On a whim, I tried a small print at 50 micron and 25 micron layer heights. Both worked! I don't have a low power microscope to take a picture of it, but it really worked. The material was eSun warm white PLA+. The item printed was about 25mm square. What I take away from this is: The extruder, hot end and z-axis controls are capable of 25 micron layers if using suitable filaments. The greatest remaining factors are the printer firmware, bed planarity and bed surface prep. Thoughts?