Depth of Field (DOF) and Hyperfocal Distance
You may have wondered, “How do pros make those wonderful landscapes where everything seems to be in focus?” Well, it is not merely by closing down the aperture of superb wide angle lenses. They maximize DOF (depth of field), the region of acceptable sharpness, by focusing at the hyperfocal distance. A simple function of focal length, aperture and the diameter of the Circle of Confusion.
The longest the focal length, the larger the hyperfocal distance and, thus, the less DoF. The smaller the aperture (large f-numbers), the shorter the hyperfocal distance and, thus, the more DoF. The wider the aperture (small f-numbers), the larger the hyperfocal distance and, thus, the less DoF.