Design of a miniature anamorphic lens with a freeform front group and an aspheric rear group

We propose a miniature anamorphic lens design that records wide-screen videos on an ordinary CMOS format. The front group consists of two freeform lenses, which achieve different focal lengths in the two orthogonal directions and thus enable the anamorphic characteristics. The rear group is made of rotationally symmetric aspheric elements that relay the image on the sensor. The annularly stitched extreme-point-based polynomial surface description is proposed to control the extreme point position and the air clearance between elements in the optimization process. An optimization method based on surface upgrade and conversion is adopted in the design. The design result offers an anamorphic ratio of 1.33 and an f-number (f / #) of 1/42, with a field of view of 65.3 deg × 35 deg. The overall length of the lens is 9.5 mm, which shows an advantage for integration into pocket devices.