Originally Posted by
peety3
IMHO, you're absolutely dreaming if you think an 85/1.2L III would actually be "fast" to focus. IIRC, v2 has eight elements, and seven of the eight elements move for focus (that rear element is quite obviously parked in place; I can't imagine trying to make it move so close to those contacts).
Back to the use case, it already is a good (err...great) portrait lens. I use mine in AI Servo and although I can hear and feel it constantly tweaking focus as I breathe and so does my subject, it's spot-on once it's in the general zone. What is so bad about the 50/1.2? What's bad about the 85/1.8? What's bad about the 100/2, 135/2, 70-200/2.8 non-IS, 70-200/2.8 IS II, or heck, either of the 70-200/4 variants? Heck, both the "old" Zeiss 85/1.4 and new Zeiss Milvus 85/1.4 include electronic focus confirmation, as do both variants of the Zeiss 100/2 Makro, the Zeiss 135/2 variants, and apparently the TS-E 90 as well.
With all of those great options on the market, we own several (50/1.2, 85/1.2 II, 100/2.8 IS Macro L, 135/2, 70-200/2.8IS v1, 70-200/4IS, 70-200/4), and yet, for my new passion in headshot work, I'm using the lowly 70-200/4 non-IS at f/5 and about 90mm for essentially all of it.