Question about DOF

So I just bought a 5D2 a few weeks ago and was playing around with the MFA a little and had a question. As you stop down a lens and the DOF gets larger, should the area that comes into focus be the same forward and back of the focus point? Or does the DOF get larger from the focus point back? Thanks..

No, the area acceptably in focus is not the same in front and behind the point of focus. Generally the area in front is smaller than that behind the point of focus.

There is a useful DoF calculator at http://www.cambridgein​colour.com/tutorials/d​of-calculator.htm which will allow you to test different settings and see how the distances change.

The DOF will be very close to 1:1 distributed around the focus plane at macro distances. As you move towards ever longer focus distances, the bias will grow towards the far side.

Think of a paramter of focus bias, where FB = in focus distance behind subject / in focus distance before subject.

The limit of FB as focus distance => 0 is 1.
The limit of FB as focus distance => hyperfocal distance is infinity.

Thanks much.. appreciate the info. I guess everything is good with my lenses then.

Here is a chart about the split of DOF at various focus distances...

Thanks Wilt, I was hoping you would pop in here and drop off some useful piece of knowledge.