The DOF is influenced by several factors
- The closer the object in focus the smaller the DOF gets.
- The longer the focal length of the lens the small the DOF.
- The wider the aperture (smaller f-stop numbers) the smaller the DOF.
- The bigger the camera digital sensor the smaller the DOF.
You can click on any of these photos to get a larger view and then flip though them using the right and left arrow keys.
You can see that even at a small f/22 aperture the depth of field is only about 2 inches. At f/2.8 it is about the width of one small waterdrop. Here's a crop of the f/2.8 shot where you can see just how small the DOF is.