The Sigma 1.4x DG EX APO Tele Converter (also known as a tele-extender) will multiply the focal length of the existing lens by 1.4x, and will cut back the amount of light by one f/stop. For example, using a 1.4x teleconverter with a 300 mm lens will effectively increase the focal length to 420mm. A lens set to f/2.8 will now be f/4.

This APO teleconverter can be mounted between select lenses and the camera body to increase the focal length by the power of 1.4 or 2. The new multi layer coating reduces flare and ghost, which is a common problem with digital cameras. They demonstrate best performance with DG series lenses. They also offer maximum photography magnification by 1.4 x or 2x, without any variation in the minimum focusing distance. Compact and lightweight, these teleconverters convert your lenses into longer focal-length lenses, so you don't have to do a lot of unnecessary footwork