Dear Joe,
On second thought, it seems to me that a vertical gap would be
even better suited to the use of a 2theta axis than a horizontal one:
if one assumes that the 2-theta axis is parallel to the Omega axis,
i.e. vertical, a small 2-theta offset by at least the angular width of
the gap would suffice to fill it completely, as it would essentially
amount to a horizontal translation. With a horizontal gap, a 2theta
offset mostly slides the gap into itself, and therefore rescues fewer
reflections from having fallen in the gap at 2theta.eq.0 .
I am probably missing some fine points that you looked into more
thoroughly.
With best wishes,
Gerard.
--
On Sun, Jul 16, 2017 at 09:24:41AM +0100, Gerard Bricogne wrote:
> 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
> > >
