Patent ID: 8773771
Filing Date: 2014-07-08
Classification: G02B

Abstract:
1. 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 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.