This question keeps coming up, partly because both third-party lens makers have interesting choices that compliment Sony's own FE mount options rather than completely duplicating them. The Z System user is jealous, because they don't have the range of choice yet in the Z-mount, and many of the Sigma and Tamron options would provide new, interesting choices in the cracks of the Nikkor lineup. For example, these lenses:
- Tamron 17-28mm f/2.8. A differently-specified, fast wide angle zoom.
- Sigma 24mm f/2. An affordable small wide angle prime.
- Sigma 28-70mm f/2.8. An affordable, fast mid-range zoom.
- Tamron 28-75mm f/2.8. Affordable, fast mid-range zoom.
- Tamron 35-150mm f/2-2.8. A fast, larger range mid-range zoom.
- Tamron 70-180mm f/2.8. A very affordable fast telephoto zoom.
- Tamron 70-300mm f/4.5-6.3. A very affordable telephoto zoom.
- Sigma 90mm f/2.8. A small, interesting portrait prime.
- Sigma 100-400mm f/5-6.3. An affordable telephoto zoom.
- Sigma 135mm f/1.8. A fast telephoto prime.
- Tamron 150-500mm f/5-6.7. An affordable extended telephoto zoom.
- Sigma 150-600mm f/5-6.3. An affordable extended telephoto zoom.
Couple just those lenses above with the available Nikkor Z options, and I doubt anyone would be complaining (much) about lens availability.
Sigma and Tamron probably know exactly when they'll offer Z-mount lenses. After all, these two companies were once dependent upon EF and F mount sales, and those are obviously declining, probably rapidly. In both cases, though, the shift in market share from Nikon to Sony in interchangeable lens cameras in the past few years offered an opportunity that both third-party makers jumped on. Both seem to be working near capacity just trying to keep their FE mount lenses in stock, and the supply chain and shipping issues don't help with that.
Which puts them in a bit of a quandary.
My understanding is that Sigma has already decided that they're late to the Canon RF and Nikon Z mounts. Whether they can do something quickly about that is another story. Tamron is a tougher bet, given that Sony is still one of the larger stockholders in the company. Tamron isn't likely to move until they know they can fill the FE mount demand and have enough manufacturing capacity left over to handle the other two big mirrorless mounts.
Given that both Sigma and Tamron are having to monitor Z System cameras for compatibility (through the FTZ adapter for people adapting their F-mount lenses), I don't think that the delay in seeing third party lenses appear is due to any inability to reverse engineer Z-mount communications. Moreover, the Z-mount has been out for long enough now that you could have easily done a full reverse engineer even without the FTZ. Of course, there is the issue that Nikon is still tweaking a few things on the mount, but Nikon themselves doesn't want to trip over incompatibilities that would force them into body firmware upgrades across the board. They've already triggered a couple of those, and I'm sure they want to minimize them moving into the future.
A number of people believe that the delay is all due to market share. I personally don't believe that. It's more due to the fact that many of Sony's new Alpha customers didn't have lenses to run on an adapter, so were strong buyers of available lenses. To think that it was solely about market share would be to believe that Sigma's and Tamron's marketing teams can't get and read charts. In full frame, Nikon mirrorless is doing just fine in terms of market share, and improving every day. We're really going to have a full-out battle between Canon RF, Nikon Z, and Sony FE in full frame in 2022 and beyond. Sony may have gotten there first, but now Sony has two primary competitors aiming full lineups at them, and Nikon, in particular, has been pricing below Sony for equivalent models, plus has a real entry model in the Z5 that is not matched in the market by Sony at the moment.
Sometimes you can't move the cavalry until the tanks have been realigned. The third party lens makers were always going to be there after the primary camera maker(s) they support. Despite Tamron's close alliance with Sony, it took a number of years before Tamron began to have a "full" FE lens lineup. The same thing is going to be true for the Z-mount.
Does my Magic 8 ball have any answer other than "Ask again later..."? To quote the late Jerry Pournelle: Real Soon Now. I suspect that CP+ at the end of February 2022 might be the earliest target for which we'd see Sigma or Tamron make an announcement. And I'd bet that we'll see the first lenses from them by summer 2022. To fail to do so would be a mistake by either company.
