These grid shadow patterns were obtained from the Oxford triplet (and other configurations) in 1989 by David Jamieson et al. They show what is probably the dominant influence of parasitic duodecapole field components in the quadrupole lens fringe fields. (Note sepia tone of the old photographs!)
1. 2. 3. 4.
Theoretical patterns (pram/oxtrace):
1. 2. 3. 4. 5.
Key - 1: Grid at image plane, 2: 1mm downstream, 3: 1mm up, 4: 2mm up, 5: 5mm upstream.