3. making too fine slices of too weak diffraction images ends up with either too weak counting statistics or inability to 'lock' the refinement. we did that for one crystal form, collecting 0.1, 0.2, 0.35, 0.5, 0.7, 1.0 from various crystals (with the same dose per degree, at SLS using a PILATUS, mosaicity 0.4-0.6) in an attempt to get better Se signal. We miserably failed to get any useful signal at the end, but learned that for these very weak diffracting plates (submicron) collecting 0.5-1.0 degrees was actually giving at the end better data.
Perhaps the reason for the better data was an instance of the redundancy-vs-long-exposure dilemma. Given, say, 1deg exposures: should one collect 500x1s exposures or 250x2s exposures? I think this has been examined, and while it does depend on the details of the parameters, it is often better to collect 250x2s exposures because there is a "flat rate per frame" noise level in the detector. I am wondering whether you just increased the number of "flat rates" in your data sets by increasing the number of frames while keeping the exposure/degree equal?
JPK
