Fig. 8.

The diffraction limited depth of field for a $2\times$, NA0.55 objective represented by the gray rectangle is 6.0 μm. The nominal shift range plotted by the solid line is 4.0 μm. The measured shift range plotted by the small dashed line is 6.9 μm. The nominal shift range of an NA0.55 monochromatic objective plotted by the large dashed line is 96.7 μm.