JPS63124011A - Distributed refractive index type achromatic lens - Google Patents

Abstract

PURPOSE:To satisfactorily correct a chromatic aberration and a tertiary aberration by a small number of lenses, by combining at least one piece each of lenses by which a refractive index of a medium is heterogeneous, especially, increases or decreases in an axially symmetric manner against an optical axis. CONSTITUTION:When (r), N00, and N10 denote a distance from an axis of a light beam 3, a refractive index on an optical axis, and refractive index distribution constant, respectively, a P lens 1 of N10<0 and an N lens 2 of N10>0 are combined by using a medium whose refractive index distribution becomes N(r)=N00+N10r<2>. Subsequently, N10 of 486.1nm, 587.6nm, and 656.3nm wavelength is denoted as N10F, N10d, and N10C, respectively, nu10=N10d/(N10F-N10C) denotes an Abbe number of a distribution constant, and Abbe numbers of the P lens 1 and the L lens 2 are denoted as nu10P and nu10N, respectively. In such a way, at the time of nu10P/nu10N>2, a primary chromatic aberration of an optical system can be corrected satisfactorily. Also, a correction of a tertiary monochromatic aberration can be performed by adjusting the distribution constant N10, and giving a curvature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technique useful in constructing an optical system in which chromatic aberration is corrected.

[Prior art]

In order to correct chromatic aberration in conventional optical systems that use lenses whose medium has a -like refractive index, it is necessary to use at least two convex lenses and one concave lens, each with a different Abbe number. A lens system of the following configuration must be used.

Furthermore, in general, in an optical system, it is necessary to correct various monochromatic aberrations other than chromatic aberration, such as Seidel's five aberrations such as third-order spherical aberration and coma aberration. It is known that a doublet made by bonding a convex lens and a concave lens with different Abbe numbers can correct first-order chromatic aberration, third-order spherical aberration, and coma aberration. However, when attempting to correct many aberrations under more severe conditions, a large number of lenses are required and the optical system becomes more complex.

[Problem that the invention seeks to solve]

In a lens made of a medium with a -like refractive index, refraction of light rays occurs only at the boundary surfaces of the medium, and the light rays travel straight through the medium. Therefore, for complex or strict aberration correction, many refractive surfaces are required, which inevitably increases the number of lenses. However, when considering the manufacturing and use of optical systems, an increase in the number of lenses not only increases product prices due to increased material costs, increased processing costs, and increased adjustment and inspection costs, but also puts a burden on buyers. This results in a product that is bulky and difficult to use.

Therefore, the purpose of the present invention is to solve the above-mentioned problems and to reduce the number of lenses and parts in an optical system by using a gradient index medium, which has not been put into practical use, as a lens, thereby achieving a low cost. , and to provide an optical system that is more compact and lightweight.

[Means for solving problems]

The present invention solves the above problems by combining at least seven lenses in which the refractive index of the medium is non-uniform, in particular, the refractive index increases or decreases axially symmetrically with respect to the optical axis. Although the number of lenses is small, it can effectively correct chromatic aberration and third-order aberration, and provides a small, lightweight optical system at a low price. Light rays are refracted not only at the interface of the medium, but also inside the medium. Therefore, even one such lens can perform the function equivalent to several lenses with uniform refractive index. The characteristics of such a lens are described in detail in U.S. Pat.
Specific practical examples are shown in /.

However, these examples are optical systems using monochromatic light, and no study has been made when using white light as a light source, where chromatic aberration would be a problem. In contrast, JP-A-4/-
Although chromatic aberration is mentioned in I10/Co, etc., the conditions required for the medium are not considered.

Generally, in a homogeneous lens system, if the Abbe number of a convex lens is ν11 and the power is φ・1, and the Abbe number of a concave lens is ν2 and the power is φ2, then φ1/Si1+φ2/
shi2 + w o (1) φl + φ2 − φ
(2) From this, φ1-shi1・φ/(shi1-shi2) (31φ
2--ν2・φ/(shi1-shi2) (41
There is an achromatic condition. All the power here is due to the refractive surface. Therefore, in a gradient index lens, if we consider that most of its power is due to the medium, the value of the distribution constant, Abbe's number, becomes important.

However, in this case, the above formula cannot be applied as is. Because (3).

