Claims
- 1. A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:
a refractive lens system that is provided with a positive lens having relatively small dispersion, a negative lens having relatively large dispersion and an additional refractive lens, said additional refractive lens consisting of an additional positive lens, said refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of said refractive lens system decreases as the wavelength becomes shorter; and a positive diffractive grating that corrects the longitudinal chromatic aberration of said refractive lens system, wherein the following condition is satisfied: 0.005<f/fD0.2 where f is focal length of the entire lens system, and fD is focal length of said positive diffractive grating.
- 2. The diffractive-refractive achromatic lens according to claim 1, wherein said refractive lens system comprises a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths, and said additional refractive lens generates longitudinal chromatic aberration such that the back focus of said refractive lens system decreases as the wavelength becomes shorter.
- 3. The diffractive-refractive achromatic lens according to claim 2, wherein the following condition is satisfied:
- 4. The diffractive-refractive achromatic lens according to claim 2, wherein said diffractive grating is formed on one surface of said additional positive lens.
- 5. The diffractive-refractive achromatic lens according to claim 4, wherein said additional positive lens is arranged at a convergent side of said refractive achromatic lens and the following condition is satisfied:
- 6. 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 positive 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 positive lens, 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: 6&LeftBracketingBar;fI·∑i=1m 1fi·vi&RightBracketingBar;<0.002where 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, τi 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.
- 7. The diffractive-refractive achromatic lens according to claim 6, wherein the following condition is satisfied:
- 8. The diffractive-refractive achromatic lens according to claim 6, wherein said diffractive grating is formed on one surface of said additional positive lens.
- 9. A diffractive-refractive achromatic attachment that is attached to a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths, 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 positive lens, decreases as the wavelength becomes shorter, said additional refractive lens comprising an additional positive lens; and a positive diffractive grating that corrects the longitudinal chromatic aberration of said refractive lens system.
- 10. The diffractive-refractive achromatic attachment according to claim 9, wherein said diffractive grating is formed on one surface of said additional positive lens.
- 11. A diffractive-refractive achromatic attachment that is attached to a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths, 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 positive lens, 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: 0.05<(fp·τp)f<0.5 where fp is a focal length of said additional refractive lens, τp is an Abbe number of said additional refractive lens, and f is the focal length of the entire lens system including said refractive achromatic lens.
Priority Claims (1)
Number |
Date |
Country |
Kind |
HEI 10-24789 |
Feb 1998 |
JP |
|
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. application Ser. No. 09/244,077, filed Feb. 4, 1999, the contents of which are herein incorporated by reference in its entirety.
Divisions (1)
|
Number |
Date |
Country |
Parent |
09244077 |
Feb 1999 |
US |
Child |
09873332 |
Jun 2001 |
US |