The total collecting area of the telescope. The greater the area, the more light can be collected.
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.