Physics:Field flattener lens
Field flattener lens is a type of lens used in modern binocular designs[lower-alpha 1] 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
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 [math]\displaystyle{ \delta_{x} }[/math] dependent on the thickness of the glass. Thus we have a thickness as a function of focal shift:
- [math]\displaystyle{ t(\delta_{x})=\left(\frac{n}{n-1}\right)\delta_{x} }[/math].
[math]\displaystyle{ \delta_{x}(y) }[/math] is given by the radius of curvature of the Petzval surface, [math]\displaystyle{ R_{p} }[/math]. It can be shown, then, that the radius of curvature for the lens that would flatten out the field is given by
- [math]\displaystyle{ R_{f}=\left(\frac{n-1}{n}\right)R_{p}. }[/math] [1]
Examples of use
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
- Petzval field curvature
- Coma corrector
Notes
- ↑ 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
- ↑ Geary, Joseph (2002). Introduction to Lens Design with Practical ZEMAX Examples. Willmann-Bell. ISBN 0943396751.
- ↑ 2.0 2.1 Cheng, A. F.; Weaver, H. A.; Conard, S. J.; Morgan, M. F.; Barnouin-Jha, O.; Boldt, J. D.; Cooper, K. A.; Darlington, E. H. et al. (2008). "Long-Range Reconnaissance Imager on New Horizons". Space Science Reviews 140 (1–4): 189–215. doi:10.1007/s11214-007-9271-6. Bibcode: 2008SSRv..140..189C.
 |  |
