Extends the focal length of your lens by 2x.This lens is only compatible with fixed focal length L-series lenses 135mm and over, as well as the EF 70-200/2.8L, EF 70-200/2.8L IS, EF 70-200/4L, and EF 100-400/4.5-5.6L Outstanding image quality thanks to new optical design and improved AF performance Highly resistant to dust and water for use in harsh conditions Built in micro computer enables effective communication between lens and camera Lens coatings are optimised to minimise ghosting and flare