[en] High-resolution laser spectroscopy has been used to measure the isotope shifts for optical transitions in HfI with wavelengths of 590.3 and 594.8 nm. The charge radii of Hf nuclei over the mass-number range A=174-182 have been determined. The results found are compared with calculations from the liquid-drop model. The change in the deformation of the Hf nuclei with increasing neutron number is discussed. 29 refs., 6 figs., 4 tabs