Dynamic Range

In most circumstances the Z7's image quality will be remarkably similar to that of the D850 (as you might expect). However, it's not quite fair to say it's the same.

Key takeaways:

  • In principle, dynamic range is comparable to that of the D850: one of the best performances we've seen.
  • However, striping and banding (caused by the addition of on-sensor PDAF) means the usable dynamic range is reduced.

Dynamic range is the range of tonal values that a camera can represent, from the brightest recorded tone to the darkest usable value. There is, of course, an element of personal taste to this.

Rather than just quoting numbers, we try to show the photographic impact. We do this in two ways: first, our Exposure Latitude test shows the effect of lifting the shadows of images shot with increasingly low exposure (as you would if you were trying to capture/retain more highlight information).

However, reducing the exposure increases the noise level, which makes it difficult to tell what's happening at the sensor level. This is where our 'ISO Invariance' test comes in. Here we shoot different ISO settings using the same exposure values. This means that any difference in noise must come from the camera. Between the two tests, we can see how tolerant the camera's files are to having addition tonal information pulled up from the shadows into the visible parts of the image.

Exposure Latitude

In many respects the Z7 performs comparably with the D850, something confirmed quantitatively in our collaboration with Bill Claff. This means it stands up well against the best of its immediate peers, and for the most part better than some other full frame rivals, with a caveat we'll get to below. There is, as you'd expect, a small noise benefit to shooting at ISO 64, rather than 100, simply because the camera can collect more total light at lower ISOs.

Look closely, though and beyond a 4EV push, a banding pattern starts to appear. You may not think that you push images by 4EV, but lifting the shadows or adding too much contrast, if you're trying to brighten the foreground of a sunset image for example, may have the same effect. And it may even be visible at print size, as the banding is easily visible in even lower resolution (8 MP) downsized images.

ISO Invariance

In terms of ISO Invariance, there's a visible noise difference between shooting at ISO 64 and brightening, vs natively shooting at higher ISO. This isn't because there's a lot of noise being added at ISO 64 (the result is at least as good, or noticeably better than its immediate peers). Instead it's because the higher ISO performance is even better.

The sensor uses a 'dual gain' design that at higher ISO uses a lower-noise readout method in each pixel (but at the cost of capacity, hence it not being used in lower ISO modes). From ISO 400 upwards, once in this higher gain mode, there's little benefit to increasing the ISO setting (you may as well keep the ISO at 400 then brighten your images when processing the Raws).

Even then, on the D850 the difference was small enough that there are times it's preferable to shoot at ISO 64, rather than 400, since this means you retain around two and two-thirds stops of extra highlight information. This benefit might outweigh the additional noise cost were it not for...

PDAF Banding and Striping

This image was shot at ISO 64 with the intention of brightening the model and the cityscape, but retaining the sunset - as you could do on the D850. However, closer examination, when trying to clean-up the masking around the model's hair revealed a banding pattern in the shadows.*

As you'll see in some of the images above, a banding pattern can appear if you try to pull darker tones into the image. The frequency of these stripes leads us to believe it's a result of the way the phase-detection rows of pixels are incorporated into the image (something supported by our collaboration with Bill Claff).

A 100% crop from the sunset image above. The banding is not especially pronounced but its repetitive nature can make it distracting.

Like all fixed-pattern noise, it's difficult to process-out, since most noise reduction algorithms are designed to suppress spatially random noise.

In addition to the banding in shadows, we've also occasionally - albeit very rarely - seen the same pattern in images with flare caused by a bright light source (a striping problem that we've seen on other cameras with on-sensor phase detection elements).

Look in the parts of this image showing lens flare and you can see the same striping pattern. The stripes are parallel to the long edge of the sensor so run vertically in this portrait-orientation image.

Again, the effect is not especially pronounced but there are times you may encounter it.

How much, if any, impact this has for you will depend on your photography. It doesn't happen in every image with a bright light source and, based on our experience with other cameras, may be lens-dependent. You also may not encounter it if you only make minor adjustments to your Raw files. However, it is something to be aware of and which shows the Z7 shouldn't be assumed to have 'D850 image quality.'


*This image was shot using a pre-production camera. However we conducted all other testing and confirmed the result using a final 'production spec' camera before publishing.