I have a Chinese no-name adapter for Nikkor lenses to my micro four thirds. The infinity focus mark on my Nikkor 50mm F1.8 lens is way off when taking a distant landscape at infinity. This is because the adapter is a tiny bit too thin. At first this made me mad, but now I see it is a huge advantage and would not want it any other way. Through testing I have found the best infinity position and marked it.
If, instead, my sharpest distant landscape was when my lens was focused on infinity (it has a stop at infinity and can rotate no further) I would always wonder if the image could be sharper if I could rotate the focus ring further. Could I really trust the skill of a Chinese shop? It would really bother me. With my adapter I have carefully found that with the center of the right circle of the infinity mark (the lazy figure 8) on my left most depth of field line I have the sharpest image possible.
It is very amazing that a very slight movement off this makes the image less sharp. I have taken many images on the left edge, center, and right edge of each of the two "circles" of the infinity symble (the lazy 8) and zooming in I can see a difference when I pixel peep the final image.
I have done this testing with F5.6, F8, and mid between.
Those who rely on their infinity mark for distant landscapes with these adapters may not be getting the maximum out of their lens. I sleep better knowing that my too thin adapter allowed me to find the precise infinity position.
