Nikon Series E 70-210 doesn't focus at infinity

[hsandler]

I've got this lens with a curious problem, and I can't find any other reports of this problem. It doesn't come to sharp focus at distances beyond about 60 metres when zoomed longer than about 120mm. It's like the helicoid just needs to turn a bit more to achieve focus, but runs into the infinity stop first. I've never seen it on another lens on my FE2, so I don't think there is anything wrong with the flange of the camera. The flange on the lens is clean; nothing is preventing it from mating closely with the camera. If I was to attempt to take it apart, is there anything inside to adjust to achieve a bit more range of the helicoid?

 

[John Koehrer]

The focusing ring on the camera or the infinity stop MAY have moved slightly. The ones I've worked on
have usually been simple fixes like loosen screw, adjust & tighten screw. Some lenses won't have an adjustable infinity stop
but the ring usually is.

 

[hsandler]

Thank you John! Your posting motivated me to take a closer look at where there were screws. I had not noticed that there is a very tiny setscrew that holds the front element onto the lens barrel. When I loosened it, I was able to unscrew the front element, clean off the grit in the threads and when I screwed it back in place, by giving it a good amount of torque, I was able to screw it another 10 degrees or so of rotation beyond where it had been, which recessed it another fraction of a mm into the lens barrel. Then I tightened up the setscrew again. That tiny amount seemed to be what I needed, as I can now get sharp focus on a streetlight a half mile away. I could see a possible mechanism of how the front element might have become a bit unscrewed over the years from the action of unscrewing tight filters. By the way, while I had the front element off, I looked inside and could not see anything near the front of the helicoids that provided a hard infinity stop, so I'm thinking that is probably at the back (flange) end of the lens assembly.

 

[shutterfinger]

Step outside with it and point it at the moon or bright star. You should be able to see the craters on the moon or a star should be a sharp dot of light.