The invention relates to reflectors for time-of-flight mass spectrometers, and especially their design. A Mamyrin reflector is provided which consists of metal plates with cut-out internal apertures, and symmetric shielding edges which are set back from the inner edges. The dipole field formed by these shielding edges penetrates only slightly through the plates and into the interior of the reflector. With a good mechanical design, the resolving power of the time-of-flight mass spectrometer increases by around fifteen percent compared to the best prior art to date.