Dear Joe, Thank you for the insights :-) . Near-exclusive exposure to synchrotron beamlines leads one to forget about 2theta axes, as they are hardly ever encountered; but indeed it is a help here. Most of all, I would assume that your default strategies would use several *crystal* orientations thanks to your quarter-Chi goniostat. That would of course help fill the gap since it amounts to tilting it, but even so, it still feels as if more low-resolution reflections would be lost because of their proximity to the rotation axis than if the gap was mounted vertically. Is that actually not the case?
With best wishes, Gerard. -- On Sun, Jul 16, 2017 at 06:19:01AM +0000, Joseph Ferrara wrote: > Gerard, > > You are correct that a vertical gap is best when 2theta.eq.0 and we did > explore orienting the Pilatus with the gap vertical early in the hardware > integration process. However, we concluded that when 2theta.ne.0 at least two > 2theta settings would be required to prevent systematically missing > resolution shells. Since most data sets are collected with 2theta.ne.0 we > decided on the horizontal gap in order to distribute the missing data evenly. > Please note the direct beam is not in the gap so low resolution reflections > are accessible. > > I would also like to point that a loaner detector was provided to John a few > days ago and we are working with Dectris to sort out the issue that began > this discussion. > > Cheers, > > Joe Ferrara > > -----Original Message----- > From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Gerard > Bricogne > Sent: Saturday, July 15, 2017 4:31 PM > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Pilatus Issues > > Dear John, > > Having just seen Andreas's message regarding the best source of support > to address your enquiry, I have a further remark to make about your > instrument. > > As this is a lab instrument, the Omega axis would be vertical, and > indeed the beam stop shadow (vertical on the top module) and the diffuse > shadow of the sample holder (vertical on the bottom module) would confirm > this. This being the case, it is quite simply *daft* to have the gap between > the two modules being horizontal. That is done on purpose on synchrotron > beamlines because of the polarisation of the beam (which is why Omega is > horizontal on such beamlines), but in a lab system the gap should be in the > vertical direction. As currently placed in your system, this gap is cutting > into perfectly good data, whereas if it were vertical instead, it would only > cut out data that are getting perilouly close to the cusp anyway. > > You should ask the manufacturer of your diffractometer to rotate your > detector by 90 degrees! Someone in the OEM world forgot about the Lorentz > factor ;-) . > > > With best wishes, > > Gerard. > > -- > On Fri, Jul 14, 2017 at 05:14:03PM +0100, John Hardin wrote: > > Hi, > > > > We have recently noticed an issue with our Pilatus (biased pixels/vertical > > lines). > > I was curious as to whether anyone else has seen this or might know what > > could have caused it? > > > > Best, > > John > >