Patent ID: 7538789

Claim:
An optical scanning device, comprising: a light source device having at least two light emitting members disposed spaced apart from each other in a main-scan direction; a rotary polygonal mirror configured to scanningly deflect at least two light beams emitted from said light source device; an input optical system configured to project the at least two light beams from said light source device onto said rotary polygonal mirror so that, within a sub-scan section, the at least two light beams are incident on a deflecting surface of said rotary polygonal mirror in an oblique direction with respect to a normal to the deflecting surface; and an imaging optical system configured to image, upon a surface to be scanned, the at least two light beams scanningly deflected by the deflecting surface of said rotary polygonal mirror; wherein said input optical system includes a converting optical element configured to transform a light beam from said light source device into a parallel light beam, wherein, when a maximum pivot angle of said rotary polygonal mirror for scanning an effective region on the scanned surface is denoted by θ max [deg], an angle defined in the main-scan section between an optical axis of said input optical system and an optical axis of said imaging optical system is denoted by 2ø [deg], a focal length of said converting optical element in the main-scan section is denoted by f col [mm], a spacing between two light emitting members, of the at least two light emitting members, which are most spaced apart from each other in the main-scan direction is denoted by a [mm], a largest one of oblique incidence angles in the sub-scan section of the at least two light beams incident on the deflecting surface of said rotary polygonal mirror is denoted by α [deg], an imaging magnification of said imaging optical system in the sub-scan section is denoted by βs, an inscribed-circle radius of said rotary polygonal mirror is denoted by R [mm], and a resolution of an image in the sub-scan direction is denoted by DPI [dot/inch], a relation  tan ⁢ ⁢ θ m ⁢ ⁢ ax cos ⁢ ⁢ ϕ × a fcol × R × β ⁢ ⁢ s × tan ⁢ ⁢ α × D ⁢ ⁢ P ⁢ ⁢ I 25.4  ≤  0.05  is satisfied, and wherein the largest angle α [deg] of the oblique incidence angles in the sub-scan section of the at least two light beams incident on the deflecting surface of said rotary polygonal mirror satisfies a relation 2 deg. ≦α≦4 deg.