I owned the D810 a few years ago and did much work with it. Where it beats the pants off the D800s is in its video capabilities. But I struggled to get some of the Nikon lenses I was using at the time to focus correctly. They liked to focus just a little further back than I would have liked. We went round and round with the fine-tuning dance and, to be fair, most of the lenses worked pretty well after we spent an entire weekend coaxing them into compliance. The shutter in the D810 is quieter and sounds off at a lower (hence more pleasant) frequency. But when it comes to ease of use and image quality there isn't much difference between the older models and the D810. But here's where the "working commercial photographer" rationale comes into play; I could buy two D800 series bodies, in good shape, for the cost of one D810 body. I still believe that no professional image maker should go on a paid assignment without a back up body. And the best back up body is one that is nearly identical to your primary camera.
Since I already own another complete system (two Panasonic GH5's and a bag of lenses) I wasn't in a hurry to drop $6800 on a couple of D850 bodies, or $4,000 on a couple of used D810 bodies when I could have two D800 series bodies for only $2,000. The buffers in the newer cameras are probably better but I'll never know because I'm not a sports photographer and just use single frame advance.
I am, sometimes, interested in being a low light photographer but when I went exploring on DXO Mark I found that the older d800's are within a gnat's whisker of matching the high ISO performance of both newer bodies. Not much of a difference in the quality of the raw files either....
All in all, the more I use the D800 cameras the more I like them. So much so that they are the cameras I packed up in order to do a P.R. shoot at the Fairmont Hotel at midday and to also haul down with me today to Matamoros, Mexico for tomorrow's photographic assignments. In fact, if all goes well I intend to shoot most of my work tomorrow with the D800 and the 24-120mm f4.0 VR.
I hope I get smarter someday. I decided to drive down here to Mexico. I grabbed a rental car from Avis, packed it up with photo goodies and headed over to the Fairmont Hotel to photograph the Boys and Girls Clubs of Austin Spring Luncheon (a nice fundraiser). I used the D800 and the above mentioned lens, along with a manual flash to cover the event. I was floored this evening, when editing the take, to see that what I saw on the rear screen of the camera as I chimped through the job matched what I ended up with in post production almost exactly. A first time for everything.
But back on topic. After wrapping up the event around 1:30 I got in the rental car and started the long trip to Brownsville, Texas. With one stop for nature and one stop to get a Whataburger hamburger with jalapeños it took right at six hours and fifteen minutes of steady, more or less 75 mph driving. That's a lot. And that only gets one halfway across the state (measuring from north to south). I logged nearly 400 miles today! No frequent flyer miles, no bags of peanuts but no groping by the TSA and no idle time sitting stationary on the tarmac.
We've got an early call tomorrow and we'll shoot all day. I'll get back to the hotel, eat dinner and crash. But if I can get myself out of bed by 5:30 am I'll have a fighting chance of getting back to Austin on Thursday just in time for the noon swim. Won't that be nice?
The short answer to my reader is that the D800s do everything I need from them and they handle really well. I'll save the bucks and see what Nikon launches in the Fall. Night....
