Figure 4.

vSAF. The left column shows a schematic of the BFP with (A) no blockage; (B) only the supercritical zone physically blocked; or (C) only the subcritical zone physically blocked. The right column is the theoretical PSF for each case, assuming a dipole oriented along x (as in Fig. 3) and a 1.49 NA objective. Theoretical calculations were done according to the methods of Axelrod (8). Although surface-selective, the super-only PSF of panel C has rather bright large rings that decrement the image quality; these are much reduced by the image subtraction scheme shown in panel D.