JPH10186226A - Telephotographic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an extremely inexpensive telephotographic lens by constituting it of a first positive lens and a second negative lens and using zonal structure having the action of a blazed diffraction lens as the structure of one surface of the first lens. SOLUTION: Since the axial chromatic aberration of the telephotographic lens contributes by the square of the incident height of a marginal light beam, it is corrected on the first lens 11 side. The chromatic aberration is corrected by providing one surface of the first positive lens 11, that means, one surface out of the surface on an object side and the surface on an image side with the action of the diffraction lens. When the telephotographic lens is used for a photograph, the diffraction lens must be provided with the blazed zonal structure because the contrast of the image is important and the wavelength width of a using light source is wide. When both surfaces are made into the diffraction and refraction hybrid surfaces at this time, the contrast is lowered because diffraction efficiency by short wavelength and long wavelength being distant from blazed reference wavelength is lowered much. Thus, only one surface of the lens 11 is provided with the structure of the diffraction lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephoto lens suitable for a 35 mm camera, a video camera and the like.

[0002]

2. Description of the Related Art In a telephoto lens, the performance of the lens is limited by chromatic aberration. Therefore, it is difficult to reduce the number of lenses by using an aspherical surface. I needed one lens.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to make a very inexpensive telephoto lens by utilizing the chromatic aberration correction effect of a diffractive lens.

[0004]

The telephoto lens according to the present invention comprises:
In order from the object side, 2 of the first positive lens and the second negative lens
The first lens is composed of two lenses, and one of the surfaces of the first lens is a diffractive refraction hybrid surface having a blazed ring-like structure having a positive diffractive lens function. "Blaze" means optimizing the shape of the diffractive surface to increase the diffraction efficiency of the diffractive lens (diffraction grating). The side that has.

Further, when the axial distance between the first lens and the second lens is L and the focal length of the entire system is f, it is preferable that the following condition is satisfied: 0.25 <L / f <0.6 (1) . Further, the first
When the focal length of the diffractive lens component of the lens is fD and the focal length of the entire system is f, it is preferable that the following condition is satisfied: 0.06 <f / fD <0.14 (2) It is preferable that at least one surface of the first lens is an aspheric surface whose positive power decreases macroscopically toward the peripheral portion. When the focal length of the first lens is f1 and the focal length of the second lens is f2, it is preferable to satisfy the following condition: -1.5 <f1 / f2 <-0.24 (3).

The second lens is a meniscus lens, and the shaping factor SF of the second lens is
Assuming that the radius of curvature of the front surface of the second lens is r3 and the radius of curvature of the rear surface is r4, the following condition is satisfied: SF = (r4 + r3) / (r4-r3), 3.4 <| SF | (4) Is preferred. It is preferable that the second lens satisfies the condition of ν2> 40 (5) where the Abbe number is ν2. When this condition is not satisfied, it is preferable that one of the surfaces of the second lens is also a diffractive refraction hybrid surface having a blazed annular structure having a negative diffractive lens effect.

[0007]

Since the axial chromatic aberration of the telephoto lens contributes by the square of the incident height of the marginal ray, it is essential to correct the chromatic aberration on the first lens side. In the telephoto lens according to the present invention, chromatic aberration correction is performed by imparting a diffractive lens function to one of the surfaces of the positive first lens, that is, one of the object side surface and the image side surface. For applications such as photography, the contrast of the image is important, and the wavelength range of the light source used is wide, so that the diffraction lens must have a blazed annular structure. At this time, if both surfaces are formed as a diffractive refraction hybrid surface, the reduction of the diffraction efficiency at short wavelengths and long wavelengths apart from the blazed reference wavelength becomes large and the contrast is reduced. Therefore, only one surface of the first lens has the diffraction lens. Have a structure.

The conditions for sufficiently correcting the field curvature with two lenses and reducing the overall length of the lens are as follows.
Equation (1). 0.25 <L / f <0.6 (1) where, L: axial distance between the first lens and the second lens, f: focal length of the entire system. If the distance between the first lens and the second lens deviates from either of the upper and lower limits of this condition, the overall length of the lens becomes longer, and the field curvature becomes insufficiently corrected.

