no other choice available for a 2x extender. version II works great, but as any extender you loose light and autofocus works much slower on any lens. remember a 200 2.8 x 2x = 400 8.0 ... a 400 5.6 is much faster and 1 stop brighter. if you need long lenses, buy long lenses. extenders are life-savers when occasionally needed
Does everything Canon said it would do. I have this attached to a Canon EF 70-200mm IS L f/2.8 and it is very sharp nearly as good as without it. Makes wildlife shooting a lot more fun! Buy one!
Very cost effecient way to extend the focal length of your lens. Have a 200mm and need a 400mm? On a limited buget? This extender should be seriously considered. No noticable loss of image quality. Drops the f/stop of your lens by two, but still acceptable for the price. Highly recommended product.