Energy deficits of field evaporated ions which limit the mass resolution of the straight TOF atom‐probe are measured by incorporating a 90° deflecting energy discriminator. The observed dependence on the mass‐to‐charge ratio shows premature evaporation during the less than perfect subnanosecond pulse front to be the cause of the energy spread. For narrow beam apertures the mass resolution may be improved by tilting the detector plane to provide a compensating shorter path for the slower ions. For wider apertures an energy focusing combination of straight path sections and a 163° toroidal deflector, as conceived by Poschenrieder, has been adapted to our atom‐probe. Offering a mass resolution of better than 1/1000 and complete rejection of artifacts, the compensated atom‐probe FIM is now a microanalytical tool of ultimate sensitivity and high reliability.