The Canon EF 1.4x II Extender is a high-quality teleconverter that preserves the image quality of the lens it's mounted to and multiplies its focal length by 1.4x.
The 1.4x extender (also known as a teleconverter) 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 300mm lens will effectively increase the focal length to approximately 420mm. A lens set to f/2.8 will become f/4.
This extender is only compatible with the following lenses: