Spherical shock waves generated by an underwater sparkgap or an explosive pellet in the first focus of different ellipsoidal segments are focused after reflection in the second focus. Shadowgraphs give an impression of the converging process whereas the field measurement is done by self‐designed piezoelectric pvdf‐needleprobes.Two different series of reflectors are tested. The first is similar to spherical mirrors, the second are deep reflectors which surround the generation point. For both variations the parameters: size of reflector, focal length, reflector material and incident shock strength, show their influence on the focusing process and the location and amplitude of the maximum pressure. In the case of the shallow reflectors, which utilize only 5% of the primary shock energy, focusing is close to the geometrical acoustic and reaches high pressure amplitudes up to 1200 bar, compared to the deep types where the higher utilized energies of 50–98% induce increased nonlinear effects which lead to wider...