Telescopes Uses a large lenses to gather light. Large Objective Lens to gather and focus light. Objective is usually a compound lens to help correct color distortions. Employs smaller secondary lenses to form images for an eye, camera, or spectrometer. The most common type of telescope in use before the early 1900s.
Long tubes are hard to keep mechanically stiff and so flex under the weight of the lens.
Lens is mounted in a 69-foot steel tube. Visit the Yerkes Observatory webpage for more info and pictures. Reflecting Telescopes Invented by Isaac Newton. Primary Mirror gathers and focuses light Use secondary mirrors to direct the light to cameras and spectrometers. All modern large telescopes are reflecting telescopes.