In the Pilatus mode these are "open-shutter" experiment, where the
Pilatus integrates over different times
- all these exposure times are slower than the frequency of the
detector, as far as I understand the setup.
So, the crystal gets the 'full blast' in all cases, and the blast is
the same for the same rotation, as we did the experiments.
btw, I have the suspicion, that for our system, it was better to do
'100 sec' in the pilatus, than 100x1 sec and read for 3-4 secs
with a CCD in between, but I have no rigorous proof for that. Its just
an observation that should be treated with caution.
Tassos
On Nov 5, 2010, at 17:11, Jacob Keller wrote:
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
P please don't print this e-mail unless you really need to
Anastassis (Tassos) Perrakis, Principal Investigator / Staff Member
Department of Biochemistry (B8)
Netherlands Cancer Institute,
Dept. B8, 1066 CX Amsterdam, The Netherlands
Tel: +31 20 512 1951 Fax: +31 20 512 1954 Mobile / SMS: +31 6 28 597791
