Wide-angle lens with freeform surface

A method to create an optical system with a target 2D object-image mapping derivative function, the optical system comprising at least one freeform surface and at least one other optical surface, the method comprising:

• a. using an initial optical design prescription as a starting point;
• b. alternating, until a final design prescription is obtained, the steps of:
• i. calculating at least one of a sag, a slope or a curvature of the at least one freeform surface to get an optical design prescription with the target 2D object-image mapping derivative function;
• and
• ii. optimizing the at least one other optical surface;
• c. building the optical system according to the final design prescription obtained, wherein the sag of the at least one freeform surface of the built optical system has at least one local minimum or local maximum across its surface and the 2D object-image mapping derivative function has at least one local minimum or local maximum.