Dear Jacob,
What I meant was that I thought it was a pleasant surprise to see
that there was enough anomalous signal at all in these noisy data
(which were collected from several crystals, suffering from radiation
damage at room temperature, from sizeable absorption effects etc.) to
get a refined value of 5. You are right to say that it was a case of 8
plus or minus 3, but I was impressed. Remember, that wasn't from data
collected on a 4-circle diffractometer (that could be fiendishly
accurate): it was the maiden flight of the A-W rotation camera with
its reliance on film cassettes, microdensitometry and all that - a set
of intrinsically much noisier ways of trying to count X-ray photons
than point detectors. It is true, however, that this technology would
have been unlikely to support phase determination by SAD.
By the way, the Fred I was addressing in my first posting was
Fred Dyda (who had floated the idea that there might not have been
much useful anomalous signal before flash freezing), and not Fred
Vellieux ;-) .
With best wishes,
Gerard.
--
On Wed, Jun 06, 2012 at 01:30:26PM -0500, Jacob Keller wrote:
> No offense taken (we all have our dour moments!), but grant me a
> sincere question: the f" occupancy value would have been just as close
> at 11 as 5 if the true value were 8, am I correct? In other words, do
> you imply by saying "doing well" that you got as *much* as 5, or that
> you got as *close* as 5? I am just trying to see whether I understand
> these things correctly.
>
> Jacob
>
>
>
> On Wed, Jun 6, 2012 at 12:21 PM, Gerard Bricogne <[email protected]>
> wrote:
> > Dear Jacob and all,
> >
> > I realise that my last statement sounds awfully dour and dismissive, in
> > a way I really didn't intend. Especially as Stefan's original posting was a
> > "Fun Question".
> >
> > Apologies to all for this over-the-top statement. I enjoyed a lot of
> > the replies.
> >
> >
> > With best wishes,
> >
> > Gerard.
> >
> > --
> > On Wed, Jun 06, 2012 at 06:09:33PM +0100, Gerard Bricogne wrote:
> >> Dear Jacob,
> >>
> >> I thought that getting 5 for each iodine was doing pretty well, given
> >> the circumstances - e.g. the noisy measurements, the primitive software
> >> running on slow computers with tiny amounts of memory, etc. .
> >>
> >> In any case my main point, directed at the original poster, was that
> >> reading the early Acta Cryst. issues ("RTFL") might be an alternative and
> >> perhaps more enlightening way of getting a picture of the evolution of
> >> phasing methods than finding some clever filter settings in the RCSB ;-) .
> >>
> >>
> >> With best wishes,
> >>
> >> Gerard.
> >>
> >> --
> >> On Wed, Jun 06, 2012 at 11:08:37AM -0500, Jacob Keller wrote:
> >> > ...Even with such primitive techniques, I can remember an HgI4
> >> > > derivative in which you could safely refine the "anomalous occupancies"
> >> > > (i.e. f" values) for the iodine atoms of the beautiful planar HgI3
> >> > > anion to
> >> > > 5 electrons.
> >> >
> >> > I am surprised--f"'s of I and Hg are supposed to be around 8 for CuKa
> >> > (or maybe you weren't using CuKa)?
> >> >
> >> > JPK
> >> >
> >> >
> >> > --
> >> > *******************************************
> >> > Jacob Pearson Keller
> >> > Northwestern University
> >> > Medical Scientist Training Program
> >> > email: [email protected]
> >> > *******************************************
