D7000 and Tamron 70-300 VC does Welsh Mountain Zoo

I find my Tamron 70-300 VC to be extremely good for shots such as these (nice captures, BTW). I just wish it could do better for far away wildlife. It seems the closer to infinity focus it goes, the softer things get. However, for subjects within a hundred feet or so, the lens is sharp, sharp, sharp!!
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K.B.