1. How correct is it? To me, it makes sense and I honestly could see how it would affect things.

2. How many third party companies (i.e. Sigma, Samyang, Voigtlander, etc) refactor their lenses for the different mounts/optical glass? I at one point was thinking of just buying a Samyang/Bower lens in F-mount and adapting it to M43 with a dumb adapter, but if their lenses are actually made different for each mount, it would make sense to buy it in the mount of the camera I actually have.

3. In the case of M43, does Olympus, Panasonic and Black Magic all use the same optical glass thickness? (i.e. is it part of the M43 spec?)

1. How correct is it? To me, it makes sense and I honestly could see how it would affect things.

2. How many third party companies (i.e. Sigma, Samyang, Voigtlander, etc) refactor their lenses for the different mounts/optical glass? I at one point was thinking of just buying a Samyang/Bower lens in F-mount and adapting it to M43 with a dumb adapter, but if their lenses are actually made different for each mount, it would make sense to buy it in the mount of the camera I actually have.

3. In the case of M43, does Olympus, Panasonic and Black Magic all use the same optical glass thickness? (i.e. is it part of the M43 spec?)

So, the interesting thing to note is the exit pupil. It seems, in regards to Nikkor glass, that it was all over the map for different focal lengths. This would also explain why my 55mm micro Nikkor renders so well on an E-M5, as looking at the lens, I am fairly certain it's exit pupil is pretty far up there.

You are obviously right. I have actually read the Roger Ciala article, but jumped conclusions. I guess that the optical package in front of the sensor needs to be taken into account when dsigning lenses.

Hmmm, very interesting. This surely helps explain why most wider rangefinder lenses perform so poorly on non-RF bodies regardless of sensor size. I'd expected the performance of these lenses on m43 cameras to be better than on APS-C bodies but this has definitely not been the case.

Here's another curious thing I've seen with certain Leica RF lenses on an A7r vs. the same lenses on my film M6 and electronic M8.2s: focus shift differences. One of my favorite RF lenses is the Rigid version of the 50mm Summicron. On Leicas there's a plateau performance-wise in the f/4–5.6 range with this lens but it's not a big deal. On the A7r, though (using the latest Voigtländer adapter), the focus shift is blatant and noticeably degrades performance in the same f-stop range (unless I work around it by focusing at the taking aperture rather than with the lens wide open). I wonder if CFA/filter stack thickness differences might be playing a role in this? I should test for proper infinity focus with the adapter too...it seems fine but I've never systematically checked it.