Presented in detail are the construction and relevant properties of a high‐pass wide band filter with a low frequency cutoff of several kilohertz and a high frequency cutoff of about 1 GHz to be used with 50 &OHgr; characteristic impedance systems. The application to absorption spectrophotometry makes it possible to bring small transient signals on very high levels of analyzing light automatically on the screen of a fast oscilloscope with negligible offset at high gain settings.