Here are a series of D810 raw histograms of a dark field at selected in-camera ISO settings. The field I chose was the back of a Sigma 50mm f/1.4 DG lenscap. To make sure it was really dark, I set the lens to f/16 and the exposure time to 1/8000 second. I used single shot mode, which makes a difference on Sony cameras, but has not had an effect on past Nikons. I turned black point subtraction off in RawDigger to make sure we got the whole histogram. I set the camera for 14-bit operation , and used lossless compressed raw. High ISO noise reduction was off.
Comments follow each histogram.
Nice, tight grouping. All 14 bits are present and accounted for.
The dropout in the blue channel is because Nikon uses digital white balance pre-scaling.
You can see that the histogram is Gaussian, and both the red and blue channels show the effects of digital white balance pre-scaling.
More of same. Bored already? Just wait.
At ISO 1250, we start to lose the 14th bit, even in the un-pre-scaled green channel. Note that it hasn’t dropped out completely, though.
The incomplete combing in the green channel continues. Now it looks like all three channels are clipping at an ADC count of about 540.
The clipping continues, and will until the end of the series. Now we have completely lost the 14th bit.
More of same.
We’re starting to lose the 13th bit, and the clipping is extreme — even more than we see at higher ISOs.
At ISO 8000, the D810 is a 12-bit camera. The clipping level has dropped to about an ADC count of 480.
At the highest non-push ISO, we have some strange partial combing. The clipping level has dropped further.
All this indicates more raw processing than I usually see on Nikon cameras.