[3dem] Low Dose Focus/Exposure

[De Carlo, Sacha]

Hello Tommi
Is the eucentric focus preset at real "zero" focus as well? If you do leave the normalization "on" for the lenses when switching form focus to exposure, and the eucentric focus preset is off by, say, two microns, then that's the cause of what you're observing ...

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On 27 Apr 2015, at 23:55, Tommi White <whitetommi at gmail.com<mailto:whitetommi at gmail.com>> wrote:

Dear 3DEM.

Perhaps the community can assist with this issue we are struggling with.  In Low Dose on our Tecnai F30, the Low Dose focus image has a different defocus value (using FFT) versus Low Dose Exposure.

I have been checking this on a relatively flat cross-grating (not cryo) specimen.  I set LD exposure to be zero defocus (with focus knob), but when I switch over to LD focus (~ 3 micron away on tilt axis) the image is defocused (~ -2 micron).

I believe there is some 200 kV procedure alignment that must not be set properly - but am not quite sure which one...any suggestions on what to tweak to get this exposure/focus area reflecting the same defocus?

Thanks for any suggestions...
Tommi

Tommi A. White, Ph.D.
Associate Director, Electron Microscopy Core Facility
Assistant Professor of Biochemistry
University of Missouri
W125 Veterinary Medicine
Columbia, MO 65211
573-882-8304
http://emc.missouri.edu

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