The Kenko 2.0x Teleplus HD DGX Teleconverter contains a set of optics which multiply the focal length of your prime lens by 2.0x, turning a 300mm lens into the equivalent of 600mm. Teleplus HD DGX converters use unique circuitry which maintains signal integrity between the camera body and lens and it also allows accurate recording of digital EXIF data. Full AF operation with the HD DGX 2.0x is possible using a lens with an aperture of f4 or brighter (except Canon EF 50mm f1.8). Please be aware that autofocus will only work if there is enough light and contrast on the subject to activate the camera's AF sensors properly, otherwise manual focusing may be required.