Patent ID: 7375847

Claim:
An optical scanning device comprising: light source means; a first optical system for converting a diverged flux of light that has been emitted from the light source means into another condition of flux of light; a rotational polygon mirror; a second optical system for focusing the flux of light that has been converted by the first optical system on a deflection surface of the rotational polygon mirror in a sub-scanning section; and a third optical system for imaging the flux of light that has been deflected by the deflection surface of the rotational polygon mirror onto a surface to be scanned, wherein the flux of light emitted from the light source is entered into a deflection surface of the rotational polygon mirror at a limited angle in a sub-scanning section, and the following conditional is satisfied: β s ⁢ tan ⁢ ⁢ α ⁢ Δ ⁢ ⁢ ( 1 + cos ⁡ ( ϕ - θ m ) ) cos ⁡ ( ϕ / 2 - θ m / 2 ) + β s ⁢ R ⁢ ⁢ cos ⁡ ( 180 / N ) ⁢ ( 1 - cos ⁡ ( θ m / 2 ) ) ⁢ ( sin ⁡ ( α + 2 ⁢ γ ) - sin ⁢ ⁢ α ) cos ⁡ ( θ m / 2 ) ⁢ cos ⁡ ( ϕ / 2 ) ⁢ cos ⁢ ⁢ α + D ⁡ ( tan ⁡ ( ( α + 2 ⁢ γ ) / β s ) - tan ⁡ ( α / β s ) ) ≤ P 10 where α represents an angle between a normal to the deflection surface and the flux of light incident on the deflection surface in the sub-scanning section, φ represents an angle between the deflection surface of the rotational polygon mirror and the flux of light incident on the deflection surface in the main scanning section when a scanning center of the surface to be scanned is scanned with the flux of light deflected by the rotational polygon mirror, P represents an ideal scanning line pitch in a sub-scanning direction on the surface to be scanned, β s represents a lateral magnification in the sub-scanning section in the third optical system, Δ represents a maximum relative difference in distance from a rotation axis of the rotational polygon mirror to deflection surfaces of the rotational polygon mirror, γ represents a maximum angle of tilt of the deflection surface of the rotational polygon mirror, R represents a circumradius of the rotational polygon mirror, N represents a number of facets of the rotational polygon mirror, θ m represents a maximum deflection angle of the rotational polygon mirror, and D represents an amount of positional shift from a conjugate point in a case that the deflection surface of the rotational polygon mirror and the surface to be scanned are in a conjugate relationship in the sub-scanning section.