  Image sensors, most notably the Charge Coupled Device (CCD), have
revolutionized observational astronomy as perhaps the most important innovation
after photography. Since the 50th anniversary of the invention of the CCD has
passed in 2019, it is time to review the development of detectors for the
visible wavelength range, starting with the discovery of the photoelectric
effect and first experiments to utilize it for the photometry of stars at
Sternwarte Babelsberg in 1913, over the invention of the CCD, its development
at the Jet Propulsion Laboratory, to the high performance CCD and CMOS imagers
that are available off-the-shelf today.
