Nikon F-Mount Adapter

bythom nikon ftz

FTZ adapter mounted on Z7 camera


Okay, let's step through things here. If you haven't already read my oft-updated article on about Nikon lens terminology, now would be a good time to do so. 

I'll step through the Nikon mount history a bit to see what's required for a "perfect" adapter for the new mirrorless system. I’ll talk about the actual FTZ adapter as we go, then sum things up.

The FTZ adapter is US$250, but will be US$150 when purchased with a Z6 or Z7 camera in 2018.

First, we had a physical mount (the metal bayonet). Because the new mirrorless system has a shorter flange distance and a wider throat opening, building a "tube" that connects the new Nikon Z mount to the old Nikon F mount is a simple enough job. There do not appear to be any restrictions at the pure physical level. (The Nikon 1 FT-1 adapter had some edge issues due to the large F-mount being restricted down to the smaller CX mount, but the opposite is true here.)

After the original physical mount, Nikon added AI (auto indexing), of which there are two variations (AI and AI-S). These require a tab on the (camera’s) F-mount that engages and moves with a tab on the lens as it is mounted (i.e. rotating the lens into the mount rotates the camera tab into different positions). The new Nikon mirrorless mount does not have this tab. In SLR and DSLR designs, this tab position was measured by the camera. With an adapter, it would require transfer of information electronically in order for the camera to see the tab position. 

The FTZ adapter does not have these tabs or the ability to measure the AI tab position automatically. Note that Nikon dropped AI indexing from many of the consumer DSLRs, currently including models up through the D7500.

As part of their move to automation, Nikon next added a mechanical aperture activation lever in cameras that physically engages a mechanism in the lens to stop down lenses during the shot (normally, they're held wide open for view and focus reasons). The new Nikon mirrorless cameras do not have this lever as the Z mount is all electronic (e.g., like E-type lenses). 

As with the AI tab, to support mechanical aperture activation an adapter needs to have a mechanical lever (though it could be controlled electronically). The FTZ adapter does have this built in. Nikkor F-mount lenses up through the G-type all use this mechanism to change apertures on the lens. (The high-end pro cameras also let you select aperture via aperture ring on the lens, but you have to make a custom setting to enable this, and the lens obviously has to have an aperture ring, which G-type lenses don't, though many D-type lenses do.)

Next, Nikon added electrical contacts to the mount (and lens). This is where things get a little complicated, because, over time, Nikon added additional contacts to support things like AF-I/AF-S autofocus, distance information for flash, VR, and relay information from teleconverters. Most recent cameras and lenses have eight such contacts, some lenses and teleconverters have extras, up to eleven. There have been subtle but real changes to communications across these contacts over the years. The new Nikon Z mount has eleven contacts. The FTZ adapter has the full set of eleven needed electrical contacts on the F-mount side, so in terms of electrical signals, the adapter seems complete. Indeed, the camera can use any CPU lens, which means some lenses such as the old AI-P ones work on the new camera.

Next, we have another mechanical part Nikon added with early autofocus lenses: a screw-drive arm that extends into the lens mount and is run from a motor in the camera. The new Nikon Z mirrorless cameras do not have a screw drive motor in the camera, nor does the FTZ adapter. D-type lenses with screw drive autofocus cannot focus using this adapter. Note that Nikon dropped the screw drive from many of the consumer DSLRs, currently including models up through the D5600. All AF-I, AF-S, and AF-P lenses do not require the screw drive. Again, the FTZ adapter does not have a screw drive. This makes it incompatible for autofocusing with non-AFS D-type lenses. The lens can be mounted and used with EVF manual focus confirmation.

As a modification that eliminated the mechanical aperture activation arm, we next got E-type lenses, which transfer aperture information between lens and camera electronically, and are thus basically a pass-through in order to support with an adapter. Pretty much all the DSLRs starting with the D3 in 2007 have had this support hidden inside the camera, even before we saw E-type lenses.

Finally, Nikon made a substantive change to the electronic signaling and communications when they introduced the AF-P lenses. Those changes wiped out compatibility with pretty much all pre-D7000 cameras, and even after firmware changes, there are still a few recent cameras that are left off the full compatibility list.

So how did Nikon do with their adapter? Did they create the perfect adapter?

