PPT Slide
Factors related to incident Xray beam
(a) incident beam intensity: variable on synchrotrons and not normally measured. Assumed to be constant during a single image, or at least varying smoothly and slowly (relative to exposure time). If this is not true, the data will be poor
(b) illuminated volume: changes with f if beam smaller than crystal
(c) absorption in primary beam by crystal: indistinguishable from (b)
(d) variations in rotation speed and shutter synchronisation. These errors are disastrous, difficult to detect, and impossible to correct for: we assume that the crystal rotation rate is constant and that adjacent images exactly abut in f. Shutter synchronisation errors lead to partial bias which may be positive, unlike the usual negative bias