The multifocus imaging technique in petrology

The present paper provides a review of an imaging tool that is relatively underused in petrographic studies: the multifocus technique. Commonly used in macrophotography, and particularly in the imaging of minerals, it can also be applied to the imaging of thin sections where inclusions or other features that are present at different depths in the section can be combined into the same image. Improvements in computer performance and in image combination software make the technique simple and efficient. Its latest developments allow three-dimensional reconstructions of inclusions and other features of petrographic interest to be visualized. The difficulties of imaging under the optical microscope at high magnification are reviewed and demonstrations of the advantages of the multifocus technique are provided. Compared to more specialized and expensive imaging methods, such as confocal scanning microscopy and X-ray computed tomography, the multifocus technique offers an inexpensive and rapid approach, which is useful as an initial check as to whether more elaborate techniques are justified.