Differences Between AI and AI-S Lenses

Differences Between AI and AI-S Lenses

How to recognise AI lenses:
In 1977 Nikon introduced a new system for coupling the lens to the camera's exposure system. This new coupling system was called Automatic maximum aperture indexing or AI for short. This change did not effect the traditional Nikon bayonet mount, thus allowing AI (and the latter AF and AIS) lenses to be fitted to older non-AI cameras.

The AI lever on a Nikon FM2n

However, while AI lenses were backwards compatible with non-AI cameras, non-AI lenses were not compatible with all AI cameras. The Nikon FM, FE, EL2, F3, F4 and Nikkormat FT3 cameras used the AI metering system but allowed non-AI lenses to be fitted due to the metering coupling lever being able to be disengaged. The F5 can have this mechanism fitted as an optional extra (please contact your local Nikon representive for more details). The F2A and F2AS were AI cameras but the AI mechanism was fitted to the removable metering prism.

Later cameras (any camera not mentioned above) without this retracting metering lever cannot be used with non-AI lenses as the rear of the aperture ring may bend the AI coupling lever on the camera when mounted and thus causing damage.
Some non-AI lenses can be modified to AI, in order to do so please contact your local Nikon agent. Please note that the parts required are no longer in production and it may not be possible to modify some lenses.

What is the difference between AI and AI-S lenses?
The AI-S lens was created in 1982 when the aperture mechanism of the AI lens was enhanced to feature automatic aperture control. This feature was to be used with cameras such as the FA, FG and F301 and allowed Program or Shutter Priority (FA only) modes to be incorporated into these cameras when used with AI-S lens. The AI-S mechanisms allows the aperture increments of an AI-S lens to be controlled more precisely by the camera than with an AI lens.
The visible indications that a lens is AI-S rather than AI are:

• The minimum aperture (both the main larger and smaller direct read out figures) are marked in orange i.e. F16,
• A notch has been taken off the rear bayonet mount, above the lens locking notch. This allows certain Nikon cameras to detect if an AI-S lens is fitted or not.