# Optical resolution

### From Online Dictionary of Crystallography

Pouvoir de résolution (Fr). Bildauflösung (Ge). Risoluzione angolare (It). 分解能 (Ja). Resolución de imagen (Sp).

By analogy with optical observations, e.g. in astronomy, the term optical resolution in structure determination, $d_\mathrm{opt}$, is used to describe the expected minimum distance between two resolved peaks in an electron-density map.

$d_\mathrm{opt} = [2(\sigma_\mathrm{Patt}^2 + \sigma_\mathrm{sph}^2)]^{1/2}$

where $\sigma_\mathrm{Patt}$ is the standard deviation of the Gaussian function fitted to the Patterson origin peak, $\sigma_\mathrm{sph}$ 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 $1/d_\mathrm{min}$, and $d_\mathrm{min}$ is the nominal resolution.

## History

The term was introduced into the protein structure determination literature by Vaguine, A. A., Richelle, J. and Wodak, S. J. [(1999). Acta Cryst. D55, 191-205. SFCHECK: a unified set of procedures for evaluating the quality of macromolecular structure-factor data and their agreement with the atomic model].