FIELD: signal recording or reproducing in optical memory devices. SUBSTANCE: data medium effective layer is arranged along mirror surface of radiator. Primary image of light signal coming from radiation source is shaped by means of first component of optical system and focused in vicinity of mirror surface by means of focusing unit of this optical system. Beam reflected from mirror surface is focused onto effective layer of data medium by means of focusing unit of second optical-system component. Defocusing is compensated for by shifting mirror surface of reflector along optical axis of focusing unit of first optical-system component. Mirror surface displacement and in-service changes in spatial position of data-medium effective layer are coordinated so that their relative position does not change with time. Longitudinally magnified optical system is used, its magnification being found from the formula given in description of invention. Device implementing proposed method had reflector with mirror surface, radiation source, and optical system with light-dividing element optically coupled with first and second optical-system components. Mirror surface and data-medium effective layer may be formed on opposite sides of record medium. Such design ensures compensation for defocusing by optical means and methods only with focusing optics motionless thereby eliminating delays in servo systems with mechanically displaced actuating members. EFFECT: enhanced speed of data recording and reproducing. 8 cl, 5 dwg
