  We report measurements of the de Haas-van Alphen effect in CeIn3 in magnetic
fields extending to ~90 T, well above the Ne'el critical field of Hc ~61 T. The
unreconstructed Fermi surface a-sheet is observed in the high magnetic field
polarized paramagnetic limit, but with its effective mass and Fermi surface
volume strongly reduced in size compared to that observed in the low magnetic
field paramagnetic regime under pressure. The spheroidal topology of this sheet
provides an ideal realization of the transformation from a `large Fermi
surface' accommodating f-electrons to a `small Fermi surface' when the
f-electron moments become polarized.
