866E-3 [Aspherical surface data of the fourth surface (r4)] ε = 1.00000000 A4 = 4.0617279E-2 A6 = 8.6644536E-2 A8 = -2.6226215E-1 A10 = 1.9590839E-1 [1st Diffractive optical surface data of (r1)] R2 = -2.6311502E-2 R4 = 2.7356807E-3 R6 = 1.9420204E-3 R8 = 6.2930221E-3 R10 = -3.9729071E-3 [Diffraction of fourth surface (r4) Optical surface data] R2 = -3.0268264E-2 R4 = 1.6587542E-2 R6 = -5.6594929E-2 R8 = 1.5150737E-1 R10 = -1.1785461E-1 [Refractive index distribution of the first lens material (GRIN1) Data] 656.28 nm 587.56 nm 486.13 nm N0 1.62073 1.62588 1.63826 N1 -1.8237026E-2 -2.2284726E-2 -2.8269699E-2 N2 -4.5618161E-2 -4.4852102E-2 -4.4504727E-2 N3 6.9471899E-3 7.7673720 E-3 9.7926245E-3 N4 2.3588243E-3 2.1034788E-3 1.4122665E-3 FIGS. 5 to 8 are aberration diagrams corresponding to the first to fourth embodiments. Each aberration diagram represents a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in order from the left.

In each of the spherical aberration diagrams, the solid line is the d line, and the dotted line is the C line.
The line and alternate long and short dash line indicate the amount of spherical aberration for each of the F lines. In each astigmatism diagram, a solid line x represents a sagittal surface, and a solid line y represents a meridional surface. Also,
The vertical axis of the spherical aberration diagram represents the incident height of the light beam with the entrance pupil diameter normalized, and the vertical axis of the astigmatism diagram and the distortion diagram represents the image height.

The following table shows the values of the conditional expressions in each embodiment.

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

[Table 3]

[0084]

[Table 4]

[0085]

As described above, according to the present invention, a high-performance lens can be provided with a small number of components. In addition, it is possible to provide a lens in which the direction of dispersion distribution of the refractive index distribution type lens is also a direction that is easy to manufacture.

Therefore, when the lens according to the present invention is applied as a component of an optical system, it contributes to a significant reduction in the number of optical systems.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system according to a first embodiment.

FIG. 2 is a configuration diagram of an optical system according to a second embodiment.

FIG. 3 is a configuration diagram of an optical system according to a third embodiment.

FIG. 4 is a configuration diagram of an optical system according to a fourth embodiment.

FIG. 5 is an aberration diagram of the optical system according to the first embodiment.

FIG. 6 is an aberration diagram of the optical system according to the second embodiment.

FIG. 7 is an aberration diagram of an optical system according to a third embodiment.

FIG. 8 is an aberration diagram of an optical system according to a fourth embodiment.

[Explanation of symbols]

 L1: First lens

Claims (4)

[Claims] 1. A lens characterized in that a medium has a refractive index distribution represented by the following formula [a], and both surfaces are diffractive optical surfaces represented by the following formula [b]. ; Here, H: height in the direction perpendicular to the optical axis, N ₀ : refractive index on the optical axis, N ₁ : second-order refractive index distribution coefficient, N ₂ : fourth-order refractive index distribution coefficient, N ₃ : 6th-order refractive index distribution coefficient, N ₄ : 8th-order refractive index distribution coefficient (Equation 2) Here, φ (H): phase function, H: height in a direction perpendicular to the optical axis, Ri: i-th phase coefficient, λ ₀ : design wavelength. 2. The lens according to claim 1, wherein the following condition is satisfied; However, N ₁ : second order refractive index distribution coefficient, νd (H): Abbe number at a height H from the optical axis, νd (0): Abbe number on the optical axis, wherein νd (H) and νd (0) is represented by the following equation: N _d (H): Refractive index for d-line at height H from optical axis, N _F (H): Refractive index for F-line at height H from optical axis, N _C (H): Optical axis Is the refractive index for the C-line at a height H from 3. The lens according to claim 1, wherein the following condition is satisfied; Where φd = −2 mR ₂ R ₂ : second-order phase coefficient, m: diffraction order, φ = φr + φd φ: combined power of the entire lens φr: combined power by refraction of the entire lens (Sum of the power due to the refraction of the surface and the power due to the refraction based on the refractive index distribution of the medium), φd: the power due to the diffraction. 4. It satisfies the following conditions:
The lens according to claim 1; Here, φ1d: power due to the diffraction effect of the first surface, φ2d: power due to the diffraction effect of the second surface, φd = −2 mR ₂ R ₂ : second-order phase coefficient, m: diffraction order.