English: Focus stacking (for extended depth of field) in bright field light microscopy. This example is of a diatom microfossil in diatomaceous earth. Top left are the three source image slices at three focal depths. Top right are the contributions (black is no contribution, white is full contribution) of that focal slice to the final "focus stacked" image. Bottom is the resulting focus stacked image with an extended depth of field. Extended depth of field by focus stacking is a powerful tool for light microscopy as at high magnification the depth of field can be extremely shallow, down to around 1 μm.