Lars,
Did you try this lens with external aperture (instead of internal iris)?
Prompted by Tair 11A optical design (iris at the front end of the system.. - and this is btw excellent lens - very sharp in centre but some coma present at APS corners and
no CA)), I found out that telelenses (
Canon FD 200 F2.8, Canon 300mm etc.) perform much better when f number is stopped down by external diafragm.