Dose (Camera Sensitivity) Calibration¶

Dose Calibration is a calibration of CCD sensitivity. This calibration is required only
once at each high tension per instrument. It can be used for three purposes:

• To obtain a scaling factor between the scope screen current and the beam current
  measured by a standardized equipment such as a Faraday cup.

• To calibrate the camera sensitivity to electron.

• If camera sensitivity is already calibrated, the value can be entered
  directly.

Determine the screen current/beam current scale factor¶

The following uses a Faraday cup

• Scope> Move the stage to an empty area or a broken hole.

• Scope> Adjust the beam so that it passes through the measuring area of the
  Faraday cup.

• Scope> Choose a magnification so that the same beam will pass within the main
  screen, too.

• Leginon/Dose/Dose Calibrator> Beam Diameter = 0.16 m for Tecnai main
  screen.

• Leginon/Dose/Dose Calibrator> Enter Screen Current to Beam Current Scale
  Factor as 1 as a starting point.

• scope> Optionally lower the screen. Dose Calibrator will automatically do this
  if the user forgets.

• Leginon/Dose/Dose Calibrator> Click Measure Dose Rate. The Dose Rate, Beam
  Current, and Screen Magnification will appear in the corresponding fields after they
  have been calculated.

• Leginon/Dose/Dose Calibrator> Adjust the Screen Current to Beam Current Scale
  Factor so that the displayed beam current is equal to that of the Faraday cup
  measurement. NRAMM Tecnai's value is 0.88.

Calibrate the camera sensitivity¶

• Scope> Move the stage to an empty area or a broken hole.

• Scope> Expand the beam so that it covers the main screen and illuminate it
  uniformly.

• Leginon/Dose/Settings> Configure camera with overide preset activated.

• Leginon/Dose/Dose Calibrator>

Beam Diameter = 0.16 m for the Tecnai's main viewing screen.

Screen Current to Beam Current Scale Factor = (as determined above or 1 to assume
good calibration by the microscope manufacturer)

• scope> Optionally lower the screen. Dose Calibrator will automatically do this
  if the user forgets.

• Leginon/Dose/Dose Calibrator> Click Measure Dose Rate. The Dose Rate, Beam
  Current, and Screen Magnification will appear in the corresponding fields after they
  have been calculated.

• Leginon/Dose/Dose Calibrator> Without changing the beam intensity, click on
  "Calibrate". An image is acquired by Leginon.

*Leginon will automatically lift the main viewing screen on the microscope. Some
users report that the function does not work on their microscopes. Do it manually if
the automatic function does not work.

• The calculated CCD sensitivity (counts / electron) will display once the
  calculation is completed.

Enter pre-determined camera sensitivity value¶

• Leginon/Dose/Dose Settings/Camera Sensitivity> Enter Sensitivity values in
  counts per electron.

• Leginon/Dose/Dose Settings/Camera Sensitivity> Click on Save.

Preset	magnification
*	any