Following on from the great news that Canon will be releasing a 200-400mm F4.0 lens in the near future, here is a image comparing the new lens to the Canon 500mm F4. The new lens looks a beast. Really going to enjoy having a play with on of these.
The 200-400 is the bottom lens. In this image you can see the system which drops a 1.4x convertor onto the the optical system. This is a fantastic idea and will be a great tool for sports and wildlife photographers