US Patent 10107993 Wide-angle optical system and image pickup apparatus using the same

A wide-angle optical system includes in order from an object side to an image side, a first lens having a negative refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, an aperture stop, a fourth lens having a positive refractive power, and a fifth lens. An object-side surface of the first lens is convex toward the object side, and the following conditional expression (1) is satisfied.1.0<(R1L+R1R)/(R1L−R1R)≤2.0  (1)where,R1L denotes a paraxial radius of curvature of the object-side surface of the first lens, andR1R denotes a paraxial radius of curvature of an image-side surface of the first lens.