Focus Stacking is a digital photography technique in which a sequence of images is taken with a relatively shallow depth of field, but with the focal plane of each image at a successively further distance within the subject matter. The sharpest pixels of each of the images are combined using post-processing techniques, resulting in a single, very sharp image, in focus from the nearest focal plane to the farthest. The final output of a focus stacked sequence is capable of producing a greater depth of field and sharpness than would be possible by stopping down the aperture for a single photograph, resulting in a higher quality, more visually stunning image.
Focus stacking is extremely useful for macro and close up work, especially at extremely high magnifications, because it eliminates diffraction, and allows incredible depth of field not normally possible.
Focus stacking requires specialized equipment and settings, and must be skillfully executed. It is also very time intensive throughout the entire process. Some subjects may prove difficult or impossible to focus stack. There are a number of other drawbacks, as noted in the summary section below.
Despite the drawbacks, focus stacking is worth the increased financial, time, and effort investments, due to the visually striking results and quality which can be obtained.