To assess the effect of motion on observer performance with an undersampled uncooled thermal imager, moving imagery from a static scene was recorded at nine different angular velocities ranging from 0 (static) to 1 pixel/frame by use of a tilted rotating mirror. The scene contained a thermal acuity test chart with triangular test patterns based on the triangle orientation discrimination test method. Visual acuity with the sensor was determined in two playback modes: normal speed and slow motion. In both playback conditions, a slow angular velocity of the test pattern over the sensor focal plane (up to $0.25\text{\hspace{0.17em} pixel}/\text{frame}$ ) results in a large acuity increase ( $+50\%$ ) in comparison with the static condition because the observer is able to utilize more phases of the same test pattern. At higher sensor velocities the benefit rapidly decreases due to sensor smear, and above $0.50\text{\hspace{0.17em} pixel}/\text{frame}$ the difference with the static condition is marginal. Up to $0.75\text{\hspace{0.17em} pixel}/\text{frame}$ , the results for the two playback conditions are similar, indicating that temporal display characteristics and human dynamic acuity are not responsible for the reduction. The results obtained with this laboratory test method correspond well with earlier perception studies on real targets for low and medium camera motion.