  The irradiance of the Sun is modulated on all time scales. Small-scale solar
magnetic elements composed of quiet-Sun network and active region plages
contribute to this modulation on solar cycle time scales. The evaluation of
their contrast as a function of their magnetic field strength is an important
constraint for models of solar irradiance variation. In this thesis, we improve
and extend the results of earlier contrast studies taking advantage of the high
resolution data delivered by the balloon-borne solar observatory Sunrise during
its science flights in 2009 and 2013. In addition to the high quality of the
Sunrise data, access to the UV wavelengths makes these data unique in this kind
of study. In the first two parts of this thesis, we find that the contrast
variation with the magnetic field strength agrees qualitatively with radiative
magnetohydrodynamic simulations of the quiet Sun. In particular, at a continuum
wavelength around 500\,nm, the contrast does not decrease at large field
strengths, indicative of having resolved these features. In addition, the
contrast at all wavelengths in the quiet-Sun network is found to be higher than
in solar plage, and the difference decreases with atmospheric height in
accordance with empirical models of flux tubes. In the last part of this
thesis, we make use of solar limb data observed by Sunrise to evaluate the
contribution of stray light to the total point spread function of the
telescope.
