Photometry is the measurement of the "magnitude" of stars and other celestial objects. Originally it depended on eye estimates. With the advent of photography, it became less subjective. Later with photoelectric methods and CCDs it became much more accurate, to 1% or better. The top shelf shows some of the instruments used to measure the infrared radiation from stars. The next shelf shows some of the many detectors used in the twentieth century for measuring the brightness of stars. They include for example photomultipliers, image tubes and photomultipliers. Many of these devices were developed for astronomy but have found uses in other fields. The third shelf shows historic instruments developed at the Cape in the 1940s. This technique, known as "Fabry photometry", was the best in the world at the time. The bottom shelf contains photoelectric photometers, a speciality of the Cape Observatory. The work done with these in the second half of the 20th century was world-renowned.