Fig. 9. (right) Analysis of movements of bead images during the course of a single mirror cycle. Any movement results in blurring during normal operation. 14 frames are collected at a flow rate of 100 ml h^–1, corresponding to approximately a 20 Hz mirror frequency and 26 mm s^–1 particle velocity. (a and b) X-component of the displacement field, perpendicular to the flow, and (c and d) Y-component aligned along the flow. The boxes show the 25th and 75th percentiles, red crosses are outliers. The red bars show the median value. By subtracting the median in (b and c) we highlight non-uniform effects resulting from non-uniform flow and imperfect alignment. The sub-pixel deviations of (c and d) show that with accurate mirror synchronisation low levels of blurring are possible.