A few things are different in the Z-mount than Nikon DSLR and SLR users may be used to, so I outline those here:
- There's now a clear designation of lens quality. Nikon uses the term S-line (and the S abbreviation after the lens specification) to signify their top quality lenses in the Z-mount. While Nikon doesn't specifically say what is required for a lens to get such a designation, it's clear that when they said "S stands for superior"—they also said "special" and "sophisticated"—that this is backed up by the evidence so far. In the F-mount, Nikon didn't have a clear designation of the optically better lenses, while Canon did with their lenses (L lenses were the upper lens lineup). That said, all the Z-mount lenses to date have been quite good, it's just that the S-line lenses have been at the top of the heap. Consistently so.
- We've moved (mostly) to stepper motors. Nikon used a variety of motor designs in the DSLR lenses, including wave motors. AF-P lenses in the F-mount were a recent addition, and use stepper motors. As it turns out, they were foreshadowing of what we find in the Z-mount. Why a stepper motor? They are fast and have high position discrimination, a killer combination (AF-S lenses tended to be fast, but sacrificed some positioning discrimination).
- A single focus element group is no longer guaranteed. Another change in focus is that some of the higher end Z Nikkors have two sets of lens elements that move independently for focus (and thus have multiple stepper motors). That adds a layer of complexity internally, but it also means incredible focus speed. The 26mm f/2.8 moves all the lens elements during focus, by the way.
- Focus is fly-by-wire. There's no longer a mechanical coupling between the focus ring and the internal focus elements (except for the manual focus 58mm f/0.95 NOCT). This makes for a very smooth focus ring, but it also means that manual focus can sometimes be frustrating. Nikon has added the ability to control the way the ring interacts for manual focus, but make sure that both your camera and your lens have the latest firmware, or else you may find that you don’t have all the options available.
- Focus is forgotten when the camera powers down. There's no guarantee that if the camera hits its Standby timer or if you turn the Power Switch Off that the lens will be in the same focus position when you return to shooting. Update: the Zf, Z6 II, Z6 III, Z7 II, Z8, and Z9 can be programmed to remember focus.
- Lenses are quiet, but not completely silent. Both focus and zoom can trigger very soft sounds as the motors reposition elements, and those sounds can be picked up by on-camera microphones when you're shooting video.
- The focus ring can be reprogrammed. (Some lenses have a third ring, which can also be programmed.) Unfortunately, right now the choices for customizing the focus ring are limited: Focus (M/A), Aperture, Exposure compensation, ISO compensation or None. Reprogramming the focus ring takes away what I feel is a useful function (manual override of autofocus; remember, we can one-button magnify our viewfinder to get precise focus positions).
- Focus breathing is typically low. Change of focus plane doesn't tend to change what's at the frame edges. Note that some of this is by lens design, but some is by correction in the camera.
- Lens corrections may be locked in. For example, on the Z50 or Z50 II with the kit lens, Auto distortion control is not user selectable, it's always on. Plenty of other examples abound. Generally, this seems to be true of lenses with a high degree of linear distortion in the design. But there's another bit, too: with the Adobe ACR and Lightroom, you can't turn off the corrections if they're enabled in the camera.
