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Figure 6
Experimental results from a FADE modulation test. (a) Power spectra of a series of images from a test sample collected at several aperture bias voltages. The contrast transfer function (CTF) Thon rings are moving inwards, indicating a defocus increase as the aperture voltage is increased. (b) The defocus values were measured by fitting the two-dimensional CTF profile in the power spectra. Different defocus values in perpendicular directions indicate the presence of image astigmatism, which is calculated as the difference between the maximum and minimum defocus axes (i.e. defocus1 − defocus2). (c) Plot of the measured absolute defocus values as a function of modulation voltage. The results are from three independent image series. The lines are linear fits of the data with slopes shown in the legend. (d) Absolute astigmatism values with linear fits. (e) Defocus modulation calculated by subtracting the 0 V intercepts of the linear fits in (c) from the data points. The linear fit in (e) is for the congregation of data points. The fit slope is shown in the legend. (f) Astigmatism modulation calculated by subtracting the 0 V linear fit intercepts in (d) from the data points. The line is a congregate linear fit and the slope is indicated in the legend.

IUCrJ
Volume 7| Part 3| May 2020| Pages 566-574
ISSN: 2052-2525
https://doi.org/10.1107/S205225252000408X