Abstract: A beam welding apparatus useful for welding a plurality of workpieces spaced along a workpiece plane during a scan of the workpieces is disclosed. A scan light and a detection means are used to detect the location of each workpiece and to supply a signal for triggering a beam source into emission upon the detection of each workpiece. The beam and scan light sources are focused on the workpieces through the same focusing lens. Further, the apparatus comprises means for maintaining a constant optical path between the lens and each workpiece that includes a translating means for moving a moveable mirror, that is disposed between the lens and the workpieces, along a path coincident with the lens axis so as to effect consistent welds during an uninterrupted scan.