This Tele Converter will multiply the focal length of the existing lens by 2x, and will cut back the amount of light by 2 f/stops. For example, using a 2x teleconverter with a 300 mm lens will effectively increase the focal length to 600 mm. A lens set to f/2.8 will now be f/5.6. Note: Due to the high optical quality of this teleconverter, this item will only fit and work with a select list of lenses. Please click here for a compatibility chart of all compatible lenses. Note: The DG denotes added coating that achieves the best color balance whilst cutting down on ghosting caused by reflections from the digital image sensor.