ESO operates four near-infrared (NIR) imagers, namely the High Acuity Widefield K-band Imager (HAWK-I), the VISTA InfraRed CAMera (VIRCAM), the SpectroPolarimetric High-contrast Exoplanet REsearch instrument (SPHERE), and Son OF ISAAC (SOFI). In addition, data for the two decommissioned instruments the Infrared Spectrometer And Array Camera (ISAAC) and the Nasmyth Adaptive Optics System/COudé Near-Infrared CAmera combination (NAOS-CONICA, or NACO) are available from the science archive1. Because these instruments have different effective bandpasses, the magnitudes measured with them are difficult to compare and doing so can lead to inconsistencies if the colour of an object is not taken into account. In this article, we present colour transformations between the ESO NIR imagers and the Two Micron All-Sky Survey (2MASS) photometric system in the J, H, and Ks bands. The coefficients can be used to compare and convert magnitudes derived from different ESO and nonESO instruments.
