| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stable beam radius and a constant speed characteristic over the entire region of the surface to be scanned by specifying the constitution of the lenses having a meniscus shaped first lens and a second lens having a positive power. SOLUTION: The constitution of the optical scanning lenses is a two group two lens constitution having a first lens N1 and a second lens N2. The lens N1 has a meniscus shape and the lens N2 has a positive power. Let f1 be the focal distance of the lens N1, f2 be the focal distance of the lens N2, r1 be the radius of curvature of the first surface of the lens N1 and r2 be the radius of curvature of the second surface of the lens N1, repectively. Then, let conditional equations -0.25<f2/f1<0.25 and 0.85<r1/r2<1.25 be satisfied. Then, even though the constituting lenses are only two group two lenses, the picture surface deformation of the main scanning and the fθcharacteristics are properly compensated for and a stable beam radius and a constant speed characteristic are obtained over the entire region of the surface to be scanned. |
