The design of wide-angle reflective optical systems has been to a large degree a pursuit of symmetry. Major systems developed in the 1970s can be broken down as modular design combinations of three classical systems--Schmidt, Schwarzschild, and Baker. These configurations are based on the following four constructional principles: 1) aperture stop and correction at the center of curvature of a spherical mirror, 2) confocality of two parabolic mirrors working at infinite conjugates, 3) concentric mirrors, 4) polar strip field coverage. Five notable wide-angle reflective systems developed in '70s are: 1) Two-Axis Baker, 2) Hughes WALRUS, 3) Honeywell Wide-Angle Conical Scanner, 4) Perkin-Elmer Ring Telescope, 5) Corrected Schwarzschild.