Lens system and optical apparatus

Abstract

A lens system includes a first lens which is formed of a medium exhibiting negative refraction, and a second lens having a positive refractive index. Accordingly, it is possible to provide a lens system in which a negative refractive index medium for which a curvature of field is reduced. Moreover, it is also possible to have a lens system in which a lens having a positive focal length and a lens having a positive focal length, which is made of a positive refractive index medium, are combined.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a structure of a lens system according to a first embodiment of the present invention;

FIG. 2 is a diagram showing a structure of a lens system according to a modified embodiment;

FIG. 3 is a diagram showing a structure of a lens system according to a second embodiment;

FIG. 4 is a diagram showing a structure of a lens system according to another modified embodiment;

FIG. 5 is a diagram showing a first concrete example of a photonic crystal 340;

FIG. 6 is a diagram showing a second concrete example of the photonic crystal 340;

FIG. 7 is a diagram for describing an image formation by a plane-parallel plate 380 which is formed of a negative refractive index medium 301; and

FIG. 8 is a diagram for describing a curvature of field.

Claims

1. A lens system comprising: a first lens which is formed of a medium exhibiting negative refraction; anda second lens which is formed of a medium having a positive refractive index.

2. The lens system according to claim 1, wherein a sign of a focal length of the first lens which is formed of the medium exhibiting negative refraction is same as a sign of a focal length of the second lens which is formed of the medium having the positive refractive index.

3. The lens system according to claim 2, wherein the focal length of the first lens which is formed of the medium exhibiting negative refraction is positive, and the focal length of the second lens which is formed of the medium having the positive refractive index is positive.

4. The lens system according to claim 2, wherein the focal length of the first lens which is formed of the medium exhibiting negative refraction is negative, and the focal length of the second lens which is formed of the medium having the positive refractive index is negative.

5. A lens system comprising: a first lens which is formed of a medium exhibiting negative refraction, and a second lens which is formed of a medium exhibiting negative refraction.

6. The lens system according to claim 5, wherein a sign of a focal length of the first lens which is formed of the medium exhibiting negative refraction differs from a sign of a focal length of the second lens which is formed of the medium exhibiting negative refraction.

7. The lens system according to claim 6, wherein the focal length of the first lens which is formed of the medium exhibiting negative refraction is positive, and the focal length of the second lens which is formed of the medium exhibiting negative refraction is negative.

8. The lens system according to one of claims 1 and 5, which includes the first lens and the second lens.

9. The lens system according to one of claims 1 to 7 which satisfy the following expression 117 −|10/fTN|≦Σ1/(fi·ni)≦|10/fTN|  expression 117

10. An optical apparatus comprising: the lens system according to one of claims 1 to 7.

11. The lens system according to one of claims 1 and 5, wherein the medium exhibiting negative refraction is a negative refractive index medium.

12. The lens system according to one of claims 1 and 5, wherein the medium exhibiting negative refraction is a medium exhibiting properties of a perfect imaging.

13. The lens system according to one of claims 1 and 5, wherein the medium exhibiting negative refraction is a photonic crystal.

14. The lens system according to claim 13, wherein a photonic crystal is used as the medium exhibiting negative refraction, andan axis of the photonic crystal having an optimum rotational symmetry is directed in an optical axis direction of an optical system.

15. The lens system according to one of claims 1 to 7, wherein the medium exhibiting negative refraction satisfies expression 5-8: −8.0≦ε′≦−0.2  expression (5-8)whereε′=ε/εc,ε is a dielectric constant of the medium of the lens, and εc is a dielectric constant of the medium around the lens.

16. The lens system according to one of claims 1 to 7, wherein a thickness of the lens which is formed of the medium exhibiting negative refraction satisfies any one of expressions 15-2, 16-2, 17, and 18: 0.1 mm≦t′≦300 mm  expression (15-2)0.01 mm≦t′≦300 mm  expression (16-2)1100 nm≦t′≦200 mm  expression (17)30 nm≦t′≦50 nm  expression (18)

17. The lens system according to one of claims 1 to 7, wherein a refractive index of the medium exhibiting negative refraction satisfies expression 142 −10≦ns≦−0.1  expression 142

18. The lens system according to one of claims 1 and 5, wherein a wavelength which is used is a visible wavelength.