[JJ_SO]

JoJu, If you already use AF, don't even bother with MF. It requires skill and good eyes, and for better results you will need focusing screen. It can be really frustrating some times and at F1.4 it is even harder. The focusing dot in the OVF is not 100% correct, but it helps. You mentioned moving birds... this is hard with MF lens. I believe this lens should be used in controlled environment where the subject can remain static during focusing or you can always re-take the shot.

Don't tell me you will buy the Zeiss if it is noticeably sharper than Sigma?

No, the Otus only wins in terms of colors and the absence of chromatic aberrations. I could not get sharper pictures out if it than with the Sigma, at least not constantly. In the extreme corners I got maybe 2 shots out of 150 where it was the Otus winning. In the majority of my examples the Sigma is better. And was easier to focus, too.

I once had a focusing screen and found it not very useful: focusing aid is always centerred and the adjustment of the screen is very close to "impossible" because of the distance frames. I'd Say if I can't adjust the focusing screen within a tolerance of +/- 0,05 mm I'd see it in wide open pictures. Less at the 55, but massively at the 85.