10.7: Optical resolution
By analogy with optical observations, e.g. in astronomy, the term optical resolution in structure determination, \(d_{opt}\) , is used to describe the expected minimum distance between two resolved peaks in an electron-density map.
\[d_{opt}=[2(\sigma^2_{Patt}+\sigma^2_{sph})]^{\frac{1}{2}} \nonumber \]
where σ Patt is the standard deviation of the Gaussian function fitted to the Patterson origin peak, σ sph is the standard deviation of the Gaussian function fitted to the origin peak of the spherical interference function, representing the Fourier transform of a sphere with radius 1 / d min , and d min is the nominal resolution.