[dave9t5]

The corners are not that extreme, in PZ tests... Case in point, the EF 35mm f2. Its real (extreme) corners are very soft, very sudden. But the PZ corners are just outside of that, showing relatively good results.

 

I too find not testing the center a bit odd.

 

Ah, I should've clarified that I meant of only testing at 3 positions for time reasons, then those 3 seem more useful.  But I have no problem with more than 3 positions.

 

No doubt there are some lenses with soft extreme corners.  But I'm pretty sure that I've no photos where there was anything of interest in the extreme corner.