The detector issue could be resolved by moving it to a different distance and recording the pattern again. In the absence of further info, my vote goes for James Holton's explanation - the effect could be due to optocal misaligenment Colin
> -----Original Message----- > From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On > Behalf Of John R Helliwell > Sent: 31 October 2010 12:47 > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Strange spots > > Dear Jurgen and Petr, > I looked at the Princeton incommensurate link kindly provided by Petr. > I see your point ie examples of a grouping of subsidiary > spots around a central spot. But not continuous circles. > > I have now checked the Atlas of Optical Transforms (my office > copy en route to Manchester United versus Tottenham Hotspur > yesterday evening). Little help there. > > I also looked at Richard Welberry's Diffuse Scattering book > (OUP/IUCr Monograph). This has a variety of > circular-continuous halo effects from inorganic, and one > organic, crystals and explanations of the crystal disorders > they arise from; these halo effects seem identical to David > Goldstone's.The main difference of the Welberry examples > versus the David Goldstone example is the latter is > restricted to one part of reciprocal space, at least from the > one pattern shown. > Basically we need more info from David Goldstone re the > fidelity of his detector, pointed out in the earlier > discussions as well, and/or more diffraction patterns, > ideally as a movie clip of patterns as his crystal is rotated. > > Greetings, > John > > > On Sat, Oct 30, 2010 at 5:06 PM, Jürgen Bosch > <jubo...@jhsph.edu> wrote: > > I second Petr's opinion. These halos are different compared > to John's book. > > Strong reflections look perfect as can be seen in the red > zoomed area. > > weaker spots show the halos because the crystal lattice was > disordered > > (or because the crystals grew in a disordered or incommensurate > > fashion). If you increase the contrast of the image you can > see more > > of those halos which have a sharp straight edge pointing at > ~six corners around the spots. > > The usual questions: > > 1. how does the diffraction look like at room temperature > in capillaries ? > > 2. have you played with more than three different cryo's ? And what > > was the result of it ? > > 3. Is my assumption right, that you tried to freeze a large > crystal ? > > Try freezing a smaller one e.g. 50 µm and see how your high > > resolutions spots behave. The rings we see are the typical > remains of > > weak ice rings ? Then you really should improve your cryo. > > 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 Oct 29, 2010, at 4:14 PM, Leiman Petr wrote: > > > > I think this is a poly-crystalline incommensurately > modulated crystal, i.e. > > incommensurately modulated crystal, which fractured upon freezing, > > resulting in averaging of satellite spots. > > > > Fig. 3b from here: > > > http://www.princeton.edu/~actin/documents/Proteincrystalscanbeincommen > > surate > > lymodulated.pdf > > > > Petr > > > > > > > > On 10/29/10 6:08 PM, "David Goldstone" > > <david.goldst...@nimr.mrc.ac.uk> > > wrote: > > > > Dear All, > > > > Does anyone have any insight into what the circles around the spots > > > > might be? > > > > cheers > > > > Dave > > > > > > > > > > -- > Professor John R Helliwell DSc >
