I'd like to find a less expensive fast (2.8) wide prime to use backpacking for taking landscape shots. Lighter weight would be a good thing. I don't want to take my 17-40L. From my research, it seems the MF lenses are less expensive. The Oly 28/2.8 and 28/2 seem like popular suggestions. Question though - are there AF versions of theses lenses? I've noticed some of these on ebay have "auto" in the title description. I'm not sure what that refers to. Any other suggestions for some fast MF wide primes for FF? Anything in the 20 mm-30 mm range.