On the accuracy of framing-rate measurements in ultra-high speed rotating mirror cameras

Rotating mirror systems based on the Miller Principle are a mainstay modality for ultra-high speed imaging within the range 1-25 million frames per second. Importantly, the true temporal accuracy of observations recorded in such cameras is sensitive to the framing rate that the system directly associates with each individual data acquisition. The purpose for the present investigation was to examine the validity of such system-reported frame rates in a widely used commercial system (a Cordin 550-62 model) by independently measuring the framing rate at the instant of triggering. Here, we found a small but significant difference between such measurements: the average discrepancy (over the entire spectrum of frame rates used) was found to be 0.66 ± 0.48%, with a maximum difference of 2.33%. The principal reason for this discrepancy was traced to non-optimized sampling of the mirror rotation rate within the system protocol. This paper thus serves three purposes: (i) we highlight a straightforward diagnostic approach to facilitate scrutiny of rotating-mirror system integrity; (ii) we raise awareness of the intrinsic errors associated with data previously acquired with this particular system and model; and (iii), we recommend that future control routines address the sampling issue by implementing real-time measurement at the instant of triggering.