Aberration Coefficients

The last two pages contain parameters related to aberrations, specifically the coefficients for various orders of aberrations. The significance of these coefficients is described as follows:

Symbol	Description
C1	Defocus (defocus)
A1	Two-fold astigmatism
B2	Axial coma
A2	Three-fold astigmatism
C3	Spherical aberration
S3	Star aberration
A3	Four-fold astigmatism
B4	Axial coma
D4	Three-lobe aberration
A4	Five-fold astigmatism
C5	Spherical aberration
A5	Six-fold astigmatism

The symbols and their meanings follow the conventions given by S. Uhlemann, M. Haider, Ultramicroscopy, 78(1999): 1-11.

In addition to setting the magnitude of the aberrations, you can also set the angles for each order of aberration. However, defocus (C1) and spherical aberration (C3, C5) are symmetric, so setting an angle will not affect them.

Once these aberrations are configured, they can be used to simulate the shape of the electron probe and vacuum diffraction disc. The aberration settings can also be used to calculate the contrast transfer function for virtual imaging and center-of-mass (CoM) imaging under the current aberration conditions.