I used my 6D and 70-200 f2.8 IS II at a night time parade. This camera/lens combo has always produced super-sharp images.
But almost all of my parade photos were soft - many had to be deleted.
My goal was to have a sharp subject, and with background people and objects with a pleasant blur. So I set the 6D to center-point,
Here's two examples. Both were shot at f4.0, ISO 12800.
This one at 1/160s, 110mm. The AF point was on her skirt. The second image at 1/250s, 182mm, AF point on her face.
BTW, I used this same camera and lens at the same parade two years ago, and the results were excellent.
Back then I set the 6D to AI Servo mode, this year to One-shot AF. I'm not sure if that makes any
difference, as most of my subjects were very slow moving.
Comments and suggestions are welcomed. Thanks.