  We present Halpha-derived star-formation rates (SFRs) for three z ~ 0.75
galaxy clusters. Our 1 sigma flux limit corresponds to a star-formation rate of
0.10-0.24 solar mass per year, and our minimum reliable Halpha + [N II]
rest-frame equivalent width is 10\AA. We show that Halpha narrowband imaging is
an efficient method for measuring star formation in distant clusters. In two
out of three clusters, we find that the fraction of star-forming galaxies
increases with projected distance from the cluster center. We also find that
the fraction of star-forming galaxies decreases with increasing local galaxy
surface density in the same two clusters. We compare the median rate of star
formation among star-forming cluster galaxies to a small sample of star-forming
field galaxies from the literature and find that the median cluster SFRs are
\~50% less than the median field SFR. We characterize cluster evolution in
terms of the mass-normalized integrated cluster SFR and find that the z ~ 0.75
clusters have more SFR per cluster mass on average than the z <= 0.4 clusters
from the literature. The interpretation of this result is complicated by the
dependence of the mass-normalized SFR on cluster mass and the lack of
sufficient overlap in the mass ranges covered by the low and high redshift
samples. We find that the fraction and luminosities of the brightest starburst
galaxies at z ~ 0.75 are consistent with their being progenitors of the
post-starburst galaxies at z ~ 0.45 if the post-starburst phase lasts several
(~5) times longer than the starburst phase.
