Sorry to extend the conversation - but lets try. But try as we might, it depends on your standards, what you are shooting, and how you wish to judge. Some personal observation on this : I've been given the opportunity to try a Leica Monochrome. It has an 18mp CCD sensor, which is generally understood to be very much at the top of the smaller cameras, equal more or less to the top DSLRs (see Sean Reid's reviews for more on this). Its CCD sensor is used to only give BW information. I have not compared it to a D800 tho, but rather used it as a small camera and tried shooting very demanding architectural and landscape scenes. The local Leica dealer calls these scenes torture tests, so the gear gets a workout. The lenses used were the 21 SE, the 28 2.8 Asph, and a 50 'cron.
Up to about 13x19 inches, the MM results looks as good as MFDB (Leaf 33 mp). Everything is there and super crisp. The standard used is looking at a print for absolute detail at about 10" (25 cm) viewing distance. The prints are gorgeous.
When taken up to 17x22, things starts to change. Here's where its tricky: for the MM, if the lens is a really good one, the shooting technique is good, and full frame, the MM holds up reasonably well. If any of those factors slip, well, you can see it. If all is good, then the results are good, very good, but… you can see a difference between the MM and MFDB at this size. At first, its not so apparent, but put the prints side by side, and one is very very nice and the other just pops. When shooting landscape (leaves, very fine texture), for example, the difference is there and it is visible, not just to me, but to others. The MFDB simply renders at 17x22 with more detail. However, if the subject is more dramatic, then the difference between the two is less obvious - that is, it is still there, but it is not so apparent. So for me, 17x22 is the upper limit for the smaller camera to make really really, blow you away, crisp results. Again, this is with prints viewed at very close distances. If you made bigger prints, the viewing distance should increase as well, and its likely larger prints would still captivate, as many others have reported.
These results were generally confirmed in observation with friends. I think if you could see the prints you'd agree. Whether you think its a critical difference - well, now we are back to art….However, these results don't necessarily match what others have reported, who say they take MM prints up to larger sizes with great success. I believe the print is the ultimate way to judge, and haven't seen their work in person. Its possible they get better results. Perhaps their trade craft is better, or have better up-rezzing techniques (which I don't use). I use only modest sharpening (LR for the MM, C1 for the Leaf). Maybe C1 is better for the MM, I don't know.
Its also possible they may apply different standards. I'm looking for a very high level of definition, as if these were 4x5 film replacements. That's a ridiculous standard, but one which, with today's technology, is practically achievable, and happily so. Not to say these are the same as 4x5, but rather to give an overall sense of the standards being used.
Other DSLR's are likely to get different results than the MM.
Two other things - where the MM really shines over MFDB is in low light and high ISO. It can hold its quality levels at 2500 ISO very easily, something MFDB can't. So handholding, low light, and small size have their place. Also, the Leaf back is a 33mp back,a few years old. A higher resolution back would permit more cropping (and still hold the quality), or much larger prints with no loss of refinement. The 33mp back has its virtues, tho, especially for use with tech cameras, or at higher f-stops, as diffraction is not so pressing an issue for the 33mp back with its larger pixels.
Hope this helps.
