Nikkor 45mm GN f/2.8 focus issue

Huss · Mar 29, 2019

This lens was working perfectly, giving me excellent results, the last time I used it. Never dropped. I then put it into my dry box, attached to the Nikon F I last used it on. 2 months later I pull it out and now the lens' focus ring will not turn from closest distance to infinity. It hits what feels like a hard stop half way through. Weird(er?) thing is after racking it to and fro about 10 times it will suddenly focus all the way through to infinity as if nothing had happened. And then go back to feeling like it hits a hard stop mid way through again.
Anyone else experience this with a lens?

Trask · Mar 29, 2019

It’s a lens that connects the focusing and the f/stop rigs based on the “guide number” you select on the bottom of the lens rings for the flash you are presumably using — or rather, that the lens designer thought you’d be using, otherwise you’d just use a regular Nikkor, right? So if your lens is set to a lower guide number, the lens will want to stop focusing at the point where, per the inverse square law, the light from your flash would have fallen off to the point that the subject would not be fully illuminated. So perhaps part of the issue is that the guide number is set to a low number; try increasing it, and see if you can thereby focus further out towards infinity. I’m unsure why the lens would occasionally focus fully out to infinity and then suddenly stop doing so — could it be that in moving the focusing ring back and forth you’re inadvertently disengaging the little fork mechanism that connect the focusing ring to the f/stop ring, and then just as inadvertently re-engaging the fork mechanism?

shutterfinger · Mar 29, 2019

This may be of help.
https://richardhaw.com/2016/03/13/repair-gn-auto-nikkor-45mm-f2-8/

Huss · Mar 29, 2019

Trask said:
It’s a lens that connects the focusing and the f/stop rigs based on the “guide number” you select on the bottom of the lens rings for the flash you are presumably using — or rather, that the lens designer thought you’d be using, otherwise you’d just use a regular Nikkor, right? So if your lens is set to a lower guide number, the lens will want to stop focusing at the point where, per the inverse square law, the light from your flash would have fallen off to the point that the subject would not be fully illuminated. So perhaps part of the issue is that the guide number is set to a low number; try increasing it, and see if you can thereby focus further out towards infinity. I’m unsure why the lens would occasionally focus fully out to infinity and then suddenly stop doing so — could it be that in moving the focusing ring back and forth you’re inadvertently disengaging the little fork mechanism that connect the focusing ring to the f/stop ring, and then just as inadvertently re-engaging the fork mechanism?

The mechanism is disengaged, but thanks for the reminder in case I did not do that.

Huss · Mar 29, 2019

shutterfinger said:
This may be of help.
https://richardhaw.com/2016/03/13/repair-gn-auto-nikkor-45mm-f2-8/

Thank you for the link, I will study it once I get home.

Huss · Apr 17, 2019

I dropped it off at Walters Camera Repair in LA. They think a set screw may have worked its way out but will not know until they open it up. $80 to fix. Fingers crossed!

Huss · Apr 19, 2019

Result - Walters took the lens apart (a bit) and found that a tiny screw on the inside of the auto aperture stop down mechanism had backed its way out and fallen into the helicoid!
Repaired, re-lubed the helicoil, back in action in under a week and for $80. Happy and highly recommend this shop.

Nikkor 45mm GN f/2.8 focus issue

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