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I can make it smoother but this will slowdown everything.
Too bad. As for the locked focus error, I can't explain it that too well, however, look at these images and compare them to your results. Especially look at the shrubs at the right side and how they change 'blur-wise'. I think you can best describe the effect as 'depth smearing', and that's what your effect lacks .. 
Photographs:
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Don't get me wrong, you're getting great results already! It doesn't trully feel like depth of field though, but maybe that's because I'm just a photograph freak,
Cheers
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