Thanks Dennis
I very quickly learned that I absolutely had to use Mirror Up!
What I've done so far is photo stacking of 30-80 images photographing at F/5.6-11. I'm using a Tamron 90mm Macro which from what I've been able to find is at its sharpest at F/5.6 BUT it suffers from considerable CA that wide so I've had to use F/11 to remove the halos.