the olympus pen f series was introduced and produced by olympus of japan between 1963 and 1966. the system consisted of the original olympus pen f, later the behind-the-lens metering pen ft, 1966–1972; and the non-metered version of the ft, known as the olympus pen fv, which was manufactured from 1967 to 1970. the design considerations used were unusual. the camera produced a half-frame 35 mm negative; it used a porro prism as a design-replacement for the conventional pentaprism thus producing the 'flat top' appearance; and the view through the viewfinder was of 'portrait' orientation' (unlike standard 35mm slrs which had 'landscape' orientation). these half-frame cameras were also exceptional in that all used a rotary shutter, rather than the traditional horizontally travelling focal-plane shutter commonly used in other slr camera designs. the camera was produced with various interchangeable lenses. the smaller image format made the pen f system one of the smallest slr camera systems ever made. only the pentax auto 110 was smaller, but the pentax system was of much more limited range in terms of lenses and accessories.