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Autofocus

The Nikkor Z 400 mm f/4.5 VR S is equipped with the VCM stepping motor. When joined with the Nikon Z7 its performance is completely noiseless but not especially fast. Running through the whole distance range and confirming the focus takes about 0.8-0.9 of a second, nothing impressive when it comes to a lens designed to capture dynamic scenes and situations. You should also mention the fact that you get a focus limiter at your disposal with a range from 6 meters to infinity. After switching it on you are able to shorten the focusing time to about 0.4-0.5 of a second.

After attaching the TC 1.4x teleconverter the mechanism remains noiseless but its speed decreases. In this case running through the whole range most often takes over one second. At the same time you can notice slight focus hunting in a form of short wavering around the proper position. Once again you can improve the focusing time if you employ the focus limiter and use the range from 6 meters to infinity - after that the focusing time amounts to about 0.5 of a second.

When it comes to the accuracy of the autofocus you can describe it in superlatives only. While testing the lens on its own, the mechanism practically always hit the point. After attaching the teleconverter the accuracy was slightly less precise but even then misses were rather sporadic. Of course, as we've already mentioned, sometimes you had to be patient. Finding the right position could sometimes entail a bit of focus hunting – going a bit further on the scale and returning to the right position.

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Photos below show clearly that the tested lens didn't have any problems with front or back focus either.

Nikon Z7, 400 mm, f/4.5

Nikon Z7, 560 mm (TC), f/6.3

Focus breathing

Focus breathing tests show reframing images as you oversharp them. We conduct the test by manually passing from the minimum focusing distance to infinity with the aperture stopped down; then we check how the field of view of the lens changed as a result.

After conducting a significant number of tests now we think we are also able to determine some reference points. A frame change ranging from 0 to 5% we consider to be low. Between 5 and 10% you can speak about medium levels. Usually such values constitute also the maximum efficiency level of any breathing compensation algorithms, present in some bodies. Between 10 and 15% focus breathing is high, above 15% its level can be called very high.

The test video of the Nikkor lens is presented below:

On the basis of the recording above, comparing freeze-frames before and after oversharpening, we can estimate that the breathing of the tested lens amounts to about 14%, so on the borderline between high and very high levels. In case of a telephoto lens with a real focal length of 397 mm it means an effective focal length change by about 56 mm. That's why correcting this aberration is so important for telephoto lenses – if it remains uncorrected the buyers get a lens with parameters that are in accordance with the official specifications only for focus set at infinity. Of course you should mention here another aspect of the breathing effect. The focal length increases when you move to smaller focusing distances so taking photos from a distance of several – more than a dozen meters you get a working focal length bigger than these declared 400 mm.