Schematic representation of the hybrid externally occulted Lyot solar coronagraph, adapted from Rougeot (2017) – Figure not to scale. The six key planes O, A, B, O′, C, and D, and key geometrical parameters are reported. The dotted lines illustrate geometrical optical paths. The variables are as follows: R radius of the external occulter; z₀, z₁ and z₂ the distances from plane O to A, plane A to O′ and plane O′ to C, respectively; R_p radius of the entrance pupil; f₁, f₂, and f₃ the focal lengths of the objectives L1, L2, and L3, respectively; R_io radius of the internal occulter; R_ls radius of the Lyot stop. See text for the detailed description.