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Nikon AI Conversion Question


John Seaman

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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.

 

Nikai.jpg.8fc63d7b7ce9c202ea7c46eccd5add1d.jpg

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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.326266204_lensconversions.thumb.jpg.a71d58fac3a33f65d0d7a6cf74b970cb.jpg , and if the lazy maker of it were not myself, I'd give him a piece of my mind.

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Good one. That old 50mm now won't meter couple with anything...

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.

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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.
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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.
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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.

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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.

Edited by JDMvW
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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.

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