On loan from a friend, I could spend some clear nights with this short-focus flat-field refractor. It has 70mm aperture and 350mm focal lenght, for an F/Ratio of F/4,9. It delivers a nice illuminated field and pinpoint stars almost to the corners of the frame. Some slight blue fringing is present near the corners. Focusing is very critical, and also very temperature-dependent. An autofocuser is almost indispensable to keep control over the focus.