Imaging system with multiple scanning assemblies

In a photoplotter or scanner, a spar 34 is supported above and extends the length of the scanning surface 16 which may be in the shape of a half cylinder. Multiple scanning assemblies 32, 33 are driven along the spar by respective linear motors 37 and carry spinning mirrors 68 for reflecting light onto or from the scanning media 17 when located on the surface 16. Light beam generators or receivers 21, 22 send or collect the light to or from mirrors 68. If generators/receivers 20, 21 are both at the same end of the apparatus as shown, their axes are offset to avoid interference of the light beams 28, 30 and assembly 33 includes a periscope arrangement 35 to re-align beam 30. The relative positions of the mirrors 68, the assemblies 32, 33 and the media 17 are calibrated initially using the light beams and one or more photodetectors (not shown) in the scanning surface 16.