Does a Lens in Different Mounts Perform the Same?

Short answer: Generally, yes. 

We now have quite a few lenses from third party makers that appear in different lens mounts. It is fairly common for me to see the Chinese lenses coming in RF, M, ZF, Z, m4/3, and E mount versions, for example. I obviously can't review every mount version of every lens, but I do now have enough experience with the same lens in different mounts to make some generalized statements. 

  • Lenses that are manual focus with no electrical contacts — I've found no differences. Indeed, because I mostly use the Z mount cameras these days, I've found that I can use, say, a Sony E-mount version with an adapter on my Z cameras with virtually all such lenses. Plus, at times, I've had the same lens in a Z mount version to compare to. I've found no differences. 
  • Lenses that are manual focus with electrical contacts — I don't see variability optically, but I have seen some small differences at times that appear to be due to image stabilization. On-sensor IS (often called IBIS), seems to work at different frequencies and assumptions across the different makers, and I suspect that how the lens is communicating with the camera was tuned only on one brand for those lenses I've seen a difference on.
  • Lenses that are autofocus and "fully compatible" — I've been surprised to see little difference between mounts here. For example, the focus performance of the f/1.4 Viltrox lenses seems to be the same on a Fujifilm XF camera as it is on a Nikon Z as it is on a Sony E. What differences in focus performance I do see tend to be because of the manner in which the camera does its focus (e.g. Nikon's Subject Tracking is different than Sony's Tracking: Spot). I don't see the differences as being lens caused. 

So, no, there really isn't much of a difference that's detectable in the various mount versions of these lenses. What difference almost always is because of some aspect of the camera, not the lens. 

I mention this because I just published a bunch of reviews on of lenses that are available in other mirrorless mounts. I'm pretty sure that what I wrote in those reviews would apply equally to the Fujifilm and Sony versions, and probably to the Canon and L-mount versions (I write "probably" because I haven't specifically tested those same lenses on those particular mounts). 

Here are some lens reviews the above applies to that I've published on to date:

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