In this work, we present Doppler free two photon optogalvanic measurements to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of hydrogen. The main aim of this article is the comparison of the measurements made with different cathode materials, stainless steel, and tungsten; both of them are widely used in the low-pressure discharges. Sputtering of stainless steel is the principle cause of the differences observed for the E-field variation, and the differences are analyzed in the frame of the sputtered material in a wide range of discharge conditions. Complementary images of the discharge luminosity allow for the conclusion; the cathode dark zone corresponds in good approximation to the cathode fall length.