[3DEM] Question about Thon rings

[Bill Tivol]

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On Jan 25, 2007, at 2:43 PM, Eduardo Sanz-Garcia wrote:

> I have a question about Thon rings. I have realized recently that when
> I take pictures using the CCD camera I get better Thon rings than when
> I take the image using film (less rings and more diffuse). The specimen
> is the same in both cases and the intensity of the beam is adjusted
> automatically in both cases. I am using a Technai  F30.
> Any clue why the film is giving me worse result than CCD?
> Thank you in advance for your suggestions. I will appreciate them a 
> lot.
>
Dear Edwardo,
	If the beam adjustment for the film is near crossover, the coherence 
will be lowered, so you won't get as many Thon rings.  You could try to 
see what you get for different spot sizes, and if low spot size number 
gives better results, then that indicates that the automatic intensity 
adjustment was choosing a pretty condensed beam.
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
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