Nikon specifications for AI modification?

[declark]

I have been unsuccessful in finding specifications Nikon AI aperture rings. I recently did perform such a conversion for a 50mm H lens that I got on the cheap and just "eyeballed" the location of the a tab relative to the aperture setting and it seems to work fine. I would like to get more accurate angles relative to the indexing "rabbit ears" if possible so I can nail it exactly with my rotary table. If anyone has a link to dimensional specs for AI rings, that would be greatly appreciated.

And in a related question, does anyone know why the AI tabs seem to vary depending on the widest aperture of the lens, whereas the rabbit ears all seem to be located at F5.6?

 

[John Koehrer]

The ai tabs vary because the camera needs to know the maximum aperture of the lens. I used to work in a repair shop & we used to modify lenses with by removing the aperture ring & use a flat file. Depth and length of the groove had to be considered but the only critical reference was maximum aperture.
The f/5.6 is a constant physical location between lenses. If you check the actual start point of the coupler on the camera you should be able to determine the start point for different lenses.
Try mounting a 1.4 lens on the camera & note where the coupling is as you stop the lens down one stop at a time. This should give you a very close approximation of where the follower has to be for lenses slower than the 1.4.

 

[ehparis]

I was under the impression that literally all factory AI conversion kits differed.

John White at

http://www.aiconversions.com/index.html

also suggests that he doesn't do conversions for all lenses. Why not?

 

[John Koehrer]

I was under the impression that literally all factory AI conversion kits differed.

John White at

http://www.aiconversions.com/index.html

also suggests that he doesn't do conversions for all lenses. Why not?

The internal couplings of the lenses differ. Coould be location of a notch thickness of a ring Many variables that aren't visible. Don't know why John won't do 'em all, he has a deeper knowledge than I.

 

[ehparis]

The internal couplings of the lenses differ. Coould be location of a notch thickness of a ring Many variables that aren't visible. Don't know why John won't do 'em all, he has a deeper knowledge than I.

Don't know. I know he somewhere lists all the lenses he will modify. It's possible I'm reading something into that which doesn't apply.

 

[resummerfield]

The "Nikon Camera Repair Handbook" by Thomas Tomosy gives instructions for AI-ing the older lenses, and a chart showing the position of the notch verses the maximum aperture of the lens.

 

[Steve Smith]

I AI'd a lens many years ago by super gluing a piece of metal onto the aperture ring. If you have some other AI lenses you should be able to judge where to put it especially if you have one with the same aperture range.

It isn't a case of lining it up with a particular f stop though as the AI doesn't tell the camera the f stop set, it tells it the difference between the f stop set and the wide open aperture which it is metering with. That's why the position varies with maximum aperture of different lenses.

Some info here: http://www.zi.ku.dk/personal/lhhansen/photo/FullAImod.htm


Steve.

 

[declark]

Steve.

Thanks for the link. That is close to what I am looking for. It would be nice to just see some plan views of the ring and the angles relative to something that I could easily index from. I'm thinking of making a plug to mount the ring on and use a dowel pin to locate to the yoke, which would be easiest. The link suggested a method I had not thought of which is to take a scan or picture of a lens of the same widest f-stop and then measure the angles directly. Otherwise I may see if I can have our QC department check on the CMM.