Here is a link
to a photo tutorial and free software download
, to use the technique of focus stacking.
Take a look at this short clip on focus stacking in action, in this video tutorial
using Helicon Focus software, or free Combine ZM software.
Focus stacking is a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field (DOF) than any of the individual source images. Getting sufficient depth of field can be particularly challenging in macro photography. The images at right illustrate the increase in DOF that can be achieved by combining multiple exposures. definition resource wikipedia