I have long recommended not using the GFX 50x ISO settings above ISO 1600 unless necessary to get adequate finder and preview image brightness. Yesterday, I reported on pushing files exposed at ISO 1600 by three stops in Lightroom Classic (LrC) and compared the results to files exposed at ISO 12800. There were white balance differences, and the tone curve appeared to be somewhat different, but I saw no reason to change my recommendation.
But then I had a thought. We know that the GFX 50x stops increasing the gain applied to the raw data after ISO 1600, and lets the raw developer perform that operation. But what if the raw developer is smart enough to ignore or modify the instructions to apply gain and have highlights that would be clipped if the gain were applied be salvageable?
I made two exposures with a GFX 50S and the 63 mm GF lens. The first was an ETTR exposure at ISO 1600. The second was the same exposure, but with the ISO set to 12800.
The two images, developed in LrC with default settings:
I then applied a three-stop LrC Exposure pull to the ISO 12800 image:
I’ll repeat the ISO 1600 Image so you can compare the two more easily:
There are white balance differences. But the highlights don’t look blown in thee ISO 12800 image. Let’s take a closer look at an area with some specularity:
The ISO 12800 shot looks a heck of a lot better than it would if the raw data were overexposed by three stops.
Let’s look at a shadow area:
I am forced to retract my advice about ISOs above 1600: go ahead and use them, and if you find that highlights are blown in the preview images, don’t worry; you can probably save the files. I’m sure this will work with Adobe Camera Raw, but I don’t know about other raw developers.