Prime lens

The invention relates to a prime lens which comprises, from an object side to an image side in turn in the optical axis, a first lens (L1) and the second lens (L2) which are both negative in focal power, a third lens (L3) and a fourth lens (L4) which are both positive in focal power, a fifth lens (L5) which is negative in focal power, a sixth lens (L6) and a seventh lens (L7) which are both positive in focal power, an eighth lens (L8) which is negative in focal power, and a ninth lens (L9) which is positive in focal power, or the third lens (L3) is negative in focal power. The prime lens further comprises a diaphragm (STOP) located between the fourth lens (L4) and the fifth lens (L5). The lens has a large view field, the view field angle can reach 144 degrees, 8 million pixels are considered, the lens is miniaturized and low in cost, the maximum image surface is 9.2 mm, and the lens is suitable for a sensor chip with a large target surface size. 本发明涉及一种定焦镜头，包括：沿光轴从物侧至像侧的方向，依次排列的光焦度均为负的第一透镜(L1)和第二透镜(L2)、光焦度均为正