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International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 7.2, p. 151
Section 7.2.3.6. Modular images
aDepartment of Physics, 162 Clark Hall, Cornell University, Ithaca, NY 14853-2501, USA, and bSwiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland |
The size of available fibre optics and CCDs and the inefficiencies of image reduction limit the practical imaging area of a single CCD system. Closely stacked fibre-optic taper CCD modules can be used to cover a larger area. Although the image recorded from each module could be treated as independent in the analysis of the X-ray data, merging the sub-images into one seamless image facilitates data processing. Each module will have its own distortion and intensity calibration. It is no longer possible to choose an arbitrary lattice onto which each distorted image will be mapped: the displacement and scaling must be consistent between the modules. This would be accomplished most easily by having a distortion mask large enough to calibrate all modules together, although it is possible to map the intermodule spacing with a series of mask displacements.
Flat-field correction proceeds as in the case of a single module detector after proper scaling of the gain of each unit is performed. There can potentially be a change in the relative scale factors between modules, since each is read though an independent amplifier chain. Multimodule systems emphasize the need for enhanced stability and ease of recalibration.
