I have the Sigma EF mount 24-105 and i use it on a Metabones adapter on Sony FS700 videocamera. For 4K video, its amazingly sharp, and i am very pleased.
While my Canon EF 24-105 which i use on my 5D for stills was at service, i tried the Sigma 24-105 on the Canon 5D and that gave me some weird experiences.
Firstly, i did some photos today and all of them are seriously back focused. Lucky it was just sea landscapes with boats and islands, and on each of my motifs i did a f/8-11 front focus to play around with the focus a little. Only on the photos where i front focused on the sea did my motifs come in proper focus. When i got home i tested this issue some more, but found no more back focusing. Now focus is spot on.
Now, it does belong to the story that when i inserted the memory card back into my 5D with the Sigma mounted, it would not boot up. Instead, the lens made this weird humming noise. Seriously loud too. Much louder and smoother noise than the OSS, or even the auto focus motor and system. I flipped the 5D off again, and the noise went away. Back on, and its normal for a few seconds, but soon starts to buzz again. I put on live view to see if its OSS or something, but no. With autofocus and live view on, its perfectly silent and working great.
I just got my Canon 24-105 back, so i put that on the 5D. No sounds. Works like a charm. But the IS do sounds alot noisier than the OSS!
Has anyone else had this sort of VRRRRRR sound from their Sigma 24-105 Art lenses? Ive sent an email to the dealership asking for help, and at the same time ordered the Sigma USB Dock since i also own the Art 35 and Art 50. Maybe its a firmware issue with the 5D mk2, maybe not.