In equation (4), if the difference between ν1 and ν2 is small, the power distribution of each lens φ1. φ2 has opposite signs and both become very large values. Here, large power suggests large lens thickness. However, since light rays travel inside a gradient index lens while meandering and curving, there is a maximum lens thickness that maintains a relationship equivalent to that of a homogeneous lens. Therefore, the power value φ1. φ2 cannot be realized. Also,
Since equations (1) to (4) are approximate conditions for a thin lens, it is unreasonable to apply them as they are to a gradient index lens whose thickness cannot be ignored in terms of refraction due to the medium.

Here, - degree (31, (looking at formula 41, φ1 and φ
It is true that the larger the difference between the two, the better. Examining from this point of view, when the Atsube numbers of the distribution constants of convex lenses and concave lenses are respectively ν10 (P) yν10 (N), the ratio is νlo (P) / ν10 (Nl > 2
(It was found that when using 5J, the seventh-order chromatic aberration of the optical system was well corrected.

Furthermore, correction of third-order monochromatic aberration can be implemented by adjusting the distribution constant N10 and adding curvature.

〔Example〕

Paraxial Hosochi chromatic aberration was determined for a lens system having the optical constants listed in Table 1. Here, the evaluation function is Δ-(FB(C)-1(Fl)/KFL(d)
(61 Defining Table 7, 7 Loung Ho 77 - Gland Wave MOe
4! .

Back focus FB(C1 and FB(
F) are both j, 7446111 m, the focal length EFL at the 7 Raunhofer line wavelength d is 6 degrees, and Δ
-0.

FIG. 1 shows the layout of the above-mentioned optical system, in which l is a gradient index positive lens, C is a gradient index negative lens, and 3 is a ray. - In this way, although the refractive surface is flat, the refractive index distribution type w
: It can be seen that chromatic aberration is well corrected just by the quality power alone.

〔Effect of the invention〕

According to the present invention, by combining at least one gradient index lens with convex lens action and one gradient index lens with concave lens action, it is possible to configure an optical system that can satisfactorily correct chromatic aberration and monochromatic aberration. can. The optical system obtained in this way has fewer lenses and fewer parts than the conventional optical system using a homogeneous medium, so it can significantly reduce the cost, size, and weight of the optical system and optical components. It is something that contributes.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, where l is a positive lens, 2 is a negative lens, and 3 is a ray. Figure 1 Procedural amendment document Showa 6 - Case of March 6, 1939 Patent application Showa/-Core/No. Relationship to the case Patent applicant address 4-8 Doshomachi, Higashi-ku, Osaka-shi, Osaka;, Subject of amendment 1' Akira m! Book'P Claims Extended and Detailed Description of the Invention Column Z Contents of Amendment (1) The entire text of the "Claims" on page 1 of the specification will be amended as shown in the attached sheet. (2) In the bottom column of the first table on page 7 of the specification, "diameter" is corrected to "radius." 2. Claims (1) An optical system in which chromatic aberration is corrected by combining two or more media whose refractive indexes are non-uniform. (2) In the optical system of claim 1, where r is the distance from the optical axis, NoO is the refractive index on the optical axis, and N10 is the refractive index distribution constant, the refractive index distribution is N(r) =N0
When using a sawtooth lens as expressed by 0+N10 r2, a P lens with N10<O, N1,
An optical system configured using at least seven 0>01!7sN lenses. (3) In claim 2, Watanabe Ko♂4.7'
nm. ! ♂7. When N10 of jnm, AtJ, and Jnm are respectively Nl0(Fl. N10fd) and N10(C1, !'10
- Nl0(d) / (Nl0(Fl = Nl0(C
1) is the Atsube number of the distributed constant, an optical system in which the ratio of ν10 of the P lens and the N lens is ν10 (Pl/ν10 (Nl>x).

Claims (3)

[Claims] (1) An optical system that corrects chromatic aberration by combining two or more media whose refractive indices are non-uniform. (2) In the optical system according to claim 1, r is the distance from the optical axis, N_0_0 is the refractive index on the optical axis, and N_1_0
is the refractive index distribution constant, then the refractive index distribution is N(r
)=N_0_0+N1_0r^2 When using a medium as a lens, an optical system is configured using at least one P lens with N_1_0<0 and at least one N_1_0>0N lens. (3) In claim 2, the wavelength is 486.1n.
N_1_0 of m, 587.6 nm, 656.3 nm,
N_1_0(F), N_1_0(d), N_1 respectively
When _0(C), ν_1_0=N_1_0(d)
/(N_1_0(F)-N_1_0(C)) is the Abbe number of the distribution constant, then ν_1_0 of P lens and N lens
An optical system in which the ratio of ν_1_0(P)/ν_1_0(N)>2.