measurements performed on the unfiltered images. Magnitudes were measured in 4 pixel diameter apertures. Aperture corrections were applied by first correcting to a 1 diameter (33.3 pixels) aperture and then Table 5 in [@sirianni2005] was used to correct from the 1 aperture to infinity. Since the PSF varies spatially across each image, the <span style="font-variant:small-caps;">PSFEx</span> model was used to compute the correction to a 1 aperture at the location of every detected source.

Point sources were selected from this catalog on the basis of shape, requiring $e \equiv 1-b/a < 0.4$, size, requiring $\mathtt{FLUX\_RADIUS} <
10~\mathrm{pixels}$, and image concentration, requiring $0.8 < C_{3-7} <
1.2$, where $C_{3-7}$ is the difference between an object’s magnitude measured in a 3 and 7 pixel diameter aperture. The $F606W,F814W$ colour-magnitude diagrams (CMDs) for point sources in the FFs are shown in Figure \[fig:cmd\]. Since UCDs are expected to be found in the densest environments [@pfeffer2013], we select UCDs in only the cluster fields and use the parallel fields to estimate the contamination from unresolved galaxies and foreground stars. The boxes shown in Figure \[fig:cmd\] are the UCD selection regions which are the apparent $F814W$ magnitudes and $F606W-F814W$ colours spanned by SSPs with formation redshifts 