I while back I compared a 36Mp file with a 24MP file (a99 and a7r), both files RAW from imaging resources. On screen there was a very clear and obvious difference in resolution. Since printing is what I do with pictures, I printed both files, on 20x30 inch, which is my normal printing size. There was a difference, but disappointingly small.
From 24 to 36Mp is only a small step in linear resolution. I was curious in what is the room left for improvement, resolution wise, for my size of printing.
So yesterday I have set up an experiment that takes such a comparison to the extreme. I made picture with my nex-7 with a Touit 12mm f2.8 mounted (used at f5.6). This is an amazing lens and it also happens to be the one I use most of the time (I get better results with this combination as from my a99 with the 16-35mm f2.8 zoom at comparable length). I made the same picture again, but now as a stitch with my nex-7 and the e50mm f1.8 at f8. This file has a size of roughly 16 times 24Mp. 4 times the linear resolution. I reduced this file to 15000x10000 pixels, to make it more manageable. Using such a large amount of data not only improves resolution, but also dramatically reduces noise, increases DR etc. The subject for this exercise was a cityscape with a lot of fine detail. There was both housing with fine brickwork and all sort of plants in the scene.
On screen the differences was ridiculous. So much more detail, like comparing mf film with 8x10. Not only was there more resolution, but since I already reduced the resolution down to 150Mp, there where less artifacts. So even at 100%, the stitched file looked better.
Anyway, I printed both files, again on 20x30 inch. There is a very obvious difference in depth of field, should probably have stopped down the 50mm a bit more to f11 or 16. But I was after resolution, and f8 is already past optimum for the nex-7.
Apart from the depth of field, it depends on the distance you look from. At 50cm there is not much to choose between the two prints. There are some very subtle visual differences. At a viewing distance of say 20cm the differences become more clear. The larger file has a more natural look. everything looks 'easy', while at this distance the 24Mp file looks a bit strained at some places. and there is some more detail in the larger file.
I would not mind having a camera that would give a result like this every time, but the gain is modest. I showed some other people and the only thing they noticed was a small difference in lighting. This was a well lid subject and I did not do any post processing. The large file could handle almost anything you could do with it. The 24Mp aps-c file would break up much sooner. But still, it is amazing what an equalizer printing is. At this size. I could print the large file 100 inch wide and it would still look great at any distance. But I never print so large.
Printing was done with Qimage (handled the scaling and final sharpening for print) on an Epson 7800. This printer is probably not as sharp as the newer ones. Could make a difference when looking at 20cm.