The Sky-Watcher ED refractors contain one element made from ED (Extra-low Dispension) FPL-53 glass. This glass minimizes chromatic aberration, provides higher resolution and superior contrast. Colour fringing around objects is completely eliminated with this type of optics. The Sky-Watcher ED refractors also feature a backlash-free 2" Crayford focuser. The focuser wheels contain brushed-aluminum hubs with ridged rubber grip rings. These ED refractors are ideal for visual applications as well as astro-photography.