  We present a small sample of Chandra X-ray sources selected from the fields
of ACIS observations which probe fluxes around the break in the hard band
source counts. The targets of these fields include 9 nearby galaxy clusters, 1
distant cluster and 2 powerful radio galaxy fields. The follow-up of this
serendipitous sample was biased towards X-ray hard and optically-dim sources
mostly not seen on the Digitized Sky Survey; for these, we present X-ray
fluxes, optical and near-infrared photometry leading to 51 photometric
redshifts in all and 18 independently measured spectroscopic redshifts. Few
sources are associated with the target fields themselves. Fifty-six of 58
sources imaged in the K-band are detected at K<~20 with K_median=18, and of
these, 38 have hard X-ray count ratios and 24 of these are significantly hard
with most of the counts emerging about 2 keV. We find that almost all are AGN
hosted in massive early-type host galaxies with a photometric redshift
distribution peaking at z~1. Two type 2 quasars with intrinsic X-ray luminosity
L>~10^{45} erg/s, Fe K_alpha emission lines and absorbing column density
nH>10^{23} cm^{-2} -- and nH>~10^{24} cm^{-2} in one case -- are discussed in
detail; the sample contains at least 12 potential type 2 quasars in all. We
discuss various detection strategies for type 2 quasars and calculate their
inferred space density. This combines and extends a number of results from
subsamples already published by us.
