F30 gun tilt alignment

[Bob Grassucci]

Hi Bill,
         When you say you save the alignments do you also save the FEG 
Registry?  This is the most important alignment to save related to the gun 
alignment.  Try that and let me know how it comes out.
         Bob

At 11:21 AM 7/29/2005 -0700, Bill Tivol wrote:
>Dear Lists,
>         We have had a peculiar situation for a while with the gun tilt 
> alignment on the F30.  When using the Alignments panel, which sets the 
> mag and spot size to default values, and measuring the intensity with the 
> Measured Exposure value, we have seen that the maximum intensity can vary 
> by a factor of about 2.  Of course we have saved an alignment file on the 
> days that the maximum intensity is good--a measured exposure of <~1 
> sec--and when the alignment maxes out at > 1 sec, we try loading the gun 
> alignments from the file.  Sometimes that works, but sometimes it 
> doesn't.  I'm sure that the poor intensity max comes from finding a local 
> max rather than the global max, and I can usually keep working until I 
> find the global max, but I don't know why the good alignment file stops 
> working, and that is bothersome.  A FEG should be more stable than a 
> thermionic filament with respect to alignments since it doesn't 
> evaporate, and the beam is remarkably stable during use, so the 
> alignments shouldn't change much.  Have any of you had the same 
> experience with your FEG instruments?
>Yours,
>Bill Tivol, PhD
>EM Scientist and Manager
>Cryo-Electron Microscopy Facility
>Broad Center, Mail Code 114-96
>California Institute of Technology
>Pasadena CA 91125
>(626) 395-8833
>tivol at caltech.edu

********************************
Robert Grassucci
Howard Hughes Medical Institute
Wadsworth Center
Empire State Plaza
Albany, NY 12201-0509

bobg at wadsworth.org
Phone: (518)474-5821
Fax:	(518)486-2191