Mittenzwey eyepiece

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The Mittenzwey eyepiece was developed by Moritz Mittenzwey in the 18th century for telescopes and microscopes. It is a further development of the Huygens eyepiece , one of the oldest almost color-pure lens systems. Huygens had shown around 1670 that the color errors ( chromatic aberration ) in the near-axis area of ​​the instruments can be significantly reduced if the then simple ocular lenses are replaced by a system of two plano-convex lenses at a suitable distance. The Huygens eyepiece, however, only had a small field of view.

Mittenzwey recognized that the chromatic aberrations are even smaller if one combines two meniscuses (concave-convex converging lenses) instead of plano -convex lenses. Above all, however, the field of view expands to almost 50 °, which has remained unsurpassed for decades.


Mittenzwey eyepiece.
Note: The lens of the eye is usually a little more curved

The Mittenzwey eyepiece consists of two concave-convex lenses at a distance of their middle focal length. The two hollow (concave) lens surfaces look backwards, facing the eye. The focal plane with a diaphragm is located between the field lens and the eye lens, which reduces disruptive reflections from the side walls of the eyepiece sleeve or the telescope.

In older specialist articles, the eyepiece is also called "aplanatic" or "euryscopic", the first term later being transferred to the aplanat lenses.

Later further developments of the system are the Ramsden and Kellner eyepieces .


The Mittenzwey design of the Huygens eyepiece is now considered obsolete because you have to bring your eye close to the eyepiece . However, it is inexpensive to manufacture and is therefore still built into inexpensive telescopes and microscopes. As a simple optical system, its components are also included in some DIY kits.

Another advantage of the Mittenzwey eyepiece over newer, optically better systems is that it works without cemented lenses (doublets). This means that it can be used for solar observations using the projection method - i.e. without a filter in front of it. With duplicates there is a risk that the intense sunlight will overheat the Canada balsam between the lenses and form streaks or even start to burn.

Mittenzwey eyepieces with a focal length of 10 to 40 mm were the standard for the Kosmos telescopes , which were quite common among amateur astronomers in the 1950s to 1970s because of their low price and numerous accessories. The extremely short focal length 5 mm eyepiece, however, had a slightly different design.


  • Rudolf Brandt : The telescope of the star friend , p. 22f. Kosmos-Verlag, Stuttgart 1958

Individual evidence

  1. Helmut Naumann: Handbook components of optics. Carl Hanser Verlag GmbH Co KG, 2014, ISBN 978-3-446-44115-6 , p. 306. Limited preview in the Google book search.