Valid points from Roy
300mm has a closer minimum focus distance ( assuming your talking about the IS version).
If you talking about the non-IS version beware some parts such as AF unit are no longer available for repair.
I use the 300mm f4 IS with and without TC. I find it very flexible as I shoot stuff at 5 or 6 feet.
The 400mm is said to be faster focusing which is better for birds in flight.
Last edited by robski; 04-07-07 at 16:41.
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