# Optical resolution

### From Online Dictionary of Crystallography

##### Revision as of 15:00, 11 April 2008 by BrianMcMahon (talk | contribs)

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

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

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

## History

The term was introduced into the protein structure determination literature by Vaguine, A. A., Richelle, J. & Wodak, S. J. [(1999).
*Acta Cryst.* D**55**, 191-205. *SFCHECK: a unified set of procedures for evaluating the quality of macromolecular structure-factor data and their agreement with the atomic model*].