  This work investigates the effect of the aperture size on derived galaxy
properties for which we have spatially-resolved optical spectra. We focus on
some indicators of star formation activity and dust attenuation for spiral
galaxies that have been widely used in previous work on galaxy evolution. We
have used 104 spiral galaxies from the CALIFA survey for which 2D spectroscopy
with complete spatial coverage is available. From the 3D cubes we have derived
growth curves of the most conspicuous Balmer emission lines (Halpha, Hbeta) for
circular apertures of different radii centered at the galaxy's nucleus after
removing the underlying stellar continuum. We find that the Halpha flux
(f(Halpha)) growth curve follows a well defined sequence with aperture radius
showing low dispersion around the median value. From this analysis, we derive
aperture corrections for galaxies in different magnitude and redshift
intervals. Once stellar absorption is properly accounted for, the
f(Halpha)/f(Hbeta) ratio growth curve shows a smooth decline, pointing towards
the absence of differential dust attenuation as a function of radius. Aperture
corrections as a function of the radius are provided in the interval
[0.3,2.5]R_50. Finally, the Halpha equivalent width (EW(Halpha)) growth curve
increases with the size of the aperture and shows a very large dispersion for
small apertures. This large dispersion prevents the use of reliable aperture
corrections for this quantity. In addition, this result suggests that
separating star-forming and quiescent galaxies based on observed EW(Halpha)
through small apertures is likely to result in low EW(Halpha) star-forming
galaxies begin classified as quiescent.
