EN
An exact equation of the isochromatic fringes of uniaxial crystals derived without usually adopted simplifications is presented. It enables to calculate the optical conoscopic figures for ideal crystals with different angular orientations of the optical axis with respect to the normal to the crystal surface. Conoscopic figures of large-size single crystals of lithium niobate and paratellurite were examined experimentally making use of a laser-based setup. The conoscopic figure evolution in operating acousto-optic devices was studied.