Wide angle eyepiece
A microscope or telescope eyepiece with a particularly large apparent field of view is called a wide-angle eyepiece . Since it requires more lenses than a normal eyepiece - especially because of the required edge sharpness - it is heavier and more expensive to manufacture.
While conventional eyepieces have a field of view of around 40 to 45 °, wide-angle eyepieces have a field of view between 55 and 80 ° (in special designs, even more). This results in a pleasantly wide field for the eye, which corresponds approximately to normal vision. However, it can only be surveyed in summary; eye movements are therefore necessary for more precise observations .
The first eyepiece with a larger field of view (up to 50 °) was the Mittenzwey eyepiece . It consists of only two convex-concave individual lenses and was developed by Moritz Mittenzwey (Zwickau) for telescopes and microscopes as early as the 18th century .
The best known and most widely used wide-angle eyepiece is the Erfle eyepiece . It was further developed by the German opriker Heinrich Erfle in 1917 for binoculars and telescopes from the Plössl eyepiece and soon also used for nautical periscopes and astronomical telescopes . As a so-called Super-Plössl it is 5-lens with a field of view of around 60 °, in a further development it is 6-lens with up to 68 °.
The Nagler eyepiece even has a field of view of 80 °, but needs 6 to 7 lenses. When using aspherical lenses (a very complex lens cut ), the image quality at the edge can be brought up to the usual image quality.
A coma corrector can provide a certain compensation for this additional effort with reflector telescopes .