Nikon AI Conversion Question

Discussion in 'Nikon' started by John Seaman, Oct 13, 2021.

  1. I recently acquired a nice old Nikkor-H 50mm F/2 which had been converted to AI in a way I haven't seen before. Instead of the usual milled notch, the "bunny ears" have been replaced with a small L-shaped metal piece which engages with the aperture follower to operate the AI feature. It seems like a neat and non-destructive idea.

    I just wondered if anyone has seen this, and whether there are any drawbacks. Also, is there a source of these little brackets? Mine does not look home made.

  2. Depends on what you put it on. I'd think it would foul some followers and possibly wreck 'em, but I don't know much about how far the ring on that vintage protrudes. Use with caution and be sure pressure isn't being applied to anything by the ring.
    bgelfand likes this.
  3. That's understood thanks Conrad. I always tread very carefully when mounting old lenses. Actually this one sits on an unmetered Nikon F so the meter coupling is not doing anything anyway.
  4. Sandy Vongries

    Sandy Vongries Administrator Staff Member

  5. That ridge would engage the aperture follower on older Nikons.
  6. Yes I've seen it because I've done it twice. Some of the very early lenses (of which this appears to be one, with the bayonet part threaded instead of held on by little screws) have skirts that do not touch the AI follower on the camera. I did a similar job on my ancient 28/3.5 lens. In this case, the skirt, though it extends far enough, is too narrow, and clears the follower. There are also some third party lenses on which the same trick works. I have an old pre-AI Vivitar 20/3.5 which also does not touch the AI follower, and I was able to convert it the same way. In this case, the skirt doesn't extend far enough back to hit the follower.

    Oddly enough, I also have now two copies of the very old 200/4 Q lens, which also has the threaded bayonet, but on both of those, the skirt is both wide and deep enough to allow (and require) a normal conversion by milling. The non-destructive bracket in question can only be used if the unconverted lens does not impinge on the camera's AI follower.

    I took the rabbit ears off the 28, simply because I did not readily find screws long enough, but the Vivitar 20 allowed me to place the rabbit ears on top of the added piece. In neither lens does the new piece interfere with the follower on my old F's. After all, the very reason one has to add that piece is that the diameter of the aperture ring is smaller than usual, so adding the piece only brings it up to the level most lenses are at already. Remember, too, that at least for the Photomic FTn, metering with an uncoupled lens (which the 28, or the 50 shown, now is) requires that you retract the follower, so there's always plenty of room.

    I don't know of a source for the brackets. Mine are both home made, one from copper and the other from aluminum. Note that the aluminum one is sloppy and hasty, meant as a prototype that was never upgraded. The bend for the Vivitar was much easier using copper. lens conversions.jpg , and if the lazy maker of it were not myself, I'd give him a piece of my mind.
  7. From the Murphy's Law Appendix- All temporary fixes become permanent. If sufficiently ugly, they persist until the end of time.
    dennisbrown and mike_halliwell like this.
  8. Good one. That old 50mm now won't meter couple with anything...
  9. I'm pretty sure it will. If the piece is properly placed, and if the ring is of a similar diameter to my old 28, it will couple just fine to any AI camera.

    I would exercise a little care when fitting it to any camera, but I bet it works.
  10. How? Factory or Dremel Ai conversion involved a specifically located notch in the aperture ring, not an extension as pictured above.
  11. Well, the lens mounts safely on an F90X / N90S and the L bracket engages correctly with the aperture follower.
  12. Funny, I've an ancient 35/2.8 of that vintage that mounts but no other NAI lens will without cramping the somewhat fragile Ai follower.
  13. I think you can modify it like that if your lens (which it is in this case) doesn't have anything protruding into the coupling area. Some you have to cut off not adding. Of course the original Nikon mod would involve replacing the entire aperture ring.
  14. I have seen this as well. As Matthew noted, only suitable on certain early Nikkors where the rear skirt of the aperture ring would not touch the AI tab. There isn't actually enough material extending beyond the bayonet mount on these particular aperture rings to mill a notch to engage the AI tab for a John White style conversion.
  15. Sandy Vongries

    Sandy Vongries Administrator Staff Member

    I can only tell you that John White of AI Conversions did a bunch of my favorite old lenses very cleanly, quickly and inexpensively. Ex a paper F Stop scale needed for a couple of cameras I rarely use, no difference from later model AI lenses. No way, at the price of getting the work done properly that I will walk around with a crap job. I actually have considerable experience with similar work from another hobby, and still wouldn't DIY it. Good equipment should be properly serviced and cared for.
    bgelfand likes this.
  16. It's not actually the distance of protrusion on some of these lenses, but the diameter of the protrusion. My old 28 protrudes as deep as other unsafe lenses, but the diameter of the protrusion is smaller, and it falls between the AI follower and the lens mount. That is why you can't just notch it out as you can with most pre-AI lenses. The new tab must be added atop the aperture ring to hit the camera's aperture follower.

    Note on both the original 50 shown and my 28 that the body of the added tab must also be recessed, not right out to the edge of the aperture ring - otherwise that part would hit the AI follower and you'd be right back with the pre-AI damage problem.

    I"ve done a few milling conversions on old lenses with success, but if the lens is not already beat up and cheap, I'd be inclined to go with a pro like Jon White. It does have to be positioned with some precision at the follower end. Some lenses also have a helper spring under the mount, that helps with aperture response. My 105/2.5 has that. It's easy to unhook by accident, hell to put back.
    gabriel_heyman likes this.
  17. I lucked into a small trove of factory Ai kits some time back for garden variety Nikkors and never bothered with Dremel jobs. I use other old Nikkors with adapters way more on MILCs anyway.
  18. If I want to use a non-AI Nikkor, I use it on a Nikon F or F2, a Nikkormat EL, or with an adapter on a Canon body. I really hate modifications that make a good-condition item look like roadkill.

    If you must modify an old lens, have it done by White, not with your own Dremel tool.
    Last edited: Oct 16, 2021
    robert_bowring likes this.
  19. I have a couple of lenses that were done, or at least partly done, by others before me, with a Dremel or other hand tool, and would agree that this is a poor fate for any decent lens, though it makes them cheap for people like me to buy. Once the damage is done, it's usually impossible to make it look any better.

    It's different with a milling machine. When an evenly milled part is painted, you're not likely even to notice the conversion unless you're looking for it.
  20. Thats a nice thing about the FTZ adapter, been able to use many pre Ai on my Z7 with nice results.

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