The varifocal mirror for 3-D display of electron microscope tomography

Three-dimensional reconstruction by tomographic procedures of objects viewed with transmission electron microscopy generates a volume of densities arrayed in raster format. This volume can be conveniently displayed and analysed employing a varifocal mirror (VFM) and an associated image processing system. We have developed a number of interactive programs useful to display and analyse the 3-D data, including depth windowing, intensity mapping, image zoom, image rotation and cursor overlay. Examples of these functions are presented, employing data from electron microscope tomography (EMT) of a transcriptionally-active eukaryotic gene, the Balbiani ring of Chironomus polytene chromosomes.