I'm sort of with DJO, Nikon should allow the use of non-AI lenses on their higher end DSLRs.

As some background early Nikon lenses had a fork on the top of the lens that would engage a pin in a clip-on meter or a photomic head. This told the light meter what the lens was doing. These lenses were a bit of a nuisance to change because you had to set the aperture to f 5.6 when you put them on the camera so that the fork and the pin would align and engage.

The next step were the "AI" lenses (automatic indexing). The camera had a pin in the mount that protruded into what was the base of the lens, the AI lens mounts had areas of the base (that was the f stop ring) missing to receive the pin. As the f stop was changed the pin would follow the movement. In the case of the TTL (photomic head) meters, I don't think they actually knew the f stop, but it knew how many stops down it is from what the meter is look through. Note: the AI only has to do with the f stop information being transmitted to the meter, nothing to do with manual or automatic.

For several years after AI lenses were introduced, the cameras with the AI pins all had the ability to press a release button and fold the AI pin out of the way allowing the use of non-AI lenses. Somewhere around the F4 or F5 Nikon stopped having the AI pin release as standard, but it was available as a repair option.

Later on with more and more electronics the actual f stop were known.

Back to the OPs comment, it doesn't seem like the kind of thing an adapter would fix, anything in between would change the distance of the lens from the sensor.

Now for the politics. I find it INEXCUSABLE that Nikon doesn't at least have available the AI pin release option for the higher end DSLR cameras. I for one have several lenses and bellows that I would like to play with on my D700 or D810. I once mention this problem to Nikon and I received a very curt response telling me that maybe it is time to get some newer lenses. I have many newer lenses but I don't want to have to re-buy all of now-and-then (eg. 1000mm reflex, 28mm PC, PB5 bellows) lenses that I have. I'v e given up any hope for the invasive fish-eye with digital.

There is no shortage of opinions (or discussions) about the Nikon DF. Good, bad or indifferent, I say to each their own. That notwithstanding, seemingly, neither is there a shortage of demand.

I think that part of the DF appeal, perhaps a large part, is the capacity to use non-Ai manual focus lenses. My question is this: Why Nikon, an enterprising third party manufacturer, or someone in their garage hasn't come up with a replacement lens mount or adapter kit for other Nikon camera bodies, using a design based on the Nikon DF or Nikon FM?

Of course not all Nikon camera bodies are the same size, but the distance from the front of the lens mount to the film plane or sensor will always be the same.

This might be a crazy idea, but it wouldn't the first time a completely crazy idea made a lot of money.

There is no need to need an adapter for non AI lenses simply have someone AI your lenses , if not do them yourself . I have done 2 myself a 55mm 1.2 , a 1.8 85 , its not that hard its just a notch that you create with a file , its the placement you need to find on the internet...The beginning and end it notch is critical that is what tells the camera how wide open it is . Without the notch it can mash or deform the the feeler pawl on the camera ,it has absolutely nothing to do with the contacts on the camera .......