Regarding quality vs age, it stems from various discussions involving Mr Brian Sweeney and others that seem to know the history of the FSU-gear more detailed and that have worked on a whole heap of lenses, spanning the 50-60 year old history of the Jupiter lens.
According to the discussions I've seen, it seems that failure-rate in lenses made between the early 50's to the mid 50's (1956'ish) is very very low. "Most are excellent" is the common conclusion. It also holds pretty true to lenses made well into the mid 60's as well, albeit with a steadily growing number of failures and faults and quality issues.
The raw-materials (especially the glass) they used in the earlier lenses, was often German glass (or higher quality glass), I am not sure when they actually ran out of it though, could have been in use for only 2-3 years after the war, or well into the 60's, no idea.
From the discussions, it seems that until the end of the 50's, they even used German workers to produce a lot of the lenses.
From what I gather, after a while, the stock-glass and materials was produced in-country (doesn't have to be any worse than the German stuff though), the German part of the labor-force was replaced by Russian/Soviet ones. (probably from the end of the 50's to mid 60's if I am going to guess).
So, according to the know-how's, the quality and quality-control steadily dropped during the 60's, because it was often about number of units produced per worker, rather than quality per-se that was central.
Then there's the ideological factor; During the 50's, the Soviet ideology and morale was high, but once you hit the 70's and 80's, economy was bad, machinery may have started to be less precise/worn(??), materials and quality not so good and morale among the people and workers was low, which affected (again from what I gather from the discussions) product quality and quality control.
All this, seem to lead to the conclusion that
- Jupiters from the 50's have very little failure rate
- Jupiters from the 50's may have German glass (maybe more often between 1946-1955)
- Jupiters from the 50's may have been assembled and controlled by German workers (or a combination of Soviet workers, trained by Germans).
- Jupiters from the 50's to mid 60's seem to have less failure rate than later lenses.
- Lenses from the 70's and onward seem to have higher failure rate and less nice optical quality.
I have three lenses, one from 1955, one from 1963 and one black one, which I assume is from the 70's.
They are all pretty equal in terms of optical quality, hell the black one is both very nice optically and very nicely built. But the black lens is a much simpler lens, as the front rotates, there is not fancy helix construction, which is a little strange, since it's the newest model of them all.
1955 lens is the most complex one, concerning the focus mechanism, the 1963 is a simplified version, which works very nicely and is easier to produce and assemble, my 70's lens is a very simple design, with a rotating front. (but very light and actually, naturally, a tad shorter than the silver versions).
I am definitely no history-buff, and I've probably said stuff wrong in this post, but googling around and reading the old discussions on the subject is very interesting.
I would definitely LOVE to get my hands on a (great) Jupiter-3, I should probably buy one soon, as he prices increase these days.
