I've got 12-24, 24-70 & 70-200 sigma lenses, I like them all, they might not have the IQ of the Nikons, but all 3 cost less than one Nikon and for my own personal use they do me (for now lol!)
Have heard Tamron 17-35mm is one of the better third-party wide FX lenses
The 24-70 f/2.8 is a cracking lens if you get a good copy. Was on my D700 80% of the time.
You don't neeeeeeeeeeeeeeeeeeeeed filters for all landscape shooting. I personally think that filters aren't anywhere near the necessity they might have been years ago.
You don't neeeeeeeeeeeeeeeeeeeeed filters for all landscape shooting. I personally think that filters aren't anywhere near the necessity they might have been years ago.
Perhaps you would care to explain that fully?
Last time I looked there is no way to replicate CPL, 10 stop ND, or some of the slightly stronger grad filters in software. A lot of my and others work heavily relies on these filters.

Sigma 12-24mm won't accept filters - a non-starter for landscapes.
What am i looking for after the 12-24 ie HSM etc