Angular intensities of 1 &mgr;A sr−1have been measured for a gas‐phase field ionization source in an optical column under practical operating conditions. The source, which was differentially pumped and cooled to 77 K, utilized a ⟨110⟩‐oriented iridium emitter and precooled hydrogen gas at 10−2Torr. The ion beam was collimated with an electrostatic lens and detected below an aperture subtending 0.164 msr. A transmitted current of ∼10−10A was measured at voltages corresponding to a field of ?2.2 V/A˚ at the emitter.