12-24-2015, 06:55 AM
Joju, things are complicated. PD AF and CD AF use different ways to command the lens. So it may well be that a Nkkor lens with PD AF does a better job than a Sigma lens, because Sigma uses their own reverse engineered PDAF logic in their lenses. I do still see quite some complaints about Sigma focus issues in Nikon forums, particularly concerning the 35mm f1.4 and 50mm f1.4. Whether that is anything to go by, I do not know.
Also, I have seen quite a number of posts about certain Nikon FF DSLRs having issue with focussing correctly with artificial light. I have not read threads about that in detail, so I can't give any pointers (not even sure if the D750 is one of those or not), but a quick google should give information about that. Also I read a thread where a 5D mk III user found that the Sigma 35mm f1.4 he used focussed differently in artificial and day light.
With my camera, PD AF still focusses when CD AF has effectively become blind.
Also, I have seen quite a number of posts about certain Nikon FF DSLRs having issue with focussing correctly with artificial light. I have not read threads about that in detail, so I can't give any pointers (not even sure if the D750 is one of those or not), but a quick google should give information about that. Also I read a thread where a 5D mk III user found that the Sigma 35mm f1.4 he used focussed differently in artificial and day light.
With my camera, PD AF still focusses when CD AF has effectively become blind.