A single focus lens includes, in order from the object side: a diaphragm stop; and first and second lens components, each lens component being of positive refractive power and each having a convex surface on the object side at least near the optical axis. Each of the two lens components has two aspheric surfaces, may be a lens element, and preferably is made of plastic. The single focus lens may include no other lens elements and the diaphragm stop may be on the object side of the single focus lens. Specified on-axis conditions are satisfied in order to reduce aberrations and to make the single focus lens compact. Additionally, satisfying a condition related to the aspheric shapes of the lens components helps reduce aberrations.