105 f2.5 AI'd No Infinity Focus

[chulster]

Ears

Thanks, Wog.

[wogears]

Thanks, Wog.

My wife is the Wog. I am the Ears. ;)

[rodeo_joe1]

See if any set screw is revealed when you focus to MFD, that is otherwise hidden.

 

Also, is it Mr. Gears or Mr. Ears?

 

This ain't my first rodeo!

The complete barrel is barren of any screw heads, at any focus setting.

 

Someone at Nikon must have been OCD about having a clean, tidy and inscrutable finish to their lenses in those days.

[chulster]

My wife is the Wog. I am the Ears. ;)

Oh! My apologies, Mr. Ears.

[rodeo_joe1]

Finally got the old 50mm f/2 apart, and I believe I've uncovered the 'proper' way to adjust infinity focus.

 

Remove the focusing ring front collar (hah!), exposing a locking set-screw for the front ring of the lens.

 

Loosen set-screw and remove front ring.

 

Undo 3 small domed screws to release the remaining part of the focusing ring and remove same.

 

You should now see the top of the helicoid exposed thus:

The piece outlined in red limits the near and infinity focus, and secures the helicoid from being fully unscrewed. Check those edges outlined for dirt or debris, which may prevent infinity focus.

 

If all clear, then look at the top of the helicoid collar.

Note the tiny set screws at 12, 4 and 8 o'clock. To adjust infinity focus, these need to be loosened - not easy because they're glued in place and require a good jeweller's screwdriver to undo.

 

When (if) the screws are loosened, the threaded collar they hold in place can be rotated slightly in its threaded cup. This changes both infinity and near focus, since the collar forms the end-stop for both.

 

Once adjusted the set-screws should be re-tightened and you're done. After re-assembly of course.

 

Close-up of tiny set-screw. It's about 1.2mm in diameter.

Edited May 11, 2018 by rodeo_joe|1

[chulster]

Nicely done. That's quite different from the 50mm f/1.8 AI design.

[rodeo_joe1]

Nicely done. That's quite different from the 50mm f/1.8 AI design.

 

- Yep.The later AI and AI-S lenses are a piece of cake compared to the over-engineered pre-AI ones.

 

P.S. Since the whole lens barrel sits inside the helicoid, and is only held in place by the front retaining ring; it's quite possible that dirt under the barrel, or a loose front ring, could cause an infinity focus error too.

[Michael R Freeman]

Close-up of tiny set-screw. It's about 1.2mm in diameter.

[ATTACH=full]1245056[/ATTACH]

 

That focus stop adjustment mechanism is typical of most Ai Nikkor primes 200mm and shorter. Exceptions are the Ai 50/1.8 and Ai 50/1.4 which uses the same very thin brass "slip ring" as the AiS "long nose" 50/1.8 and other small AiS primes to adjust the focus stop.

[chulster]

That focus stop adjustment mechanism is typical of most Ai Nikkor primes 200mm and shorter. Exceptions are the Ai 50/1.8 and Ai 50/1.4 which uses the same very thin brass "slip ring" as the AiS "long nose" 50/1.8 and other small AiS primes to adjust the focus stop.

The more you know!