Weird Apparation

[rgregory1965]

So I was out in the back yard doing my own focus and sharpness test on my Sigma 70-200 OS.

I saw this little bird land on the fence about 12.5 meters away, I was at 200mm and decided to try a shot.....If your familiar with the D7000 focus square in the viewfinder, this little guy only filled half, so it was a challenge to focus on him.

Anyhow I got the strange Apparation in a few shots, it dont look natural to me.....could this be dirty sensor????

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