I can see that my remarks about Dynamic Range have sparked quite a bit of discussion. Thank you all. This is very healthy and quite interesting.
So let me explain where I am coming from:
About a year ago I was very curious about how the dynamic range of DSLR's compared to film. Part of my curiosity came because I had heard a few professional photographers complain that DSLR's could not approach film in this regard. I made a number of calls to Canon, Nikon, Kodak and Fuji. There was a universal consensus among the technical experts at these companies that top DSLRs delivered roughly 7 F/stops of dynamic range while most transparency film (there are obviously variations) delivered about 8 F/stops of dynamic range. The point was that they were relatively close. Negative film had somewhat higher dynamic range, according to Fuji about an extra F/stop.
It is important to note that during those discussions dynamic range meant how many F/stops you could capture and still deliver texture and detail.
No, I did not perform any tests. Since there was universal agreement, I took them at their word.
Now, turning to Medium Format, the factory spec for PhaseOne backs is approximately 13 F/stops. I know from experience shooting with these backs that they do deliver this kind of dynamic range.
This is how I came up with the numbers.
My experience with a Canon 1DsMKIII and my P65+ back certainly bears out a huge difference in dynamic range capabilities. I have never done a side-by-side measurement, but there is definitely a very large difference; 6 F/stops would not surprise me at all.
The reason for my comment of 30 feet is based on recent anecdotal evidence. About one week before I started writing the article, I went to the camera store and I had with me an 8x10 inch print from an image that I shot using an ALPA camera with the P65+ back. A couple of photography enthusiasts entered the store, and from about 30 feet away I heard one of them say "WOW, look at the dynamic range in that picture". Then, they approached me and kept asking how many shots it took, and how I did the HDR processing of the multiple shots, etc. They were stunned that this came from a single image capture. They also commented that "you could never get that kind of dynamic range out of a single image with a small format DSLR". There are two salient points here: First: One of the striking things about high end Medium Format backs is their dynamic range capabilities. Second: You can detect it from quite far away. If you do not like 30 feet, then make it 10, or whatever makes you feel good.
I would never state as fact something based on a single instance of anecdotal evidence, but this short piece of anecdotal evidence is typical and constantly repeats itself. I find that (if the original subject has it), the first thing that strikes the viewer about a Medium Format digital image is the dynamic range. The second thing is the level of detail retrieval and natural looking sharpness.
Having said all that, I am always interested in new evidence and new data, and if there is proof that some newer small DSLR (I have never used or tested a D3x for example) can match the Medium Format backs in dynamic range, I will be the first one to be ecstatic that the technology is getting better, and I will also stand corrected. If anyone has the right measurements and/or the proper visual experience, please be so kind as to share it.
To summarize: My visual experience to date, combined with what I have heard from the manufacturers themselves points to a very significant difference in Dynamic Range capabilities between Medium Format and smaller DSLR's.
I hope this is helpful, and again thanks to all of you for the discussion.