Dear James,
Many thanks for the detailed explanation. I do find
your results very interesting and (when time allows
!) I will certainly investigate this effect in more
detail and see if I find similar results for data
that shows significant levels of radiation damage (as
Andrew! You don't believe me? Well, I suppose it serves me right for
not explaining where the idea came from (see below).
I do, however, agree with Andrew's assessment that the default-chosen
gain in MOSFLM is adequate for all practical purposes. Any error in
GAIN will be almost exactly
I have to say that I don't fully agree with James' recommendation to
adjust the GAIN in MOSFLM until the calculated SDFAC parameter in
SCALA is 1.0.
(Background information, the sigmas from Mosflm sd(I) are corrected in
SCALA according to
sd(I) corrected = SdFac * sqrt{sd(I)**2 +
Dear Bryan,
The quick answer is no. As David Waterman
mentioned, it has a default value for the gain for each type of
detector that it can deal with.
A more detailed answer. An incorrect value for the gain can be
indicated by values of the BGRATIO which differ
Dear All,
spotted a mistake in my response, please see the correction below (in
bold):
There are a host of caveats in this procedure. For example, if the
images contains significant diffuse scatter around the Bragg spots,
the BGRATIO may be above 1.0 ... this is probably the commonest
I have found that the best way to get the GAIN right in MOSFLM is to
have a look at the optimum Sdfac parameter at the end of SCALA (the
first of the three SDCORRection values). Specifically, if SDFac is 1,
then you need to increase the GAIN. This is because SDFac1 means that
the spots were
Usually Mosflm will use a default value for the gain that depends on the
type of detector used. This value is not realistic for CCD detectors, that
is it is not really equal to the ratio of ADUs to incident X-ray photons,
however it satisfies typical images under the assumptions of pixel
