Scanning optical apparatus and image forming apparatus using the same

A scanning optical apparatus comprising:

• a light source unit;
• a rotational polygon mirror having a plurality of deflection surfaces configured to deflect a light flux emerged from the light source unit;
• an incident optical system configured to image the light flux emerged from the light source unit, as a line image elongated in a main scanning direction in the deflection surfaces of the rotational polygon mirror;
• and
• an imaging optical system configured to image the light flux deflectively scanned by the rotational polygon mirror on a surface to be scanned and to bring the deflection surfaces of the rotational polygon mirror and the surface to be scanned into a conjugate relationship with each other in a sub scanning section,
• wherein:
• the imaging optical system includes, in an optical path between the rotational polygon mirror and the surface to be scanned, a first imaging lens, a mirror, and a second imaging lens in order from the rotational polygon mirror side;
• the second imaging lens has a lens surface formed into a non-arcked shape in the sub scanning section;
• the non-arcked shape comprises a non-arcked shape including an aspherical coefficient of fourth or higher order, and the aspherical coefficient of fourth or higher order changes in the main scanning direction of the imaging optical system from a center portion to a peripheral portion of the imaging optical system;
• the mirror is rotatable around an axis parallel to the main scanning direction;
• and
• the imaging lens is adjusted so that the light flux deflectively scanned by the rotational polygon mirror passes through a meridional line of the second imaging lens throughout all area of the imaging lens in the longitudinal direction.

A scanning optical apparatus comprising:

• a light source unit;
• a rotational polygon mirror having a plurality of deflection surfaces configured to deflect a light flux emerged from the light source unit;
• an incident optical system configured to image the light flux emerged from the light source unit, as a line image elongated in a main scanning direction in the deflection surfaces of the rotational polygon mirror;
• and
• an imaging optical system configured to image the light flux deflectively scanned by the rotational polygon mirror on a surface to be scanned and to bring the deflection surfaces of the rotational polygon mirror and the surface to be scanned into a conjugate relationship with each other in a sub scanning section, wherein:
• the imaging optical system includes, in an optical path between the rotational polygon mirror and the surface to be scanned, a first imaging lens, a mirror, and a second imaging lens in order from the polygonal mirror side;
• the second imaging lens has a lens surface formed into a non-arcked shape in the sub scanning section;
• the non-arcked shape comprises a non-arcked shape including an aspherical coefficient of fourth or higher order, and the aspherical coefficient of fourth or higher order changes in the main scanning direction of the imaging optical system from a center portion to a peripheral portion of the imaging optical system;
• the second imaging lens is rotatable around an optical axis of the imaging optical system;
• and
• the imaging lens is adjusted so that the light flux deflectively scanned by the rotational polygon mirror passes through a meridional line of the second imaging lens throughout all area of the imaging lens in the longitudinal direction.

An image forming apparatus comprising:

• a scanning optical apparatus comprising:
• a light source unit;
• a rotational polygon mirror having a plurality of deflection surfaces configured to deflectively scan a light flux emerged from the light source unit;
• an incident optical system configured to image the light flux emerged from the light source unit, as a line image elongated in a main scanning direction on the deflection surfaces of the rotational polygon mirror;
• and
• an imaging optical system which includes at least one imaging lens and is configured to image the light flux deflectively scanned by the rotational polygon mirror on a surface to be scanned and to bring the deflection surfaces of the rotational polygon mirror and the surface to be scanned into a conjugate relationship with each other in a sub scanning section,
• wherein:
• the imaging lens has a lens surface formed into a non-arcked shape in the sub scanning section;
• the non-arcked shape comprises a non-arcked shape including an aspherical coefficient of fourth or higher order, and the aspherical coefficient of fourth or higher order changes in the main scanning direction of the imaging optical system from a center portion to a peripheral portion of the imaging optical system;
• the imaging lens is movable in at least one of shifting in a sub scanning direction and a rotational direction around an optical axis of the imaging optical system;
• and
• the imaging lens is adjusted so that the light flux deflectively scanned by the rotational polygon mirror passes through a meridional line of the imaging lens throughout all area of the imaging lens in the longitudinal direction;
• a photosensitive member disposed on the surface to be scanned;
• a developing device configured to develop an electrostatic latent image formed on the photosensitive member with a light flux scanned by the scanning optical apparatus, as a toner image;
• a transferring device configured to transfer the developed toner image to a transfer material;
• and
• a fixing device configured to fix the transferred toner image on the transfer material.