Standard cryo-EM 3D reconstruction algorithms are based on modelling particle images as tomographic projections of the underlying 3D structure. This assumption is fundamental to the derivation of reconstruction algorithms, has enabled structures to be solved with resolutions well below 2Ã…, and is an excellent approximation to the underlying physical process governing the formation of the image. However, due to the specifics of electron wave diffraction, the projection approximation breaks down at very high resolutions. The details behind this follow the geometric construction known as the Ewald sphere. The nature of the problem was described well by DeRosier in the context of electron microscopy [1], and since then, various algorithms have been proposed for correcting for Ewald sphere curvature in cryo-EM. Relatively recently, structures have been solved by cryo-EM to such high resolutions that the curvature of the Ewald sphere limits their resolutions [2]. As such, work surrounding the correction of Ewald sphere curvature has recently proved useful in the recovery of structures from experimental data [3, 4].