The condition for better correcting the chromatic aberration of the first lens is given by the following equation (2). 0.06 <f / fD <0.14 (2) where fD is the focal length of the diffractive lens component of the first lens, and f is the focal length of the entire system. This condition is satisfied when a material having low dispersion is used for the first lens, a low dispersion material is used for the second lens, and when a chromatic aberration is corrected by introducing a diffractive lens also for the second lens. Indicates the power that the lens should have. If the power of the diffraction lens is weaker than the lower limit,
In order to correct axial chromatic aberration, the second lens must be made of a high-dispersion material, and the chromatic aberration of magnification increases. When the power of the diffractive lens exceeds the upper limit and the power of the diffractive lens is high, a high-dispersion material is used for the first lens, which increases the weight of the lens, increases the number of zones in the diffractive structure, and increases the light amount loss.

When the front group of the telephoto lens is constituted by one lens as in the present invention, in order to obtain a lens brighter than F number 5.6, at least one surface of the first lens is macroscopically corrected to correct spherical aberration. It is preferable to use an aspherical surface whose positive power becomes smaller toward the peripheral portion. Here, when the aspherical surface and the diffractive lens effect are set to the same surface,
Since the power at the boundary of the annular structure becomes microscopically unstable, the shape of the refractive lens excluding the diffractive lens component is called a macroscopic aspherical shape.

The condition for favorably performing the field curvature correction together with the conditional expression (1) is the following expression (3). -1.5 <f1 / f2 <-0.24 (3) where f1 is the focal length of the first lens, and f2 is the focal length of the second lens. If the negative power of the second lens is relatively large below the lower limit of conditional expression (3), the Petzval sum takes a large negative value and the image plane becomes over. When the negative power of the second lens exceeds the upper limit and is small, the field curvature cannot be corrected, and the image plane is under.

Since the first lens has a high incidence of marginal rays, spherical aberration and coma are likely to occur. Therefore, it is preferable that the first surface on the object side has a strong convex surface and the second surface on the image side has a shape having a larger radius of curvature than the first surface so that occurrence of spherical aberration and coma aberration is reduced.
On the other hand, since the astigmatic difference always remains in this shape, the second lens needs to have a shape for correcting the astigmatic difference. In this telephoto lens having two groups and two lenses, the power of the second lens is weak,
Since the correction effect of the astigmatic difference is insufficient with the biconcave shape,
It is preferable to form a meniscus shape that satisfies the following conditional expression (4). 3.4 <| SF | (4) where the shaping factor SF of the second lens is
When the radius of curvature of the front side surface of the second lens is r3 and the radius of curvature of the rear side surface is r4, it is defined as SF = (r4 + r3) / (r4-r3). If the range of the conditional expression is not satisfied and the degree of meniscus of the second lens is not strong, the meridional image plane tends to be lower than the sagittal image plane. The value of SF may be either positive or negative (that is, the second lens may be either a meniscus lens convex to the object side or a concave meniscus lens as shown in the embodiment). The second lens has a concave surface facing the first lens surface, and off-axis light is directly incident on the second lens at a small incident angle.
There is an advantage that generation of distortion is small. On the other hand, SF
Has a negative value, the marginal ray incident on the second lens is directly incident at a small incident angle, so that there is an advantage that the occurrence of spherical aberration is small and the tolerance during manufacturing is easily loosened.

The condition for suppressing the chromatic aberration of magnification when the second lens is a single lens is the following conditional expression (6). ν2> 40 (6) where ν2 is the Abbe number of the second lens. If this condition is not satisfied, it is difficult to correct lateral chromatic aberration when the lens is a bright lens. However, if the F value of the lens is large (dark), conditional expression (6)
Is satisfied, it is possible to prevent the chromatic aberration of magnification from causing a problem by selecting the position of the stop (see Embodiment 8). Further, the chromatic aberration of magnification can also be corrected by providing a blazed ring-shaped structure having a function of a negative diffractive lens on any one surface of the negative second lens. In this case, it is not necessary to satisfy the expression (6) because the second spectrum of the axial chromatic aberration can be reduced by selecting a glass material having a large dispersion for the second lens due to the partial dispersion characteristics of the glass material.

