It is a noticeable difference in sharpness from the D800, my regular way of sharpening seemed to be over the top with this camera.
In general terms I think the Nikon D810 is a step in the right direction, with the new shutter mechanism + electric front curtain it is a dream combo for the enthusiast landscape photographer.
The ergonomics is better as well, if just feels so much better in the hand, and even though it is just 20 grams lighter due to the difference in grip it feels more like 100 grams, and it is not a camera you tire of carrying in your hand for longer durations.
The optics of the 24mm F1.4G is very good, but you will not be able get the full power of the sensor with this lens.
With the D810 and the Sigma 50mm F1.4 Art things starts to get quite ridiculous.
I have seen sample shots paired against medium format cameras like the Pentax 645Z and the Phase One IQ250, the Nikon D810 does not get up to such heights as those medium format cameras with 50Mp sensor or higher but it is not far from it either and for the price of the D810 and what you are getting in terms of image quality it can almost be called a bargain.
I have shot 8 minute exposures where I could count hot pixels on one hand, also shot 3 hour timelapse sequences using high iso and 30 sec exposures with barely any thermal noise with the Nikon D800.
I noticed the same thermal noise with exposures as fast as 1/3., not as severe but I am not paying a premium for such a camera to only shoot from a quarter of a second and faster, I want to get clean images at least to 30 seconds as I am getting with the D800.
Adding the fact that it took me almost 5 hours to clean up the pixel mess, in the long run it is not worth it for me, hence I am returning the D810 and getting myself a D800E instead.
I did a quick few searches on the web to see if others was experiencing simular problems, and it did not take more than a couple of minutes to find the first, and then it just kept piling on.
Based on my own findings and what I have found browsing the web I decided that I do not want to keep testing out new D810´s and hope I get lucky and get one that does not have this issue in such severity so I decied to instantly go to the D800E, and the difference between the D800E and D810 in terms of image quality is minimal.
* Shoot a series of long exposures - 15s , 30s, 1 min, 2min, 3min. ( if the images are clean skip the next step and be happy) :)
* If you discover thermal noise in your images you can try a pixel remap of the sensor, I can´t take credit for this I only discovered it browsing the web, but I did notice less thermal noise between my own images after applying this.
Perform in camera sensor cleaning 2 times in quick succession, I have no idea why and how this works for thermal noise, but apparantly it does as I am not the only one who has noticed it taking care of a lot of the problem, maybe it is that rapid vibration of the sensor I can´t say, but it does work and really is harmless anyways, so should be no problem to apply.
* Repeat step one / Do a 5 minute exposure - If your images are then clean you should be fine, if they are not then I am sorry you do have a camera that does not meet expectations.
In summary the Nikon D810 really has everything going for it, all the changes implemented really makes shooting a better experience, I can´t say if the thermal noise is a universal problem or if it is just a few unlucky customers who have gotten cameras with the issue, but if it is then it would be the oil spots on the D600 all over again for Nikon and in all likelyhood even worse.
At a 13:1 magnification it was easy to see just how many bright pixels there was and if I say that every 5th to 6th pixel has elevated brightness value it is not far from the truth.
Nikon is in the works with a firmware fix for this problem, if it fixes it or not I can´t say, it will most certainly make it better, but at the end of the day it boils down to what can be expected for a premium camera like this.
Based on all the information I have found in this regard, there is no way I can recommend the Nikon D810 to anyone, if Nikon manages to fix it completely on all cameras then sure, but until then, absolutely not.