Structure of haemoglobin determined at 100 keV. (a) Typical micrograph after motion correction. Contrast is adjusted to ±3σ from the mean intensity. (b) 2D class averages. (c) Sharpened masked 3D reconstruction of haemoglobin from N = 19 444 particles with C2 symmetry. (d) Gold-standard FSC plot corresponding to the calculated map, showing the correlation between the phase-randomized (yellow), unmasked (blue) and masked (red) half-maps. The plot terminates at the Nyquist frequency. (e) Orientation distribution of the haemoglobin particles contributing to the final reconstruction (Mollweide projection). All Euler angles are assigned within one asymmetric subunit for the C2 symmetric particle. The colour scale (linear) corresponds to the normalized density of views (blue, low; red, high). E = 0.9 is the efficiency of the orientation distribution, indicating nearly uniform sampling of the particle views.