Originally posted by jcdoss Nice article!
Two minor corrections:
1. The lens does have filter threads -- 77mm -- built into the petal hood. Thus it can take filters but they may vignette on fullframe (not on APS-C if I remember correctly), especially with strong left-right shifting in landscape orientation (or up/down in portrait orientation).
2. Thus, the lens does accept filters. In fact is does so in two places! In addition to the filter threads on the hood, the back of the lens has a holder for gelatin filters (which you did mention at the end).
P.S. One trick for getting the right amount of shifting for architecture is: 1) use the electronic level of the camera to point the camera straight-level at the horizon (that ensures that all vertical lines will be vertical); 2) use the shift to compose the object (without tilting the camera off of level).