I have both cameras, so I think I can offer the most comprehensive comparison between the two.

First of all, they are both lovely cameras, and to suggest one is clearly better than the other is frankly baseless. I hung on to both because I can’t bear to let either one go – an expensive proposition no less, as I have a significant investment in glass for both systems.

What I have come to realize is that both systems are a compromise on some level. Since Nikon upgraded the firmware, the differences in AF performance have closed significantly. It now really comes down to glass. In a studio test, with both mounted with their respective 70-200′s, the D800 was superior, but the 5D3 performed perfectly.

When comparing both with the latest 24-70s, the Canon LII lens is superior until F5. At that point, the D800 pulls away.

Generally speaking I have to be more careful with AF on the D800. It is still not as good as the Canon AF system and the 36 mpx resolution is very unforgiving on AF accuracy and motion blur.

On the 5D3, I have to really cautious about exposure. One can get pretty lazy on the D800, given the latitude one has to fix problems in highlights and shadows. Not so on the 5D3. In fact, when it comes to back lit subjects – especially blonde people or bald, the D800 smokes the 5D3. The clipped highlights on the Canon files are beyond salvation. The D800 copes really well in general.
As for pushing shadows, well, we already know that score. So
The 5D3 is definitely a better generalist camera and I tend to use it more often – mainly out of practicality. The raw files are obviously smaller and more manageable so it’s better suited to every day needs.

On the other hand, the D800 files always give me a buzz when I open them for the first time. I don’t get this rush with the Canon files. The Canon cannot touch a D800 file that is perfectly sharp. I can spend ages inspecting a landscape shot looking at all the details – faces on people I didn’t even know where there.

I tell you, i am D800 user now, i was 5D2 before. I am absolutely not a faithfull brand guy, i just want the right thing for my money so i give you my most objective observations:

First of all, i tried all cameras. the 5D3 is the most delightful camera to use i have to admit. AF is snappier and accurate like a tamed dog. menus are as always more clear, the lcd is better and i personnally prefer the canon colors. jpegs out of camera are better (i don’t care i shoot raws). the handling seems better to me, a surprising improvement compared to the mark II i owned. just would love some more high to fit my little finger. but as said, the color noise and banding effect at 100 isos is just unbelievable, unconceivable.

The D800 shows somehow A BIT more noise, but after post processing the raw files match the same level as 5d3. the wide dynamic range is a huge improvement! you don’t have to choose anymore between highlights or shadows. you can recover that easily dark shadows or highlights where the canon can’t. The AF grab target in extremely low light situations and you can have a VERY useful AF illuminator in total darkness coupled with AF red light in the viewfinder. Also if you read some more serious review in some rare occasion 5D3 can show moiré when D800 doesn’t. seems weird but true! the nikon does also show some in some occasion.

now if you really want to spit on nikon, as i told you i’m not a faithfull customer, i give you some real reasons. but there are none directly about image quality.
first of all, the D800 suffers from minor bugs and lonngggg image treatment especially using the live view. Digit 5+ processor is faster than Expeed nikon. the battery life is better on the canon. if you take time to use the lcd screen the autonomy falls from 750 to 450 images! this is ridi-nikon-culous. while my 5d2 handled close to 850 in the same conditions. it is said also the case for new canon products but not as bad and i heard for such new norm in japan, but i guess it is to sell more batteries! the new AF system should indeed be tested by dxo, who i presume are using live view mode which is perfectly accurate on every camera. lots of d800 and certainly d4 from the first series (like mine..) suffers from the same left focus issue, and in my case a terrrible backfocus in the center issue making lenses unusable under 2.8 aperture or at the risk to miss 50% of your shots with wide open primes. the AA filter seems to me sometimes a bit too strong, making some fine details not as sharp as you would get unless you close your lens at 4-5.6. yes… they had to do that to justify the existence of a D800E after all!

Now you have real stuffs about nikon. and i don’t even mention the fact that my camera came back from repair with left focus issue fixed but with a damn front focus in the center now… -_-’ but again about IQ itself, when you can get your shots accurate, canon and their 5d3 -as we say in french- “went to pick up strawberries” while nikon and sony made a piece of art with this 36 Mpix sensor.

That said, if megapixels doesn’t count, dynamic range does. a lot! and i’m really looking forward to see my camera fixed. if i’m still not 120% satisfied of it i will just have to consider selling it as long as its price is high. and at this moment will looking maybe forward to the so rumored canon 5Dx 39-46 Mpix with a non dissimulated pleasure.

Also i would like to remember you not to forget Nikon might be not your real ennemy on a long time term. fuji and its Xtrans sensor from the Xpro one are from one part the BEST in term of reproducing skin tones under everykind of light, but also capable to match if not outperform iso noise even at 12800 from CANIKON on a ridiculous APS-C sensor! of course, without AA filter and moiré free and this, on a 1500 euros camera. which is btw in the same category as a 5000 euros leica M9, precisely outperformed in everything. ah.. leicaists are bying leica because it’s leica i forgot.. since rumors are talking about a X-pro2 full frame, there is something to be worried about your favorite product, then you will have to accept the superiority of another brand.

You simply appreciate the 5D Mark III over Nikon D800, so do 90% of the professional I know who shoot fashion and beauty for a living for Vogue and other high-end magazines

That’s as much due to legacy reasons as any other. Investing in systems in pricey so there’s little incentive to change other than for a very good reason. After all, professionals who shoot fashion and beauty for a living for Vogue and other high-end magazines would do most of their work on Medium Format anyway.

