Photographic Definitions & Questions

Nikkor Ai-P lenses

All auto-focus Nikkor lenses have what Nikon refer to as a built-in Central Processing Unit, or CPU, (strictly speaking it is not a CPU but an encoding micro-chip that passes information to and fro between the lens and camera body). The advanced automatic features and exposure control available with many of the current range, and more recent AF Nikon SLR cameras require AF Nikkor lenses to have this technology in order that they can operate with full compatibility.

Generally, manual focus Nikkor lenses do not have a CPU. However, Nikon does produce three manual focus lenses that do include a CPU. They are the:

• Nikkor 45mm f/2.8 P
• Nikkor 500mm f/4 P
• PC-Micro Nikkor 85mm f/2.8D

These are usually referred to as an Ai-P, or P-type Nikkor lens, although it is somewhat confusing that the latter carries the 'D' designation (in common with many AF Nikkor lenses) in place of the 'P' designation. All three lenses provide full functionality with the exposure modes and TTL metering systems of compatible manual focus and auto-focus Nikon cameras.