PPT Slide

Optimization of Data Collection

Pre-process at least one image (preferably two at 90º to each other) to obtain:

• Cell parameters, crystal orientation and putative Laue group

• Estimate of mosaicity

• Effective resolution limit

• Crystal to detector distance

• Exposure time

• Strategy for data collection

Remember! This is the last experimental stage - if you collect bad data now you are stuck with it. No data processing program can rescue the irredeemable!

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It is always worthwhile spending some time prior to the full data collection to determine sensible parameters for the data collection. For example;

• are you using the full area of the detector?

• does useful diffraction go beyond the edge of the detector? Does it stop halfway to the edge?

• check for overloads - are there a lot? Are you using the full dynamic range of the detector? Consider a low and a high-resolution pass. Increase or decrease the exposure time.

• check that the predicted spots do coincide with their positions on the image(s); is your initial estimate of the mosaicity realistic?

Remember to use prior information! If you have experience of your particular sample or experimental setup, use your knowledge. If something looks odd, investigate it.