Patent ID: 7283288

Claim:
A scanning device, comprising: a light source unit that emits a light beam; a collection optical system that converges the light beam emitted by the light source unit; a deflector that deflects the light beam converged by the collection optical system; an image forming optical system that converges the light beam deflected by the deflector onto a scan target surface to form a beam spot scanning in a main scanning direction, wherein the scanning device satisfies a following condition: − 1 <S 1 −S 2 < 1 (A) where S 1 = ( y 1 ⁢ _max - y 1 ⁢ _max ′ ) 2 ( y 1 ⁢ _ ⁢ 0 - y 1 ⁢ _ ⁢ 0 ′ ) 2 × ( 1 L 1 + 1 L ⁢ ⁢ cos ⁢ ⁢ θ ) 2 ( 1 L 1 + 1 L ) 2 , S 2 = ( y 2 ⁢ _max - y 2 ⁢ _max ′ ) 2 ( y 2 ⁢ _ ⁢ 0 - y 2 ⁢ _ ⁢ 0 ′ ) 2 × ( 1 L 1 + 1 L ⁢ ⁢ cos ⁢ ⁢ θ ) 2 ( 1 L 1 + 1 L ) 2 , y 1 — max represents a height from an optical axis of the image forming optical system to a position at which an outer edge light ray of the light beam proceeding to a maximum image height enters a first surface of a max-power lens having a maximum power in the main scanning direction of all lenses in the image forming optical system, y′ 1 — max represents a height from the optical axis to a position at which an inner edge light ray of the light beam proceeding to the maximum image height enters the first surface, y 1 — 0 represents a height from the optical axis to a position at which the outer edge light ray of the light beam proceeding to a scanning center enters the first surface, y′ 1 — 0 represents a height from the optical axis to a position at which the inner edge light ray of the light beam proceeding to the scanning center enters the first surface, y 2 — max represents a height from the optical axis to a position at which the outer edge light ray of the light beam proceeding to the maximum image height enters a second surface of the max-power lens, y′ 2 — max represents a height from the optical axis to a position at which the inner edge light ray of the light beam proceeding to the maximum image height enters the second surface, y 2 — 0 represents a height from the optical axis to a position at which the outer edge light ray of the light beam proceeding to the scanning center enters the second surface, y′ 2 — 0 represents a height from the optical axis to a position at which the inner edge light ray of the light beam proceeding to the scanning center enters the second surface, θ represents an angle formed between the optical axis and a chief ray of the light beam proceeding, immediately after deflection by the deflector, to the maximum image height, L represents a distance between the first surface and a position of an image formed in the main scanning direction by an optical system located on the light source unit side of the max-power lens, and L 1 represents a distance between the second surface and the scan target surface.