Scanning lens
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorTakashi Iizuka
Life of this patent
Estimating the term…
Abstract
An f.theta. scanning lens arrangement, arranged from a polygonal mirror side to an imaging surface side, including a first, second, third, and fourth lens with having negative, positive, positive, and negative power, respectively, in the main scanning and subscanning directions is provided. The ratio of the focal length in the main scanning direction of the fourth lens versus the focal length in the main scanning direction of the entire f.theta. lens is selected to simultaneously minimize astigmatism, field curvature, and linearity error. Further, the ratio of the focal length in a subscanning direction of the first lens versus the focal length in the subscanning direction of the second lens is selected to minimize curving of scanning lines displaced from the optical axis.
Claims37
A scanning lens for imaging light beams, deflected in a main scanning direction by a deflector, onto a scanned surface, said scanning lens comprising, in order from said deflector toward said scanned surface:
- a first lens having a negative power in at least said main scanning direction, a scanned surface side of said first lens comprising a cylindrical surface having negative power in a subscanning direction;
- a second lens having a positive power in at least said main scanning direction;
- a third lens having a positive power in at least said main scanning direction;
- and
- a fourth lens having a negative power in at least said main scanning direction.
A scanning lens for imaging light beams, deflected in a main scanning direction by a deflector, onto a scanned surface, said scanning lens comprising, in order from said deflector toward said scanned surface:
- a first lens having a negative power in at least said main scanning direction, said first lens having a negative power in a subscanning direction, the power of said first lens in the subscanning direction being more negative than the power of said first lens in the main scanning direction;
- a second lens having a positive power in at least said main scanning direction;
- a third lens having a positive power in at least said main scanning direction;
- and
- a fourth lens having a negative power in at least said main scanning direction.
A scanning lens for imaging light beams, deflected in a main scanning direction by a deflector, onto a scanned surface, said scanning lens comprising, in order from said deflector toward said scanned surface:
- a first lens having a negative power in at least said main scanning direction;
- a second lens having a positive power in at least said main scanning direction, said second lens having a positive power in a subscanning direction, the power of said second lens in said subscanning direction being greater than the power of said second lens in the main scanning direction;
- a third lens having a positive power in at least said main scanning direction;
- and
- a fourth lens having a negative power in at least said main scanning direction.
A scanning lens for imaging light beams, deflected in a main scanning direction by a deflector, onto a scanned surface, said scanning lens comprising, in order from said deflector toward said scanned surface:
- a first lens having a negative power in at least said main scanning direction;
- a second lens having a positive power in at least said main scanning direction;
- a third lens having a positive power in at least said main scanning direction, said third lens having a positive power in a subscanning direction, the power of said third lens in the subscanning direction being greater than the power of said third lens in said main scanning direction;
- and
- a fourth lens having a negative power in at least said main scanning direction.
Dependencies are inferred from the claim text.