[3dem] Low Dose Focus/Exposure

[Wim Hagen]

Hi Tommi,

It can depend on the settings you are using. I always advice users to keep focus and exposure settings exactly the same, but I have seen many people who always use a higher magnification for focus and then things become alignment dependent: in the alignment procedures there is a magnification dependent defocus step which often is neglected.

What are your settings for focus and exposure in this case?

Cheers,

Wim Hagen
EMBL Heidelberg

> On Apr 27, 2015, at 11:52 PM, Tommi White <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 <http://emc.missouri.edu/>
> 
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