US Patent 10281682 Optical imaging system

An optical imaging system includes a first lens group having a first group of lenses. A foremost lens of the first group of lenses is a lens closest to an object side and has a positive refractive power. The optical imaging system also includes a second lens group having a second group of lenses. A rearmost lens of the second group of lenses is a lens closest to an imaging plane and has convex surfaces. The first and second lens groups are sequentially disposed from the object side to an imaging plane. An expression TL/f1<2.0 is satisfied, where TL represents a distance from an object-side surface of the foremost lens to the imaging plane and f1 represents a focal length of the foremost lens.