Although the technology had been available for some time, it wasn’t until nearly the turn of the century that a truly successful prismatic binocular was developed. In 1894, Professor Ernst Abbe teamed up with the Zeiss Company to produce the Feldstecher (German for field glass), using Porro prisms. The largest model magnified to 8x. It has individual screw focusing eyepieces and a hinged bridge connecting the two tubes, thus is adjustable for eye separation. Prismatic optics revolutionized the binocular by using two prisms back to back or other arrangements of prisms to rebound light and effectively extend the distance between objective and eyepiece thus compacting the tube while at the same time increasing the ratio of focal lengths between the two lenses, resulting in higher magnification. The prisms also widen the distance between objective lenses thus enhancing the stereographic perspective or perception of depth. By 1910 binoculars were produced in large quantity for both military and civilian use in several countries and invariable come with leather sling cases. Binoculars became more diverse and large, heavy, rugged brass binoculars made for navy boat decks contrast with small, dainty feminine opera glasses. Illumination and brightness were greatly improved in the 1930s when a thin coat of magnesium fluoride was applied to glass surfaces to reduce distracting reflections.