Английская Википедия:Field flattener lens

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Field flattener lens is a type of lens used in modern binocular designsШаблон:Efn 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>\delta_{x}</math> dependent on the thickness of the glass. Thus we have a thickness as a function of focal shift:

<math>t(\delta_{x})=\left(\frac{n}{n-1}\right)\delta_{x}</math>.

<math>\delta_{x}(y)</math> is given by the radius of curvature of the Petzval surface, <math>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>R_{f}=\left(\frac{n-1}{n}\right)R_{p}.</math>

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. LORRI was a reflecting telescope but incorporated a field-flattening lens, with three elements.

See also

• Petzval field curvature
• Coma corrector

References

Шаблон:Optics-stub