Aaron Bauer and Jannick Rolland of the Institute of Optics recently published an article “Design of a freeform electronic viewfinder coupled to aberration fields of freeform optics” in Optics Express 23(22), 28141-28153 (2015).
Abstract: The newly formulated theory of aberration fields of freeform surfaces describes the aberrations that freeform Zernike polynomial surfaces can correct within folded powered optical systems. This theory has guided the design of an OLED-based reflective freeform electronic viewfinder covering a 25° full field-of-view with a 12 mm eyebox, which is reported together with a detailed methodology that begins with developing an unobscured starting point and ends with an optimized freeform design, analyzed both in display and visual spaces. In addition, tolerancing of the system points to the potential low sensitivity of these systems to manufacturing tilt (10 arcmin), decenter and despace (100 μm), and figure errors (λ/2 @ 0.632 μm).