Telescopes with star diagonal

Reversing lens

— the presence of a reversing lens in the scope of delivery of the telescope.

Such a lens is designed to turn the inverted image, initially formed by most telescopes, into a true one. Such a possibility is not particularly critical for astronomy, but when considering terrestrial objects, one simply cannot do without it. Accordingly, refractor telescopes of relatively low magnification are mainly equipped with a reversing lens — they are considered optimally suited for ground-based observations.

Note that, in addition to "clean" lenses, there are also inverting systems based on prisms. The native magnification of a reversible lens usually does not exceed 1.5x, and many such accessories do not provide any magnification at all (1x).