In my last post I mentioned this shot that I had taken after the light had gone from the Okareka boardwalk so thought it a good opportunity to write about recovering an underexposed Nikon D500 image. My camera was in manual mode as usual and had been left at the settings used as the sun had set (1/2500s f5.6 ISO 400). A reflex shot at a pair of landing Grey Teal had significantly underexposed for the light levels rendering an almost black preview but I have found that the D500 sensor seems very forgiving and recovering exposure in Lightroom can achieve a pretty usable image. It seems to behave as a fairly ISOless sensor with little penalty for recovering exposure in Lightroom compared to shooting at higher ISO in the field. This ISO invariance seems to be a quality of a number of Nikon and Fujifilm sensors and I have had similar experiences with files from my Nikon D810 and Fujifilm XT1.

If I had set my camera to shoot in the conditions I would have had to increase my ISO to 3200 and drop my shutter speed to 1/2000 as I was stuck to the maximum f5.6 of the 500mm f4VR with the TC14 teleconverter. The image quality in this file shot at ISO 400 and boosted 3+ stops in Lightroom is the equivalent of what I would expect from a file shot at ISO 3200 and is quite usable. 

This second image illustrates the same point but is a little different. It was again shot at the end of a session when the light was going but hadn’t quite gone, this time at Matata lagoon. The issue was photographing a Grey Teal in the last warm rays of sunlight. The “correct” exposure of the teal in duckweed could have been more than the 1/1600s at f5.6 ISO 800 except that I knew that if the bird preened and did a wing-flap the white underwing coverts/axillaries would be horribly overexposed and lose all highlight detail. Knowing that I could extract usable images from “underexposed” images of the swimming duck I was prepared and maintained highlight detail when it did co-operate with a wing-flap.

For a good article explaining more on this see ISO Invariance Explained on Photographylife.

Both sets of photos taken with Nikon D500, Nikon 500mm f4VR and TC14 teleconverter.