The title of the thread threw a very different type of answer into my head. Early forties probably
Old lenses were just fine, but their coatings weren't nearly as good and so they can suffer from flare and sometimes low contrast. There are articles on how to check for coatings.
Check for how it feels. The grease gets old and hard to the point where turning the focus is difficult and the aperture blades get sticky and inconsistent. A nice old prime costs about $150 to clean, old zooms much more, and they decline to fix some of the more complex ones.
oh no you didn't...
Thank you, that was informative!
could you show me such an article?
Actually, other things to consider, how much of a price difference is there between that used lens and a new one with warranty? SOmetimes the savings is so little, that buying a new lens is a no brainer.When buying a lens used, how old would it have to be, for you to start considering the risks too great? like AF/IS motor failing etc.