This is an issue that recently occurred to me, and I have not found any mention of it so far: There are four mounts that I have little knowledge about. So far, the "common" mirror-less mounts (M4:3, Sony E, Pentax Q) will freely take "foreign" lenses. That is to say if you use even a cheap adapter, you can mount a Nikon or Canon lens and the camera does not do anything that I would not expect. I can use Auto Shutter Speed and Auto ISO to get reasonable auto-exposure. In some cases, I can even go further and adapt auto-focus and auto-aperture, but that gets pricey and sometimes pretty slow. But it can be done. So, what about Nikon Z, Canon R and Canon M mounts? We know that a Nikon F lens can be stuck on a Nikon Z with their special adapter and except for "screwdriver focus" the camera will make good use of it. What happens if I get a cheap Pentax SLR adapter for it (if there aren't any yet, there will be)? Will it all be similar or does the camera become crippled? What about one of the two Canon mirror-less mounts? I expect the Canons to be crippled because the EF mount did something like that. This is why you need adapters with special "chips" to get the Canons to accept the off-brand lenses. The same question goes for the Leica mount, though it has been around longer. I don't know anything about that mount, except that Leica cameras have been using it for a long time now.