Brain sections cut at 20-50 um on a cryostat or vibratome have inherently uneven surfaces — warping, folding, and variable mounting thickness create Z-variations of tens of microns across a single section. At 20X or 40X magnification, the depth of field is only a few microns, so a fixed focal plane produces large out-of-focus regions.
PanoBrain's adaptive autofocus continuously adjusts Z during scanning, sampling the focal quality at each tile position and tracking the tissue surface in real time.