Photometric uncertainties of the NACO K_s and L′ observations of the Quintuplet cluster for Fields 1 through 5 (top to bottom). The left panels show the first epoch and the middle panels the second epoch K_s uncertainties for the two epochs from which proper motions were derived. The K_s photometry in Field 1 was combined from short and long exposures, with a saturation transition at K_s = 14 mag. The transition is marked by the prominent improvement in photometric performance in the long exposure data. L′ photometric uncertainties (right panels) indicate the large differences in performance in the L′ observations due to thermal background variations. While Fields 2, 3, and 5 show comparable sensitivities, Field 4 is compromised by background fluctuations. Field 1 features significantly deeper photometry, such that the L′ selection was truncated at L′< 15 mag to obtain the excess fraction consistently across the entire cluster area.