Ok, here is hows it done.

1. Create a camera

2. go to camera view.

3. Go to Display > Heads Up Display > Object Details. Now you should have a Distance From Camera: up in your right hand screen.

4. Select the object of focus, (that you want to be the focus point)

5. There should be a number of the distance from your camera to the focus object. Like 7.473.

6. Go into your camera attributes.

7. Go down to the Depth of Field, click on the little white box that says Depth of Field. In Focus Distance, put in the number that is in your upper right screen under "Distance From Camera"

8. In F Stop, I always put in like around 50. If you put in let say 5. the DOF blur is really stronge. The 50. is what I use for the slauhterhouse martyr scene

Anyways hope that helps.

If you have anymore questions, just ask