lens has a focal length of 55mm and when the focus point is
about 20 feet.
the aperture set at f8 the depth of field extends out on both
sides to the distance marked by the two red lines, in this
case just over 30feet and down to just below 15feet.
however we changed the aperture to f16 the depth of field
would be extended up to infinity, and down to 10feet.
however we changed the aperture to f4 the depth of field is
reduced from below 30 feet to just over 15feet.