Question: My interest is photography of "places and things", i.e. outdoor and landscapes. I was under the impression that a wide would give great DOF from close up to infinity, would you choose this above a 25 or 28 mm for that application or do I just not get it?
It's really hard to shoot an 18mm well for landscape; it's a lot of space to fill up (sometimes toes and legs do the trick by accident!). I do not recommend 18mm as a first lens. A favorite landscape lens of mine is the 85mm f/2.8D PC-Micro Nikkor!
To dispel the myth that a wide angle provide enormous depth of field, subscribe to DAP and check out the sample images in the Canon EF 14mm f/2.8L II review. It’s mostly about magnification, not focal length. The use of tilt is the only way to get truly deep depth of field. For this, you need specialty lenses like the Nikon PC-E 24mm f/3.5, the Nikon PC-E 45mm f/2.8D or the PC-E 85mm f/2.8D (Canon has 24mm, 45mm and 90mm equivalents).
If you shoot the same scene with an 18mm vs a 25mm, you’ll get similar depth of field provided that the magnification of the subject is the same. Photograph a rock in the landscape, making it the same size in the image with both focal lengths, and there will be modest differences in actual depth of field, though the required perspective change (to maintain size) will heighten the effect, making the 18mm seem to have more DOF, mainly because more distant objects will be much smaller! Human visual perception dominates here—the 18mm will appear to have more DOF, but the image it renders will be vastly different as well.
Don't choose a lens based on non-choices like depth of field. Choose the focal length that matches how you see or what kinds of images you want to make. Of the 18/25/28mm choices for landscape, my first choice would be the 25mm for "places and things", but that's me. The 28mm would be great also, and at one stop faster, great for low-light shooting. For all around use, I’d go with the Zeiss ZF 28mm f/2 Distagon.
While the Zeiss ZF lens line is terrific, and used for most of my shooting, the Nikon 14-24mm zoom would be a better *first* choice for the wide angle range, for its versatility. On the other hand, a fixed focal length forces more careful compositions and teaches better than a zoom can.