Patent ID: 7149019

Claim:
An optical scanning system, comprising: light source means; deflecting means configured to deflect a light beam emitted from said light source means in a main-scan direction; and an imaging optical system configured to image the light beam, deflected by said deflecting means, on a scan surface to be scanned; wherein, in a sub-scan sectional plane, said imaging optical system is configured to place a deflecting surface of said deflecting means and the scan surface in a conjugate relationship with each other; wherein a curvature, in the sub-scan sectional plane, of both of a light entrance surface and a light exit surface of at least one imaging optical element that is a constituent component of said imaging optical system changes, inside an effective region, continuously from an optical axis of said imaging optical system toward a peripheral portion of the same, and wherein a sign of each of the curvatures of the light entrance surface and the light exit surface of said imaging optical element with respect to the sub-scan sectional plane is reversed within the effective region; wherein, when a curvature radius of the light entrance surface of said imaging optical element at the optical axis thereof, with respect to the sub-scan sectional plane, is denoted by rl 0 and when a least quantity of an absolute value of the curvature radius in the sub-scan sectional plane of a portion inside the effective region, in which portion the sign of the curvature is reversed with respect to the curvature of the light exit surface of said imaging optical element at the optical axis thereof, in the sub-scan sectional plane, is denoted by |r2| min , the following relations rl 0 <0 and |rl 0 |<|r2| min are satisfied; and wherein, when a shape x of the light entrance surface or the light exit surface of said imaging optical element in a main-scan sectional plane is expressed in terms of a function x=g(y) of an arbitrary coordinate y in the main-scan direction inside an effective scan region of said imaging optical element and when an absolute value of a difference between a second differential quantity of x at the coordinate y and a second differential quantity of x at a coordinate y+0.01 is denoted by |δd 2 x/dy 2 |, both the light entrance surface and the light exit surface of said imaging optical element satisfy the following relation |δd 2 x/dy 2 |<0.00003.