How to set depth of field strength (or Z-depth strength)?

Hi all,
I have a scene that is small, yet I wish to have some DOF in it.
I have a camera focus set up, but all is sharp (I did play around with the focus point). Then I took a look at my Z pass and it was all white. Guess it is because of the small scene. How to increase the strength of the DOF, or the Z pass?
Thanks in advance.

If it’s cycles dOf can be gotten hereabouts

Not sure Internal has the feature.

I meant Cycles, yes of course.
I found that one can tweak setting using the compositor. Thanks anyway!

Using the Active Camera’s DoF settings is a much more versatile means of controlling depth of field than using the Compositor, as it emulates focal blur as it actually occurs in a camera setup, and does not require pre-rendering to be seen in the viewport (good for fine-tuning). I prefer the F-stop option to the Radius choice but that’s because I did photography for many years and am comfortable with the process.