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Increasing astigmatism during aberration free image collection

Added by Michael Cianfrocco about 2 years ago

Hi Anchi,

I've set up aberration correction on our Glacios & Krios and it looks stable when I check the image shift coma alignment.

However, during data collection, we see that there is progressive objective astigmatism even though there was not any astigmatism when we started.

It makes me wonder if there is a cumulative image shift problem, which manifests as objective astigmatism.

What is causing this? Is there an option that I'm missing to check/uncheck?

Thanks!
Mike


Replies (1)

RE: Increasing astigmatism during aberration free image collection - Added by Anchi Cheng about 2 years ago

What is the time frame of changed behavior ? Of the aberration that we can correct, the stability of coma is best, and then 2-fold stigmatism, and then defocus. On some scopes we see 2-fold stigmatism correction calibration required changed significant after a few month or after some event that affect the optics stability. When it behaves well on Krios, the correction should give you a cluster of astigmation distribution plot in your ctfreport somthing like this:

The unit is micron. Typical central cluster is about 0.03 micro-meter in diameter and roughly round. When it goes bad, the distribution becomes broader and the cluster often become elongated

ctfgraph_astig_distr.png (6.28 KB) ctfgraph_astig_distr.png
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