The diffractive lens can be manufactured by providing a thin film made of resin on a glass lens such as a glass mold or a bonded aspherical surface. In addition, it is preferable to use a resin mold lens that has low material cost, good moldability, and low cost of the mold. Further, the resin mold lens has an advantage that the weight is reduced.

[0015]

Embodiments of the present invention will be described below with reference to numerical embodiments. Each of the following Examples 1 to 8 includes, in order from the object side, a biconvex first lens 11 and a negative meniscus lens 12 having a convex surface facing the object side. In any of the embodiments, the first lens 11 has a diffractive lens structure on its object side surface or image side surface. In the fifth and sixth embodiments, the second lens 1
2 also has a diffractive lens structure on its object side. Except for Example 8, the object side surface or the image side surface of the first lens 11 is a rotationally symmetric aspherical surface. In these numerical examples, r is the radius of curvature of the surface, d is the surface interval, nd is the refractive index at the d-line, and νd is the Abbe number for the d-line. f is the focal length, F _NO is the F number, and 2ω is the angle of view. The surface marked with * after the surface number is the diffractive refraction hybrid surface. The aspherical surface has a height h in a direction perpendicular to the optical axis, a displacement amount in the optical axis direction at the height h of ΔX (h), a radius of curvature near the optical axis r, a cone coefficient K, and an nth-order non-spherical surface. Assuming that the spherical coefficient is An,
It is represented by the following equation. ΔX (h) = (h ² / r) / (1+ (1- (1 + K) h ² / r ² ) ^1/2 ) + A2h ² + A4h ⁴ +... The additional amount of the optical path length that the lens should have is represented as a function of the height h from the optical axis (optical path difference function) ψ (h). The optical path difference function is represented by the following equation, where the n-th order optical path difference function coefficient is Pn and the wavelength is λ. ψ (h) = (P2h ² + P4h ⁴ +...) λ The wavelength λ can be any wavelength used when evaluating the first-order diffracted light. This representation has a paraxial manner positive power when the coefficient of the term of h ² is negative, the coefficient of the term of h ⁴ is the negative power towards the periphery at the time of positive increases. The aspherical coefficients and optical path difference function coefficients not shown are 0.

Embodiment 1 FIG. 1 is a diagram showing a lens configuration of a telephoto lens according to a first embodiment of the present invention, and Table 1 shows numerical data thereof.

TABLE 1 _{f = 300.00 F NO = 4.0 2ω} = 8.1 ° face r d nd νd 1 * 117.406 15.000 1.51633 64.1 2 -1407.681 120.000 3 60.000 5.000 1.80400 46.6 4 41.013 98.098 aspheric coefficients dihedral A4 = 6.770 × 10 ^-8 , A6 = -1.84 × 10 ^-12 , A8 = 9.000
× 10 ^-17 Coefficient of optical path difference function ψ (h) 1 surface P2 = -0.214668, P4 = -3.8858 × 10 ^-6 , P6 = -1.5668
× 10 ^-10

FIG. 2 is a diagram showing various aberrations of the first embodiment. In the spherical aberration diagram, SA indicates spherical aberration, and SC indicates a sine condition. Solid lines and dotted lines show chromatic aberration of spherical aberration with respect to the wavelength of each spectral line. In the lateral chromatic aberration diagram, each dotted line indicates lateral chromatic aberration of the wavelength of each spectral line with respect to the d-line. In the astigmatism diagram, the solid line S indicates the sagittal image, and the wavy line M indicates the image plane of the meridional image. The distortion diagram shows distortion at the main wavelength.

The power φD of the diffractive lens is −2 × P2 ×
λ, which is 0.00058756 mm (d-line) in Example 1.
Then, -2 × -0.214668 × 0.00058756 = 0.000252261 / mm The focal length fD is 3964.2 mm from 1 / φD.

