Enabling Depth of Field.
Depth of Field is controlled by the f-number that can be found in Camera Settings. The default value is “Pinhole” and it totally removes the DOF effect from the scene. By selecting any other value, you can control DOF.
Another way to control depth of field is to enable and change the ‘Depth of Field (%)’. Lower values will make DOF narrower.
Setting the focus distance.
By default, Camera settings have Auto-Focus enabled and this means that even if you set a custom focus distance, it will be overridden by auto-focus. Unchecking Auto-Focus will make Thea use the focus distance that was set by the user.