  The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters
of galaxies is derived by computing the statistical excess of galaxy counts in
the cluster direction with respect to control fields. Due to the wide field
coverage of the digitised POSS-II plates, we can measure field counts around
each cluster in a fully homogeneous way. Furthermore, the availability of
virtually unlimited sky coverage allows us to directly compute the LF errors
without having to rely on the estimated variance of the background. The wide
field coverage also allows us to derive the LF of the whole cluster, including
galaxies located in the cluster outskirts. The global composite LF has a slope
alpha ~ -1.1+/-0.2 with minor variations from blue to red filters, and M* ~
-21.7,-22.2,-22.4 mag (H_0=50 km/s/Mpc) in g, r and i filters, respectively.
These results are in quite good agreement with several previous determinations
and in particular with the LF determined for the inner region of a largely
overlapping set of clusters, but derived making use of a completely different
method for background subtraction. The similarity of the two LFs suggests the
existence of minor differences between the LF in the cluster outskirts and in
the central region, or a negligible contribution of galaxies in the cluster
outskirts to the global LF.
