Few tools have proved more valuable to research scientists than the scanning electron microscope. Magnifying their targets 50,000 times or more, these instruments have explored so deeply into the heart of matter that they can distinguish features only 100 atoms in diameter. Yet for all their sharp-eyed versatility, the microscopes have a serious drawback: they have such a large depth of field that in their two-dimensional pictures it is often difficult to distinguish cracks from ridges or pits from lumps.
Now a scientist at Canada's Ontario Research Foundation has found a convenient way...