Lens systems (particularly eyepieces ) that reduce disruptive distortions through optical compensation are referred to as orthoscopic . This involves combining lenses of different thicknesses or curvatures.
The best known is the orthoscopic eyepiece , which Ernst Abbe developed around 1870 for high-quality Zeiss microscopes . It consists of a cemented triple lens and a planoconvex lens on the eye side. Today it is also used in many telescopes .
However, completely distortion-free optics are not always desired, because otherwise the observer will perceive an annoying globe effect when swiveling the telescope . Oculars that are used visually therefore often have a slightly pincushion distortion.
See also : Aplanat