This post has been in the works for a while, hence the green plants (since I started it sometime during the summer, probably July or August). If you haven't seen it, Zack Arias has a fantastic video about this here:
All credit goes to Zack Arias.
The main argument against Full Frame is obviously the greater expense that goes along with it. Your lenses have to be larger in order to create a larger image circle necessary to cover that larger sensor, thus making the lenses more expensive. The Sensor technology itself is also more expensive, with the sensors being around 2.3 times the overall area of an APS-C sensor (or crop frame sensor).
Now this comparison is just done with a couple cameras and a couple fairly comparable lenses and my own opinions. This'll sort of end up being a bit of a comparison between the X-T1 and D4, as well (Though I want to do some sports comparisons when I get the Fuji 50-140mm f/2.8 to compare to my Nikon 70-200 on the D4).
All the photos here were taken in Oak Park, in Minot North Dakota during a walkabout with my Wife.
I'll start out with some photos taken with the D4 and 50mm f/1.4G vs the X-T1 and 35mm f.1,4R. While these aren't as comparable, they were surprisingly close.
Now that plus the two shots at the top are all that I really got comparing the 50mm equivalents, so lets move on to the 85mm equivalent lenses. The Nikon 85mm f/1.8 and the Fujifilm 56mm f/1.2 are as close as it gets to the same (I realize I should have used an 85 f/1.4, but I don't have one and I prefer the 1.8 version anyway).
these two photos are the main point of the post, and I am not going to put which camera each was taken on below the photo like normal, just to make the point that they are ridiculously close. Both pictures are of my lovely Wife who had just gotten her GoPro Hero 3+ Black that day!
Since people will ask, though, the top one was taken with the Fuji, and the bottom with the Nikon.
Here are a few more pictures taken with each camera taken wide open for some more comparison.
Now does anyone want to donate to my "Pentax 645Z fund" so I can compare Crop vs Full Frame vs Medium Format?