The AFB940 is Sigma's 55mm EX DG, Digitally Optimised, UV (Ultra Violet) Multi-Coated Glass Filter. Digitally Optimised (DG) Filters EX DG filters benefit from Sigma's multi-layer lens coating, developed to counteract the highly reflective characteristic of image sensors. With older style filters, light would reflect off the image sensor, bounce off the lens and filter elements and re-enter the image sensor, creating a ghost image. The multi-layer coating dramatically reduces this effect. In addition to this, an optimum, neutral colour balance is ensured, increasing the white balance accuracy of the digital camera. Multi-coated UV Filter This filter perfectly eliminates the harmful effect of ultraviolet light. The multi-coated UV filter can be used with both colour and black-and-white film anddigital sensors. This is the most suitable filter for protective use and generalphotography.