Eric,

You are spot on. I am now convinced that the DOF in my case is the main factor contributing to the images being out of focus. Checked the DOF tables: f2.8 on D7000 at 55 mm has roughly the same DOF as f4 on D800 at 85 mm. I am now not going lower than f4 and the results are much better.

Still wondering about the shutter speed though. As I use my SB700, my settings are f4, 1/160s, iso 400. I am afraid to go below 1/160s and have VR activated as well. I think it is an overkill, VR should make a difference. Will try to go lower as I get more comfortable.

One specific question I have is about VR and AF-ON button combination. Say I am in AF-C mode holding the AF-ON button to track my son's movement. The instant I am ready to shoot, I press the shutter release button, but if I do it fast, VR will not have time to stabilise the picture. If I do it slowly, I am loosing the precious moment, e.g., my son is no longer smiling or he is looking not in the lens and the picture is gone. Is VR usefull in such situation?

Cheers,
Aziz