What Is a CPU Lens?by Steve Lander
Nikon first started making CPU lenses when they debuted autofocus lenses in 1986. Although the term "CPU" usually refers to a central processing unit, the term is misused here since the lenses lack an actual electronic brain. What CPU lenses offer is a chip that transmits basic information about the lens back to the camera so that the camera can use advanced metering functions.
CPU-Equipped Autofocus Lenses
Nikon introduced the CPU feature with their first autofocus lenses in 1986. To allow the lens' chip to communicate with the camera, they have at least four spring-loaded metallic terminals on the lens mount that match up with sensors inside the camera's lens mount. Some auto focus CPU lenses have as many as 10 CPU terminals.
CPU-Equipped Manual Focus Lenses
The first manual focus lenses that included a CPU chip were the AI-P series that Nikon first started selling in 1988. They have the same aperture indexing pin as every other Nikon manual focus lens made since 1979, but add the CPU chip. These CPU manual focus lenses allowed Nikon to offer advanced electronic metering with lenses that were not yet ready to be transitioned to autofocus technology.
Enhancements to Nikon CPU Technology
The original CPU lenses only transmitted basic lens data, such as focal length and aperture setting, to the camera. In 1992, Nikon introduced D-type lenses. These lenses added additional CPU terminals so that they could also transmit data to the camera on the distance at which they were focused or on the focal length to which they were zoomed. Some Nikon cameras used this data to better expose flash images.
Pre-CPU Nikon Lenses
Nikon made F-mount lenses for 27 years before introducing the CPU-equipped autofocus lens. F-mount lenses made between 1979 and 1986, or 1988 for manual focus lenses, lacked CPU chips. While they will work with many modern Nikon cameras, the camera will not be able to use advanced metering or put lens information into the metadata stored with the image file. F-mount lenses made between 1959 and 1979 not only lack CPU chips but also lack the physical aperture indexing pin. They can damage many modern Nikon SLR cameras.