A quantitative analysis and adequate theoretical and practical steps employing a near-field scanning optical microscope (NSOM) are currently quickly developing areas of near-field optics. The basic task of the analysis consists in the correct description of tip - surface system geometry together with an electromagnetic field propagation through the system. This article deals with the results characterising tips applied in a scanning electron microscope technique and modelling field in the scanning optical microscope. Results are compared with practical measurements obtained with simple structures.