I have recently brought a Canon EOS 5D Mark II second hand. A few weeks ago I shot a wedding and noticed some of my shots where not composed well, first I thought this was me not paying attention but after the wedding I noticed that even though I didn’t recompose my shots, something in the camera is moving and altering what I see through the view finder, this happens more often when shooting portrait rather than landscape. Any idea why this is happening? Is there something in my camera which needs to be fixed?