Hi dengzq1987,

You don't say how many axes are long. I will assume one. In that case, here is a compilation of what others have already recommended, with some additions:

1. Orient the crystal so that the long axis is along the rotation axis. It can be done during mounting the crystal on the loop or, if the goniostat is equipped with multi-axis goniometer, then after mounting your crystal on the goniometer. But try to pre-orient your crystal as much as you can when scooping it.
2. Increase sample to detector distance: It can help but it will not work if your long axis is along the beam. Overlaps in that case will be more function of the frame width. In that case, see 3.  
3. Decrease the angular range measured in a single frame: It will alleviate the problem not solved in 2. When you do that, you may have to also decrease the exposure per image using less intense beam and/or less exposure time. Otherwise, you radiation dose per degree of data will increase killing you crystal before you collect complete data.
4. Find the detector with a smaller point spread function.
5. Find a synchrotron beamline with a smaller beam.
6. Find a synchrotron beamline with less divergent beam. Keep in mind, that some times (but NOT ALWAYS), 5 and 6 are mutually exclusive. 

4, 5, and 6 will have less effect than 1, 2 and 3.

Good luck!
Nukri


-----Original Message-----
From: CCP4 bulletin board on behalf of dengzq1987
Sent: Tue 4/5/2011 12:05 AM
To: [log in to unmask]
Subject: [ccp4bb] how to Collecting Data from Long Unit Cell Axes ?
 
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