Notably these guys shoot DMF and speak of experience, the others do not (if I missed someone please raise hand);
Having shot the D800E side by side with my AFi-ii 12, its really hard to believe those DXO charts. Color of the D800E was not all that great and large areas of skin seemed flat compared to the MFDB. The D800E captures significant detail and a good value considering the price. But it misses on the color and also does not have the depth of the MFDB file.
One thing to keep in mind is the sensor size. For landscape, maybe a smaller sensor is a good thing since getting everything inside the DOF will be easier? Besides the color, that was that other thing that really stood out in our studio tests. The d800e shooter shot at f/10 and I shot at f/16 and he had way more DOF with the same framing.
I've posted this before, but here is the differences in crops in regards to formats.

Keep in mind a P30, is not a 1.3 crop it is 1.24 where a almost FF mfd P45 is 1.14, so the differences are not near as pronounced as the sales literature suggests.
I know that this forum loves to post mtf graphs and micro sharpness, but those are just relevant when your bleeding your eyes on a computer screen.
To me the one reason to shoot medium format is the look of non aa filtered CCD's. They just look different than cmos and my studio and I have worked thousands of images from most makers of cmos cameras (Nikon, Canon, Panasonic, RED,) and CCD non AA filtered cameras (leica, Phase, Leaf, Hasselblad, Kodak and Fuji) and there is just a different look to the ccd cameras.
I won't say 3dish, or any of that and I'm not comparing micro detail but I believe the ability to work a file deep with MFD is easier than a cmos file and produces an overall different look than a dslr.
As far as cameras I'd use what camera you feel comfortable with, but I would never buy without testing in some form, because everybody has a different perspective on cameras, files, lenses.
I'd test whether it was a $2,500 dslr or a $30,000 medium format system. It's not just the costs, it's the years of living with it that matters.
I'd also test and shoot something relevant. No alleys, brick walls, or leafs in the backyard, but load up, go out and shoot something pretty. Then you can work the files in post and find the system that's right for you.
You will hear a huge volume of buzz around the Nikon D800 and I'm sure it's a capable camera. You will also here a lot of people say it's not the camera, it's the artist.
Both are true, but the camera really does matter and it always has. Nobody spends more time with their eye on a viewfinder than a movie first operator or DP and though they rarely own cameras, usually rent, they have their favorites and will go to almost any length to use them.
It's not unheard of to hear a dp absorb part or all of a cinema camera and lens package costs into their fees, just too shoot with the camera they are comfortable with.
It's the same for stills and the one plus for medium format is (at least for me) is I continue on with the same equipment for a long time. My dslrs, maybe 2 or 3 years, my mfd backs, easily 3 times that.
As far as reliability, my Phase backs have never had a repair and I've worked them damn hard. My Contax(s) just one repair where some assistant put a thumb through a shutter curtain.
My Canons and Nikons have all gone in for shutter failure, or focus adjustments.
For weight, I don't look at the camera, I look at the case and the difference between my Canon and Contax/Phase case is less than a pound.
Still, the only answer is test and decide for yourself.
IMO
BC
There is indeed a new price cut of 1,000 usd on the H4D (but it is not announced - you get it when you ask). Moreover, I hear that some dealers offer a little better prices to liquidate heir stock (to be sure their stock is out before the H5D ships).
So, I would recommend you the H4D40 at usd 14,000-14,500. A cheap second hand 80mm with low use, you can find easily and it should not set you back more than 750-1,000 usd.
For 15-16k, you will have a top DMF, which will hold its value for a good time.
Do be tad cautious of some of other posts that you read, because with each new dslr with more pixels there are folks that tad seem to believe it is like a miracle machine, and some select others such as Fred seem to be on a rampage against all of medium format digital industry (while some of us are waiting for him to yet post a single good image he shot with his medium format back...).
Reliability of MFD cameras does not come close to that of high end 35mm DSLR cameras.
Repair costs for even the smallest things are expensive with MFD.
If you are shooting landscapes you should consider stitching. At least try it before you go for heavier MFD cameras that really only offer a small advantage
over a D800E. A simple 4 frame stitch with a D800E would give you better quality than a single shot with a MFDB. You would also have better shadow detail too.
Above is plain nonsense. I have not had one camera, back or lens break down over the past five years I have shot medium format digital. They are made for heavy and extensive professional use. I am on my third medium format back, in part because I first went with faulty designed ZD which I kept only for few months due to a problem related to its design. Since then I have shot Leaf and they are as durable as Phase One. I do not know about Hasselblad, they may also be same durable, I simply do not know. I am on my second Leaf because I knew I could trust their products for durability and to deliver top notch image quality which I cannot get with DSLR.
There is a significant difference and advantage in the raw files compared to dslrs. The files can be pushed more and do give a superior character. Sure, dslrs such as D800E have improved... and so have medium format sensors, thus both have if you look at newer generations.
The 44x33mm sensors can actually be bargains, yet nevertheless give unique character images compared to dslr. It is also the way you work an image. Medium format slows you down some, which improves your images because you think more before you press the shutter. When I went with Leaf I first choose the 28MP 44x33mm sensor because it was more cost effective than the 22MP 48x36mm sensor, and because it was one generation newer sensor, thus with slight improvements in ISO and noise performance. I was very pleased with that back indeed. Price is important when choosing, and I would recommend you to compare Hassy vs. Leaf and Phase One. The other side is support. Do purchase from a reputable agent that will back you, then you have support and also some warranty. My Leaf agent in Hong Kong is superb and even answer phone in evenings and weekends... and help out even when outside of warranty. Any problem, even if something I am missing on camera! Nope, I did not purchase my cameras from them, only my Leaf backs, but... they know by giving this support chances are I will upgrade in future because in part of their support, but also because Leaf products are stellar in durability and image quality. I did upgrade last year, at free choice, not by them marketing, which is loads of different from all marketing of dslrs, including all articles you read on internet of dslrs...
Since 1 year I shoot 80MP Leaf AFi-II 12 with a 645 sized sensor on a Rolleiflex Hy6 camera. The Hy6 camera is arguably the best camera for medium format digital and the lenses are likewise reputed as best. It can be worth checking out. Else, as mentioned in above the choice is individual. And no... stitching dslr frames does not yield same image quality as medium format digital... there is much more than pixels. Best is to like said in above to make a demo, have them explain the differences to what you are used to shooting and for you to inspect it yourself, and shoot actual subjects and even PM folks in these forums to send you some sample raw files from their actual shooting. Then you will get to work on a file shot by someone who is used to handling the camera and back.
Leaf files are known for a more film like character, but are else on pair in image quality with Phase One backs (or is it the other way around??). Though I personally have a liking to Dalsa sensors that I find to have better characters. All Leaf backs have Dalsa sensors. Newer Phase One backs have Dalsa. I also believe some Hassy may use Dalsa, but I am not sure. I use Capture One Pro for processing, and it is the best for Leaf and Phase One files since Phase One owns also Leaf, and since both Phase One and Leaf engineers are involved in work for Capture One. For Adobe they are not...
Personally, I would not think of trading medium format digital for dslr, no way. I much enjoy my current tool because it helps me get better images and better image quality, but that is all it is; tool. Each of us need to investigate what works for us, and decide.
I shoot both landscape and people; andersloof.com. I actually like the larger sensor for that too, because it enables to control out of focus far better, thus brings yet another character. And the way to shoot with a Hy6 with its 6x6cm focus screen in wist level finder clearly beats dslr but also other medium format digital offerings.

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Best regards,
Anders