Helmholtz Metadata Collab.EM Glossary #WordOfTheWeek
Focal Point: Point which is defined by the intersection of the optical axis and the backwards extrapolated path of a ray that (1) is tending towards infinity, (2) was parallel to the optical axis in the Incident Beam, and (3) that was deflected by an electron lens.
You can view the full entry here: https://emglossary.helmholtz-metadaten.de/term/em-focal-point
