What do you consider long ? 200, 300 ? 600 A ? Before shooting try to run strategy or xplan. Move the detector back to first reliably be able to determine your cell. Then double your estimated mosaicity and see what strategy suggests. If you don't get many overlaps (<5%) then try a closer distance. Don't rotate 1degrees but take 1/2 of the mosaicity. Obviously you want to make good use of the detector area so adjust the edges to where your crystal really diffracts. And if that resolution leads to too many overlaps then limit your resolution and get first a good datasets home. You then can play with 2theta for a higher resolution dataset. Another obvious thing to do and you don't mention what reduction program you use is to let XDS sort your problem out. Unless you collected to high resolution without being cautious XDS could help. If not, well then you had your experience and now should know better. SSRL has options to collect 450 A cells to 3A without much hassle. That was my largest cell so far. Jürgen
...................... Jürgen Bosch Johns Hopkins Bloomberg School of Public Health Department of Biochemistry & Molecular Biology Johns Hopkins Malaria Research Institute 615 North Wolfe Street, W8708 Baltimore, MD 21205 Phone: +1-410-614-4742 Lab: +1-410-614-4894 Fax: +1-410-955-3655 http://web.mac.com/bosch_lab/ On Apr 5, 2011, at 1:05, dengzq1987 <dengzq1...@gmail.com> wrote: > hello all, > does anyone have the experience of Collecting Data from Long Unit Cell Axes > ? I have a crystal that diffracts to about 4 A. in some direction the spots > overlap. we can't use the data to index .we think it is because that there is > a long unit cell axes. so is there any method to solve this problem? > > best wishes. > > 2011-04-05 > dengzq1987
