Is there another cause of this other than camera shake...?
Motion blur is caused by motion, obviously; but the source of that motion can be a number of things. There's poor technique (how you press the shutter (there's more to it than most people know)) or shaking the camera during the shot. Other reasons for blurry images could be a too slow of a shutter speed, too high an ISO/digital "noise" and/or mirror slap.
The guideline I try most to adhere to for getting pin-sharp images is shooting at the lowest possible ISO while, at the same time, maintaining a shutter speed that is twice my focal length (e.g. if I'm shooting at 85mm then my minimum shutter speed needs to be above 1/170 which I would round up to 1/250). When one has to "give" to a significant degree, it's ISO. Also, if you haven't discovered just how much difference shooting with a mono-pod can make, I suggest you try one. Force yourself to use a mono-pod for your next one-hundred shots and see if I'm not right about this. You don't have to spend a lot to get a decent 'pod either, which is nice. My favorite is a
Slik that came with a ball head all for about fifty bucks. If you shoot with monster-sized zooms, you'll need something more substantial but this little gem handles my D7100 with a Sigma 50-150mm DC APO lens just fine, and that's no small package.
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