Physics · Ch 6 — Optics
Terrestrial Telescope
Terrestrial Telescope
A terrestrial telescope is used to view objects on the ground, where an erect (rather than inverted) final image is essential. It is built exactly like an astronomical telescope, but with an additional erecting lens inserted between the objective and the eyepiece, whose sole purpose is to flip the intermediate inverted image produced by the objective back to an erect orientation, before the eyepiece magnifies it furt …
What this figure shows. Parallel rays from a distant terrestrial object first form a real, inverted intermediate image through the objective, exactly as in an astronomical telescope; before this image reaches the eyepiece, however, an additional erecting lens is placed in its path, forming a second real image that is now erect (right-way-up) relative to the original object. Only after this re-inversion does the light reach the eyepiece, which magnifies the now-erect image into the final view -- giving an erect, easily interpretable final image, …