Thanks for the replies; it really is a puzzle out there today.
I used to have a 2/50mm Nikkor that I bought along with my F all those decades ago. From a single misguided impulse born from listening too much to stock agents, an impulse that started rolling by my going from Hassy to 6x7 Bronica and then expensively back, totally, to 35mm, I had traded my entire 35mm system for 6x7 Pentax. A year or so later I was buying back into Nikon and feeling a prize idiot to fnd myself pouring money into my own folly. Anyway, back to the 2/50mm. It was my least-used optic, most of the stuff that I would now shoot with it was, then, handled by a 2.8/35mm because of the slightly greater distortion that was fashionable in some sectors of fashion photography, most of mine included. For the other type, I used Hassy and tripods.
For some reason I can't quite recall, I had exchanged the 2/50mm for a new, manual 1.8/50mm, and the first thing I discovered was that the front section is loose! I had imagined this a one-off flaw, but after the swapping back from Pentax, the new manual 1.8/50mm is exactly the same. It wobbles. But it still seems to give great images. But the damage has been done, in my mind, because I have no great confidence that, one day, it won't just spin apart as I turn the focus ring.
Based on my experience of Zeiss and 'blad, the old silver lens range, there really was a problem with flare on backlighting, especially with the 150mm. I never did buy into the black lens range as I already had what I needed before they came along.
As I said, it is a puzzle out there; the world must be going nuts, just as I did for some years.
Rob C