I have for sale a canon 1.4x mkiii extender for sale used a couple of times for sports photography before purchasing a 400mm f2.8 lens so it is no longer required. You will lose 1 stop of light when using it so if your putting on a f2.8 it will become f4. The Canon Extender EF 1.4x III Teleconverter is a high-quality lens accessory designed for Canon cameras, offering a maximum aperture of f/1.4 and a fixed focal length. This teleconverter is compatible with Canon EF mount cameras and allows for both auto and manual focus options, providing versatility for photographers. Made in Japan, this Canon Extender EF unit is ideal for extending the reach of your lens, perfect for capturing distant subjects with precision and clarity.