High Quality Content by WIKIPEDIA articles! The following is a list of the largest optical telescope of the 20th century with a focus on objective diameters. Aperture rank currently goes approximately by the usable physical aperture size and not by aperture synthesis, although interferometers attained some of the highest angular resolutions at visible and infrared wavelengths compared to traditional telescopes. Diverging methods of construction and use for reflecting telescopes in that area make comparing synthesized aperture irregular.