Rare Conversion: Factory Nikkor AI Conversion Rings

The back catalog of pre-AI/non-AI Nikkor lenses remains large on the used market but mounting non-AI lens on a nearly all modern Nikon DSLR/SLRs will result in irreversibly damage the camera. This is due to the solid non-AI aperture ring crushing the camera's aperture metering coupler/feeler tab. When AI lens and cameras were released Nikon originally sold factory AI conversion services and kits that would replace the non-AI aperture ring with a AI aperture ring for a set of lenses. In current day this Nikon service has long gone but there is another ...



There exists one place on the internet that still has new-old stock Nikon factory AI conversion rings and that is offered by Roland Vink, the same who maintains the wonderful Nikon lens db for sreial number and specifications over in New Zeland.

The Nikon factory AI conversion kits come with the rabit ears and once assembled you cna switch out the current non-AI ring with the factory kit.



The ring here is the #21 kit which is for the Nikkor 20mm f/4 K. Replacing the original aperture ring is relatively easy and involves removing the bayonet mount via the 3-5x JIS screws, pullling the original ring and dropping in the AI ring.

The difference between the non-AI and AI ring is visible below - the non-AI ring has no ridges and (typically) solid rabbit ears, metering coupling prong, sit backwards when compared to AI/AI-S lens which also have holes punched in the ears: the holes were to allow illumination of the aperture ring's smaller numbers:


^{non-AI/K aperture ring sits underneath the AI ring - notice the uniform solid nature of the non-AI/K ring}

The meter coupling ridge is seen on the AI ring which would push the camera body's metering coupler tab - that tab informs the camera of the widest aperture of the mounted lens. This is why mounting a non-AI lens on a modern Nikon body will cause damage.



A short visual on how to convert the non-AI/K lens to AI-spec.