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Field flattener lens

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Field flattener lens is a type of lens used in modern binocular designs[a] and in astronomic telescopes to improve edge sharpness. Field flattener lenses counteract the Petzval field curvature of an optical system, mitigating the field-angle dependence of the focal length of a system.

Details

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The object in designing a field flattening lens is to create a lens that shifts the focal points of the Petzval surface to lie in the same plane. Consider inserting a pane of glass in a focusing beam. Due to refraction, the focal point of the beam is shifted by dependent on the thickness of the glass. Thus we have a thickness as a function of focal shift:

.

is given by the radius of curvature of the Petzval surface, . It can be shown, then, that the radius of curvature for the lens that would flatten out the field is given by

[1]

Examples of use

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In the 21st century, the New Horizons spacecraft, which was an unmanned space probe sent past Pluto and the Kuiper belt, had a telescope instrument called the Long Range Reconnaissance Imager.[2] LORRI was a reflecting telescope but incorporated a field-flattening lens, with three elements.[2]

See also

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Notes

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  1. ^ E.g. Canon 10 x 42 L IS WP, 18 x 50 IS All Weather and Swarovski EL 8.5 x 42, EL 10 x 42.

References

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  1. ^ Geary, Joseph (2002). Introduction to Lens Design with Practical ZEMAX Examples. Willmann-Bell. ISBN 0943396751.
  2. ^ a b Cheng, A. F.; Weaver, H. A.; Conard, S. J.; Morgan, M. F.; Barnouin-Jha, O.; Boldt, J. D.; Cooper, K. A.; Darlington, E. H.; Grey, M. P.; Hayes, J. R.; Kosakowski, K. E.; Magee, T.; Rossano, E.; Sampath, D.; Schlemm, C.; Taylor, H. W. (2008). "Long-Range Reconnaissance Imager on New Horizons". Space Science Reviews. 140 (1–4): 189–215. arXiv:0709.4278. Bibcode:2008SSRv..140..189C. doi:10.1007/s11214-007-9271-6. S2CID 118330150.