| 摘要 |
PROBLEM TO BE SOLVED: To reduce curvature of field, to improve speed equality (to improve linearity), and further miniaturize an optical system by making at least one surface of a lens for optical scanning or correction optical system aspherical and specifying the sum of the quantities of aspherical surface variation of respective surfaces. SOLUTION: A scanning optical system which is arranged between the deflection reflecting surface 4a of an optical deflector 4 and a scanned surface 7 is composed of an fθlens 5 of two-element constitution and a long-size optical element 6. The surface of the long-size optical element 6 as the correction optical system on the side of the optical deflector 4 is made anamorphic. The quantity of aspherical surface variation of an aspherical surface at the position (height) where the maximum view angle light beam of luminous flux deflected by the optical deflector 4 crosses the aspherical surface is denoted asΔX. The focal length of the whole system in a horizontal scanning direction is denoted as fm. The sum of the quantities of aspherical surface variation of the respective surface satisfiesΣΔXi/fm<0 (ΔXi: aspherical surface variation quantity of (i)th surface counted from the deflection reflecting surface 4a). |
