I have a data set collected on Arctica with SerialEM in 3 x 3 pattern. I have separated cleaned up /refined particle stack into 9 exposure groups (there are ~30K particles per group). Running Global CTF Refinement significantly alters Spherical Aberration for 5 out of 9 groups: G1 = 2.706, G2 = 37.6, G3 = -43.4, G4 = -24.7, G5 = -56.5, G6 = 2.7, G7 = - 38.92, G8 = 2.71, G9 = 2.67 mm.
Is the extreme SA value a some sort of local minimum? Is there anything we can do to limit the search range (or is this data just particularly awful)? For this job I have used default settings with 5 iterations. The large SA value is estimated on the 1st iteration and changes only slightly with later runs. Fit resolution range used was 10 A for Min and 8.7A was estimated for Maximum. I am currently re-running several groups and varying fit resolution values. Version 2.12.4.