The SAL-20TC AF 2x (D) Teleconverter- for Select Sony & Maxxum AF SSM & APO Lenses from Sony will increase the focal length of a lens by 2x, and reduces the lens aperture by approximately 2 f-stops. It was specifically designed to provide full AF compatibility with a select range of Sony (or equivalent Minolta) pro-level G-series lenses (with Minolta, only with Maxxum 7/5/4/3 or newer cameras). For example, using a 2x teleconverter with a 300mm lens will effectively increase the focal length to 600mm. A lens set to f/2.8 will now be f/5.6.