Tecnai on-line help manual -- Alignments - UT Southwestern

<strong>Tecnai</strong> on-line help Alignments 32<strong>Tecnai</strong> 12 Software version 2Note: The magnification system (projector lenses) is normalized when the magnification is changed tomake the image position better reproducible.6.10 Mi cross-over shiftPurpose: Aligning the Mi cross-over shift to ensure that the differential pumping aperture does not(partially) block the beam and causes a cut-off of the image.Importance: ESSENTIAL for avoiding partial image cut-offs at low Mi magnifications.Method: Move the shadow of the differential pumping aperture so it becomes centered around thescreen center.ProcedureThe alignment procedure consists of one step in which a shadow from the aperture (if visible) is movedso it does no longer obstruct the image.Notes:• If an aperture casts a shadow in the image for the lowermost Mi magnification, but this shadow doesnot move with the change of the Multifunction knob settings, and instead another aperture comes intoview and starts blocking the beam, the original shadow is not that of the differential pumpingaperture, but of the fixed SA aperture. The latter aperture cannot be "moved" by changing the optics.• Because of the need to have the beam (which in this case means the diffraction pattern) centeredproperly in the differential pumping aperture, it is not possible to change the position of the diffractionpattern when you enter diffraction from an Mi magnification (because that would ruin this alignment).In principle you should always go to diffraction from an SA magnification.6.11 Align diffraction patternPurpose: Set the zero position for the diffraction shift.Importance: CONVENIENCE for easy resetting of the diffraction shift to the screen center.Method: Center the diffraction pattern using Multifunction X,Y.ProcedureThe alignment procedure consists of a single step.DescriptionThe diffraction shift has two components, an alignment value and a variable 'user' value. If properlyaligned, the alignment value will have the diffraction pattern centered on the screen. It then is onlynecessary to reset the 'user' value to zero to have the pattern back at the screen center.6.12 Align camera lengthsPurpose: Determine the shifts necessary for aligning all camera lengths, so that the diffraction patternremains in the center when the camera length is changed.Importance: CONVENIENCE for having the diffraction patterns centered when the camera length ischanged.Method: Center the diffraction pattern for the reference camera length (~500 mm), then align all cameralengths to the reference camera length. Focus all camera lengths.