Caveat: Several filters display systematic flux offsets in multi-filter SEDs. The filters and the flux levels for which these artifacts were found are listed below.
m filter: positive flux offset from +10% at
flux level 50Jy to factor of 2 at background level.
m filters: +15 to +30% at background level.
m) in apertures considerably smaller than
the 180arcsec aperture (including the 23arcsec default
aperture for these filters) usually do not give any meaningful
results, because the measurement is dominated by dark signal.
It is assumed that the background level is at or a few times above the lowest possible sky background.