  Aims: We performed a detailed photometric analysis of the lensed system UM673
(Q0142-100) and an analysis of the tentative lens models. Methods:
High-resolution adaptive optics images of UM673 taken with the Subaru telescope
in the H band were examined. We also analysed the J, H and K-band observational
data of UM673 obtained with the 1.3m telescope at the CTIO observatory.
Results: We present photometry of quasar components A and B of UM673, the lens,
and the nearby bright galaxy using H-band observational data obtained with the
Subaru telescope. Based on the CTIO observations of UM673, we also present J-
and H-band photometry and estimates of the J, H and K-band flux ratios between
the two UM673 components in recent epochs. The near-infrared fluxes of the A
and B components of UM673 and their published optical fluxes are analysed to
measure extinction properties of the lensing galaxy. We estimate the
extinction-corrected flux ratio between components A and B to be about 2.14
mag. We discuss lens models for the UM673 system constrained with the positions
of the UM673 components, their flux ratio, and the previously measured time
delay
