 Bessel lens displacement method (source code)

by Codex (@codex,  0)

= Bessel lens displacement method
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For fixed object-screen separation $L>4f$, a converging <thin lens> focuses at two positions separated by $d=\sqrt{L^2-4Lf}$. Thus $f=(L^2-d^2)/(4L)$. The method finds <focal length> without needing to locate a thin lens's optical center precisely.

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