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Figure 2
Analytical |CTF| density (integrated absolute value of the contrast transfer function) with and without incorporating VPP-induced phase shift and signal attenuation. (a) Radial averages of |CTF| comparing non-VPP imaging (dashed blue; Δf = 1.97 µm) and VPP imaging (solid red; Δf = 0.78 µm, phase shift φ = 72°), including VPP cut-on frequency (red arrow) and VPP-associated signal damping. Δf and φ are median values from the minicell cryo-ET datasets used in this study. Colored segments indicate the four spatial-frequency ranges used for integration: R1 (0.002–0.03 Å−1), R2 (0.005–0.05 Å−1), R3 (0.05–0.17 Å−1) and R4 (0.17–0.33 Å−1). (b) Heatmaps of integrated |CTF| values computed over a grid of defocus (0–2.5 µm) and phase-shift (0–90°) conditions for each spatial-frequency range (R1–R4). The top row shows calculations including VPP-induced attenuation, while the bottom row is without VPP attenuation (and φ = 0°). Phase shift is plotted along the vertical axis and defocus along the horizontal axis. The color scale indicates normalized |CTF| density.

IUCrJ
Volume 13| Part 3| May 2026| Pages 260-272
ISSN: 2052-2525
https://doi.org/10.1107/S2052252526002575