Modern tasks of high precision astrometry demand optical coordinate systems including more faint stars than are available now in current conventional systems (Hipparcos). For this purpose it is suggested to use old photographic observations accumulated in the Pulkovo Observatory. Extensive observational data have been obtained at Pulkovo Observatory during the last century in the framework of several programs, e.g. Pulkovo Galaxy plan, etc. Observations have been made with the Normal Astrograph from 1894 to the present. The data are investigated with the aim of extending the Hipparcos catalog to stars fainter than 11th magnitude. All available observations are taken into account. A description of the material considered is given. The distribution of the selected plates over the celestial sphere is shown as well. Coordinates of faint stars in the Hipparcos system are calculated for selected areas. The accuracy of computed star coordinates is analyzed. Results of the investigation are presented.