eyepiece lens

The eyepiece lens is a crucial component in refracting telescopes, which are used to observe celestial bodies like the Moon, planets, and binary stars. This type of telescope works by bending light, a process called refraction, as it passes through a lens.1

The primary lens that light first encounters is the objective lens. After passing through the objective, the light forms an inverted image at its focal plane. The eyepiece lens is then positioned behind this focal plane. Its function is to magnify this inverted image, allowing the observer to see a clearer, enlarged view of the distant object. The magnification is determined by the ratio of the objective lens's focal length to the eyepiece lens's focal length. The Keplerian telescope, a precursor to modern refractors, also utilizes an eyepiece lens to achieve magnification.12