A 2X teleconverter, also known as a teleconverter or tele-extender, is a lens accessory used in photography to increase the focal length of a lens. It effectively magnifies the focal length of the lens by a factor of 2x, hence the name "2X teleconverter". For example, if you attach a 2X teleconverter to a 100mm lens, it will effectively turn it into a 200mm lens. This can be useful for getting closer shots of distant subjects without needing to invest in a longer lens. However, there are some trade-offs involved.2X HD OPTICAL CONVERTER FOR CANON EOS REBEL T7 WITH 75-300MM LENS MAKES IT 600MM