The Canon EF 1.4x III 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. This upgraded version features redesigned optics and improved data communication between lens and camera.
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: