Patent ID: 8310517

Claim:
An optical scanning device comprising: a light source that has a plurality of luminous points; a first optical system that shapes a plurality of beams of light emitted from the light source; a rotary polygon mirror that has deflecting surface and that deflects the beams of light output from the first optical system by the deflecting surface; and an optical scanning system that causes the beams of light that are deflected by the rotary polygon mirror to form images on a surface to be scanned, wherein after chief rays of the beams of light are output from the first optical system, the chief rays strike the deflecting surface with different angles with respect to the optical axis of the optical scanning system within a deflecting/scanning surface of the rotary polygon mirror, β is assumed to be half of an angle formed between the optical axis of the first optical system and the optical axis of the optical scanning system within the defiecting/scanning surface, δ is assumed to be a distance between an intersection dc and an intersection hh, the distance being when an angle of β is formed between the optical axis of the first optical system and a normal perpendicular to the deflecting surface, and the normal passing through the rotation axis of the rotary polygon mirror, where the intersection dc is the intersection of the optical axis of the first optical system and the deflecting surface, and the intersection hh is the intersection of the deflecting surface and the normal passing through the rotation axis of the rotary polygon miller, R i is assumed to be a radius of an inscribed circle of the rotary polygon mirror, Ω is assumed to be a maximum value of an angle formed between the chief ray of any of the beams of light output from the first optical system and the optical axis of the first optical system, θ max− is assumed to be a maximum scanning angle of view of the chief ray in a negative image height toward the optical scanning system with respect to a light flux passing through the axis of the first optical system or a chief ray of virtual light flux, θ max+ is assumed to be a maximum scanning angle of view of the chief ray in a positive image height toward the optical scanning system with respect to a light flux passing the axis of the first optical system or a chief ray of virtual light flux, and δ is set to be a value that satisfies Equation 2: δ = - sin ⁢ ⁢ βsinΩ + sin ⁢ Ω 2 ⁡ [ sin ⁡ ( β + θ max + 2 ) + sin ⁡ ( β + θ max - 2 ) ] sin ⁢ ⁢ βsinΩ ⁢ R i ( 1 ) given that δ is defined positive when the intersection dc is present on the optical-scanning side of the intersection hh, and that an angle of view θ of the rotary polygon mirror is zero degree.