Back in 1999 I wrote about a lens that was near perfect for the initial Nikon DSLRs: the 58mm f/1.2 NOCT. That lens, mounted on those early DX bodies, was an incredible choice for portraits (87mm effective). Sure you had to manually focus, but back then the autofocus systems weren't all that great to start with, particularly in low light.
Within a week of me writing about the desirability of the NOCT on the new digital bodies, NOCT prices sky-rocketed as others suddenly realized what I had pointed out. Prices on the used market went from just over a thousand dollars to about US$2500 very quickly, partly because Nikon hadn't produced many of these incredible lenses in the first place. (Today a NOCT in perfect shape should go for somewhere close to US$4000.)
So here we go again (I really should buy up the supply of these lenses I write about before I publish my remarks).
In examining the Zfc, I started thinking about what existing lenses really belong on this camera. Once again there's a lens that makes perfect sense to me: the 45mm f/2.8P (make sure it's the P version). This highly compact lens has a bunch of things going for it: (1) at 67mm effective focal range it's a really nice portrait lens for the Zfc, though not as long or as fast as a NOCT; (2) even on an FTZ adapter, the result on the front of a Zfc body is still very compact; and (3) the P in the lens designation means that the lens is "chipped," so it reports focal length and apertures to the camera. Heck, the painted colors in the etching on the lens go really nicely with the sand-colored Zfc, if you're trying to make a fashion statement ;~).
Like the NOCT, the petite 45mm P wasn't produced in huge volumes. Only a bit over 35,000 were made over about five years of production. At the moment they're hard to find, and one in really good shape is going to set you back US$400 or so (as I write this, probably more soon ;~). Once people discover that this lens is an excellent match with the Zfc (and the silver version looks like it belongs on the Zfc so much that people are going to want to paint their FTZ adapters silver, too), the supply is going to get even lower and the price move up higher.
But the 45mm f/2.8P is manual focus you complain. Sure, but the Zfc has plenty of manual focus tools that work due to that chip to render that complaint mostly moot. If you're going to complain about anything with this lens, you should complain about its simple Tessar-design optics. The center is very sharp and contrasty, but the corners tend more towards blurry. However, since I'm suggesting this lens—as I did with the NOCT—as a portrait lens, I don't think you'll find the corner performance all that bad, and wide open you'll also get some gentle corner vignetting that complements portraiture, too.