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This is clearly a case of a crystal with a very long unit cell; a case which should be approached mindfully. HKL2000 has a default search for indexing solutions such that diffraction along the longest unit cell will be resolved, with the assumed spot size. The problem with such diffraction has 2 aspects: 1) how to process the already collected data where the spots are close to each other; 2) how to collect future data. Ad 1) The best solution is to reduce the spot size, so the spots are resolved. This may require an adjustment of spot size by a single pixel; one should not only change spot radius, but also change the box size between even and odd number of pixels in the box dimensions. Just changing the spot radius changes the spot diameter by an even number of pixels, so if one wants to change the spot diameter by one pixel, one has to change the box size. This is the consequence of the spot being in the center of the box. Just during indexing, there is also a workaround by specifying the command before indexing: longest vector followed by a number that defines the upper limit of the cell size. This may help finding indexing, but will create overlaps between spots during refinement and integration. This dataset presents a problem of collecting data by rotating on the axis perpendicular to the long unit cell. In consequence, the Image 1 has essentially (barely differing in centroid position) overlapping spots, so it would be hard to process them meaningfully by any program. Ad. 2) What would be a better way to collect data in the future? > Hi CCP4 folks > > I have a data set which is looks twinned ( see the image-1 - I zoomed on > to the image so that one can spot the twinning. Furthermore, the spots are > very smeary from ~ 30 - 120 degrees of data collection, see image 2) I > tried using HKL2000 and mosflm to process this data but i cannot process > it. I was wondering if anyone has any ideas as to how to process this data > or comments on whether this data is even useful. Also, I would really > appreciate if someone could share their experiences on solving twinning > issues during crystal growth > > Thanks in advance ! > > Mahesh[image: Inline image 2][image: Inline image 3] > Zbyszek Otwinowski UT Southwestern Medical Center at Dallas 5323 Harry Hines Blvd. Dallas, TX 75390-8816 Tel. 214-645-6385 Fax. 214-645-6353