I've found an awesome description for how to build your own tilt/shift lens (http://www.creativepro.com/article/build-a-tilt-shift-camera-lens-peanuts) that mentions using, for example, a lens for the now obsolete Pentacon 6 format. What other lenses could be used for this purpose? Are there any other concerns than it having to be a lens for a larger format than the target one (DX, in my case)?
Ideally, it would be a lens of great optical quality that you can get hold of cheaply (though I realize that posting this question doesn't really help with that).