You may also want to consider how fast your lens is. If it is an F4, for example, the converter will make it equivalent to an F8 which is kinda slow and may even affect the ability of the camera to autofocus. When I used one with film cameras, I had to have the lab do a 1 or 2 push on developing for good exposure. With EOS, you can see what's going on immediately, and make any exposure changes needed right away when shooting on manual. If you do get one. get the best optics you can. Personally, if I had a need for a longer lens, I would buy one in lieu of the 2x. The more light you can get to the CCD, the more options you will have for creativity. If you only plan to go long occasionally, and in bright light, the 2x would do. Also, when considering the 2x, don't forget to consider any filters you may be using as some of those cut down the light, too, and the 2x will double that loss as well.