I think the amazement at Nikon need their heads examined. Why they refuse to stick an D600 sensor in a D800 body and create a true D700 successor s beyond me. The D600 is a nice option, but it is too hampered.

Surely they must have figured out that not all D700 owners are upgrading to the D800 because the D800 clearly does not serve the same purpose; thus they can’t seriously believe D800 sales would suffer if there was such a camera.

I’ll keep the D800 for studio etc, but Nikon are are pushing me to invest in a 5D3 and lenses because there is no real D700 successor. It is infuriating.

The AF on the 5DIII is much more robust and predictable and this is probably the single most crucial factor between these bodies.

Colour wise, I don’t feel that either is perfect. The 5D is kinder on skin tones but produces a garish magenta hue. The D800 handles reds much better but has the yellowish hue. Neither of which are a concern for me as they can be handled without a problem with camera profiles. Capture One does this really well.

If the 5DIII had a sensor like the one on the Nikon D600, it would be the perfect camera. Having been a Nikon shooter, it was hard to ignore the difference in dynamic range. It’s not just about pushing shadows, it’s about capturing more tone and detail in skies.

In terms of high ISO shooting, the difference was small to insignificant. The 5DIII has a slight edge, but that has more to do with AF accuracy and precision than sheer noise handling. Personally, both handled ISO6400 very well indeed and I would only go above that in rare instances.

At the end of the day, the stand out issues were AF and lenses. Canon’s 24-70 (2.8) and 70-200 (2.8) are newer and therefore better than Nikon’s equivalent, as one would expect, but not by as much as I anticipated. In terms of primes, I compared the Nikon 85 1.4 vs Canon 85 1.2 and the Nikon 105macro vs the Canon 100 Macro. There wasn’t a lot in it, though the Canon primes were better at handling CA.

I came away deciding that I am going to use both systems for now. The D800 in the studio and the Canon for general use and weddings. It’s not ideal, as I would prefer sticking to one system, but for now, it’s the best way to cover all my bases.

Please Canon, move up your ass to produce sensors without banding or high read noise.

I have always been an avid Nikon user but last week I requested to sell off my Nikon gear and tomorrow, Monday, I will order a 5D Mark III and a couple of prime lenses, one of them them naturally the 50mm 1,2.

A final comment, I find the territorial pissings of Canon vs. Nikon fans quite ridiculous – People appreciate the history of each brand, and their product-range for their own reasons and needs. Why can’t we just accept that we all have different taste and demands. I have never heard professional photographers argue with each other IRL which system is better. One photographer bring a Nikon to the studio, the next a Canon. No questions asked, except holding and weighing the other system in their hands, both giving an appreciative nod to the other when handing the camera back.

Keep up the good work

“Canon has confirmed that, depending upon the shooting conditions, it may take slightly longer for the EOS 5D Mark III and EOS-1D X digital SLR cameras to acquire focus when using the Speedlite’s AF Assist Beam, compared with that of the EOS 5D Mark II and 1dx digital SLR cameras using the Speedlite’s AF Assist Beam. We are developing a firmware update to enhance the focusing feature for the EOS 5D Mark III and the EOS-1D X. The schedule for release of this firmware update will be announced shortly.”
http://forums.usa.canon.com/t5/EOS/5D3-AF-assist-beam-slower-focus/m-p/13107#M1450

so Canon 1Dx and 5D3 about 20 mp make Nikon loose nowedays altouch the body is more solid and qualitycontrol either.

It you like 5D3 not enough go to Phase One bud you must spent 20.000 as a start

kind regards

Here is a vid comparing the D800 to the Hasselblad H4D-40
http://www.youtube.com/watch?v=9UBTE4xpvpk

D800 vs D800E
http://www.youtube.com/watch?v=I3M0VHBFiek

The 5Dm3 is a phenomenal camera as is the Nikon D800(E), know your shooting style and pick your poison, the end!

the 5d3 has more cross type focus points…the d800 has a much better dpad than the fiddly controller on the 5d3.

Both are high end professional SLRs yet each one shine in some areas, no all. Therefore, you need to choose the one that is suitable for your own use & brings out the best in your shots.

I think people these days expect ‘all in one’ camera’s but seriously the true photographer would know the D800 is going to be targeted at landscape and studio photographers. The 5d3 clearly is a all in one camera that does most things well. Lets face it most wedding ‘togs’ either use D4′s or 5d3′s I’d really like to know how many serious wedding photographers out there use a D800. How anyone who does 3 weddings a weekend at say 1500 shots per wedding could edit these files is beyond me. Oh one more thing the DOF on the D800 is so small its incredibly hard to master in a fast paced situation. Do yourself a favor and buy a 5d3 That Af system is worth it alone. Unless of course you have the money for a D4 or a 1Dx

What a bunch of amateurs.

http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/(appareil1)/795%7C0/(brand)/Canon/(appareil2)/792%7C0/(brand2)/Nikon

The D800e is also rated as the best sensor, D800 next, D600 3rd, 5dM3 way down the list at 13th.

http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Ratings

Portrait colour depth .. 5dmk3 is 15th .. Nikons entry level D3200 is rated better, lol.

I guess I am half expecting for my post to be either deleted or the Canon fanboys to moan that DX0Mark are way off the mark ..