  • AI/AI-S — Partly. Mounts and provides exposure control if camera set properly (non-CPU lens data). No rangefinder focus help.
  • Mechanical aperture activation — Yes.
  • Full electrical pass thru — Yes.
  • Screw drive focus motor — No. Not supported. This means that D-type lenses that aren't AF-S or AF-I are not supported for autofocus (though D-type lenses have rangefinder focus help; pre-D with screwdrive does not). So, AF-I, AF-S, and AF-P autofocus lenses are supported, but older versions of autofocus lenses aren't. D-type lenses with screwdrive have electronic rangefinder focus confirmation in EVF, though.
  • Electronic aperture activation — Yes. The new mount is also electronic aperture activation in design, so this was an easy pickup.
  • AF-P lens communication — Yes.

AF-I, AF-S, and AF-P lenses use phase detect autofocus exclusively when mounted on the FTZ Adapter (native Z lenses may use a contrast focus step followup). 

I should point out that I worry that Nikon has again made a mistake by adding a built-in tripod adapter that’s not removable. The problem here is that Nikon seems to be unaware how that became a problem on the Nikon 1 and its FT1 adapter, and I’m going to guess it’s going to be an issue with some Arca-Style plate usage and with lenses that have their own tripod mount that extends back near the back of the lens. Do we really need this tripod socket at all? 

It worries me a bit that perhaps Nikon put that tripod mount on the adapter because they think that the electrical contacts will be problematic if you mount a lens on the FTZ adapter and mount the camera on a tripod.

Sensor Shift VR is still performed with lenses mounted on the adapter, though only in three axes. Lenses with VR in them can add the other two axes.

Finally, someone asked if the adapter changes effective focal length or aperture. No, it doesn't. Nor does it change infinity focus capability. Adapted lenses sit exactly the same distance from the sensor as they used to, so there are no "effective changes."

Some people probably want to know about other mount adapters (e.g. Canon to Nikon, Sony to Nikon, etc.). 

Here things are again interesting. Any DSLR lenses (e.g. Canon EF, Pentax K, and Sony A) could have adapters designed to work with the new Z system cameras. That's because there's enough space between the mount registration distance (mount to sensor) and in the absolute angle of view (edges of sensor to edges of mount) to accommodate an adapter. The all-electronic Canon EF mount seems like a natural for an adapter.

Mirrorless lenses, however, might be a problem. Nikon has chosen a shorter mount to sensor distance and a wider opening. There almost certainly isn't enough room to easily build an adapter that would put Canon EF-M, Fujifilm X, m4/3, or Sony E/FE lenses on a Nikon Z camera. Of course, other than the Sony FE lenses, none of the others are full frame, so that wouldn’t be a big loss.

This has some implication for third party mirrorless lenses, too: it means that it isn't necessarily a simple change that they'll need to make to mount their existing lenses on a Nikon Z camera. Some may have an awkward lip at the back to fit the larger Nikon mount if you just do a quick adaptation. Sigma, for instance, could do what they did with Sony FE, and just add a barrel to their existing DSLR Art lenses. The Zeiss Loxia or Batis and other Sony FE lenses shouldn’t be too difficult to modify, either. 

But, of course, there's the need to reverse engineer the lens mount communications, too, as Nikon is not releasing that information to anyone that I know of at the moment. I don't think it will terribly long before we see third party lenses for the Z system, but it's not going to happen as quickly as some are hoping. And the first third party lenses we see may very well be manual focus ones.

Nikon likes beating to their own drum and dislikes it when others join in. The Z mount is a new drum, and for the time being, only Nikon will be making any sounds.

Finally, one point that everyone should be looking at: the “focal plane” of a DSLR is actually a complex optical design. The thickness of the UVIR filter (and AA, if applicable), the setoff of the UVIR filter from the actual sensor, the depth of the microlenses and Bayer filtration, and the photo diode position and depth all play a part in collecting the photons from a lens at the right spot. You can have a perfect adapter but get less than perfect results if the focal plane optics have changed and your rear lens element isn’t aligning the light properly. 

So one thing I’ll be looking at closely is whether Nikon is maintaining the current optical system at the sensor or has made changes on this new system. We’ve already had a minor change with the flip to BSI in the D850, which has made some older wide angle lens designs perform a little worse at the corners, some a little better.

Correction: an earlier version of this article said the adapter would be US$100 with camera in 2018.
Correction: an earlier version said AI/AI-S lenses couldn't be used.

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