The Sigma 2x EX APO Tele Converter (also known as a tele-extender)
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: Sigma APO Tele Converter 1.4x and 2x are dedicated
teleconverter lenses. Due to the high optical quality of this
teleconverter, this item will only fit and work with a select list of