Small lens system

A small lens system comprising a first lens, a second lens, a third lens, and a fourth lens arranged along an optical axis from an object,

• wherein an iris diaphragm is located between the first lens and the second lens,
• the first lens has a negative refractive power and comprises a concave surface on an object side and a convex surface on an image side,
• the second lens has a positive refractive power and comprises convex surfaces on both sides,
• the third lens has a positive refractive power and comprises convex surfaces on both sides,
• the fourth lens has a negative refractive power and comprises concave surfaces on both sides, and
• all surfaces of the first to fourth lenses are aspherical, wherein (i) a focal length f1 of the first lens, a focal length f2 of the second lens, a focal length f4 of the fourth lens satisfy 0<(f1/f2)+(f1/f4)<1 and/or (ii) a center thickness L1_CT of the first lens, a center thickness L2_CT of the second lens, a center thickness L3_CT of the third lens, and a center thickness L4_CT of the fourth lens satisfy 1.3<(L3_CT+L4_CT)/(L2_CT+L1_CT)<1.6.