Exercise: Focus at different apertures

For this exercise I used the old railway viaduct crossing the river North Esk, north of Montrose. All images are set at ISO100 and 18mm. Image 1 at f4,320th sec; Image 2 at f10, 1/40 sec; Image 3, f22, 1/20 sec, Pictures taken on 1.1.2012 in the morning. Image 1, shows the least dof, sharpness just reaching the second arch. In Image 3 most of the viaduct appears sharp in focus