A 27.5-m-diameter, 210° spherical mirror was housed in one of the pavilions at Expo 70, Osaka, Japan. The mirror was constructed by G. T. Schejdahl on the same principle as the Echo and PAGEOS satellites and made of 12.5-µ Melinex. It was held in place by a negative pressure behind the mirror. This was the first time a number of optical effects could be seen inside a mirror of this size. These are photographically shown and discussed. In addition to the simple first-order real images, higher order image rings were observed. The photographs also indicate the nonparaxial distortion which occurs.
J. W. Klüver, "Photographic Recording of Some Optical Effects in a 27.5-m Spherical Mirror," Appl. Opt. 10, 2754-2759 (1971)