An update for those of you I haven't been chatting with elsewhere. It turns out that THIS particular mirrorless shooter could NOT find happiness with a DSLR. I'm sending the Df back rather than taking it on my trip to the Bay Area this Friday.
There was a lot to like about the Df - the sensor really is all it's advertised to be, battery life is amazing, the OVF is wonderful, I LIKE the way it feels in the hand and I like the control options (even though two of the three retro dials were little more than decoration for the way I use the camera). And of course it's VERY responsive, but I guess that's pretty much a given in the DSLR world. I'm pretty sure that if I was to end up buying a DSLR, this would be the one. And I had decided to buy it for a while, to the extent that I sold my much beloved RX1, a move I regret slightly but not enough to buy another used one to get it back given what I've learned in this process...
There were two basic factors that led me away from the DSLR world in particular, and one that's leading me away from full frame altogether. for a while at least:
1. First, as much as I love a good OVF (and I liked the one in the Df a lot), I really ALSO like having a good constant live view setup. And given the quality of today's EVF's, a good EVF combined with a good live view setup (particularly with a flip up screen) is a better combination for me than a great OVF and a barely useable live view. In a perfect world there'd be a combination of a great OVF and a great live view setup. Fuji has that with the fixed lens X100s and X-Pro 1, but the OVF in the X-Pro 1 only really works well with a small few of Fuji's growing lens lineup. So it's not a perfect world and given the imperfect options, I'm still more of a mirrorless guy in this respect.
2. Second, DSLR's require some degree of MAINTENANCE! I did not experience the need to fine tune focus on the lenses I used during this trial run and focus problems do not seem to be a particular issue with the Df (unlike the D800, for example), but this is something I assume I'd run into with a purely PDAF focus system at some point and it's not something I'd particularly want to deal with.
But the bigger deal to me is the way dust get's into the body of a DSLR and moves around, I guess because of all of the air that moves with that very high speed mirror movement. All too much of that dust ended up on the sensor and I found trying to deal with that a hassle I wasn't interested in taking on. I learned about wet sensor cleaning, something I don't think would have to be done often, but would be periodically. And using one of those bulbous air blowers to blow dust off of the sensor and, ideally, out of the camera altogether. I could temporarily get if off of the sensor but I didn't seem able to get it out of the camera body and some would always find it's way onto the sensor after taking a few shots. I'd start a day with a basically clean sensor (maybe a bit of dust near the bottom of the frame where I'd never see it), but within a dozen or so shots, dust spots would start appearing in the sky and I'd have to clone them out during processing. I talked to a number of other DSLR shooters about this and it sounds like the degree of the issue varies and not everyone has the problem to the extent I seem to. But it sounds like its not uncommon to have to clean the sensor daily or at least a few times per week when you're shooting a lot. When I'm shooting a lot, on a trip or some sort of project, is exactly when I would NOT want to have to deal with sensor cleaning. I could probably solve, or learn to manage this problem, but it's not honestly worth it to me. Photography is not my job - it's what I do for fun and relaxation. In four years of shooting a lot of mirrorless cameras I've never once even had to consider the need to clean a sensor. With the Df, it was a daily issue, at least for me. Just not something I want to deal with.
3. More generally, I concluded that the major benefits of full frame cameras don't really come into play unless you're willing to shoot fast glass with them. And in the DSLR world at least, the fast lenses that give you that advantage are very large, very heavy, and very expensive. Maybe it will be different with the A7 / A7r once Sony has developed a line of lenses, but no indication of that yet. And even though I found the Df comfortable enough to carry and shoot with using the small prime lenses I'd decided to try it with, I found it far larger and heavier than I'd want to deal with using larger lenses. I briefly handled it with a Nikon zoom similar in size but still smaller than the fast 24, 28, and 35mm lenses I'd be interested in and I didn't even like holding the camera with one such lens, let alone carrying a bag of them around. I was FINE with the size of the camera when I was using small lenses, but DSLR's earned their reputation for being big and heavy with premium lenses and it's with those lenses that you get the biggest benefits out of the format...
Using the small, slower lenses I was willing to use, the benefits over a good APS system are pretty minimal. One quick example - the Df sensor is roughly one stop better in low light than the Fuji X-trans sensor available in various Fuji APS camera bodies. Maybe a bit more, but about that. That's significant - a big deal. But the lenses I was willing to shoot with were generally about one stop SLOWER than comparable APS format lenses. I was shooting with a Nikon 35mm f2.0 lens, similar to the 35mm f2.0 lens in the RX1 (although not nearly as nice!). This was a reasonable size lens for me to shoot with. But the Fuji 23mm (35 equivalent) is a full stop faster at f1.4. It's slightly larger than the Nikon 35 but the cameras are so much smaller that overall it's also a very comfortable setup to shoot with. And that lens with the Fuji gets you back the one stop of both low light capability that the sensor gives up and the DOF is basically the same between a 23mm at f1.4 and a 35mm at f2.0. So there's little if any advantage to full frame there. To really take advantage of the significantly better sensor in the Df, you'd need to shoot with the Nikon (or Sigma) 35mm f1.4, which then gives you a full stop of benefit. But f1.4 full frame lenses are a good deal larger and heavier and more expensive than f1.4 APS lenses - bigger and costlier than I'd be willing to buy or carry. I could give you similar examples at 24 and 28 and 85mm. Only in the "neutral" focal lengths around 50mm can reasonably fast full frame lenses be built at similar sizes to APS systems (There are Nikon 50 f1.8 lenses abut the same size as the Fuji 35 f1.4, so the full frame lens is actually faster AND smaller. But that's a focal length I almost never use, so not much benefit to me.
So, while there are clearly advantages with a full frame sensor, whether DSLR or mirrorless, at this point the lens options largely negate that benefit unless you're willing to deal with the larger, heavier, more expensive glass that brings out the full potential of full frame. Not to mention with zooms and telephotos, which are huge and weren't even remotely on my radar. The real benefits of full frame frankly comes at a cost I'm not willing to pay. The benefits of a full frame setup don't add up for me, at this point. Maybe Sony will engineer some smaller fast lenses for their mirrorless full frame system or maybe some competitor will come along and do it and maybe I'll take another look. But until that happens, the benefits of full frame aren't there for me, although if you're OK with carrying the big glass, there surely are notable benefits.
So my loaner is going back. I'm going to take the money I got for the RX1 and GX7 and a couple of m43 primes and dive back into the Fuji world with an XT1 and 3-4 primes, more or less the setup I was going to use with the Df. But Fuji has more and better prime lenses than they had when I last relied on it. The 23 and 56mm lenses are pretty stellar additions. So I'm likely to be right back where I was two years ago when the X-Pro 1 and Olympus EM5 showed up on the scene with largely the same sensors as Fuji and Olympus are still using today. Fuji APS for walk around primes, m43 for zooms and longer lenses. Still not sure where I'll end up for ultra-wide - there are good options in both formats. But the lens options are better in both formats now and I have a much better pocket / street camera (Nikon A) than I had back then.
So, another lesson learned - a chance to really experience and flesh out the pros and cons for myself. And I seem to have come full circle. But no DSLR for this mirrorless shooter...
-Ray