At just under 3 kg, the new tele is relatively light. The counterpart for the f-mount is a good 750 g heavier. In addition, it must be taken into account that there is now a teleconverter integrated. My 500mm is almost the same weight, but because the weight is further forward than the new 400mm, the 500mm seems to be a bit heavier. Due to the low weight, the 400mm is also very good for handheld photography. As usual with Nikon, there are 4 Fn buttons on the front of the lens. There is also an L-Fn button on the left side of the lens, slightly behind the tripod base. Next to the focus ring is an additional function ring for aperture, ISO or exposure compensation and a ring for resetting to specific focus positions.
The 4 buttons on the lens are a bit larger than on the 500mm f/4. I don't use the buttons very often, but they are very handy when filming animals and the bigger size makes them easier to use.
The L-Fn button on the side, on the other hand, I find a bit strangely placed. You can't really reach the button when photographing handheld and generally I don't know anything that would fit here. However, this could probably be due to the fact that I only had a little time with the lens.
I disabled the ring that you can set for aperture, ISO, or exposure compensation because I got to the ring too easily when shooting handheld and then changed settings unintentionally.
The front-most ring, on the other hand, I find very useful again. When I first read about it, I was a bit unsure about how exactly this ring was supposed to work and what the benefit might be. In the two days of testing, however, it turned out that the ring is quite helpful. You can rotate it a few degrees to the left and to the right and thus retrieve a certain, previously saved focus distance. The ring then turns back to the center with the help of a spring. If, for example, you are photographing at a location where birds often land in two different places, you can save these distances for the two directions of rotation. Meaning: If you turn the ring to the left, the lens will focus on one spot, if you turn the ring to the right, the lens will focus on the other spot. If two focus positions are not enough, you can also assign additional positions to buttons on the Z9.
So far, I've really only been able to rave about the lens. The only thing I'm not completely satisfied with is the position and feel of the focus ring. It's behind the ring for aperture/ISO/exposure compensation. However, I would rather have the two just the other way around so that I could keep my hand on the lens a little further forward. For birds in flight, in fact, I have developed a technique where I need manual focus, and there I noticed in the 2 days with the lens that the position of the focus ring does not suit me that well. With the 500, the focus ring is much better, although it should be noted that this lens has no other rotating rings. In addition, the focus ring on the 400 is not as easy to turn as it was on the 500. Of course, the focus ring shouldn't be able to rotate too quickly either, and perhaps it was also because the test lens was fairly new. However, I would have preferred a slightly easier rotation.
There are also two switches on the lens that allow you to turn the autofocus on and off, as well as limit it to a certain distance. So either 2.5m-Full or 7m-Full. I would also find a position of 2.5m-7m, as found in the Sony 400mm for example, interesting. From my point of view, this would make photographing birds in flight even easier.
The focus position ring, function ring, and focus ring (not pictured here) all have different textures. The four buttons are all around the front of the lens and slightly larger compared to my 500mm f/4.