When the Nikon D5 arrived in our office on Friday we immediately wanted to answer a few questions: How is the low light performance? How good is the autofocus? How is the Raw dynamic range? After running our Exposure Latitude and ISO Invariance tests we've found that while the D5's sensor is clearly optimised for low-light image making, it represents a rather surprising - and disappointing - step backwards in terms of low ISO dynamic range.
Let's take a closer look, starting with our Exposure Latitude test scene. There are two pages in this article, so don't miss page 2, where we'll look at ISO invariance.
In this test we look to see how tolerant of pushing exposure the D5's Raw files are. We've done this by exposing our scene with increasingly lower exposures, then pushed them back to the correct brightness using Adobe Camera Raw. Examining what happens in the shadows allows you to assess the exposure latitude (essentially the dynamic range) of the Raw files.
Because the changes in this test noise are primarily caused by shot noise and this is mainly determined by the amount of light the camera has had access to, the results are only directly comparable between cameras of the same sensor size. However, this will also be the case in real-world shooting if you're limited by what shutter speed you can keep steady, so this test gives you an idea of the amount of processing latitude different formats give.
Even at a modest 3 stop push, we see the D5 has already contributed a considerable amount of noise to its low ISO images compared to the 24MP D750. After a 5 stop push the gap widens, with the D750's 5 stop file looking more like the 3 stop file from the D5. In fact, the D5's performance closely resembles the performance seen from the, with just a bit more color noise showing in the 6D's file.
After very aggressive pushes, an interesting series of bands appears at the top and bottom of the image. We don't know what's causing this additional noise (which appears to be confined to specific read-out rows) but it's interesting to note.