Originally posted by interested_observer hope that helps....
That's all pretty much what I would have said, if I'd been awake then.
I'll note that while moderate wide angles are often used (with good effect) in landscapes, ultra-wides are best for getting close to a subject, as they push the background away. (The 28mm lens mentioned above isn't really wide, not on a dSLR.)
Ultra-wides (rectilinear) are effective in grabbing interiors. Fisheyes too, with the distortion you mention. I do love my DA 10-17. But some lenses that are fisheyes on film cameras, like the Zenitar 16/2.8 mentioned above, aren't really that wide on a dSLR, just distorted. I must be very careful when using mine. The DA 10-17 is neither super-fast nor super-slow; I hand-hold it when interiors aren't too dark, or with a multi-flash setup. Very few (if any) single flashes will light its wide view.
Of course, there are always tripods to put under ultra-wides and fisheyes in darker rooms. And under faster wide-to-normal lenses too, for stitching panoramas. Stitched interior panoramas are tricky -- unless care is taken to rotate the camera around its nodal point, foreground objects may not stitch correctly. Lines won't line up, some objects may appear twice, etc. And people in the room may move between shots. That may be a desired effect, of course.
So, which lens is right for interiors? That depends on 1) how bright, 2) how large, and 3) how stable the interior is, and 4) how much noise and distortion we're willing to tolerate, and 5) how much we want to spend. By how stable, I mean, is there movement in the room while you're shooting?
Besides the other lenses mentioned above, Sigma has announced a (I think) 8-16mm ultrawide zoom, the widest rectilinear ever made for dSLRs. I don't recall how fast or expensive it is.