Leginon

h1. 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.

h2.  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.

h2.  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.

h2.  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.

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