The Newest Nikon Hunts an Eye Most Cameras Ignore

A fish does not have an eyelid, and it does not hold still for you. It has no iris you can read the way you read a dog's or a bird's, and under glass and water the light bends wrong. That is the eye Nikon's autofocus engineers set out to find.

Nikon announced the Z5IIC on September 28: a full-frame mirrorless body built around accessible handling rather than a new sensor or a new mount, the C in its name standing for compact. Buried in the announcement, with none of the fanfare that goes to a megapixel count, was a new subject-recognition mode trained specifically on fish.

Subject recognition works the same way whether the target is a face, a bird, or a fish: a model is trained on a large set of images of that one kind of eye, learns the pattern that separates it from everything else in the frame, and then holds a focus point on it as it moves, even when it is small, side-on, or half-hidden by a fin. A human face gives the model a lot to work with: skin tone, brow, two eyes roughly level. A fish gives it almost nothing — a flat silver body, no fixed expression, an eye that can look identical to a bright reflection on scales. Training a model to tell the two apart, at speed, through a tank wall, is a genuinely different problem from tracking a jogger's face, and Nikon built a mode for it rather than folding it into an existing one.

Digital Camera Watch's own tester took an early Z5IIC into an aquarium for a review still in progress, and reported, plainly, that the autofocus held on a fish's eye through the glass more reliably than she expected — not a verdict, a note from someone who had the camera in hand.

I have not had a Z5IIC in my hands, and I am not going to tell you what its autofocus does until I have put a card in one myself and pointed it at something that is trying not to be photographed. But I will be at Shinjuku's aquarium before the week is out, and I intend to find out whether a camera really can find an eye that nature built to disappear.