you are totally right. Just like any zooms (or probably any lens

when f is wide open or totally closed down,the optical quality is compromized. So, at f4,its quality can't beat your 300/f2.8. But .when you close f down,their qualities are probably pretty close.  I remember a user test report that claimed that at 300 with f two steps down, the 200-400 was a better performer than 300/2.8.  It's kind of hard to believe though. But I believe their qualities are pretty close at right fs.

So, as I said, this lens is slower.  Hopefully with camera's ISOs are improved greatly in recent years, it would not be a bit problem.

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• Thanks. -Big_Benz- ♂ (72 bytes) () 07/12/2011 postreply 19:17:14