Vivitar Series 1 90/2.5 -- won't focus to infinity
Just got one of these with a Nikkormat FTn and Vivitar macro flash for dirt cheap. The lens worked fine when I first got it but now it won't focus all the way to infinity -- stops at around 10 feet, and seems like a pretty hard stop. Weird. Briefly it also wouldn't focus close either, like under 3 feet, but that seems to be working OK, albeit with a noticeable catch when I hit that spot on the helical.
It was very cold here yesterday and I initially put all this down to old and congealed helical grease after it sat in the car all afternoon, but the lens has since warmed up enough for that to presumably no longer be the problem.
Thoughts? I really don't want to engage in a teardown of this lens, since I think that's beyond my capabilities. The good news is that the macro capacity is unaffected, which of course is the lens's main function. But not being able to focus past 10 feet is annoying.