  A widely used method to measure the bending rigidity of bilayer membranes is
fluctuation spectroscopy, which analyses the thermally-driven membrane
undulations of giant unilamellar vesicles recorded with either phase-contrast
or confocal microscopy. Here, we analyze the fluctuations of the same vesicle
using both techniques and obtain consistent values for the bending modulus. We
discuss the factors that may lead to discrepancies.
