A system for processing a multi-device panel, comprising a substrate having front and rear surfaces with a first array of device regions located on the front surface and a second array of device regions on the rear surface, by vector direct-write laser ablation, comprising: a first processing station comprising a pair of opposedly-mounted processing heads, each processing head comprising a laser beam delivery apparatus comprising a laser beam scanner (72,72') and a lens unit (73,73'), and a distance measurement means; and mounting means for mounting the panel between the processing heads of the first processing station, the mounting means and/or the first processing station being movable in a stepwise manner such that the relative position of the panel and the first processing station can be adjusted in a step and scan mode so that the processing heads are successively brought into alignment with selected device regions to be processed; each processing head is arranged, for each device region as it is processed, to perform the following steps for both the front surface and the rear surface: a) make an estimate of the distance between the lens unit (73,73') and the surface of that device region using the distance measurement means; b) control the focus of the lens unit (73,73') dependent on said estimate; and c) vector direct-write the device region, and to repeat steps a) to c) for each device region as it is processed, wherein: the distance measurement means comprises a directed light source (74,74') for directing a beam at an angle to the nominal normal of the panel surface towards the panel surface and a camera unit (75,75') for imaging the area of the panel surface upon which the beam is incident in order to achieve distance sensing; the camera unit (75,75') is positioned so that optic axes of the camera unit (75,75') and the lens unit (73,73') are normal to the panel surface and offset relative to each other; and the camera unit (75,75') is arranged additionally to assist with alignment of the lens unit (73,73') with each device region. a first processing station comprising a pair of opposedly-mounted processing heads, each processing head comprising a laser beam delivery apparatus comprising a laser beam scanner (72,72') and a lens unit (73,73'), and a distance measurement means; and mounting means for mounting the panel between the processing heads of the first processing station, the mounting means and/or the first processing station being movable in a stepwise manner such that the relative position of the panel and the first processing station can be adjusted in a step and scan mode so that the processing heads are successively brought into alignment with selected device regions to be processed; each processing head is arranged, for each device region as it is processed, to perform the following steps for both the front surface and the rear surface: a) make an estimate of the distance between the lens unit (73,73') and the surface of that device region using the distance measurement means; b) control the focus of the lens unit (73,73') dependent on said estimate; and c) vector direct-write the device region, a) make an estimate of the distance between the lens unit (73,73') and the surface of that device region using the distance measurement means; b) control the focus of the lens unit (73,73') dependent on said estimate; and c) vector direct-write the device region, and to repeat steps a) to c) for each device region as it is processed, the distance measurement means comprises a directed light source (74,74') for directing a beam at an angle to the nominal normal of the panel surface towards the panel surface and a camera unit (75,75') for imaging the area of the panel surface upon which the beam is incident in order to achieve distance sensing; the camera unit (75,75') is positioned so that optic axes of the camera unit (75,75') and the lens unit (73,73') are normal to the panel surface and offset relative to each other; and the camera unit (75,75') is arranged additionally to assist with alignment of the lens unit (73,73') with each device region.