Figure 5

Assessment of SIM processing parameters. (a) 2D-SIM reconstructions of three nano-patterned structures for different regularization parameters \(\mathrm{w}\) and for different exponents \(\upbeta\) of the triangle apodization function. The fine grid (orange arrow) is resolved in SIM with low \(\mathrm{w}\), but not with (too) high \(\mathrm{w}\). The resolving power of SIM is isotropic, as can be seen from the just resolvable line spacing in the chirped grids with different orientations (pink arrows). For low \(\mathrm{w}\) and for low \(\upbeta\) contrast is higher, but at the expense of reconstruction induced noise. For balanced conditions the small lines on the sides of the small square (blue arrow) can be clearly recognized, for too low \(\mathrm{w}\) the lines cannot be clearly separated from the noise structure, for too high \(\mathrm{w}\) the small lines cannot be seen as was the case for wide-field (cf. Fig. 3a). The reconstruction induced noise is also visible in the background for low \(\mathrm{w}\) and low \(\upbeta\), but not for high \(\upbeta\). (b) Imaged edge and (c) edge response (average and standard deviation indicated) for wide field and SIM (\(\mathrm{w}=1\times {10}^{-4}\), \(\upbeta =0.7\)). (d) Apparent MTF derived from the edge response in (c), and expected MTF from reconstruction. The contrast and spatial frequency cut-off for SIM is improved compared to wide field. The reconstruction induced noise on the imaged plateau for low \(\mathrm{w}\) makes the estimation of the MTF unreliable for this case. The overshoot at low spatial frequencies for SIM is probably due to a non-ideal underlying fluorescent edge object. A possible root cause is fluorescent material that accumulates close to edge. (e) Power spectral density on logarithmic scale for the Sky and Water I with \(\mathrm{w}=1\times {10}^{-4}\), \(\upbeta =0.7\). The periodicity in the pattern clearly appears as peaks in the power spectral density. Comparative images for the other parameter settings can be found in the Supplemental Figure S3. Scale bars in (a) are 3 µm, in (b) 2 µm.