Summary: Take a series of shots from a locked position to demonstrate the depth of field available at different apertures

f2.8

f4

f5.6

f8

f10

f16

f22

The below shows three shots, at f2.8, f8 & f22 respectively, with the relative sharpness highlighted. From this we can conclude that the wider the aperture the shallower the depth of field. The shallower depth of field is very useful to isolate a subject from the background and to create smother blur, or bokeh which is best highlighted at the top of the f2.8 shot.