In order to determine the actual microscopic shape of the lens from the data of the embodiment, the height h of the boundary between the annular zones and the integral multiple of the wavelength of the optical path length are obtained from the optical path difference function ψ (h). Is determined to obtain a Fresnel lens-shaped optical path difference function ψ ′ in which the above component is eliminated. The height h of the switching point of the annular zone is a point at which a value obtained by dividing the phase difference function ψ (h) by λ has an equal value after the decimal point, that is, M
OD (ψ (h), 1) = C. However, MO
D (X, Y) is a function that gives a remainder obtained by dividing X by Y. The constant term C is a constant for setting the phase at the boundary position of the annular zone, and takes an arbitrary value from 0 to 1. FIG. 3 shows a schematic diagram of the microscopic shape of the diffraction lens when C is set to 0.5. At the boundary of the ring zone, the microscopic shape shown by the solid line has a phase difference of ± 0.5 λ with the macroscopic shape shown by the broken line. In the case of having a constant term C, the optical path difference function ψ ′ for a microscopic shape becomes as follows: ψ ′ (h) = (MOD (ψ (h) −C, 1) + C) λ This optical path difference By determining the difference S between the macroscopic shape and the fine shape in the optical axis direction so as to satisfy the above condition and creating data for lens processing, a diffractive refraction hybrid surface can be manufactured.

Embodiment 2 FIG. 4 is a diagram showing a lens configuration of a telephoto lens according to a second embodiment of the present invention, Table 2 is numerical data thereof, and FIG. 5 is a diagram showing various aberrations.

Table 2 _{f = 200.00 F NO = 4.0 2ω} = 12.1 ° surface r d nd νd 1 98.609 10.000 1.51633 64.1 2 * 1537.173 100.500 3 26.000 4.000 1.80400 46.6 4 23.129 79.511 aspheric coefficients first surface K = -0.53 optical path difference function ψ (h) coefficient 2 plane P2 = -0.285415, P4 = -3.0227 × 10 ^-8

[Embodiment 3] FIG. 6 is a diagram showing a lens configuration of a telephoto lens according to a third embodiment of the present invention, Table 3 is numerical data thereof, and FIG. 7 is a diagram showing various aberrations.

TABLE 3 _{f = 300.00 F NO = 4.0 2ω} = 8.1 ° face r d nd νd 1 * 121.884 15.000 1.51633 64.1 2 -2270.000 120.000 3 72.857 5.000 1.48749 70.2 4 44.825 98.098 aspheric coefficients one surface A4 = -4.550 × 10 ^{- 8} , A6 = -3.23 × 10 ^-12 Coefficient of optical path difference function ψ (h) 1 surface P2 = -0.212172, P4 = -3.5710 × 10 ^-6 , P6 = -4.3741
× 10 ^-10 , P8 = -2.9368 × 10 ^-14

Embodiment 4 FIG. 8 is a diagram showing a lens configuration of a telephoto lens according to a fourth embodiment of the present invention, Table 4 is numerical data thereof, and FIG. 9 is a diagram showing various aberrations.

Table 4 _{f = 300.00 F NO = 4.0 2ω} = 8.2 ° face r d nd νd 1 * 80.153 15.000 1.49176 57.4 2 268.763 120.000 3 -48.638 5.000 1.48749 70.2 4 -70.693 110.000 aspherical coefficients one surface A4 = -6.270 × 10 ^-8 , A6 = -1.11 × 10 ^-11 Coefficient of optical path difference function ψ (h) 1 surface P2 = -0.244907, P4 = -9.5342 × 10 ^-6 , P6 = -5.0001
× 10 ^-10 , P8 = -3.2072 × 10 ^-13

Embodiment 4 is an example in which an acrylic resin is used. In the telephoto lens, since the positive lens in the front group is preferably made of a material having a low dispersion and a low refractive index, there is almost no demerit in aberration correction as compared with other embodiments using a glass material.

Embodiment 5 FIG. 10 is a diagram showing a lens configuration of a telephoto lens according to a fifth embodiment of the present invention, Table 5 is numerical data thereof, and FIG. 11 is a diagram showing various aberrations.

