Patent ID: 9223113
Filing Date: 2015-12-29
Classification: G02B

Abstract:
1. An imaging optical system comprising, in order from an object side to an image side: an aperture stop; a first lens element with a positive refractive power having a convex object-side surface; a second lens element with a negative refractive power having a convex image-side surface in the vicinity of an outer circumference; a third lens element with a positive refractive power having a concave object-side surface in a vicinity of an optical axis and a convex image-side surface in the vicinity of the optical axis; and a fourth lens element having a concave image-side surface in the vicinity of the optical axis and a convex image-side surface in the vicinity of the outer circumference; wherein a sum of thicknesses of the first, second, third, and fourth lens elements is ALT and a sum of total air gaps between the first, second, third, and fourth lens elements is AAG, and they satisfy the relation: wherein a thickness of the first lens element is T1, an air gap between the second and third lens elements is AG23, and they satisfy the relation: wherein a back focal length is BFL, and it satisfies the relation: