Abstract: In an f .theta. lens system in an optical scanner, a light beam from a light source is formed as a line image extending in a main scanning corresponding direction and is deflected at an equal angular velocity by a rotary polygon mirror having a reflecting face in the vicinity of an image forming position of the line image. The f .theta. lens system focuses and forms the light beam deflected by the rotary polygon mirror as an image on the scanned face and comprises a functional device having a function for connecting a reflecting position of the rotary polygon mirror and the scanned face in an approximately conjugate relation with respect to a secondary scanning direction, and an f .theta. function for moving the deflected scanning light beam on a scanned medium face at an approximately equal speed with respect to a main scanning direction; and two groups of first and second lenses sequentially arranged from the side of the rotary polygon mirror toward the scanned face side.

Abstract: An optical scanner comprises a light source device; a linear image forming device for forming an approximately parallel light beam from the light source device as a linear image extending in a main scanning corresponding direction; a rotary polygon mirror having a deflection-reflecting face in the vicinity of the image forming position of the linear image; and an image forming optical system arranged between the rotary polygon mirror and a scanned face and setting the scanned face and a deflecting start point of the deflection-reflecting face in an approximately conjugate relation in geometrical optics with respect to a secondary scanning direction, the image forming optical system forming the deflected light beam from the deflection-reflecting face as an image of a light spot on the scanned face.

Abstract: In an f.theta. lens system in an optical scanner, a light beam from a light source is formed as a line image extending in a main scanning corresponding direction and is deflected at an equal angular velocity by a rotary polygon mirror having a reflecting face in the vicinity of an image forming position of the line image and is then formed by an image forming lens system in the shape of a spot on a scanned face to optically scan the scanned face. The f.theta. lens system focuses and forms the light beam deflected by the rotary polygon mirror as an image on the scanned face. The f.theta. lens system comprises a functional device having a function for connecting a reflecting position of the rotarty polygon mirror and the scanned face in an approximately conjugate relation in geometrical optics in a secondary scanning direction, and comprises an f.theta.