1. An optical system comprising: an assembly arranged to collect short coherence length light from a sample, a spectrograph including a dispersing element and detector array; an interferometer arranged to receive the light collected from said sample and divide said collected light into at least two optical paths and pass it to said spectrograph, said interferometer comprising a fixed optical delay device for introducing a delay which causes interference in the collected light, operative on at least a portion of the light collected from the sample; such that said spectrograph forms a self-interference signal from light collected from the sample, representative of structure of said sample over a depth and corresponding to said delay wherein the assembly collects light from a line or region of the sample and the system produces a depth image of that line or region.