The Canon EF 400mm is a telephoto lens designed for Canon's digital SLR cameras. It features a focal length of 400mm, making it ideal for capturing distant subjects, such as wildlife and sports. The lens is known for its sharp image quality and fast autofocus, which helps photographers achieve clear and detailed shots. This lens is available in different versions, including a lightweight Canon EF 400mm f/5.6L and a more advanced Canon EF 400mm f/2.8L IS III, which offers image stabilization. Both options are popular among professional photographers for their durability and performance in various lighting conditions.