  Focal plane wavefront sensing is an elegant solution for wavefront sensing
since near-focal images of any source taken by a detector show distortions in
the presence of aberrations. Non-Common Path Aberrations and the Low Wind
Effect both have the ability to limit the achievable contrast of the finest
coronagraphs coupled with the best extreme adaptive optics systems. To correct
for these aberrations, the Subaru Coronagraphic Extreme Adaptive Optics
instrument hosts many focal plane wavefront sensors using detectors as close to
the science detector as possible. We present seven of them and compare their
implementation and efficiency on SCExAO. This work will be critical for
wavefront sensing on next generation of extremely large telescopes that might
present similar limitations.
