Brain sections cut at 20 to 50 µm on a cryostat or vibratome have 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.
According to Meca Scientific, PanoBrain focuses on the surface of thick brain slices and keeps focal planes consistent across all channels.