Hi,
I have made exhibition quality prints from 12MP APS-C in A2-size. Many of my best images were shot on 12 MP APS-C, and I have made many very good prints from those.
At the time I went from 12MP APS-C to 24MP on full frame I was stunned to see how little difference there was between A2-prints from those formats.
So, I feel that say 16-24 MP can be perfectly good for A2 size prints.
Two and a half year ago I bought into medium format shooting 39MP, and I could not at that time see differences from 24MP to 39MP in A2 size prints. I did not make any print comparisons between my A7rII and my other cameras yet, but I have seen some issues with raw conversion on the A7rII using Lightroom 6.2. RawTherapee with the AMaZE algorithm did a much better job on this:
Here is a link to a full size image.
I had a discussion on this on LuLa as I feel Adobe needs to work on their raw conversion. On that thread Mark Segal pointed out that those artefacts are not visible in a 45" print. I did a print a crop of corresponding size and made some very interesting observation.
Some facts: I am 60 years old (a couple of days not counting) and I am nearsighted. Have around 20/20 vision with corrective glasses.
So, what I have found was that I could see those jagged lines viewing close (say 12" / 30 cm) without glasses. Moving away from the print I could no longer observe those jaggies. With progressive glasses I was not able to observe those jaggies at any distance. A young person with good accommodation of vision would probably be able to see them easily.
That said, I still would prefer an image without those artefacts, but fact is that our vision is limited and can hide a lot weaknesses in rendition. Still I feel that good and correct rendition is a good thing, but once we are past the 12 MP on A2 (or so) we are entering the diminishing returns region. We still get benefits from increasing resolution but those benefits may be less obvious.
Best regards
Erik
And to think some of us have to struggle with the wimpy 12mp from the Sony A7S.