The C1860-X3 is a telecine cathode-ray tube and uses magnetic deflection through a low angle.
The tube indicates that it was made for Rank Mk VIIIB slide scanners as well as other flying spot scanners.
A flying spot scanner uses a CRT to illuminate a transparent film with a raster scan pattern. A photomultiplier or photocell is used to determine the illuminate at each point. Thus when synchronised to the CRT raster the video signal is a complete TV picture.
The base and electron gun.
The bell with identification and warning labels. The internal colloidal graphite (Aquadag) coating can be seen at the base of the bell.
The faceplate is optically flat and to withstand the stresses involved the face id made very thick.
The phosphor coating. It is probable that the raster drawn on the face of the tube is much smaller than the maximum size possible. It is also probable that the raster is much larger than the film to be scanned and optics focus it down onto film. This would achieve the effect of a much smaller spot size.
The end window envelope is 35 mm in diameter, and excluding the IO base pins is 530 mm tall.