Exposure Latitude

In this test we look to see how tolerant of pushing exposure the GX8'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 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.

The GX8 shows similar performance to its Micro Four Thirds competitors - which is a good thing, as most modern mFT cameras exhibit very low levels of read noise that allow them to sometimes match performance of some larger sensor cameras (more on that below). The GX8 exhibits an expected increase in visible shot noise with progressive pushes, but even after a 3 EV boost, noise is acceptable and appears pleasantly random. There's a hint of banding at 4 and 5 EV pushes in the darkest regions of the image, but it's fairly subtle - and similarly present in the PEN-F. Overall exposure latitude is similar to what we saw with the Olympus E-M5 II. DXO tends to place mFT cameras at around 12.5 EV base ISO dynamic range, and we expect the GX8 will measure similarly.

Differences in sensor size and base ISO limits our ability to directly compare this performance with larger-sensor cameras. In a nutshell, though, a similarly performing larger sensor will always do better, but a poorer performing larger sensor may actually do worse. For example, the larger APS-C sensor in the Nikon D7200 far surpasses the dynamic range and latitude of the GX8, when compared by the degree to which they've been pushed. However, the Canon 70D performs slightly worse than the GX8. Because the APS-C cameras have a base ISO of 100, they received 1 EV more light in these comparisons (on top of the 2/3 EV additional light from their larger sensors). That means that despite the GX8 receiving nearly 2 EV less total light, it at least matches the 70D. It outright trounces it when compared at the same shutter speeds, despite receiving 2/3 EV less total light (it's still behind the D7200, though, when compared this way).

ISO Invariance

A camera with a very low noise floor is able to capture a large amount of dynamic range, since it add very little noise to the detail captured in the shadow regions of the image. This has an interesting implication: it minimizes the need to amplify the sensor's signal in order to keep it above that noise floor (which is what ISO amplification conventionally does). This provides an alternate way of working in situations that would traditionally demand higher ISO settings.

Here we've done something that may seem counter-intuitive: we've used the same aperture and shutter speed at different ISO settings to see how much difference there is between shooting at a particular ISO setting (and using hardware amplification) vs. digitally correcting the brightness, later. This has the advantage that all the shots should exhibit the same shot noise and any differences must have been contributed by the camera's circuitry.

In the midtones, we see the camera behave much like any ISO-invariant camera; noise levels remain largely the same as files given the same focal plane exposure, but progressively lower ISO settings, are pushed 1, 2, and 3 stops. This means that instead of using a high ISO setting in a contrasty scene, you can decrease your ISO setting while holding your exposure the same. Although this will lead to a conventionally underexposed Raw file, you can selectively brighten the shot later in post-processing with little noise cost compared to if you'd used a higher ISO setting to begin with.

That said, if we look further down the greyscale, we do see that as exposure levels near the noise floor, the camera's electronics do contribute a small amount of noise that manifests itself largely as magenta color noise. This places some limits on the ability to continue using a low ISO in low-light situations, with the intention of processing later to protect the highlights, but shows there is still a good degree of flexibility.

e-Shutter

The GX8 shows a marked improvement in electronic shutter (e-Shutter) performance compared to, for example, the G7. There appears to be no dynamic range cost to e-Shutter vs. a mechanical (standard) shutter: ISO 200 pushed 3 EV appears the same regardless of the shutter mode used. There's essentially no noise cost at all to using e-Shutter: high ISO noise levels and base ISO dynamic range are indistinguishable compared to standard shutter mode. The same cannot be said for the G7, while the PEN-F performs similarly to the GX8, albeit with a magenta cast in e-Shutter shadows.

We're increasingly seeing this parity between standard and electronic shutter performance with modern sensors (the Sony Cyber-shot X100 IV, for example), and it bodes well for the complete replacement of mechanical shutters (a certain eventuality, in our opinion).