[Scythels]

When I said 'lots' in quotes it really was because the level of spherical aberration is not too high.  The astigmatism is much stronger with sigma's lens than with canon's which leads me to believe the sagittal and tangential fields bend in opposite directions which will hamper the performance as the lens is stopped down, but the sigma's performance looks quite good wide open and I would expect very good results stopped down regardless due to the very deep DoF.  The limiting aberration is just primarily higher order spherical aberration i.e a similar aberration characteristic to samyang's 24/1.4, but better correction on the whole.