Hi Walter, I'm sure thre are more knowledgeable people here, but here's my little help.

1. Go to render setting and check "Depth of Field"  box.

Then select the camera you are using to render, and get the parameter dial displayed.

Set the f stop you like to use, and then move the "Focus_Distance" dial, and pay attention to the screen. When you slide the dial, you will see the cross target mark displayed for a brief moment.

Use that target to select focus point. Default setting for that parameter is rather rough increment, so double click the focus_distance dial and set it to finer increment.

Now, you are ready to render.

If you use wider f stop, it will add considerable amount of time to render, so experiment.

lam2