Photography using glass plates was for nearly a century the main method for recording astronomical data. The Cape was famous in the past for its pioneering sky surveys.

Some photography also took place at Sutherland in the 1970s but this technique has long neen superseded.

The McClean darkroom is the only one remaining of several that used to exist on the Cape Town site. It was used for processing the glass plates taken with the McClean, Astrographic and Photoheliograph telescopes and the films from the Lyot Coronagraph and the Gill Reversible Transit Circle.

Apart from the post-exposure work it was used in its later years for sensitising plates before exposure by "hydrogen soaking", a process that enhanced the sensitivity of photographic plates.

The contents of the darkroom have not been sorted and catalogued and therefore access has to be specially requested so that it can be supervised.

Several collections of plates taken at Cape Town, Sutherland and the Radcliffe Observatory in Pretoria remain at the SAAO but many of those judged to be of no long-term interest have been discarded