EN
Lattice relaxation accompanying phototransformation of In bistable centers from the ground, deep state to the shallow state in CdF_{2} crystal has been measured with the use of scanning tunnelling microscope. It is shown that relatively small macroscopic changes of the crystal length in the order of 1.8×10^{-6} accompany the phototransformation of In ions. Lattice expansion upon the influence of population of shallow donor levels in CdF_{2} explains the observed small changes of lattice constant during the process.