US Patent 7995292 Image pickup lens and image pickup apparatus

An image pickup lens includes, in order from an object side, a first lens element having a positive refractive power and a convex surface facing the object side, an aperture stop adjusting the amount of light, a second lens element having a negative refractive power, a third lens element having a positive refractive power and a concave surface facing the object side, and a fourth lens element having a negative refractive power. In the image pickup lens, the following conditional expressions are satisfied,0.6<|f2/f|<1.80≦f2/R4<1.7where f denotes a focal length of an entire lens system, f2 denotes a focal length of the second lens element, and R4 denotes a curvature radius of an object-side surface of the second lens element.