TABLE 5 _{f = 300.00 F NO = 4.0 2ω} = 8.1 ° face r d nd νd 1 * 119.987 15.000 1.51633 64.1 2 -1350.953 120.000 3 * 63.546 5.000 1.62004 36.3 4 41.756 110.000 aspherical coefficients one surface A4 = -5.300 × 10 ^-8 , A6 = -4.00 × 10 ^-12 Coefficient of optical path difference function ψ (h) 1 surface P2 = -0.251308, P4 = -4.3646 × 10 ^-6 , P6 = -5.9625 ×
10 ^-10 , P8 = -4.2529 × 10 ^-14 3 sides P2 = 0.431768, P4 = 2.6695 × 10 ^-5 , P6 = 3.5779 ×
10 ^-9

[Embodiment 6] FIG. 12 is a view showing a lens configuration of a telephoto lens according to a sixth embodiment of the present invention, Table 6 is numerical data thereof, and FIG. 13 is a diagram showing various aberrations.

[Table 6] _{f = 300.00 F NO = 4.0 2ω} = 8.2 ° face r d nd νd 1 73.376 15.000 1.51633 64.1 2 * 260.715 117.200 3 * -44.895 4.000 1.77250 49.6 4 -78.178 110.000 aspherical coefficients one surface A4 = -9.000 × 10 ^-8 , A6 = -1.690 × 10 ^-11 , A8 = -1.980 × 10 ^-15 , A10 = -6.800 × 10 ^-19 Coefficient of optical path difference function ψ (h) 2 planes P2 = -0.340382, P4 = 1.0748 × 10 ^-5 , P6 = -3.7976 ×
10 ^-9 , P8 = 2.7042 × 10 ^-14 3 sides P2 = 0.559846, P4 = 6.9460 × 10 ^-5 , P6 = 1.7038 ×
10 ^-8 , P8 = 6.4617 × 10 ^-12

[Embodiment 7] FIG. 14 is a diagram showing a lens configuration of a telephoto lens according to a seventh embodiment of the present invention, Table 7 is numerical data thereof, and FIG. 15 is a diagram showing various aberrations.

TABLE 7 _{f = 300.00 F NO = 4.0 2ω} = 8.2 ° face r d nd νd 1 78.910 15.000 1.49176 57.4 2 * 254.143 117.000 3 -49.272 5.000 1.49176 57.4 4 -78.374 110.006 aspherical coefficients one surface A4 = -7.170 × 10 ^-8 , A6 = -6.530 × 10 ^-12 , A8 = -2.2
20 × 10 ^-15 Coefficient of optical path difference function ψ (h) 2 planes P2 = -0.280087, P4 = -1.0842 × 10 ^-6 , P6 = -8.5622
× 10 ^-12

Embodiment 8 FIG. 16 is a diagram showing a lens configuration of a telephoto lens according to an eighth embodiment of the present invention, Table 8 is numerical data thereof, and FIG. 17 is a diagram showing various aberrations.

Factor 1 side of Table 8 _{f = 300.00 F NO = 8.0 2ω} = 8.2 ° face r d nd νd 1 * 75.500 10.000 1.51633 64.1 2 175.023 89.500 3 -33.512 5.000 1.80518 25.4 4 -37.565 179.713 optical path difference function [psi (h) P2 = -0.193421, P4 = -8.4769 × 10 ^-6 , P6 = -7.9371
× 10 ^-10

Embodiment 8 is an example in which an aspheric surface is not used for the first lens. In this embodiment, F _NO = 8.0, but F _NO = 6.7
Good performance can be obtained without using an aspheric surface to the extent.

Table 9 shows values corresponding to the conditional expressions of each embodiment. Conditional expression (1) 0.25 <L / f <0.6 Conditional expression (2) 0.06 <f / fD <0.14 Conditional expression (3) -1.5 <f1 / f2 <-0.24 Conditional expression (4) 3.4 <| SF | (5) ν2> 40

[Table 9]

[0030]

As described above, according to the present invention, 2
Despite having the minimum number of lens elements for a telephoto lens with a two-element configuration, it can sufficiently correct axial chromatic aberration, spherical aberration, coma aberration, field curvature, astigmatism, distortion, and chromatic aberration of magnification. It is possible to provide an inexpensive telephoto lens which can be reduced to a practically sufficient amount. Furthermore, if the first lens is a resin lens, it is highly effective in reducing the weight of the lens and improving productivity.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a telephoto lens according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating various aberrations of the first embodiment.

