In many optical systems, reflectors, particularly those used in telescopes, exhibit the property of producing an inverted image. This phenomenon occurs because the optics—such as mirrors and lenses—refract and reflect light in a manner that flips the image vertically and sometimes horizontally. This is common in Newtonian telescopes and some refractor telescopes, among other designs.
If the goal is to view the image in its natural, upright position, additional optical components are necessary to correct the orientation. One popular solution is employing an erecting prism or an erecting eyepiece. These components are designed to re-invert the image, thus compensating for the inversion introduced by the primary optics.
For instance, in a telescope, a diagonal mirror can be added just before the eyepiece to correct the image orientation vertically. An Amici prism, often used in spotting scopes and some binoculars, can also be employed to ensure both vertical and horizontal corrections, providing a correctly oriented view suitable for terrestrial observations.
In practical applications, the choice of method depends on the specific optical design and user requirements. Such optical adjustments are critical for activities like terrestrial viewing, where orientation matters greatly, as opposed to astronomical purposes, where the orientation is often less of a concern.