Adding to the previous post and the idea of the X100s as a portrait camera / 23mm f2 Fujinon as a portrait lens; you can see in the shots below (also from yesterday) that even at f4 you can get some moderately blurry out-of-focus area to the rear with an APS size sensor. Not as much as a full frame camera, but it’s still nice, and, I’d argue, enough. The bokeh aji (flavour of the blur) is particularily nice with this lens too.
The point to note here, is that the top photo below is a crop. I wasn’t even all that close to get this degree of blur. The original photo, actually a test shot for exposure, is at the bottom below.
With a 50mm (equivalent) teleconverter, you’d of course get just as much out of focus area when keeping the subject at the same relative size in the frame, and even more if you closed in for even tighter shots. Naturally, at f2, you would get even more. I guess that my point here, as well as illustrating something useful to consider when taking portraits, is that one of the often touted arguments for going full frame is not in fact all that compelling.