| 摘要 |
A scanning optical system for use in a laser beam printer which is small and available at low cost, and yet is capable of effectively compensating for tilting and beam shaping. The scanning lens unit in this optical system has two-element composition consisting of, in order from a deflector side, a first lens of a negative lens element having a concave spherical surface on the deflector side and a concave cylindrical surface oon the scanning surface side having a curvature in the auxiliary scanning cross section, and the second lens having a planar surface on the deflector side and a convex toric surface on the scanning surface side which has a stronger curvature in the auxiliary scanning cross section. The scanning lens unit has a shorter focal length in the auxiliary scanning cross section than in the main scanning direction and forms an image at a finite distance with the object point lying at focusing point where image is formed by the cylindrical lens. Thus, the scanning lens unit greatly reduces the effects of tilting of the deflector positioned between the focusing point and the scanning lens unit. |
