A thumbnail sketch of protein crystallography

In brief, determining the structure of a protein by X-ray crystallography entails growing high-quality crystals of the purified protein, measuring the directions and intensities of X-ray beams diffracted from the crystals, and using a computer to simulate the effects of an objective lens and thus produce an 

The resulting model is often the only product of crystallography that the user sees. It is therefore easy to think of the model as a real entity that has been directly observed. In fact, our view of the molecule is quite indirect. Understanding just how the cry stallographer obtains models of protein molecules from diffraction measurements is essential to fully understanding how to use models properly. 

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