Patent ID: 8773771

Claim:
An image pickup optical system having four lenses, comprising in order from an object side: a first lens having a biconvex shape, and a positive refractive power; a second lens having a biconcave shape, and a negative refractive power; a third lens having a meniscus shape with a concave surface thereof directed toward the object side, and a positive refractive power; and a fourth lens having a biconcave shape, and a negative refractive power, wherein a diaphragm is disposed nearest to the object side, and the image pickup optical system satisfies the following conditional expressions −0.9 <f 4 /f< 0 (1) −0.04<( r 8 +r 9)/( r 8 −r 9)<0.9 (2) −0.03<( r 4 +r 5)/( r 4 −r 5)<0.55 (4) where, f4 denotes a focal length at a near-axis of the fourth lens, f denotes a focal length of the overall image pickup optical system, r8 denotes a radius of curvature of a surface on the object side of the fourth lens, and r9 denotes a radius of curvature of a surface on an image side of the fourth lens, r4 denotes a radius of curvature of a surface on the object side of the second lens, r5 denotes a radius of curvature of a surface on the image side of the second lens, and wherein the surface on the object side of the fourth lens does not have a point of inflection.