Turns Your 300mm into a 420mm ( with lose of one stop,, from a F4 to a F5.6) Or Your 70mm-200mm from a 200mm to a 280mm. This is the tele to get,, The Canon 2.0 tele converter loses quality on the image.... ( And Remember,,, Image is Everything) Camera , Glass, is but a tool for that Image.. Well, OK, there is such a thing as " Style Points" and that is where cool " Retro FIlm Cameras " come into the picture............