A fast, efficient, qualitatively high-grade shim is enabled in a magnetic resonance apparatus having a displaceable patient bed and an examination region of the patient that is to be examined is larger than an imaging region of the magnetic resonance apparatus. Field inhomogeneities are measured while the examination region is moved through the imaging region by a continuous displacement of the patient bed with the patient positioned thereon. Information representing field inhomogeneities is acquired at multiple positions of the patient bed from respective magnetic resonance signals received at these positions, by excitation of multiple respective slices before the readout of the echo of the first of these slices, with one echo train composed of multiple echoes being generated per excitation signal. Shim parameters of the magnetic resonance apparatus are adjusted dependent on the measured information.