Vignetting, pincushion, S-distortion and veiling glare
A reference square grid shown deformed three ways. Left: pincushion distortion, straight lines bow inward with the periphery magnified, caused by the curved input phosphor imaged through electrostatic focusing onto a flat output. Middle: S distortion, vertical lines warped into an S shape by external or Earth magnetic fields deflecting the electron paths. Right: vignetting, the grid geometry stays square but the dots fade from bright centre to dark periphery, from peripheral electron loss and optical fall-off. All three are image intensifier artefacts, reduced or absent with flat-panel detectors.
Practice the Physics paper
FRCRX is a Part 1 Physics question bank: true/false items with explanations, timed mocks and topic analytics.