Diffractive-refractive achromatic lens
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorTetsuya Abe
Life of this patent
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Abstract
A diffractive-refractive achromatic lens includes a refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter and a diffractive grating for correcting the longitudinal chromatic aberration of the refractive lens system. The refractive lens having such a chromatic aberration includes a positive lens having relatively small dispersion and a negative lens having relatively large dispersion. Further, the following condition (1) should be satisfied: 0.005<f/fD<0.2 where f is a focal length of the entire lens system, and fD is a focal length of the positive diffractive grating.
Claims17
A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:
- a refractive lens system that comprises a refractive achromatic lens that is corrected in chromatic aberration at two wavelengths and an additional refractive lens, said refractive achromatic lens being provided with a positive lens having relatively small dispersion and a negative lens having relatively large dispersion, said refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that a back focus of said refractive lens system decreases as the wavelength becomes shorter;
- and
- a positive diffractive grating that corrects said longitudinal chromatic aberration of said refractive lens system,
- wherein the following condition is satisfied:
- 0.005<f/fD<0.2
- where
- f is focal length of the entire refractive lens system, and
- fD is focal length of said positive diffractive grating.
A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:
- a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths;
- an additional refractive lens that is arranged at a convergent side of said refractive achromatic lens, said additional refractive lens including a lens having a strong convex surface directed to said refractive achromatic lens to generate longitudinal chromatic aberration such that the back focus of the refractive lens system, which includes said refractive achromatic lens and said additional refractive lens, decreases as the wavelength becomes shorter;
- and
- a positive diffractive grating that is formed on one surface of said additional refractive lens to correct said longitudinal chromatic aberration of said refractive lens system,
- wherein the following condition (4) is satisfied:
- [LeftBracketingBar] f I · ∑ i = 1 m 1 f i · ν i [RightBracketingBar] < 0.002 ( 4 )
- where
- fI is a focal length of said refractive achromatic lens,
- fi is a focal length of an i-th lens of said refractive achromatic lens counted from an object side,
- νi is an Abbe number of said i-th lens of said refractive achromatic lens counted from the object side, and
- m is a total number of lenses of said refractive achromatic lens.
A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:
- a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths;
- an additional refractive lens that is arranged at a convergent side of said refractive achromatic lens to generate longitudinal chromatic aberration such that the back focus of the refractive lens system, which includes said refractive achromatic lens and said additional refractive lens, decreases as the wavelength becomes shorter;
- and
- a positive diffractive grating that is formed on one surface of said additional refractive lens to correct said longitudinal chromatic aberration of said refractive lens system,
- wherein the following condition (8) is satisfied:
- 0.4<L/f<b 0.9 (8)
- where
- L is an air gap along the optical axis between said refractive achromatic lens and said additional refractive lens, and
- f is a focal length of the entire lens system.
A diffractive-refractive achromatic attachment that is attachable to a refractive achromatic lens being corrected in chromatic aberration at two different wave lengths, said attachment comprising:
- an additional refractive lens that generates longitudinal chromatic aberration such that the back focus of the refractive lens system, which includes said refractive achromatic lens and said additional refractive lens decreases as the wavelength becomes shorter;
- and
- a positive diffractive grating that corrects said longitudinal chromatic aberration of said refractive lens system.
Dependencies are inferred from the claim text.