First, apologize if this is a dump question. Thanks to the big holiday sales, I bought 17/1.8 in addition to 12mm and 25mm I have already had. I kind of like the form factor, but the build quality, which is not as good as my Japan version 12mm, especially the focus ring; while the black color is nicer. I have not figured out whether I really will use them all, since I find the FOV gap from 12mm and 25mm isn't that significant. I guess at the end I may end up moving by my feet to adjust rather than switch the lenses. Any thoughts? BTW, I am also thinking about a zoom 12-40, but really do not know when using zoom, should I fix the zoom first and then move or the other way.