The size of a bulky electron source (so-called celadonite source) is determined by using a lens to enlarge the recording hologram and measuring the smallest detail on the image: the last visible fringe order (p_l = 18). Here, the source size is s < 2.6 nm. Magnification: G = 235000, electron source potential V = −280 V, source-screen distance D = 86 cm, source-object distance d = 13.3 μm.