Fig. 3.

An autofocus algorithm captured pipette images, computed their Laplacian variance focus measure, and then moved the pipette accordingly to maximize focus. The pipette was moved in one direction until the focus measure crossed a local maximum, then the direction was reversed and the process was repeated with the next step size (sequentially: 20 µm, 5 µm, 2 µm, 0.5 µm) to obtain increasingly fine focus on the pipette tip.