ISO-invariance

Editors' note: This page has been edited from content originally published here on August 31, 2016.

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.

The 5D Mark IV isn't entirely ISO-invariant: pushing an ISO 200 underexposed by 5 stops by 5 EV in post-processing yields slightly higher noise levels than a native ISO 6400 exposure. An ISO 100 exposure pushed 6 stops fares even worse. However, above ISO 400, the camera does, for the most part, exhibit ISO invariance, meaning that you could underexpose a traditional ISO 6400 exposure by 4 EV by shooting it at ISO 400 (while maintaining the shutter speed and aperture for ISO 6400), and then raise exposure 4 EV in post. This technique would afford you 4 EV of highlight headroom, with little to no noise cost, relative to shooting at ISO 6400.

Compared to its predecessor, the 5D Mark III, this is a massive improvement. With the Mark III, one could not simply underexpose to protect highlights without paying a significant noise cost when boosting shadows in post, meaning you had to make your choices about which tones you wished to presere on the spot, at the time of the exposure. Even compared to the 5DS, the Mark IV shows vast improvements. It even slightly edges out the 1D X II. In a nutshell, the 5D Mark IV will be far more capable at dealing with high contrast scenes without the need for workarounds.

The 5D Mark IV will be far more capable at dealing with high contrast scenes without the need for workarounds.

How does the 5D Mark IV stack up against some of its other peers? Its performance is much better than any other offering from Canon, but it's still not quite as ISO-invariant as the Nikon D810 or D750, or even the APS-C D7200 for that matter (refer back to widget above as you click links). You're unlikely to notice these differences from ISO 400 upward, but below ISO 400, the 5D Mark IV, while competitive, does fall behind in performance.

What does this mean?

The Canon 5D Mark IV, like the 1D X II, represents a significant step forward for Canon with respect to dynamic range. While it still lags behind some of the best of its (even APS-C) peers, we can confidently say these cameras bring the massive improvement many Canon shooters had wished for in this department. The increased exposure latitude, and ability to shoot in an (almost) ISO-invariant manner frees up the photographer to make unconventional exposure decisions in challenging scenes to retain more tones than might have previously been possible. Ironically, this may have more of an impact on fast-paced photography than landscapes, the latter affording more time to work around camera limitations using techniques like filters, and bracketing.

The 5D Mark IV will handle scenes like the one above with more finesse than the 5DS did here. I chose a background exposure that placed the beautiful orange to yellow gradient close to clipping in the Raw, but that still meant a noisy and banded tonemapped foreground due to the limited dynamic range of the 5DS for this type of post-sunset scene. The 5D IV's increased dynamic range will bring flexibility for these types of situations that are less amenable to workarounds like graduated filters or multiple exposures. Photo: Rishi Sanyal

The ability to deal with camera exposure errors that are not caught due to inability to chimp in the moment, or to unabashedly decrease exposure to protect highlights as I've done above in the 5DS shot to retain the beautiful color gradient in the sky, is sure to be welcome by many (and, naturally, balked at by others).