What is a practical and simple way to calculate dof in the field? I do a lot of "people" photography (not just portraits) outdoors and bring a set of homemade plasticized dof tables with me to cover most situations. Is there a handheld calculator I can buy that allows me to get fairly precise dof answers? From what part of the lens do I measure?
Finally, are there any good primers on how to use dof effectively in real situations? I really don't want tons of math - just some basic info on "how to get that rock in the foreground in focus and the trees in the near distance out of focus."