| 摘要 |
PROBLEM TO BE SOLVED: To reduce a sensitive degree with respect to manufacture error/ assembly errors in respective optical parts and to restrain the change quantity of line pitch intervals to be small. SOLUTION: The difference in image-forming magnification is reduced by narrowing the interval of two luminous fluxes and suppressing an incident angle difference in a position, where light is made incident on an image-forming lens face to be small. More specifically, a sensitive degree with respect to line pitch interval change quantity when a manufacture error and an assembly error occur in respective optical parts is reduced, so that auxiliary scanning direction pixel density is set to be A and (dms.Lap)/(fco.k)<=(1.6/A) is satisfied. It is desirable that a diaphragm 3b deciding the luminous flux width of a main scanning direction be arranged nearest the side of a polygon mirror 5 among optical parts constituting an incident optical system, since it is effective to have it nearer to a deflection reflection face 5a. Thus, the diaphragm 3 is arranged between a cylindrical lens 4 and the polygon mirror 5. |
