  The Small Magellanic Cloud (SMC) hosts a large number of high-mass X-ray
binaries, and in particular of Be/X-ray Binaries (BeXRBs; neutron stars
orbiting OBe-type stars), offering a unique laboratory to address the effect of
metalicity. One key property of their optical companion is H{\alpha} in
emission, which makes them bright sources when observed through a narrow-band
H{\alpha} filter. We performed a survey of the SMC Bar and Wing regions using
wide-field cameras (WFI@MPG/ESO and MOSAIC@CTIO/Blanco) in order to identify
the counterparts of the sources detected in our XMM-Newton survey of the same
area. We obtained broad-band R and narrow-band H{\alpha} photometry, and
identified ~10000 H{\alpha} emission sources down to a sensitivity limit of
18.7 mag (equivalent to ~B8 type Main Sequence stars). We find the fraction of
OBe/OB stars to be 13% down to this limit, and by investigating this fraction
as a function of the brightness of the stars we deduce that H{\alpha} excess
peaks at the O9-B2 spectral range. Using the most up-to-date numbers of SMC
BeXRBs we find their fraction over their parent population to be ~0.002-0.025
BeXRBs/OBe, a direct measurement of their formation rate.
