Sigma issued a bulletin which states its older lenses could have "OS and AF issues in Live View" on Nikon's new D5300 and Df bodies. I've let Sigma know that I thought their older lenses have serious AF system flaws with the D7100 bodies I tried too. Outer AF points were severely back-focused. Only the center 9 points could be trusted. I used a Sigma 17-50mm f2.8 HSM OS, a 70-200mm f2.8 HSM OS, and a 30mm f1.4 "Dirty Thirty". All were incredibly sharp on the center points with low chromatic fringing. None focused properly on any of the three D7100 bodies' outer AF points. All focused properly on my D300 body, but that wasn't the point. I needed them to work right on the ultra-sharp D7100's 24mp non-AA filter. They simply wouldn't. This isn't to say that Sigma builds a bad lens. They build a very good lens, and they make their quality lenses in Japan. There's a lot to be said in that. Nikon has evidently decided to change something in their AF system and how it operates, and this leaves third party lens makers scrambling. Only screw-drive designs will not have a problem, as the body itself has control over proper focus. Again, this defeats the purpose of buying modern lens designs with high-refractive glass, anti-reflective coatings, and Hyper-Sonic ring motors for faster focusing. If it cannot repeatedly nail the focus with the AF system in the body to which it is affixed, then it's not worth the money. For 2013, I cycled through a bunch of lenses trying to come up with an "optimal quality" setup without spending the big Nikon buck. Alas, I've come to believe that Thom Hogan might be right; it just might not be possible to use third party lens makers at this time. My D300 can shoot anything, everyone has it figured out. I'm not sure about the newer cameras now, and it becomes incredibly frustrating to carry a camera and lens out on a shoot and not be able to use more than one-third of its AF points, or 3D focusing, or multiple points, simply because there's some sort of communication issue between a lens and a body. The choice becomes this; shoot with cheaper Nikon lenses which work, or shoot with expensive Nikon lens which work. There's no in-between. And that's sad. In a disappointing turn, the cheaper Nikon 35mm f1.8G I purchased would only focus properly on low-contrast objects about 25% of the time. Sharp, but wildly inconsistent. And made in China. Read into that what you want. This boy will only buy Japanese-made glass from now on, and probably just the pricy stuff from Brand N. It'll be a long time before I'll be able to save up for some of these expensive pieces.