Completeness of point source detection as a function of I_F814W magnitude for the four control fields. The red line shows the expected turnover magnitude of the globular cluster luminosity function at I_F814W ≃ 27.3 mag. Detection of point sources is nearly 100% complete down to this magnitude in all four control fields. The completeness fraction at faint magnitudes is greatest for the GO-9411 field, which has the longest total integration time.