Ed Dozier
- Apr 19

Nikon Z8 versus D850 Autofocus Wars

When I got my Nikkor 500mm f/5.6 PF lens, I was excited to try it out with my 1.4X teleconverter (mine is the Sigma TC-1401). This would give me a 700mm f/8 lens. At the time, my best camera was the Nikon D850, which reviewers have praised for its auto-focusing capabilities. Outside in bright light, this 700mm combo worked just fine, but then a bird flew into the shade. Disaster ensued.

Nikon Z8 with 500mm f/5.6 PF and 1.4X teleconverter

Nikon claims that the D850 autofocus system is the same as what’s in the D5 and D500 cameras, and focuses down to -4EV. In my own experience, I haven’t gotten even close to this. Additionally, they don’t specify how slow the autofocus gets when illumination gets low. I think that somewhere in the fine print Nikon mentions something about this only working with an f/1.2 lens, and I’m fresh out of f/1.2 700mm telephotos.

The Nikon Z8 and Z9 cameras are specified as being able to autofocus down to -7EV (-9EV in Starlight mode). I just know that with a real telephoto in actual low-light shooting conditions, it just plain works.

I quickly gave up using this unreliable D850/700mm combination, and instead stuck with the 500mm f/5.6 by itself. As much as you try, animals just don’t obey your wishes and stay in good lighting conditions. It occurred to me that I haven’t re-tried using this 700mm setup with my Nikon Z8 or Z9 cameras; big mistake on my part.

Trying to crop 500mm shots to what a 700mm combination (500 + 1.4X teleconverter) gives you is never as good. I’m not saying crops of the 500mm shots are bad, but the quality takes quite a bit more of a dip than using a teleconverter. With birds especially, it seems like you can never have too much focal length. Tracking that bird at 700mm is quite another story, however!

Before wasting time doing a potential known-to-fail test, I tried out the Z8 with the Nikkor 500mm PF with the 1.4X teleconverter on birds under heavy clouds conditions. Amazingly, the lens focused extremely quickly and didn’t appear to suffer from focus-hunting, either. The quality of light in these conditions can be really nice, which is why I’m interested in shooting like this in the first place. Beware of shooting flying birds against a cloudy sky, however; you risk getting nothing but near-shilouettes or else burned-out backgrounds.

Z8 with Nikkor 500mm f/5.6 PF and 1.4X teleconverter

The shot above is 1/2000 shutter, f/8, ISO 9000 with the 700mm combination. This shot hasn’t had any light or color adjustments, to demonstrate the quality of light in cloudy conditions. This light level equates to EV 9.4, and the Z8 focused the lens quickly in these conditions. The D850 does quite a bit of focus-hunting in these conditions, and successfully finds focus only about half of the time. The Z8 viewfinder is bright, while the D850 viewfinder is quite dim in this deep shade. Also, the D850 focus points away from the viewfinder center are even less sensitive and capable, although Nikon claims that 15 of the points support f/8 lenses.

I might mention that the Z8/Z9 cameras also have focus ‘detection’ modes, while the D850 doesn’t. I used bird-detection in the above shot, where the camera immediately finds the near eyeball of the birds. In addition, I no longer have to worry about autofocus fine-tune calibration, which is different for all of my DSLRs and different with/without a teleconverter, too.

I decided to do a comparison of the Z8 (equivalent to the Z9) and the D850 in cloudy and then indoors conditions. As usual, I do my testing by using a 120-frames-per-second video while filming the lens focus distance scale.

Test #1: 3 meters start, 100 meters finish, EV 11.5

The first test was to focus on a distant tree in cloudy conditions, so that the target had good contrast. I knew that both the Z8 and D850 could focus on this, but I was interested in both focus speed and any focus-hunting that might occur. I set the focus ring on 3 meters (10 feet), and took a video while the lens focused at about 100 meters.

A sample photo of this target was 1/2000s, f/8, ISO 2200 (EV 11.5)

The D850 took 52 video frames (0.433 seconds). I noticed that the D850 over-shot the target, backed up to 21 meters, and finally focused at about 100 meters.

The Z8 took 41 video frames (0.341 seconds). This camera had the lens hesitate at 14 meters, and then finished focusing on the target at 100 meters. Even the Z8 (and therefore the Z9) could stand some improvement in how it acquires the target focus, but I can’t complain about the 0.341-second result.

This amount of focus change is much more severe than you’d normally encounter in the field, where it would typically change focus over a few meters nearly instantly.

Test #2: 3 meters start, 8 meters finish, EV 6.6 (indoors)

For a much tougher test, I shot a medium-contrast target indoors with only some window lighting. A photo check here indicated 1/200s, f/8, ISO 12,800 for an Exposure Value of 6.6. The room I tested in wasn’t 100 meters long, so I settled for a target at 8 meters away.

The D850 totally failed to find focus, and just hopelessly cycled back and forth between minimum and maximum focus distance. No surprises here. And so much for that -4EV spec.

The Z8 accomplished the 5-meter focus change in 32 frames, or 0.267 seconds. Really, really fast. There was no hesitation in focus during this test with the 700mm combination. Also, this camera doesn’t care where you place the focus point; it works the same everywhere. That’s very impressive indeed.

Summary

The Nikon Z8 and Z9 cameras are just amazing in their focus capabilities in poor lighting conditions. You don't even need to worry about lower-contrast subjects. The DSLRS just can’t compete. Honestly, I thought the contest would be closer than it turned out to be. Using my 500mm with a teleconverter is no longer a problem under any but the dimmest of lighting conditions!