[3DEM] CM-100 and cryo-tomography

[Benoît ZUBER]

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Dear Community,

We try to set up tomography of vitreous specimens on our CM-100 microscope,
using TVIPS' CCD camera and acquisition software. 
Since our specimens are not flat, we need to keep the focus and tracking
positions close to the exposure position. Thus, in order to avoid
irradiating the exposure area, we need to use a quite focused beam in the
focus and tracking position. Here comes the problem: during the acquisition,
the beam shifts from its central localization, and eventually does not cover
the whole camera anymore in the focus and tracking positions. 

Some potential sources of the problem are: 
1) The steps of the shift X and Y buttons on the CM are not fine enough to
calibrate precisely the beam shift in TVIPS software.
2) After changing spot size, we note the position of the beam. Then we put
the beam blank and remove it. The beam is not in the same position anymore.
Afterwards, we can put the beam blank and remove it without any other beam
displacement.

We are of course in contact with the engineers of FEI and TVIPS but they
don't know how to solve these problems. If someone could give us some tips,
we would be very grateful.

Best regards,
 
Benoît Zuber
Université de Lausanne
Laboratoire d'analyse ultrastructurale
Bâtiment Biophore
CH-1015 Lausanne
Switzerland

tel: +41 21 692 4289 ou +41 21 692 4283
fax: +41 21 692 4285 
e-mail: Benoit.Zuber at unil.ch



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