Patent ID: 8022975

Claim:
A line head comprising: a positive lens system having two lenses with positive refractive power; an image-side lens array in which the image-side lens of the two lenses is arrayed in a plural number in first and second directions; an object-side lens array in which the object-side lens of the two lenses is arrayed in a plural number in the first and second directions; a light emitter array in which a plurality of light-emitting elements are arrayed on an object side of the positive lens system for the one positive lens system; and an aperture plate that forms an aperture diaphragm, the aperture plate being disposed between the image-side lens array and the object-side lens array so that an image side is telecentric or approximately telecentric, wherein assuming that the row number of lenses arrayed in the second direction of the image-side lens array is m, a gap between effective regions of the two image-side lenses adjacent to each other in the first direction is α, an image-side angle of aperture (half angle) of the positive lens system is θ i , a width (full width) of a plurality of light-emitting element images in the first direction, which are images on image surfaces of the plurality of light-emitting elements arrayed for the one positive lens system, is W i , a focal length of the image-side lens is f 2 , and a distance from an image-side principal plane of the image-side lens to the image surface is S i , the following conditions, f 2 ≦( mW i −α)/(2θ i ) W i ≧2 S i θ i /( m− 1)+α/( m− 1) are satisfied.