  The lensing of background QSOs by foreground galaxies is a powerful probe of
the mass density of the Universe and the power spectrum of mass clustering.
However, the 2dF QSO survey suggested that a strong anticorrelation effect at
g<21 was seen for both galaxies and clusters which implied that galaxies are
anti-biased (b~0.1) on small scales at a higher level than predicted by the
standard cosmology (Myers et al., 2003, 2005) whereas results from SDSS
suggested that the effect was much smaller (b~0.6) and in line with standard
expectations (Scranton et al., 2005). We first cross-correlate the SDSS
photo-z, g<21, 1.0<z_p<2.2 QSOs with g<21 galaxies and clusters in the same
areas. These results are somewhat less negative than the results based on the
2QZ QSOs found by Myers et al. But contamination of the QSOs by low-z NELGs and
QSOs can cause underestimation of the anticorrelation lensing signal. When a
correction is applied to the photo-z QSO sample of Scranton et al. the
anticorrelation increases and the agreement with the results of Myers et al. is
improved. When we also take into account the fainter r<21 galaxy limit of
Scranton et al. as opposed to g<21 for Myers et al., the two observational
results appear to be in very good agreement. This therefore leaves open the
question of why the theoretical interpretations are so different for these
analyses. We note that the results of Guimaraes, Myers & Shanks based on mock
catalogues from the LCDM Hubble Volume strongly suggest that QSO lensing at the
levels detected by both Myers et al. and now Scranton et al. is incompatible
with a galaxy bias of b~1 in the standard cosmological model. If the QSO
lensing results are correct then the consequences for cosmology may be
significant (see Shanks 2006).

Astrophysics