Patent ID: 7817320
Filing Date: 2010-10-19
Classification: G02B,H04N

Abstract:
1. A two-element fθ lens with short focal distance, applied to a laser scanning unit, and said laser scanning unit including a light source for emitting a laser beam, a polygon mirror for scanning said laser beam to form a scanning light, and a target for sensing a light; and said two-element fθ lens with short focal distance along an optical axis from a polygon mirror side to a target side comprising, a first lens, in a meniscus shape, and having a concave surface toward said polygon mirror; and a second lens, in a meniscus shape, and having a concave surface toward said polygon mirror; wherein, said first lens includes a first optical surface and a second optical surface, having positive refractive power in main scanning direction on optical axis of said laser scanning unit; wherein, said second lens includes a third optical surface and a fourth optical surface, having negative refractive power in main scanning direction on optical axis of said laser scanning unit; said fourth optical surface having an inflection point in SAG counted from the optical axis to peripheral portion and its paraxial portion is convex toward the polygon mirror side; said first optical surface, said second optical surface, said third optical surface and said fourth optical surface are aspherical surfaces in the main scanning direction; satisfies the conditions of: wherein d