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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Strehl ratio ： ウィキペディア英語版 Strehl ratio The Strehl ratio is a measure of the quality of optical image formation, originally proposed by Karl Strehl (1864-1940) after whom the term is named.〔Strehl, K. 1895, ''Aplanatische und fehlerhafte Abbildung im Fernrohr'', Zeitschrift für Instrumentenkunde 15 (Oct.), 362-370.〕〔Strehl, K. 1902, ''Über Luftschlieren und Zonenfehler'', Zeitschrift für Instrumentenkunde, 22 (July), 213-217. ([PDF file] )〕 Used variously in situations where optical resolution is compromised due to lens aberrations or due to imaging through the turbulent atmosphere, the Strehl ratio has a value between 0 and 1, with an unaberrated optical system attaining the value of unity. ==Mathematical definition== The Strehl ratio $S$ is frequently defined as the ratio of the peak aberrated image intensity from a point source compared to the maximum attainable intensity using an ideal optical system limited only by diffraction over the system's aperture. It is also often expressed in terms not of the peak intensity but the intensity at the image center (intersection of the optical axis with the focal plane) due to an on-axis source; in most important cases these definitions result in a very similar figure (or identical figure, when the point of peak intensity must be exactly at the center due to symmetry). Using the latter definition, the Strehl ratio $S$ can be computed in terms of $\backslash delta(x,y)$, the offset of the wavefront due to an on-axis point source, compared to that produced by an ideal focusing system over the aperture A(x,y). Using Fraunhofer diffraction theory, one computes the wave amplitude using the Fourier transform of the aberrated pupil function evaluated at 0,0 (center of the image plane) where the phase factors of the Fourier transform formula are reduced to unity. Since the Strehl ratio refers to intensity, it is found from the squared magnitude of that amplitude: :$S\; =\; |\backslash langle\; e^\; \backslash rangle|^2$ = |\langle e^ \rangle|^2 where ''i'' is the imaginary unit, $\backslash phi\; =2\backslash pi\backslash delta/\backslash lambda$ is the phase error over the aperture at wavelength λ, and the average of the complex quantity inside the brackets is taken over the aperture A(x,y). The Strehl ratio can be estimated using only the statistics of the phase deviation $\backslash phi$, according to the formula of Mahajan〔http://www.wolframalpha.com/entities/calculators/Strehl_ratio_formula/av/uo/vo/ Strehl ratio formula〕 :$S\; \backslash approx\; \{e^\{-\backslash sigma^2\}\}$ where sigma (σ) is the root mean square deviation over the aperture of the wavefront phase: $\backslash sigma^2\; =\; \backslash langle\; (\backslash phi\; -\; \backslash bar\backslash phi)^2\; \backslash rangle$. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Strehl ratio」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.