Extended ISO

The following examples refer to the results of examining the behavior of still photos of the Nikon Z6 (Firmware 3.6) at 14-bit uncompressed RAW 6048 x 4024 developed in Capture One 16.3.2.32 and RawDigger 1.4.7 on macOS Sonoma 14.1.2.

Highlight Recovery

To achieve the same light quantity, shutter speed was adjusted accordingly by half step increments. Looking at highlights outside the window, we can see ISO 400, 200 and 100 preserve the same amount of detail when pulling down exposure by 4 stops in Capture One. Extended ISO 50 ‘Lo 2.0’ shows clipping at around 1 stop earlier as seen in the lower right hand image, cutting a significant amount of dynamic range.

Note the lack of detail blown out around the house roofs, not simply the lower white point.

It would be easy to conclude now that Extended ISO has no benefit, but we must now consider noise levels in the shadows.

Shadow Recovery

First we must completely disable Sharpening, Noise Reduction and Lens Correction in Capture One to achieve an unaltered RAW file (Base Characteristics must be applied; the Nikon Z6 ProStandard ICC Profile and Film Standard Curve were chosen).

After rising exposure by 4 stops the shadow noise difference between Extended ISO 50 and even ISO 100 is significant.

Conclusion

1) Pushing and pulling an image by + /- 4 EV is not practical in real world terms and a photo is generally considered incorrectly exposed if such edits are necessary, therefor these examples are issued more to illustrate a point. That said, also in the real world are times where a client enjoys a photo even though it’s rather under/overexposed and you must do whatever it takes to recover it because the scene content itself is captivating. In these scenarios you’ll take every bit of dynamic range / low noise headroom as one can get.

2) Images are not viewed at 400% zoom, so even though noise levels seem significant at these magnified levels, they are all but indistinguishable from each other while viewing scrolling through your phone at 100%.

3) Go take a meaningful photo.