According to the video in the attachment, there are different batches/serial numbers. I suspect a first and second production. Apparently the lens was ground a little differently in the second production, which is why the focus on 40cm should be better in the new batch.
My question is: How do I know whether I am getting the "new" or the "old" production line?
Video:
https://youtu.be/XXJAQH9bVe...