| 摘要 |
In an f theta lens system in an optical scanner, an approximately parallel light beam from a light source device is formed as a line image extending in a main scan-corresponding direction and is deflected at an equal angular velocity by a rotary polygon mirror having a reflecting face in the vicinity of the position of the formed line image. The deflected light beam is formed by an image forming lens system as an image in the shape of a spot on a scanned face to optically scan the scanned face at an approximately equal speed. The image forming lens system forms the light beam deflected by the rotary polygon mirror as an image on the scanned face. The f theta lens system includes a functional device having a function for setting a reflecting position of the rotary polygon mirror and the scanned face in an approximately conjugate relation in geometrical optics with respect to a cross scanning direction, and an f theta function with respect to a main scanning direction; and two groups of first and second lenses are sequentially arranged from the side of the rotary polygon mirror toward the scanned face side. The lenses have first to fourth lens faces which are counted from the side of the rotary polygon mirror and respectively have shapes of an arc, an arc, a straight line and an arc on a deflecting plane sequentially from the first lens face toward the fourth lens face.
|
