Top panel: photometric precision of our observations in I band as a function of instrumental magnitudes. Middle panel: root mean square (rms) scatter in I band as a function of instrumental magnitudes. Red circles denote the selected candidate variables in the top and middle panels. Bottom panel: Stetson’s J-index for all sources in our field as a function of instrumental I-band magnitudes. Red circles and triangles represent the variables with light curves available in RI and VI bands.