(news & commentary) Updated
Two new Nikon cameras (D5300 and Df), two service advisories from Sigma.
Nikon has a go-it-alone attitude. They consider their mount and all physical connections to their cameras completely proprietary, and it's rare that they share any of this information with anyone. There are rumors of a few joint projects with Tamron, but basically when Nikon changes something they not only don't communicate it to others, they don't care if things break.
The recent Sigma lens problems relate to operation of Sigma's OS (which if you recall, Nikon sued Sigma over in a patent dispute) and real time focus performance via Live View (which isn't using the phase detect system and thus has a different timing system to reverse engineer). Neither work properly when most Sigma lenses are mounted on a D5300 or Df. One difference with the Df incompatibility: lenses without internal focus motors are impacted (the D5300 doesn't autofocus with those lenses, so obviously doesn't have this issue).
Sigma has service advisories about both cameras: D5300, Df. If you own one of those and also own Sigma lenses or are considering them, you need to read those advisories. Bottom line: if the Sigma lens you're using can is supported by the Sigma USB Dock, you can download a firmware update and install it yourself via that accessory. If you have an older Sigma lens, you'll need to send it into Sigma for update. All new lenses coming out of Sigma will have a label on the side of the box indicating D5300, Df, and/or D5300/Df compatibility if you're concerned about this problem with a future purchase.
Still, that's not a perfect solution. First, not all lenses can be updated, apparently. This is more of a problem for the Df, where you might have an older lens that predates HSM that you want to use with the camera (the D5300 requires HSM lenses to focus since it doesn't have a screw drive). Second, I've heard from one reader that Sigma is asking people to show proof of purchase of a D5300 or Df to get an update via their repair service. It's true in the UK, and that's the wrong policy, AFAIC, as it sends the wrong message to customers.
I'll give you an example from my emails (and note how this will hurt both Sigma and Nikon):
This news has opened up a whole new can of worms for those heavily invested in Sigma lenses. I own the Sigma 15mm f2.8, 150mm f2.8 (macro), 150-500mm f4-f6.3(zoom) and 1.4x teleconverter. The quandry for me is, I have been using a D100 and D300 but have been waiting for the D400 or whatever it will be called. If Nikons latest cameras (D5300 and Df) have compatibility issues with Sigma lenses then it is likely that a D300 replacement will also have the problem. So would a D400 be worth buying when it comes out if it's going to have compatibility problems? I have been thinking of changing from Nikon to M4/3 (probably Olympus OM-D E-M1) because of the lighter weight of camera and lenses.
Right. So she can't update her Sigma lenses in anticipation of getting a new Nikon body, and if she can't do that, she now has to consider just moving to another system. This is why I talk about DSLRs (and mirrorless cameras) as being ecosystems. You're only as good as your ecosystem. If parts of the ecosystem are weak or start to die, everything is compromised. Nikon's unwillingness to license Sigma could cause Nikon a loss of future camera sales. A good ecosystem is greater than the sum of its parts. A bad one is worse than the sum of its parts. Nikon's is bad at present. m4/3's is good at present. Those things can and do change with time, so it's high time Nikon addressed this.
As for the problem itself: two basic possibilities seem possible: Sigma didn't take something into account when reverse engineering the mount communications, or Nikon changed something deliberately hoping to break compatibility.
Nikon, as usual, won't comment. You won't find mention of these kind of third-party lens issues in their support knowledge base, either. Nikon's policy for software, accessories, and lenses has long been "if it doesn't say Nikon or Nikkor on it, we won't do anything to help you fix your problem; go see the maker of that product for answers."
This means that Nikon cameras are a "closed" system. If someone else gets something to work with the Nikon gear, great, but there's no guarantee it will continue to work if Nikon changes something, exactly the situation that Sigma has found itself in.
Frankly, I think that Nikon likes shooting itself in the foot. The Nikon "system" would be much richer, deeper, and desirable even if they were to license third parties, even more so if they disclosed without limitations as some of the other camera systems are now doing. Nikon is now the most closed of the camera systems, as hackers have managed to figure out how to change and extend Canon's firmware and Canon, while not endorsing this, is also not trying to shut it down (Canon cameras can execute in external card space, while Nikons can't, which limits what you can do in a hack to available firmware space).
My advice to Nikon? They should have gone to a managed and licensed third party system a long time ago. By pursuing the proprietary route all they're doing is enabling competitors who have a more open, modern view of the world.