In Image four, I have adjusted
the focal length to 70mm (as opposed to 35mm in the previous examples).
As you can see from this image the lines on the lens barrel are
almost totally hidden. Set again to focus at 5m with an aperture
of f5.6 (the same as used for image 3) the DOF is from 4m to 8m,
this is a big change compared to 35mm. Here you can see the effect
that focal length can play in effecting the DOF on any given image.