[3dem] streaks in FFTs

[Norm Olson]

-- 
3DEM:  We are seeing vertical streaks in FFTs from images recorded 
with our Gatan 4K CCD camera.  We were wondering if any of you have 
seen this and how we can solve the problem.

Take a look at this image here for an example:
http://cryoem.ucsd.edu/streak.jpg

We are using our program, ROBEM, to box virus particles from our 
recorded images.  From there we calculate an averaged FFT from the 
individual image FFTs to determine the defocus of our image.  This is 
just standard stuff...

The streaks are very apparent in the averaged FFTs but we also see 
them in FFTs calculated in ImageJ from our entire 4K X 4K images. 
The intensity of the streaks is greater in extremely low dose images 
but they are also visible in normal, and high dose images.  The FFT 
included here is from an image taken at 300KV (problem appears to be 
KV independent), ~59,000X, and with a dose of ~27 electrons/A 
squared.  The sample was a carbon film.

Any ideas?  Thanks

Norm Olson

______________________________________________________________
Norm Olson
Cryoelectron Microscopy Facilities Manager
1510 Bonner Hall
Department of Chemistry & Biochemistry, MC-0378
University of California San Diego
La Jolla, CA 92093-0378
nholson at ucsd.edu
http://cryoem.ucsd.edu
Cell:  (858)220-2183
(858)822-6718 - Office; (858)534-5846 - Fax
______________________________________________________________