| 摘要 |
In a scanning image forming lens used in an optical scanner, a light beam from a laser light source is coupled and deflected at an equal angular velocity by an optical deflector and is converged as a light spot on a scanned face by the scanning image forming lens to optically scan the scanned face at an equal speed. The scanning image forming lens is constructed by first and second plastic lenses such that the first lens is constructed by a positive meniscus lens having a concave face directed onto an optical deflector side. The second lens is arranged near a scanned face side of the first lens. At least one face of each of the first and second lenses is constructed by an aspherical surface. | theta 1/ theta 2| has a local minimum near an optical axis of the scanning image forming lens and is increased from the optical axis toward a peripheral portion of the scanning image forming lens when theta 1 is set to an acute angle between the optical axis and the light beam incident to the second lens and theta 2 is set to an acute angle between the optical axis and the light beam emitted from the second lens.
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