Field flattener lens explained

Field flattener lens is a type of lens used in modern binocular designs 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

\delta _{x} dependent on the thickness of the glass. Thus we have a thickness as a function of focal shift: t(\delta _{x} ) = \left( (n)/(n -1) \right)\delta _{x} . \delta _{x} (y) is given by the radius of curvature of the Petzval surface, R _{p} . It can be shown, then, that the radius of curvature for the lens that would flatten out the field is given by R _{f} = \left( (n -1)/(n) \right)R _{p} . ^[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.0709.4278. 10.1007/s11214-007-9271-6. Long-Range Reconnaissance Imager on New Horizons. 2008. 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.. 118330150. Space Science Reviews. 140. 1–4. 189–215. 2008SSRv..140..189C. LORRI was a reflecting telescope but incorporated a field-flattening lens, with three elements.

See also

• Petzval field curvature
• Coma corrector

Notes and References

1. Book: Geary, Joseph. Introduction to Lens Design with Practical ZEMAX Examples. 2002. Willmann-Bell. 0943396751.