US Patent 7701649 Fixed-focus lens

A fixed-focus lens including a first lens group and a second lens group is provided. The first lens group has a negative refractive power, and consists essentially of a first lens, a second lens, a third lens, and a fourth lens arranged in sequence from an object side to an image side. Refractive powers of the first, second, third, and fourth lenses are negative, negative, positive, and negative respectively. The second lens group is disposed between the first lens group and the image side, and has a positive refractive power. The second lens group includes a fifth lens and a sixth lens arranged in sequence from the object side to the image side. Refractive powers of the fifth lens and the sixth lens are both positive.