US Patent 7733363 Line head and image forming device using the same

A line head includes a lens array having a plurality of positive lens systems in a first direction. Each positive lens system has a pair of lenses with positive refractive power. A light emitter array disposed on an object side of the lens array has a plurality of light emitting elements disposed corresponding to the positive lens systems. An aperture plate forms an aperture stop on the object side of the pair of lenses. A focal distance f1 of one of the pair of lenses disposed on the object side satisfies the conditional formula f1≦d0/(1+W0/D1).