[3dem] Falcon 3 output

[Morgan, David Gene]

Hi,

I have a stupid question about the MRC files output by our Falcon 3 camera.  I just acquired a set of movies in counting mode where the total dose should be on the order of 25 electrons/ A^2, spread over 22 frames.  My pixel size is just under 1 A, so my images should have on the order of 20 - 25 electrons per pixel.  At least the average over all the pixels after summing or motion correction should be close to that...

When I examine the MRC files output by EPU, I find the following min/max/mean for an example acquisition:

  1.  file with fractions (22 frames): min = 0, max = -1, mean = -2 (obviously bogus values)
  2.  fractions after recalculating min/mix/mean:  min = -23, max = 549, mean = 108.27
  3.  summed image (non-motion corrected single frame output by EPU): min = 1239, max = 3809, mean = 2382

My stupid question:  How do these numbers relate to what should be the counted number of electrons that hit the specimen?

I suspect that I am seeing some stupid effect of an "average counts per electron" in these images, but I had previously (and I suppose foolishly) assumed that in counted mode images, one count would mean one electron...

Thanks for any input you can offer, and Happy New Year.

--
    politics is more difficult than physics.
                                             A. Einstein

            David Gene Morgan
        Electron Microscopy Center
             047E Simon Hall
             IU Bloomington
          812 856 1457 (office)
          812 856 3221 (3200)
      https://urldefense.com/v3/__http://iubemcenter.indiana.edu__;!!Mih3wA!E-FcoZUZdcr3llQ_tQ7nra_aC45SHHOofl5vsdk4RilKOYWBacUzdW1K8BzGLp3U7LbXIfTjwt3E1eA8hKRTl-Y$ 
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