Manufacturers make the depth of field scale based on the size of the circle of confusion. If I recall correctly, Leica uses 0.003". The D.O.F. scale is a only guide, not a true indication for all possible uses of the camera and film.
If you consider the blur caused by the shallow D.O.F. to be a flaw, of course it will be magnified as you enlarge the negative to a bigger print size. Someone else may consider that same effect a bonus [search for "bokeh"].
There's an article on depth of field on Wikipedia.
If you find, by experience, that the depth of field guide gives negatives [and therefore prints at the end-size] with too shallow D.O.F., take appropriate measures to remedy that [stop down]. If setting the focus by hyperfocal technique, use one stop smaller to increase depth of field to your liking. Suppose exposing at f/5.6. Use the near/far marks for f/8 instead. Or even f/11.
Again, the D.O.F. scale is only a convenient guide that will satisfy most [not all] users. It is not a universal cure-all.
Last edited by Larry.Manuel; 07-09-2009 at 10:04 AM. Click to view previous post history.
Reason: correct punctuation.