a, Estimated photon count for a 45-nm-diameter bead imaged with an aberration-corrected microscope as a
function of analysis area on the camera. The three curves show the counts for fitting with a fully fledged vectorial PSF model, a
simplified Gaussian PSF model, and TRABI. FWHM, 214 5 nm; pixel size, 80 nm. Aperture diameter of 2 × 1.86 × FWHM
used as suggested by Franke et al.1. b, The photometric ratio
(Gaussian fit over TRABI value) across six bead measurements as a function of the axial position. The shaded error band indicates
one s.d. Area of fit, 7×7 pixels; aperture radius, 1.86 × FWHM. c, Effect on the photometric ratio for
beads single-mode aberrated with r.m.s. aberration coefficients set at half (36 mλ; top row) and full diffraction limit (72
mλ; bottom row). d, Axial estimation error for seven typical aberration uncorrected microscopes.
Wrms is the mean measured wavefront error. Sim., simulation; Exp., experiment.