OPTICAL SCANNER, LINE IMAGE FORMING OPTICAL SYSTEM IN OPTICAL SCANNER, IMAGE-FORMATION ADJUSTMENT METHOD IN OPTICAL SCANNER AND IMAGE FORMING DEVICE

摘要

PROBLEM TO BE SOLVED: To effectively reduce an image plane fluctuation in the main scanning direction and the subscanning direction caused by a temperature change, by using an optical element made of a resin easy in processing and assembling, without using a mechanical mechanism nor narrowing the latitude of designs. SOLUTION: The line image forming optical system in an optical scanner which sets a beam from a light source 1 as a beam having a prescribed beam form with a coupling optical system 2, image-forms the beam as a long line image in the main scanning direction with line image forming optical systems 3, 4, deflects it with a light deflector 5 having a deflection reflecting surface near the image forming position of the line image, condenses a deflection beam toward a surface to be scanned 7 with a scanning image forming optical system 60, forms a light spot on the surface to be scanned 7 to perform the optical scanning of the surface to be scanned 7 has one or more lenses 3 made of a resin, and one or more glass lenses 4. The lens 3 made of a resin includes two planes having negative power in the subscanning direction and at least one plane having negative power in the main scanning direction. The power of each surface of the lens 3 made of a resin is set so that the image plane fluctuation caused by the temperature change of the coupling optical system and/or the scanning image forming optical system is effectively reduced.