  We have obtained deep J and K' images of a 90 arcsec square field containing
the z=2.0 QSO that is viewed through the z=0.4 rich cluster A851. Brightnesses
of individual galaxies are measured from these data, and archival F702W WFPC2
images from HST. The results are used to construct 2-colour diagrams,
colour-magnitude diagrams, and luminosity functions of galaxies in A851 and the
faint objects discovered by Dressler et al (1993) near the QSO. The QSO faint
companions appear to form a separate population from other faint galaxies in
the field. Comparisons with the GISSEL models covering redshifts from 0 to 3
indicate that (1) the A851 galaxies have ages between 3 and 10 Gyr, and (2) if
they are at the QSO redshift, the QSO companion galaxies are within 1Gyr of
cessation of star-formation.
