F30H objective aperture & low dose

[Bill Tivol]

Dear Lists,
	A problem has come up with using the objective aperture in conjunction 
with the low dose kit.  When the aperture is centered in the Exposure 
state, it is off-center in the Focus state by an amount that varies 
with the focus shift.  The problem is the same using TEM mode or EFTEM 
mode.  Logically, this should be related to image shift pivot points, 
but that alignment is right on, and a complete set of TEM-HM alignments 
did not solve the problem.  Both our local service guy and an expert 
FEI guy have looked at the problem, but have not been able to solve it 
(although we thought they had on a couple of occasions).  Has anyone 
else seen this, and, if so, what fixed it.  TIA.
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