And what is the difference between pre-AI and AI lenses?
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The difference between pre-AI (Non-AI) and AI (Aperture Indexing) lenses primarily lies in how they communicate aperture settings to the camera’s metering system. Nikon introduced AI lenses in 1977 to simplify and speed up lens mounting and metering.
1. Pre-AI (Non-AI) Lenses (1959–1977)
Key Features:
- Coupling System: Uses a meter coupling prong (a pair of metal “rabbit ears”) to connect with the camera’s metering system.
- Mounting Process: Requires a “double twist” method to properly index the lens with the camera meter:
- Mount the lens.
- Rotate the aperture ring to the smallest and largest f-stop to engage the meter coupling system.
- Aperture Ring: Has a smooth design without special cutouts.
- Compatibility:
- Works on pre-AI cameras like the Nikon F, F2 Photomic, Nikkormat FT series, etc.
- Can be used on AI cameras in stop-down metering mode (manual aperture adjustment without full communication).
- May damage the AI metering tab on newer Nikon bodies unless modified (AI-converted).
2. AI (Aperture Indexing) Lenses (1977–1986)
Key Features:
- Automatic Aperture Indexing: No need for the manual “double twist” process. The camera instantly reads the maximum aperture when mounting.
- Coupling System: Still has the “rabbit ears” but also features a metering ridge (AI cut)—a small cutout on the back of the aperture ring that engages with the AI tab on compatible cameras.
- Improved Mounting: Faster and easier lens changes, eliminating the need to manually align the aperture ring with the camera meter.
- Compatibility:
- Works on both AI and pre-AI cameras (if the camera has a foldable AI tab, like the Nikon F3).
- Not all AI lenses work on digital Nikon cameras without modification.
- Can be converted to AI-S (later refinement).
Key Differences Between Pre-AI and AI Lenses
| Feature | Pre-AI (Non-AI) Lenses | AI Lenses |
|---|---|---|
| Metering System | Manual coupling via “rabbit ears” | Automatic indexing with AI ridge |
| Mounting Process | Requires “double twist” to set meter | Mounts directly with instant indexing |
| Aperture Ring | Smooth design | AI cutout (ridge) for metering tab |
| Compatibility | Works on pre-AI cameras; limited on AI bodies | Works on AI and some pre-AI cameras |
| Ease of Use | Slower, manual indexing required | Faster, no manual indexing needed |
How to Identify an AI Lens
- Look at the aperture ring—if it has a second ridge near the mount, it’s AI.
- Check the “rabbit ears”—AI lenses often still have them for backward compatibility.
- Verify the mount cutouts—AI lenses have extra metal cutouts to engage the AI tab.