Not everyone agrees that setting the lens at the hyperfocal distance is always the best way of shooting landscapes. There are many cases when biasing the depth of field towards infinity, or simply focusing on infinity, may be preferable.
Depth of field is all about setting the limits of acceptable blur. If you set the lens to the hyperfocal distance the horizon will not be in sharp focus, but it will be out of focus - in fact it will be just on the limit of acceptable blur. Theoretically the blur will be undetectable to a human at the print magnification and viewing distance that was used for the DoF calculation. At closer viewing distances or greater magnifications it will look out of focus. It may even seem a little fuzzy to some people at the designed magnification, particularly if there are sharper parts of the picture. In many cases the horizon is the most important part of the picture to have sharp.
There is a good case for setting the lens to the hyperfocal distance for an aperture two stops wider than the one in use. This means that the horizon will not be at the limit of acceptable blur, but should be safely below the limit. The actual aperture can be used for determining the near limit of depth of field because it is generally less critical than having the horizon razor sharp. Every case is different and should be judged on the particular circumstances.
" (focal length)squared/f-number x diameter of the circle of confusion = hyperfocal distance."
Do you mind if I rewrite that?
h = f^2 / (NC)
f is the focal length
N is the f-Number (ie 2.8, 5.6, 16 etc, not 1/2.8, 1/5.6, 1/16 etc)
C is the diameter of the c-o-c.
The units should be consistent -ie everything in millimetres, or everything in metres, or everything in inches.
Best,
Helen