We describe the design of the near UV filter imager SuFi onboard Sunrise, which was successfully flown in the stratosphere in June 2009. During its five days flight SuFI captured the highest contrast images of solar granulation ever. SuFI is a diffraction limited filter imager with an effective focal length of 121m, working in 5 distinct wavelength bands between 210nm and 397nm. It is based on a two mirror modified Schwarzschild microscope, which is integral part of the central Image stabilization and light Distribution unit (ISLiD) of Sunrise, which acts as the reimaging optics between the 1m telescope and the science instruments. The key technical features of the instrument are presented under the view of the specific demands of balloon-borne optical systems. First results obtained with the instrument are presented to demonstrate the capabilities of the instrument.