Using Older Nikon Lenses

Usable Manual Focus Lenses. Nikon differs from Canon in one major respect: The made a conscious effort to accommodate the owners of “legacy” lenses. Only the earliest lenses, sometimes called “Non AI” lenses CANNOT BE USED. They can be identified by the solid “ears” on the aperture ring. “AI” stands for “Aperture Indexing”, and it basically means that aperture information is communicated through the inside of the camera, not through the external ears. The ears remained for use with the older Nikon metering systems.

 

In this photo, you can see an AI lens. Notice that two holes in the aperture ring “ear”. Such a lens would be safe to use, but you’ll need to focus, and set the aperture manually.

A warning: AI lenses cannot communicate with you Nikon Speedlight, so you’ll need to use your speedlight in manual mode.
"If the lens has ears, then shed no tears,

But there are no holes, then let it go"