I really wanted to stop and go practice my guitar playing, but I just can’t leave this alone. I got a variable neutral density filter so I could do a SNR vs ISO series at 1/30 of a second, only with the green count around 500, which is Zone III with a 14-bit ADC.
Same as the previous Zone VI plots, 16 samples per setting. ISO 100 gets f/2.8, ISO 200 gets f/4, ISO 400 gets f/5.6, and so on until ISO 6400, which gets f/22. Variations in aperture and shutter speed are corrected for. Since we’re closer to the noise floor, I subtracted the noise floor at each ISO from the signal for the SNR calculation. It didn’t make any visible difference except at ISO 3200 and 6400, where the changes were slight. Here’s the SNR vs ISO graph:
It shows the SNR falling off like the Zone VI graphs from before. There is no gain in the shadow noise from turning up the ISO level on the camera versus cranking up the Exposure slider in Lightroom.
Here’s a look with the half-a-stop/stop slope subtracted out:
At ISO 6400, the downward kink is mostly due to the inherent rise in the noise floor as you turn up the ISO setting, and a bit to the subtraction of the noise floor from the signal. It’s clear that there’s little advantage in shadow SNR to be gained from increasing the ISO on the D4 over 100, and none at all over ISO 200. The equivalent Zone VI graphs presented a few posts ago indicated that there was a tiny gain up to about ISO 400.