  We discuss the relative merits of using UV and H_alpha as star formation
indicators from galaxy surveys. In particular, comparing UV and H_alpha in the
CFRS gives a limit of a factor 2.5 for the UV(2800 Angs.) flux extinction from
dust, using the conversion factors of Madau et al. 1998 (Salpeter IMF, 0.1-125
solar mass). Our strong correlation between B and H_alpha luminosities argues
for a universal IMF slope. The H_alpha luminosity function at z = 0.2 shows a
faint end slope of alpha = -1.35, which is consistent with fading of short
bursts of star formation. We also discuss the contribution of AGN to UV and
H_alpha luminosities.
