DIY AI Conversion for Old Nikon Lenses

55mm f3.5 Nikon Micro on the left, 200mm f4 Nikkor Q on the right.
After modifying to work with a Nikon D80.

Some great lenses are available out there for dirt cheap. But they won't directly mount on a DSLR body without modification.


A while back, Nikon changed the traditional F-mount to include auto exposure functionality. It called that change the "Ai mount". The physical mount is pretty much the same, but Nikon added the indexing pin to the bodies, and the indexing ears to the lenses.

More information is available here: http://www.aiconversions.com/

So what does this mean to us DSLR owners? It means that owners of non-Ai lenses have been dumping them for next to nothing for years. High quality glass for ridiculously cheap prices.

My first lens modded:
200mm f4 Nikkor Q

But we cannot use the lenses directly on our DSLR bodies. There's a maximum aperture lever on the front of your body. That lever is moved by a pin on the lens to tell the body what the lens' maximum aperture is so it can calculate exposure. A non-Ai lens will break that lever if it is mounted to a modern body. An amount of material has to be removed from the aperture adjustment ring.

Machining the lens requires careful work disassembling the lens and removing material from the aperture ring. If you don't want to deal with that, the link above offers this service for $35. I'm too cheap/broke to do that, so I figured it out on my own.

NOTE: If you do get them mounted on your DSLR, the camera will no longer meter exposure. You will have to figure the exposure out on your own. Nor will you have autofocus! If these two feature losses are unacceptable, skip these lenses and buy newer ones made for modern bodies.

I've done two lenses so far. A Nikkor Q 200mm f4 and a 55mm f3.5 Micro. I had originally used them with uncoupled extension tubes. But that only allows them to be used as macro lenses. I wanted a bit more flexibility. So I went ahead with the conversion.

Shot with the Nikkor Q 200mm F4
on a Nikon D80

I used my Tamron 28-80 f3.5 lens as the template. Since I'm not metering through the body, getting the maximum aperture setting close is all I needed to do. f3.5 is close to f4.

I removed the aperture ring (sorry, disassembly is NOT covered here. There are plenty of resources on the net!) and lined it up with the Tamron. I marked where the Tamron has removed the material from that ring then hit the ring with a Dremel and a carbide grinder bit. I had to remove the indexing ears to allow the material removal identified by the Tamron. Unfortunately, that left the lens unable to meter with Ai bodies now.

It was slow work. And the bit kept wanting to jump and cut other places. The final result is ugly but functional. I tested it and the lens works quite well. A 200mm prime is a nice addition to my lens collection! And I only paid $30 for it!

55mm f3.5 Micro
After Ai conversion.

Next I modded my 55mm f3.5 Micro lens. I decided to only remove material around the maximum aperture pin instead of everywhere. That worked just as well. And it left the lens fully functional with Ai bodies since I didn't remove the indexing ears.

Both lenses work great with my Nikon D80. I don't mind the loss of auto focus or TTL metering. Especially with a digital camera since I can check the exposure immediately on the LCD.

Pick up a cheap lens and give it a try. You may like the result!