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:[email protected]] On Behalf Of Gerard
> Bricogne
> Sent: Saturday, July 15, 2017 4:31 PM
> To: [email protected]
> 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
> >
