Patent ID: 7859763

Claim:
A fixed-focus lens, comprising: a first lens group disposed between an enlarged side and a reduced side, having a positive refractive power, and comprising a first lens, a second lens, and a third lens arranged in sequence from the enlarged side to the reduced side, wherein the first lens is closest to the enlarged side in the fixed-focus lens, and a first surface of the first lens facing the enlarged side is a concave surface; a second lens group disposed between the first lens group and the reduced side, having a positive refractive power, and comprising a fourth lens, a fifth lens, and a sixth lens arranged in sequence from the enlarged side to the reduced side, wherein a lens surface closest to the reduced side in the second lens group is defined as a second surface; and a third lens group disposed between the second lens group and the reduced side, having a positive refractive power, and comprising a seventh lens, wherein a lens surface closest to the enlarged side in the third lens group is defined as a third surface, wherein an overall length of the fixed-focus lens is L, a distance between the second surface and the third surface is L 1 , and the fixed-focus lens satisfies 0.1<L 1 /L<0.5.