title: A pitfall in the calculation of higher order aberrations.
abstract: When calculating aberration coefficients of secondary and higher order, there is a danger of misinterpreting the result. An example is given for a homogenous magnetic field and the source of the difficulty is described.
authors.affiliation: Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, vvi, Královopolská 147, Brno, Czech Republic.
authors.forename: Bohumila
authors.initials: B
authors.lastname: Lencová
authors.forename: Michal
authors.initials: M
authors.lastname: Lenc
authors.forename: Peter W
authors.initials: PW
authors.lastname: Hawkes