Prime lens

The invention discloses a prime lens, which sequentially comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens from an object side to an image side along an optical axis, the object side surface of the second lens is a convex surface; the object side surface and the image side surface of the third lens are convex surfaces; the fourth lens has focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power; the sixth lens has focal power, and the image side surface of the sixth lens is a convex surface; the seventh lens has negative focal power; the number of lenses with focal power of the prime lens is seven, the positive and negative attributes of the focal power of the second lens and the focal power of the fourth lens are different, and the positive and negative attributes of the curvature radius of the image side face of the fifth lens and the curvature radius of the object side face of the sixth lens are