FIG. 3 is an explanatory diagram for determining a fine shape of a diffraction lens.

FIG. 4 is a lens configuration diagram of a telephoto lens according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating various aberrations of the second embodiment.

FIG. 6 is a lens configuration diagram of a telephoto lens according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating various aberrations of the third embodiment.

FIG. 8 is a lens configuration diagram of a telephoto lens according to a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating various aberrations of the fourth embodiment.

FIG. 10 is a lens configuration diagram of a telephoto lens according to a fifth embodiment of the present invention.

FIG. 11 is a diagram illustrating various aberrations of the fifth embodiment.

FIG. 12 is a lens configuration diagram of a telephoto lens according to a sixth embodiment of the present invention.

FIG. 13 is a diagram illustrating various aberrations of the sixth embodiment.

FIG. 14 is a lens configuration diagram of a telephoto lens according to a seventh embodiment of the present invention.

FIG. 15 is a diagram illustrating various aberrations of the seventh embodiment.

FIG. 16 is a lens configuration diagram of a telephoto lens according to an eighth embodiment of the present invention.

FIG. 17 is a diagram illustrating various aberrations of the eighth embodiment.

Claims (10)

[Claims] 1. An annular structure having a positive first lens and a negative second lens in order from the object side, wherein one of the surfaces of the first lens has a blazed positive diffraction lens function. A telephoto lens, characterized by having a diffractive refraction hybrid surface. 2. The condition that 0.25 <L / f <0.6 is satisfied, where L is the axial distance between the first lens and the second lens, and f is the focal length of the entire system. Item 10. A telephoto lens according to Item 1. 3. The condition that 0.06 <f / fD <0.14 is satisfied, where fD is the focal length of the diffractive lens component at the d-line of the first lens, and f is the focal length of the entire system. Item 3. The telephoto lens according to item 1 or 2. 4. The apparatus according to claim 1, wherein at least one surface of the first lens is an aspheric surface whose positive power decreases macroscopically toward a peripheral portion.
A telephoto lens according to claim 1. 5. When a focal length including a diffractive lens component of the first lens is f1 and a focal length of the second lens is f2, a condition of -1.50 <f1 / f2 <-0.24 is satisfied. Claims 1, 2,
The telephoto lens according to 3 or 4. 6. The second lens comprises a meniscus lens, and the shaping factor SF of the second lens is
When the radius of curvature of the front surface of the second lens is r3 and the radius of curvature of the rear surface is r4, the following condition is satisfied: SF = (r4 + r3) / (r4-r3). Claims 1, 2,
The telephoto lens according to 3, 4, or 5. 7. When the Abbe number of the second lens is ν2, a condition of ν2> 40 is satisfied.
The telephoto lens according to 3, 4, 5, or 6. 8. The method according to claim 1, wherein one of the surfaces of the negative second lens is a diffractive refraction hybrid surface having a blazed annular structure having a negative diffractive lens effect. The telephoto lens according to 2, 3, 4, 5, or 6. 9. A positive lens comprising a positive first lens and a negative second lens in order from the object side, wherein the first lens is made of resin, and one of the surfaces is a blazed positive diffraction lens. A telephoto lens having a diffractive refraction hybrid surface having an annular structure having a lens function, wherein the second lens is a meniscus lens, and further satisfies the following conditions. 0.25 <L / f <0.6 0.06 <f / fD <0.14 -1.5 <f1 / f2 <-0.24 3.4 <| (r4 + r3) / (r4 -r3) | where L: axes of the first lens and the second lens Upper interval, f: focal length of the entire system, fD: focal length of the diffractive lens component at the d-line of the first lens, f1: focal length of the first lens, f2: focal length of the second lens, r3: second lens R4 is the radius of curvature of the rear surface of the second lens. 10. The diffractive refraction hybrid surface, wherein one of the surfaces of the negative second lens has a blazed annular structure having the effect of a negative diffractive lens. The telephoto lens as described.