Terrestrial Telescope
A refracting telescope incorporating an additional erecting lens system between objective and eyepiece to yield an upright image for ground observation.
Governing formula
M = f_obj / f_eye, Tube Length L = f_obj + 4 f_erect + f_eye
SI unit
Dimensionless (×)
In depth
The intermediate erecting lens flips the inverted image right-side up without changing magnification, extending total tube length.
Examples in the real world
Spyglasses and spotting scopes used for maritime navigation, wildlife observation, and target shooting.