ghost

Definition: (1) Secondary image adjacent to the main image, caused by reflection e.g. as seen in back-surfaced mirror: the reflecting surface is the main image, the reflection from the front of the glass is the ghost. (2) One or more spots or shapes of light superimposed on an image, caused by images of the lens aperture reflected within optical components. (2) False spectral line caused by irregularities in diffraction gratings.

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