>I started this thread to address the wide end and prefer not >to dilute with comments about the long end --- which might be >better if you started a separate post addressing the pros and >cons of each at the long end. But, I will address some of the >above below.
Albert, I was simply responding to your comment: "Compare the investment of a superwide zoom addition for DX to the cost and weight of a longer lens in Fx." Perhaps you should have started a separate post.
All I was trying to point out is that there are applications where the long end isn't that critical. I've had a D3 since they became available. I haven't bought any longer lenses and don't plan to. But that's me. (Of course, I still have my D2X if I really need to stretch the limits.)
But you want to talk about the wide end, so let's do that. FX does provide some real advantages there, especially considering what's available now. I'm moving from a 17-55 DX lens to a 24-70 FX lens as my main landscape and walk-around lens. Both lenses, which cover roughly similar FOV, are excellent -- best-of-class for their respective formats. But there is little question that the 24-70 is superior in several ways, most notably in flare and distortion.
To go wider, there is the 14-24. I'm not crazy about that due to the filter issues, but it's a gorgeous lens that goes really wide on FX. (Nothing short of a fisheye will get you there on DX, although you can get close with third-party lenses.) But I also have the outstanding 17-35 available to me.
Of course, you can use those FX lenses on a DX body. If it's the 24-70, you'll probably be hitting the stop at the 24 end a lot! Even the 14-24 only gets you to an 80° FOV -- wide, but not nearly as wide as on FX. And then if you want to go wider, you can go to the lesser-quality 12-24. Third-party lenses offer some relief -- I like my Tokina 12-24 -- but still aren't in the class of what's available for FX.
There's another element that should be mentioned, which is that the FX sensor does exhibit better dynamic range and lower shadow noise. Not by a lot, mind, but it is a real effect that does make a difference in some situations.
While I'm happy to shoot wide on DX, I think it really is the case that FX provides some advantages. Not necessarily deal-breaker issues, but advantages nonetheless in both lens selection and sensor performance. Nobody (that I know of) is saying WA isn't possible on DX, only that it is better on FX.
Whether those advantages are worth the money may depend on whether we are talking about my money or your money.