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Publisher Summary This chapter discusses the image tube characteristics of importance in X-ray diffraction studies. In protein crystallography, it is necessary to measure the relative intensity of diffraction spots occurring over the entire cathode area to an accuracy of a few percent with a dynamic range of the order of 1000:l. It is thus necessary to correct observed intensities for nonuniformities of image tube response over the sensitive region. For X-ray diffraction studies, however, the MTF has not been found to be as useful as a related measure of resolution, the point spread function (PSF). The PSF is easier to measure and interpret and it contains information that is often difficult to extract from the MTF. Two point spread functions can be combined to form a resultant point spread function with the aid of a simple computer program. For X-ray studies of crystalline proteins performed to date, it has been necessary to resolve diffraction spots approximately 0.5 mm in diameter, separated by at least 1 mm center to center, over an intensity range of 500:l. |
