Fotodiox Pro Autofocus 2x Teleconverter - AF Doubler x2.0 for Canon EOS EF, EF-S Camera and Lens (APS-C & Full Frame) Doubles the focal length of a Canon EF/EF-S lenses (2.0x Magnification Factor) Lens construction features 4 elements in 3 groups for sharp images Communication Between Lens & Camera Enables Auto Focus, Auto Iris & Image Stabilization A maximum aperture of f/4 or greater is required in order to fully utilize the autofocus capabilities. 24 Month Fotodiox Warranty