Teleconverters are additional optical elements designed to extend the focal length. The teleconverter is inserted between the lens and the camera body, which raises the question of mutual compatibility, which we will discuss below. By installing a teleconverter, we usually extend the focal length of the lens by 1.4x or 2x. This means that from a 200mm lens we get a 400mm lens. This can be a very inexpensive way to get a large telephoto lens. However, it is fair to ask yourself under what circumstances it is appropriate and possible, when it brings some limitations and when you are better off buying a cheaper lens of the required focal length.