Globe effect

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The globe effect is a phenomenon that can occur with visually used optical instruments, especially binoculars or telescopes . If such an instrument is constructed free of optical distortion , then when the instrument is pivoted the impression of an image rolling on a (convex) curved surface occurs. This effect was already described in 1949 by the Zeiss employee Horst Köhler. In his textbook on optics, he later introduced the term image bending , which, however, could not prevail in the long term. To eliminate the globe effect, he proposed the implementation of a certain pillow-shaped distortion in binoculars, and experimental studies by August Sonnefeld confirmed an improvement in the imaging properties of visually used telescopes with pillow-shaped distortion.

The causes of the globe effect remained in the dark for a long time. Köhler speculated about the “unnatural perspective ” that arises when panning binoculars over “an object field structured in depth”, but ignored the fact that the globe effect can also be observed in the starry night sky, i.e. H. in the absence of any perspective distortions. Recently, a connection between the globe effect and the special properties of human visual perception was shown, in which an additional barrel-shaped distortion flows into the image. The quantity of this distortion differs from person to person, which also explains the fact that individual observers perceive the globe effect to different degrees.

An alternative approach to explaining the globe effect comes from the journalist and optics specialist Walter E. Schön. He explains that the observed effect is not that of a rolling ball, but rather resembles a vertically rotating cylinder. The apparent spherical shape noticed by some users comes from the fact that the field of view in a telescope or binoculars is circular. The illusion of a rotating cylinder when panning is created by the horizontal movement of the image, which (due to the angular magnification of the optical instrument) is faster and more even (with less parallax ) compared to seeing with the naked eye. Another reason that plays a role here is that when looking through the magnifying optical instrument, the natural connection between head and image movement is canceled. When the brain tries to interpret these contradicting signals, it creates the illusion that the image is moving more slowly on the left and right edges than in the center, giving the impression of a rotating cylinder. It would therefore be more appropriate to speak of a cylinder effect instead of the term globe effect . With this in mind, it has recently been proposed to use cylindrical optical elements to reduce the globe effect during horizontal panning, which in most applications defines the dominant direction of movement.

Individual evidence

  1. ↑ H. Köhler: Basics of telescope viewing. German Optische Wochenschrift No. 35, Vol. 6, p. 41 (1949)
  2. ↑ A. König, H. Köhler: The telescopes and rangefinders , Springer Verlag, 3rd edition 1959, p. 120
  3. ↑ A. Sonnefeld: About the distortion in optical instruments that are used in connection with the looking eye. Deutsche Optische Wochenschrift No. 35, Vol. 13, p. 97 (1949)
  4. ^ H. Merlitz: Distortion of binoculars revisited: Does the sweet spot exist ?. JOSA A, Vol. 27, No. 1, pp. 50–57 (2010)
  5. ↑ AHJ Oomes, JJ Koenderink, AJ Doorn, H. de Ridder: What are the uncurved lines in our visual field? A fresh look at Helmholtz's checkerboard. Perception No. 38, p. 1284 (2009)
  6. ↑ H. Merlitz: Hand Binoculars: function, performance, selection , 2nd edition, published by Europa-Lehrmittel, ISBN 978-3-8085-5775-4 , (2019)
  7. ↑ Explanation of the globe effect, Walter E. Schön, http://www.juelich-bonn.com/jForum/read.php?9,288850,288850#msg-288850
  8. ↑ Jan Koenderink: Telescopic horizon scanning. APPLIED OPTICS, Vol. 53, pp. 8556-8563 (2014)

literature

  • Lambert Spix: television viewer. Binoculars for Astronomy and Nature Observation , 2009 (pages 12–13). ISBN 978-3-938469-28-6
  • Walter J. Schwab, Wolf Wehran: Optics for Hunting and Nature Observation , 2011 (Section 1.8: Distortion). ISBN 978-3-00-034895-2

Web links